Browse Topic: Pistons

Items (3,800)

Design and Analysis of a Large Hydraulic Cylinder Maintenance Device

2026-99-0214

7/31/2026

Addressing the challenges in maintaining large hydraulic cylinders and the lack of specialized equipment, this study presents a dedicated maintenance system developed through a case study of a large hydraulic lifting cylinder. Through a comprehensive analysis of maintenance requirements, we developed a six-component maintenance system comprising a foundation base, a mounting bracket, a cylinder support frame, a piston rod bracket, a drive cylinder bracket, and hydraulic components. The paper systematically explains the structural configurations and functional specifications of each component, details the operational workflow of the maintenance system, and conducts theoretical design and strength verification for critical load-bearing brackets using principles from theoretical mechanics and structural mechanics. A static analysis module from ANSYS Workbench finite element software was employed to validate the overall structure. Results demonstrate that the key components meet operational strength requirements. This innovative maintenance system proves highly feasible and serves as a valuable reference for designing similar hydraulic cylinder systems.

Qiao, Xiaodong, Du, Chao, Long, Yuheng

Performance Analysis of a Gasoline Direct-Injection Opposed-Piston FPEG: A Coupled Study of Injection, Scavenging, and Dynamics

2026-01-5063

7/28/2026

The opposed-piston free-piston engine generator (FPEG) is a promising high-efficiency energy conversion architecture, featuring reduced heat transfer and favorable NVH characteristics for applications such as auxiliary power units and vehicle range extenders. While significant progress has been made, existing studies often focus on isolated parameters. The coupled effects of key operational parameters, including injection pulse width, scavenging pressure, rebound cylinder base pressure, and mover mass, on the performance of gasoline direct-injection opposed-piston FPEG remain insufficiently explored. To bridge this gap, we develop and validate a thermodynamics zero-dimensional combustion simulation model against bench tests, with peak pressure errors below 5%. This model enables a systematic investigation into the interactive effects of these parameters. Results indicate that piston dynamics are most sensitive near dead centers and in the first half of the expansion stroke. Indicated thermal efficiency peaks at 35.87% with a 4.5 ms injection pulse width and increases from 35.02% to 36% as scavenging pressure rises from 1.3 bar to 3 bar. Scavenging pressure dominates compression ratio and efficiency, rebound pressure mainly affects operating frequency, and injection width governs indicated work and peak pressure. This study establishes a coupled analysis framework, providing concrete insights for optimizing opposed-piston FPEG performance through parameter coordination.

Wu, Limin, Ji, Kaixuan, Feng, Huihua, Jia, Boru, Zuo, Zhengxing

Effects of Engine Geometries on the Combustion Characteristics of a Heavy-Duty Hydrogen Spark-Ignition Engine

2026-37-0046

6/9/2026

For heavy-duty applications, hydrogen (H2) internal combustion engines offer a practical solution for future transportation. However, the influence of cylinder head flow characteristics and piston geometry on lean H2 combustion remains insufficiently understood. This study presents a comprehensive computational investigation of three engine configurations characterized by distinct in-cylinder flow dynamics: mild swirl and tumble (Engine a), strong tumble (Engine b), and strong swirl (Engine c). High-fidelity three-dimensional computational fluid dynamics simulations were performed for both port-fuel injection (PFI) and direct injection (DI) strategies. The impact of piston geometry was evaluated by comparing the baseline piston with a flat piston, while the spark timing was optimized to achieve favorable combustion phasing. Combustion and NOx formation were modeled using a G-equation-based combustion framework incorporating diffusive-thermal instability effects and a validated in-house H2 chemical mechanism. Turbulence-flame interactions were further characterized using Borghi-Peters diagrams. Under PFI operation, the strong-tumble configuration (Engine b) generated the highest turbulent kinetic energy (TKE), resulting in faster flame propagation, more advanced combustion phasing, and improved thermal efficiency. The flat piston further enhanced efficiency by reducing mixture confinement within piston-induced recirculation zones. Under DI operation, H2 injection significantly increased turbulence intensity, and a flat piston promoted higher TKE near spark timing in Engines b and c by reducing mixture-wall interaction, leading to faster combustion compared with the baseline piston. In contrast, the original piston produced higher TKE within the piston bowl in Engine a due to stronger recirculation. Additionally, the strong-tumble configuration achieved the most homogeneous mixture distribution under DI conditions. These results demonstrate that in-cylinder flow structure, piston geometry, and DI injection strongly affect turbulence generation, mixture formation, and combustion performance. The strong-tumble configuration shows the greatest potential for achieving high thermal efficiency with controlled emissions in lean H2 spark ignition engines.

Liu, Xinlei, Menaca, Rafael, Cenker, Emre, Silva, Mickael, Qahtani, Yasser A., Pei, Yuanjiang, Turner, James W.G., Im, Hong G.

Investigation into Cooling Loss Reduction Associated with Changes in In-Cylinder Flame Distribution by Offset Orifice Nozzle

2026-37-0003

6/9/2026

An increase in compression ratio has been widely recognized as one of the essential technologies for improving the thermal efficiency of heavy-duty diesel engines. However, a higher compression ratio tends to result in increased cooling loss, which could diminish the thermal efficiency gains. It was found that an offset orifice nozzle, in which the orifices are drilled with a small offset from the radial center of the nozzle, improves thermal efficiency and reduces cooling loss simultaneously. This study investigates the mechanism of cooling-loss reduction associated with changes in flame distribution when using an offset orifice nozzle, through in-cylinder combustion observations, two-color method image analysis, and local heat-flux measurements. High-speed combustion visualization was conducted to capture the growth of luminous flames. Radial profiles of the mean and standard deviation were computed at each crank angle to quantify spatial temperature non-uniformity. Furthermore, multiple thin-film thermocouples embedded in the piston were employed to measure transient surface temperature and to derive heat flux over the entire cycle. The results indicated that the luminous flame distribution with the offset orifice nozzle was significantly different from that with a conventional nozzle, leading to reduction in the spatial non-uniformity of high-temperature regions in the observed area. The piston surface temperature measured at multiple points suggested reduced spatial non-uniformity in surface temperature, with suppressed instantaneous heat flux. These findings confirm the hypothesis that cooling-loss reduction is achieved by suppressing localized hot spots on the piston surface through the altered flame distribution.

Mukayama, Tomoyuki, Enomoto, Yoshiteru, Mikami, Naotaka, Nomoto, Shigeru, Uchida, Noboru

A Predictive Methodology for 3D-CFD Simulation of Piston Thermal Field in Sustainable High-Performance Engines

2026-37-0002

6/9/2026

In recent years, especially in high-performance spark-ignition engines, the thermal stress of pistons has gradually increased due to the implementation of various technologies, aimed at meeting emission reduction and specific power increase requirements. If the heat is not properly dissipated, cracking and plastic deformation of the material as well as formation of hot spots triggering pre-ignition in the combustion chamber mixture can occur. This last aspect is even more true considering innovative fuels such as hydrogen. To overcome these problems, one or more jets of oil are directed towards the piston under-crown region, impacting at high speed. This technique ensures immediate cooling and allows the engine performance to be increased without compromising the useful life. In order to optimize the oil jet effectiveness, 3D-CFD can be proficiently adopted. In this regard, the aim of this work is to define a robust numerical methodology able to simulate oil jet impingement and piston thermal field. In particular, a 3D-CFD Volume-of-Fluid (VoF) simulation is used to numerically assess the oil jet impact and provide a map of heat transfer coefficients, which, in turn, is adopted in a 3D-CHT model to estimate the piston thermal field. The proposed methodology is validated against experimental data on a high-performance engine piston. In particular, a pair of oil jets is investigated and the resulting heat transfer coefficient map is exploited to obtain the thermal field of the piston, which is finally compared to the available experimental temperature measurements. The results show that the predicted temperatures agree with the experimental data within an error lower than 2.5%.

Duni, Andrea, Berni, Fabio, Breda, Sebastiano, Fontanesi, Stefano, Gilioli, Filippo

Development and Validation of a One-Dimensional Model for an Opposed-Piston Free-Piston Engine Generator with Parametric Analysis

2026-37-0021

6/9/2026

Opposed-piston free-piston engine generators (OFPEGs) are emerging as a promising technology for next-generation hybrid and electrified transportation systems due to their high efficiency, reduced mechanical complexity, and improved noise, vibration, and harshness (NVH) characteristics. However, due to eliminating the conventional crankshaft mechanism and directly coupling a free-piston engine with linear generators, performance of OFPEG systems is governed by a strong coupling between piston dynamics, in-cylinder combustion processes, and electrical loading conditions. This coupling presents substantial challenges for system design, control, and optimization, limiting the further development and application of OFPEGs. Existing researches lack a comprehensive numerical model that integrates detailed in-cylinder thermodynamic process with control system of linear generator, and quantitative analysis of the effect of piston motion trajectory on system performance remains insufficiently explored. In this study, a novel one-dimensional OFPEG model is developed in Gasdyn and coupled with a linear motor model and a control strategy in MATLAB/Simulink, thus forming a complete numerical model for OFPEG. The model is validated against experimental measurements, demonstrating effective prediction of thermodynamic and dynamic performance with acceptable errors. Based on the validated model, the effects of varying piston motion trajectory on system performance are analyzed. Lower Rt and higher Ωcom and Ωexp are recommended for higher performance. When Rt is reduced to 2.5:1, thermal efficiency and indicated power improve to 36.3% and 3.4 kW, respectively. When Ωcom is increased to 0.6, thermal efficiency and indicated power improve to 35.5% and 3.22 kW, respectively. When Ωexp is increased to 0.6, thermal efficiency and indicated power improve to 36.0% and 3.41 kW, respectively. These improvements are primarily attributed to reduced heat transfer losses and enhanced scavenging efficiency under the modified trajectories. The results provide valuable insights into the optimization of piston motion trajectory to achieve higher performance. Furthermore, the proposed numerical model provides an effective tool for OFPEG design, optimization, and control strategy development, supporting the advancement of high-efficiency, low-carbon OFPEG systems for future transportation applications.

Wang, Jiayu, Morandi, Nicola, Lucchini, Tommaso, FENG, HUIHUA, Jia, Boru, Ren, Peirong

Achieving 70% Urban Fuel Consumption Reduction: An Opposed-Piston Engine-Based Mild-Hybrid Powertrain Architecture for Light Commercial Vehicles (JLA-2/JLA-T)

2026-01-0432

4/7/2026

This paper proposes a novel powertrain architecture for the urban Light Commercial Vehicle (LCV) segment, leveraging the compact JLA-2 opposed-piston (OP) engine paired with the reconfigurable JLA-T mild-hybrid architecture. Within SAE literature, OP engines are consistently associated with simplicity. As highlighted by Tom Ryan III (2008 SAE President) in the foreword of Opposed Piston Engines: Evolution, Use, and Future Applications, this architecture is characterized by its manufacturing simplicity” and described as a “relatively simple, robust, and cost effective” power unit solution. The present work builds on this established view. The JLA-2 engine solves traditional packaging constraints by reducing the block width by 30% for horizontal installation and is volumetrically self-sufficient, eliminating external compressors. Although the gear train required for crank synchronization introduces design challenges, explicitly accounted for in our model, the elimination of the cylinder head and valve train reduces component count. The study utilizes a comprehensive computational methodology—incorporating 0D/1D thermodynamics, 3D CFD, and FEA—to evaluate the system against a standard Ford Escape baseline. The JLA-T module mechanically blends torque using a planetary gear-set and a low-voltage 48V electric assist, capturing electrification benefits without the high costs and safety complexities of high-voltage systems. Simulation results suggest significant performance improvements, notably achieving a sub-9-second 0-100 km/h acceleration and enabling Zero Emission Vehicle (ZEV) compliance in restricted zones. Most significantly, the analysis indicates that this platform delivers up to a 70% reduction in urban fuel consumption when operated as a PHEV, driven by the system’s modularity and optimized energy recovery. This paper presents the system architecture, control logic, and performance comparisons, demonstrating a feasible technical pathway for decarbonizing urban transport fleets. (Note: “JLA” serves as the proprietary designation for the engine and electromechanical hybrid system series proposed by the authors).

Nigro, Norberto, Aguerre, Horacio, Carignano, Mauro Guido, Alonso, José Luis, Juni, Carlos A.

Analyzing Fastened Joints in Hydraulic Dampers Using Simulation and Experimental Methods

2026-01-0585

4/7/2026

The main purpose of this study is to develop and validate an accurate calculation model for a hydraulic damper piston valve joint, enabling reliable torque specification and clamp behavior without full prototype iteration. Joint stiffness is a primary interest point. The joint features a bolted interface with a laminated shim stack of many thin disks with varying outer diameters. Analysis of such joints are uncommon in literature, making it challenging to quantify the effects of load distribution, truncation, and surface contact effects between members. The proposed models discussed in this paper are based on frustum load distribution combined with annular-plate bending and elastic-foundation effects to capture the effects of washer cupping. Concrete outputs of the calculator include member load distribution, bolt and member stiffnesses, torque-to-preload relationships, and an external-load simulation that predicts when individual members lose clamp load. Detailed internal hydraulic flow through piston valve orifices and shim hydrodynamics are outside the present scope. For model correlation, axisymmetric finite-element analyses of contact pressure and joint compression were conducted, and a 30-sample torque-to-failure study quantified general joint behavior and friction characteristics. The proposed virtual development method allows early selection of joint geometry and torque specification prior to physical builds. The performance characteristics of a representative joint are presented, with simulation and experimental results that show improved preload prediction.

Dresen, Gabriel, Vollmar, Race, Roy Chowdhury, Sourav

CFD Investigation of Oil Ingestion and Aeration in a V6 Engine Oil Pan During Vehicle Maneuvers

2026-01-0279

4/7/2026

A computational investigation was carried out using SimericsMP+ to analyze oil distribution and aeration behavior in a V6 engine oil pan during severe vehicle maneuvers. The model accounted for the crankshaft/camshaft rotations and piston motions, which allows for capturing realistic oil distribution in cylinder head drainbacks, engine bay and sump after initializing the crankcase with prescribed oil levels to establish baseline aeration prior to applying dynamic maneuver profiles. Of particular interest was the response of the main oil gallery (MOG) pressure and the exposure of the oil pickup tube during kickoff conditions at multiple fill levels. Both a baseline configuration and a modified sump featuring a containment “doghouse” were examined. Results obtained from the kickoff maneuver show complete uncovering of the pickup tube in the baseline design, leading to unstable lubrication. The first doghouse design only delayed pickup tube uncovering briefly, as oil pooled at the rear gap and air ingestion still occurred. Full fill avoids air ingestion; however, high interaction with the crank shaft results in higher oil aeration longer term after kickoff maneuver ends. The findings highlight the complexity of oil behavior in engine environments, where unpredictable interactions during dynamic maneuvers can easily lead to ingestion and aeration. Despite this complexity, the computational strategy developed in this study was able to accurately reproduce and predict these events which were seen in the test scenario as well in the form of pressure readings at the pump inlet. Since these high-aeration events were validated against experimental measurements, this simulation approach proves to be highly valuable for guiding product design and optimization, allowing engineers to identify risks early and improve lubrication performance in the engines before physical testing.

Jia, Kun, Rahman, Ashique, Pandey, Ashutosh

CFD-Guided DoE-ML Optimization Methods in a Heavy-Duty Hydrogen Engine

2026-01-0326

4/7/2026

This study introduces a CFD-guided design of experiments (DoE) and machine learning (ML) framework for the co-optimization of piston and pre-chamber geometries in a passive pre-chamber heavy-duty hydrogen engine operating at medium and low loads. Starting from a reference configuration, an omega-type piston and a methane-optimized pre-chamber, the design space was parameterized using seven geometric variables. A Sobol sequence was employed to generate 96 randomized design variants in the DoE, each evaluated through high-fidelity 3D-CFD simulations to capture key combustion and performance metrics. The resulting dataset served as the foundation for developing and evaluating several ML regression models. A rigorous ML workflow was adopted, featuring 5-fold cross-validation and hyperparameter tuning via Bayesian optimization to ensure generalization and robustness. Model selection was based on multi-metric performance criteria including prediction accuracy, error stability, and sensitivity to design changes. The selected model demonstrated strong predictive capabilities across the design space and was integrated into an iterative optimization loop that continuously refined geometry predictions by incorporating additional CFD runs. This adaptive simulation-learning framework led to improved model accuracy and enabled rapid exploration of high-potential design regions. Beyond reducing time for technology deployment relative to expert-guided design strategies, the ML models offered interpretability by exposing key geometric sensitivities and highlighting high-impact design directions for enhanced hydrogen combustion.

Menaca, Rafael, Shakeel, Mohammad Raghib, Liu, Xinlei, Mohan, Balaji, AlRamadan, Abdullah, Cenker, Emre, Silva, Mickael, Zhang, Anqi, Pei, Yuanjiang, Im, Hong

Development and Preliminary Combustion Experiments of a Prototype Engine with Sleeve Valves Based on the Focusing Compression Principle

2026-01-0295

4/7/2026

Our laboratory has proposed the focusing compression principle which employs pulsed super-multi jets of gas colliding around the chamber center. This principle aims to achieve high thermal efficiency by reducing both exhaust and cooling losses. Exhaust loss is minimized due to relatively-silent high compression. Cooling loss is reduced due to thermal insulation caused by fuel-air mixture being confined to the chamber center and the compressible flow effect. In previous studies, we conducted fundamental gasoline combustion experiments on a proof-of-concept opposed-piston engine which incorporated this principle. This engine featured eight intake nozzles in an octagonal configuration and utilized non-sinusoidal and strongly asymmetric piston movements. The results indicated the possibility of high thermal efficiency based on less knocking under high compression, and the potential for stable combustion under lean-burn conditions. As a next step towards practical application with durability, we have developed a new opposed-piston engine with a small displacement of 123 cc which maintains intake ports of octagonal configuration, featuring a unique valve system. This unique valve system is characterized by setting a cylindrical-shaped sleeve-valve in between the inner and outer- cylinders. On operation, these sleeve-valves move along the central axis of cylinders, opening or closing all eight ports on the cylinder walls simultaneously. In this paper, we first show details of the present new engine developed and its preliminary experiments including non-combustion motoring experiments, and also combustion experiments using gasoline. The engine was successfully motored up to 750 rpm with no gas leakage around the sleeve-valve at compression process. Combustion experiments were initially tested from slightly-lean conditions.

Nishizawa, Tomohiko, Naitoh, Ken, Baba, Shotaro, Ukegawa, Hiraku, Yamada, Sota, Ozono, Yuka, Abiko, Mirei, Suzuki, Yosuke, Hara, Namito, Ito, Yoshikuni, Matsubara, Kosaku, Uenoyama, Kazuyuki

Development of BYD Flat Engine for Luxury Hybrid Vehicles

03-19-02-0007

2/24/2026

To meet the requirements of luxury hybrid vehicles regarding engine power, torque, size, and NVH performance, BYD independently developed a 2.0 T flat engine. Designs such as increased intake valve lift, widened intake valve profile, swept piston bowl, and extended exhaust backflow region optimized in-cylinder airflow, enabling the BYD flat engine to achieve a maximum power of 180 kW and a peak torque of 380 N·m. This engine is 820 mm in length, 430 mm in width, and 420 mm in height, saving approximately 45% in volume compared to a competitor engine. The lubrication challenges of the flat engine were addressed through the coordinated implementation of a dry sump system, a multifunctional oil pump, and piston ring orientation design. A novel parameterized modal analysis methodology (considering phase and amplitude) was used for optimizing NVH performance. In synergy with the sandwich-type soundproof plates and four-sided acoustic encapsulation, the noise level (1-m sound pressure level, four-point averaged) of the BYD flat engine is 2.2~2.9 dB(A) lower than the lower limit of AVL’s scattering band. Owing to its desirable performance in power output, packaging compactness, and NVH characteristics, the BYD flat engine has been integrated into the powertrain of the Yangwang U7 model.

Pan, Shiyi, Zhang, Nan, Wang, Qiang, Liu, Jun, Liu, Jing, Xu, Zhiqin, Zheng, Junli, Li , Cunshuo

Control Strategy and Dynamic Characteristics of a Hydrogen Opposed-Cylinder Free-Piston Engine Generator

2026-01-5017

2/23/2026

Free-piston engine generator (FPEG), as a novel energy conversion device, has the advantages of good fuel adaptability and high energy utilization. Combustion variation between cycles poses a significant challenge to the running control of an FPEG. A hierarchical control strategy, including motion, combustion, and generation power controllers, is designed in this paper to achieve the stable and efficient running of a hydrogen-fueled opposed-cylinder FPEG prototype. Piston motion is controlled by adjusting the generation current, which is adjusted through iterative learning using piston displacement feedback and adaptive control using piston velocity feedback. Generating power is regulated by controlling the throttle opening angle, which is adjusted through iterative learning. A multidisciplinary joint mathematical model is developed to simulate the dynamic characteristics and verify the control strategy. The simulation results reveals that the dead center position accuracy can be maintained within ±0.3 mm when accounting for 25% combustion variation between cycles and misfires. The power generation can be adjusted between 20 kW and 30 kW, with the adjustment error maintained within ±0.3 kW. The prototype achieved an indicated power of 30.5 kW and an indicated thermal efficiency of 43.4% during the standard cycle. Hardware-in-the-loop testing was conducted for cold start, stable operation, and misfire conditions, confirming that the electronic controller meets the control requirements of the FPEG system.

Wang, Jiesheng, Liu, Liang, Xu, Zhaoping

Simulation Driven Design of Crank-train Systems for Elevated In-Cylinder Combustion Pressures for Existing Architecture

2026-26-0400

1/16/2026

The work demonstrating a novel approach to the optimization of crankshaft design for heavy-duty commercial vehicle engines, specifically targeting non-automotive applications with elevated power ratings. The research focuses on a 6-cylinder, 5.6-litre diesel engine, originally rated at 160 kVA and upgraded to 200 kVA, where the challenge was to enhance the crank-train system’s robustness within existing packaging constraints. By fundamentally altering the crankshaft’s geometry and structural parameters, the new design achieves higher load-bearing capacity while inherently mitigating torsional vibrations, thereby eliminating the need for viscous dampers traditionally used in place of rubber dampers. Advanced simulation tools, notably AVL Excite, employed to iterate and evaluate the balance between crankshaft balance ratio, weight, and torsional behavior. The optimized design then validated through both simulation and physical vibration trials, with sixth-order angular displacement maintained within prescribed limits. Further refinement of the simulation model achieved by optimizing the torsional stiffness of the ring gear to ensure strong correlation with physical measurements. This work demonstrates an effective alternative to viscous dampers and provides a pathway for future crankshaft design in high-power commercial engines.

Khandelwal, Meha, Kaundabalaraman, Kaarthic, Rathi, Hemantkumar

Optimization of Negative Crankcase Pressure Mechanism to Minimize Oil Pumping into Combustion Chamber and Ensure Particulate Number Compliance in Euro VI Emission for Natural Aspirated Gas Engine

2026-26-0223

1/16/2026

Emissions regulations, such as Euro VI, drives the Automotive industry to innovate continuously in Engine development. One significant challenge is the engine oil pumping from the crankcase into the combustion chamber, where it participates in combustion, which contributes to increased Particulate Numbers and fails to meet Euro VI emission compliance. This issue is most noticeable during engine idling and motoring conditions. During this time, a higher negative pressure difference develops between the intake manifold, which is acting above the combustion chamber and the engine crankcase. This pressure difference drives oil-laden blow-by aerosols past piston rings during the intake stroke and through the valve stem seals, allowing oil into the combustion chamber. The impact of the pressure difference between the intake manifold and crankcase was studied by varying the crankcase pressure through crankcase ventilation system. The results confirm that oil entry into the combustion chamber, contributing to combustion, occurs primarily through the piston rings, contributing to increase in Particulate Number (PN). To address this issue, it becomes necessary to introduce a mechanism that optimizes negative crankcase pressure across varying engine operating conditions. By reducing the pressure difference between the intake manifold and crankcase, this mechanism prevents oil entering the combustion chamber, thereby minimizing Particulate Number emissions and ensuring Euro VI compliance. This study focuses on the development and implementation of a negative crankcase pressure control system via the crankcase ventilation system. Through targeted optimization, it provides an effective way to control oil pumping into the combustion chamber, thereby enhancing emission control and advancing the development of cleaner Naturally Aspirated Gas engines.

R, Mahesh Bharathi, Bondfale, Shubham, Jeyaprakasan, Dharoon Gautham

Combustion Chamber Geometry Comparison in Natural Gas Engines under Conventional and Dethrottled Operation

2025-36-0217

12/18/2025

Growing interest in cleaner energy has spurred progress in engine technology, focusing on greater efficiency and lower emissions. Methane-based fuels, like compressed natural gas (CNG), have become an alternative for spark-ignition engines, especially in Brazil. Among performance strategies, dethrottled operation stands out by reducing intake restrictions and minimizing pumping losses, a major inefficiency in conventional spark ignition engines. This improves thermal efficiency and reduces both fuel consumption and emissions. This study experimentally examines the performance and combustion of a CNG-powered Hyundai HR 2.5 16V engine, converted from diesel to spark ignition with natural gas, comparing factory (omega) and custom (reentrant) piston geometries under both conventional and dethrottled modes. The research evaluates how piston design affects combustion stability, efficiency, and emissions across different load strategies. Tests were conducted at 7, 8, and 9 bar loads, as well as full load, with engine speed at 1800 rpm. In conventional mode, load was controlled by the throttle at stoichiometric conditions (λ = 1); in dethrottled mode, the throttle was fully open, and load was controlled by mixture enleanment (λ > 1). The reentrant piston was designed to intensify turbulence at ignition, supporting faster flame propagation and combustion stability for methane fuels, especially under lean conditions. Results showed that the custom piston consistently delivered lower COVimep, shorter combustion durations, and higher thermal efficiency compared to the factory geometry. Dethrottled operation significantly reduced specific fuel consumption at low loads and improved indicated efficiency, despite increased THC. These effects were mitigated in part by improved combustion quality from the custom piston. Overall, the combination of dethrottling and optimized piston design offers a promising approach to improving the performance of natural gas engines operating under partial-load conditions.

Silva, Cristian Douglas Rosa da, Garlet, Roberto Antonio, Dapper, Jackson Mayer, Fagundez, Jean Lucca Souza, Lanzanova, Thompson Diórdinis Metzka, Martins, Mario Eduardo Santos

Hydro-Pneumatic Suspension Optimization for Mining Explosion-Proof Vehicles in Underground Coal Mines

2025-99-0106

11/11/2025

This study investigates the critical factors influencing the performance of hydro-pneumatic suspension systems (HPSS) in mining explosion-proof engineering vehicles operating in complex underground coal mine environments. To address challenges such as poor ride comfort and insufficient load-bearing capacity under harsh mining conditions, a two-stage pressure HPSS was analyzed through integrated numerical modeling and field validation. A mathematical model was established based on the structural principles of the suspension system, focusing on key parameters including cylinder bore (195–255 mm), piston area (170–210 mm), damping orifice diameter (7–8 mm), check valve flow area, and accumulator configurations (low-pressure: 1.2 MPa, high-pressure: 6 MPa). Experimental trials were conducted in active coal mines, simulating typical mining scenarios such as uneven road surfaces (120 mm obstacles), heavy-load gangue transportation, and confined-space operations in thin coal seams (<1.5 m). This study conducted experimental validation of a hydro-pneumatic suspension system (HPSS) for mining explosion-proof engineering vehicles under multi-condition operational scenarios in active coal mines. Field tests were performed to simulate typical mining environments, including uneven road surfaces (120 mm obstacles), variable-speed driving (constant speed, acceleration, deceleration), and inclined terrains (uphill, downhill, and near-horizontal road surfaces). Comprehensive performance evaluations focused on dynamic stroke stability, vibration attenuation, and safety metrics were carried out by replicating real-world mining conditions. Results demonstrated that optimizing the cylinder bore diameter and adjusting the piston area significantly enhanced dynamic stroke stability, ensuring consistent load-bearing capacity across diverse mining terrains. Furthermore, tuning the damping orifice diameter effectively improved anti-rollover capability while maintaining ride comfort, achieving a balanced trade-off between vibration suppression and operational safety. Parameter adjustments to the HPSS, validated through rigorous field trials, proved critical for enhancing driving stability and safety in complex underground mining environments. These findings provide actionable insights for designing robust suspension systems tailored to the extreme demands of mineral extraction operations.

Song, Yan, Liang, Yufang

Advanced Multi-Fidelity Simulation of Piston Oil Jet Cooling in High-Performance Engines

2025-32-0081

11/3/2025

The development of next-generation hydrogen-fueled engines introduces critical challenges related to thermal loads within the combustion chamber, particularly in high-performance applications. To address the extreme temperatures encountered, effective piston cooling strategies, such as oil jet impingement, are essential. Accurately predicting thermal stresses to prevent component failure is therefore crucial. However, numerical simulations often come with significant computational costs. This paper presents a comprehensive multi-fidelity modeling approach to predict the thermal behavior of pistons under these demanding conditions. The model integrates a simplified 3D thermal representation of the piston, a lumped-parameter mechanical model of the piston-liner assembly, and convective boundary conditions obtained at various levels of fidelity, from high-level Computational Fluid Dynamics (CFD) simulations to literature correlations. Additionally, the study examines the influence of different approaches to defining boundary conditions on the model’s predictive capability. Calibration of the model was achieved using experimental temperature measurements obtained by sampling residual surface hardness at 8 points on the piston crown after prolonged stationary operation at maximum power in a conventional naturally aspirated high-performance gasoline engine test case. The results demonstrate a strong correlation between experimental data and numerical predictions, validating the model's accuracy. Additionally, the study investigates the influence of piston crown thickness and the positioning of the cooling oil injection point on the maximum temperatures reached during operation. Findings reveal the critical role of both geometric design and cooling strategies in optimizing thermal performance. This work provides a robust, flexible, and affordable simulation framework for evaluating piston thermal behavior, contributing to the design of reliable engines capable of withstanding extreme thermal conditions.

Sassoli, Andrea, Romani, Luca, Ferrara, Giovanni, Paolicelli, Giovanni, Balduzzi, Francesco

Study of Combustion Characteristics of a Two-Stroke Opposed Piston Engine using Low-Octane Fuels

2025-32-0028

11/3/2025

Various fuels are being considered as the next generation of carbon neutral fuels, including methanol, ethanol, and SAF. These have widely different ignition properties. Methanol and ethanol are high-octane fuels, so there are no major problems with their use in gasoline engines. However, SAF is a hydrocarbon with a large molecular weight, so it has a fundamentally low octane rating and is not easy to use in SI engines. In order to put carbon-neutral fuels of various properties into practical use, it is effective to develop a technology that allows fuels with low octane to be operated in SI engines. Therefore, in this study, basic research was conducted on the combustion of fuels with low octane using PRF fuel in opposed-piston engines. Opposed piston engines are characterized by their light weight due to the absence of a cylinder head, low S/V ratio due to the ultra-long stroke, reduced cooling loss due to the long stroke, and reduced vibration due to the offsetting of the reciprocating inertial forces of the left and right pistons, resulting in high efficiency and output. In addition, one of the disadvantages of low-octane fuel is that it tends to auto-ignite, but combustion under high residual gas conditions has the effect of suppressing fuel auto-ignition, and by using a 2-stroke engine with a high percentage and high concentration of residual gas and locally high temperatures, auto-ignition is suppressed and low The use of two-stroke engines with high residual gas content and high concentration and high local temperatures can be expected to suppress auto-ignition and allow the use of low-octane fuels.

Yamazaki, Yoshiaki, Okawara, Ikumi, Liu, Jinru, Iijima, Akira

Ca Additive and In-Cylinder Condition on Promotion of Abnormal Combustion in Supercharged SI Engine

2025-32-0004

11/3/2025

Recently, global warming is becoming seriously. In the field of internal combustion engine, the thermal efficiency has to improve in the practical use. One of the current trends with spark ignition engine (SI engine) is “downsizing” which is equipped supercharger with the downsized displacement. The downsizing engine is popular in the field of the SI engine. However, one of the problems is the abnormal combustion so called Low Speed Pre-Ignition (LSPI) [1]. The LSPI occurs the engine operation which is low speed and high load condition. It has to be avoided, because the SI engine is broken and the improvement of thermal efficiency is obstructed. A lot of researchers have been reported about the mechanism of LSPI [2, 3]. One of the sources of LSPI would be the lubricating oil droplets in cylinder. One of the methods to avoid LSPI, it has been adjusted the ingredients of oil additive in lubricating oil. The state of the art of lubricating oil standard has been established anti-LSPI performance. However, in the future, many kinds of fuels will be adapted to the SI engine on the point of CO2 emission. So, it would be needed that the mechanism of LSPI would be cleared essentially. It has been reported that the ingredients of oil additive strongly effect on the occurring the LSPI. There are two kinds of information in our previous research. First, the data show that frequency of abnormal combustion is 1/10 of frequency of scattering lubricating oil from the piston crown [4]. Second, autoignition timing of scattering lubricating oil is almost at ATDC, however, several autoignition advanced the timing for BTDC continuously. The results of previous our research have been mentioned about the relation lubricating oil droplet behavior in cylinder and abnormal combustion occurrence which include LSPI [5]. Here, this research focuses on the effect of Ca additive in lubricating oil on the frequency of abnormal combustion which is conducted to the LSPI.

kitano, Kaito, Tanaka, Junya

Development of CAE Technology for the Design Support of Piston Pin Circlip

2025-32-0015

11/3/2025

This study focuses on the technology for establishing design criteria for the piston pin circlip (hereinafter referred to as "circlip"), which is a component that holds the engine piston pin. During the development of high-revving engines, failure of the piston sometimes becomes a problem, and the main factors are fatigue failure of the piston and falling of the piston pin. The falling of the piston pin is caused by the circlip disengaging from the groove by the inertial force due to the vertical motion of the piston. The circlip is compressed to the size of the piston circlip groove and assembled to the piston. Therefore, in order to prevent the circlip from falling out, it is necessary to compress it more and increase the reaction force acting on the groove. However, this measure raises concerns about the deterioration of the ease of assembly of the circlip. Therefore, it is necessary to establish evaluation criteria that prevent the circlip from disengaging and deterioration of its ease of assembly. To enable appropriate design of the circlip during the engine specifications review phase, we developed the following two technologies. The first is the development of a surrogate model that predicts the amount of plastic deformation of the circlip due to compression during the circlip assembly process and thermal loads during engine warm-up. This surrogate model was created using data obtained from actual measurement tests and CAE analysis, using a regression model. The second is the development of CAE technology that predicts the likelihood of the circlip disengaging, considering the amount of plastic deformation. These technologies were developed to support the optimization of circlip design and to contribute to improving the reliability of the engine.

Ishizuka, Atsushi, Watanabe, Naoto

An Investigation into the Impact of Cylinder Count on the Efficiency of Opposed Piston Two-Stroke Compression Ignition Engines

03-18-06-0037

10/9/2025

The gas exchange process of opposed piston two-stroke (OP2S) diesel engines is primarily driven by the pressure differential between the intake and exhaust, making them susceptible to cylinder-to-cylinder crosstalk, and therefore to cylinder count. This study examined how cylinder count influences brake efficiency in OP2S engines. Using an experimentally validated 1D engine model, three architectures, ranging from two to four cylinders, were created and simulated across their full operating ranges. To isolate the impact of cylinder count, all configurations employed identical cylinder and port geometries, and identical but scaled electrically assisted turbocharger based airpaths. The engines were also controlled to consistent trapped conditions at a given operating condition, resulting in comparable closed-cycle efficiencies. Comparisons were then made using both scaled electrified airpaths and by assuming isentropic airpath work, to assess the impact of airpath efficiency on the results. With electrified airpaths, the two- and four-cylinder architectures had approximately 4.1%rel and 2.2%rel lower brake efficiencies, respectively, than the three-cylinder configuration on average. Additionally, the three-cylinder engine was found to be less sensitive than the other architectures to airpath efficiency, as on a per-cylinder basis it had up to a 17% lower power requirement for the turbocharger compressor, and recovered up to 3% less energy from the turbocharger turbine. These trends were also present when assuming isentropic airpath work, with the magnitude of the efficiency penalty of the two- and four-cylinder architectures reducing to 0.8%rel and 0.6%rel, respectively due to the lower overall magnitude of airpath power requirements. In all cases, the dominant contributor to the above results was the differing scavenging characteristics of the engines due to cylinder-to-cylinder interactions, demonstrating that cylinder count has a measurable impact on OP2S efficiency, and should be a key factor in designing an efficient OP2S engine.

Vorwerk, Erik Scott, Prucka, Robert, Lawler, Benjamin, Huo, Ming

Approaches for Mechanical Development and Validation of Hydrogen Internal Combustion Engines

2025-01-0398

10/7/2025

Hydrogen Internal Combustion Engines (H2 ICEs) are seen as a viable zero-emission technology that can be implemented relatively quickly and cost-effectively by automotive manufacturers. The changed boundary conditions of a hydrogen-fueled engine in terms of mechanical and thermal aspects require a review and potential refinement of the design especially for the 'piston bore interface' (liner honing, ring and piston design) but also for other engine sub-systems, e.g. the crankcase ventilation system. The influence of oil entry into the combustion chamber is even more important in hydrogen engines due to the risk of oil-induced pre-ignition. Therefore, investigations of the interaction between friction, blowby and oil transfer into the combustion chamber were performed and are presented in this paper. During the investigations, experimental tests were carried out on a single-cylinder engine ('floating liner') and on a multi-cylinder engine. The 'floating liner' concept allows the crank angle resolved measurement of friction force between piston, rings and liner. A baseline and three different liner honing variants were measured during hydrogen operation and were compared to a baseline measurement during gasoline operation. In parallel, the oil consumption was determined by balancing all carbon-containing components in the intake air and exhaust gas. This is only possible when using a carbon-free fuel, like hydrogen. In addition, the measured influences on the single-cylinder engine were validated on the multi-cylinder engine. The aim is to find solutions that are advantageous for hydrogen propulsion, both in tribological terms and in terms of the tendency for oil-induced combustion anomalies. The measurement results are a very good base to identify further potentials for optimization and can be used as input for simulation models. The overall approach also supports the implementation of digital twins for a targeted and effective mechanical development and validation of future hydrogen engines.

Plettenberg, Mirko, Gell, Johannes, Grabner, Peter, Gschiel, Kevin, Hick, Hannes

Study on Oil Film Thickness of Piston Skirt Pattern Coating in a Commercial Vehicle Diesel Engine

2025-01-0397

10/7/2025

In recent years, there has been a trend towards lower engine speeds and downsizing of diesel engines to improve fuel efficiency. This has the advantage of reducing frictional losses in the hydrodynamic lubrication condition but causes severe lubrication in the mixed lubrication condition. In order to reduce friction losses without the risk of abnormal wear or seizure, pattern coatings of the piston skirt area have been proposed. In this study, the oil film thickness between piston and cylinder was measured to investigate the effect of pattern coating on the oil film thickness. The oil film thickness between the piston and cylinder were measured by the laser-induced fluorescence method using the optical fibers embedded in the cylinder. The oil film thickness on the piston skirt was successfully measured under the engine operating conditions for the medium duty Direct Injection (DI) diesel engine. The oil film thickness for the pattern coatings was compared with that for the solid coating. It was found that the dimples created by the pattern coating on the piston skirt anti-thrust side caused thicker oil film on the piston skirt upper point in the latter half of compression stroke. Based on the relationship between oil film thickness and the piston speed/side force ratio, it was found that dimples on the piston skirt have the potential to reduce oil starvation. In particular, at measurement points with higher piston speeds, pistons with dimples were confirmed to form a thicker oil film compared to those without dimples. Furthermore, the effect of the depth of the dimple on oil film thickness was also investigated, and it was suggested that an optimal dimple depth might exist.

Tanimoto, Keisuke, Ito, Akemi, Sumoto, Masayuki

Effect of Flow Speed and Turbulence on Methane Combustion in a Rapid Compression Machine

2025-01-0393

10/7/2025

Recent experimental work from the authors’ laboratory demonstrated that applying a boosted current ignition strategy under intensified flow conditions can significantly reduce combustion duration in a rapid compression machine (RCM). However, that study relied on spark anemometry, which provided only localized flow speed estimates and lacked full spatial resolution of velocity and turbulence near the spark gap. Additionally, the influence of turbulence on combustion behavior and performance across varying flow speeds and excess air ratios using a conventional transistor-controlled ignition (TCI) system was not thoroughly analyzed. In this study, non-reactive CFD simulations were used to estimate local flow and turbulent velocities near the spark gap for piston speeds ranging from 1.2 to 9.7 m/s. Simulated local velocities ranged from 0.7 to 96 m/s and were used to interpret experimentally observed combustion behavior under three excess air ratios (λ = 1.0, 1.4, and 1.6). Combustion was analyzed using pressure-based normalized cumulative heat release (NCHR) durations and high-speed shadowgraph imaging. At stoichiometric conditions (λ = 1.0), combustion duration decreased by over 70% with increasing flow speed, with optimal behavior observed between 33 and 72 m/s. At 96 m/s, durations increased again due to early spark kernel displacement and greater convective losses. For λ = 1.4, the shortest durations occurred near 23 m/s, corresponding to an 87% reduction in flame initiation time. At higher flow speeds, ignition consistency declined, with complete misfires at 72 m/s. For ultra-lean mixtures (λ = 1.6), stable combustion was only observed at low flow speeds (≤ 9 m/s); beyond this, ignition failed entirely due to heat loss and limited mixture reactivity. Shadowgraph imaging confirmed that larger, faster-growing flame kernels formed at optimal flow speeds, correlating with shorter combustion durations and higher peak pressures. At excessive flow intensities, however, early flame kernel disruption and elevated convective losses led to slower combustion or complete misfire.

Haider, Muhammad.Shaheer, Jin, Long, Yu, Xiao, Reader, Graham, Zheng, Ming

A Study of Variables Affecting Piston Skirt Loads on the Oppossed Piston Two Stroke Diesel Engine

2025-01-0499

9/16/2025

A kinematic model of primary piston motion was developed along with a simplified combustion model for the purpose of evaluating various factors that could impact the piston skirt thrust loads of an Opposed Piston Two Stroke Diesel engine. The assessment considered connecting rod length, wrist pin mass, peak cylinder pressure, indicated torque, and wrist pin offset. The results show that small changes in connecting rod length could realize significant improvements in piston skirt friction as well as increased engine performance. The results indicate that small increases in overall engine width should be considered when optimizing for reduced oil consumption and enhanced piston skirt lubrication.

Srodawa, John

Enhancing Robustness of Electro-Hydraulic Brake-by-Wire Actuators via Linear Active Disturbance Rejection Control

2025-01-0341

9/15/2025

In recent years, motorsport has increasingly focused on environmental concerns, leading to the rise of hybrid and fully electric competitions. In this scenario, electric motors and batteries take a crucial role in reducing the environmental impact by recovering energy during braking. However, due to inherent limitations, motors and battery cannot fully capture all braking power, necessitating the use of standard friction brakes. To achieve an efficient balance between electric motors and friction brakes, the brake pressure can no longer be directly controlled by the driver. Instead, it must be computed by the Vehicle Control Unit (VCU) and sent to a smart actuator, i.e. the Brake-By-Wire (BBW), which ensures that the required pressure is applied. The standard approach to achieve precise pressure control is to design a nested Proportional-Integral-Derivative (PID) control architecture, which requires an accurate nominal model of the system dynamics to meet the desired tracking performance. However, in motorsport applications, actuator dynamics are complex to identify, car-dependent, and, most importantly, time-varying due to factors like temperature changes and wear. These challenges make PID controllers based on nominal models less robust, both in terms of stability and tracking performance. To address these challenges, this paper proposes a robust architecture based on a cascade Linear Active Disturbance Rejection Control (LADRC) scheme for an electro-hydraulic actuator. The architecture consists of an inner loop, based on a second-order LADRC, which controls the piston position, and an outer loop, which employs a first-order LADRC to regulate the pressure. Compared to standard PID controllers, the LADRC approach promises two key advantages: it is faster and easier to tune while offering increased robustness. The proposed control scheme is experimentally validated on a test bench using a state-of-the-art BBW system and a racing car hydraulic line highlighting an increased robustness compared to a standard PID scheme.

Gimondi, Alex, Dubbini, Alberto, Riva, Giorgio, Cantoni, Carlo

The Challenges of Measuring Residual Brake Drag using Different Test Apparatuses and Methods to Mitigate Inaccuracies

2025-01-0343

9/15/2025

As automotive manufacturers have tried to set themselves apart by reducing emissions, and increasing vehicle range/fuel economy by eliminating any energy loss from inefficiencies on the vehicle, the brake corners have been an area of interest to reduce off-brake torque to zero in all conditions. Caliper designers can revise some attributes like piston seal grooves, and pad retraction features to reduce drag, but even if a caliper is designed perfectly in all aspects, trying to measure it in a reliable and repeatable manner proves to be difficult. There are many ways to measure brake drag all with ranging complexity. Some of the simplest measurements are the most repeatable, but it excludes the majority of the vehicle inputs. The most vehicle representative testing requires the most complex equipment and comes with the most challenges. This paper will focus mainly on the different ways residual brake drag can be measured, the benefits and challenges to each of them, the problems trying to measure zero, and what future measurement methods might look like.

Retting, Joshua

Effects of Piston Pre-Heating and Friction Reduction on Cold-Start Charge Preparation for DI Methanol Engine: An In-Cylinder CFD Study

2025-24-0040

9/7/2025

Methanol is gaining interest as a renewable fuel for Internal Combustion Engine (ICE) applications. A key challenge for this fuel is its low evaporation rate at low temperatures, which makes cold-starts problematic, particularly in cold climate conditions. The first combustion cycles are characterized by a low combustion chamber temperature and high engine friction. In previous work by the authors, a practical approach was presented to pre-heat the pistons and pre-condition the bearings, thereby reducing friction. In this article, in-cylinder Computational Fluid Dynamics (CFD) modeling is used to study the charge preparation of a DI-SI methanol ICE up to the end of compression. The model is calibrated in-house using measurements from a warm methanol engine. The piston temperature is varied within the range expected from the pre-heating and pre-lubricating device. Friction reduction is translated into the reduced amount of fuel needed to generate the IMEP required to idle the engine. Engine starting conditions at -20°C, 0°C, and +20°C are simulated. For these global conditions, different combinations of piston pre-heating and friction reduction are investigated. Warm engine conditions (90°C) are also modeled for comparison. The results show that the piston is a primary target for fuel spray. As expected, for a warm engine, the injected fuel is completely evaporated. For an ordinary cold-start at 20°C, the fuel distribution at the end of compression is 81% evaporated, 15% remains as film, and the rest as suspended droplets. In the cold-start at -20°C, only 23% of the fuel is evaporated at the end of compression, while the majority is deposited as a fuel film. By pre-heating the piston alone, the evaporated fuel increases to 37%. Alternatively, reducing the friction load to match warm engine conditions, drastically reduces the total fuel injected, resulting in 59% evaporated fuel. This demonstrates the potential of the proposed technology to improve methanol cold-start emissions.

Bovo, Mirko, Mubarak Ali, Mohammed Jaasim

Thermal Stress Reduction in Diesel Engine Pistons Using Semitransparent Ceramic Coatings: A 3D Numerical Study with OpenFOAM

2025-24-0003

9/7/2025

This research focuses on the thermal analysis of internal combustion engine pistons, evaluating the effects of high-temperature exposure during operation. A three-dimensional numerical study is conducted using OpenFOAM, modifying the software’s governing equations to analyze temperature distribution in different piston geometries. The study aims to assess the spatial temperature variation within the entire volume of the piston, providing a detailed understanding of heat transfer mechanisms. A multilayer approach is implemented, considering various configurations of ceramic coatings with distinct thermal and optical properties. The investigation incorporates an internal heat source model, where the heat absorption characteristics of the coating material influence the thermal behavior of the system. By evaluating aluminum- and titanium-based ceramic coatings, the study examines how semitransparency and heat radiation absorbance affect heat accumulation and transfer. The results highlight the significance of optical properties in modifying the thermal response of coated surfaces, demonstrating that coatings with heat radiation absorbance capabilities provide enhanced thermal insulation compared to traditional ceramic coatings. The numerical solution of the heat equation, incorporating experimental absorbance data, reveals that coatings with optimized optical properties reduce heat penetration into the piston substrate more effectively than models based solely on thermal conductivity. The findings contribute to the development of advanced thermal barrier coatings, improving the efficiency and durability of internal combustion engine components.

Gutierrez, Marcos, Taco, Diana, Bösenhofer, Markus

Schaeffler optimizes rolling bearings for hydraulic and axle drives

25TOFHP08_06

8/1/2025

Rolling bearings with optimized friction and performance characteristics can have a significant influence on reducing the power loss, design envelope and weight of hydraulic motors and pumps, gearboxes and axles in construction machinery. If correctly designed, rolling bearings can make a significant contribution to reducing carbon dioxide emissions. Most construction machinery is still operated conventionally, using diesel engines and hydraulic components. In the widely used adjustable axial piston pumps and motors, the input and output shaft are usually supported by two tapered roller bearings that are adjusted against each other. When designing the bearing support, it is advisable to reduce the preload to precisely the required minimum allowed by the load spectrum. The lower bearing preload leads to permanently lower axial forces between the tapered roller end face and inner ring rib and, therefore, to a corresponding reduction in frictional torque.

Scharting, Stefan

Method for Externally Controlled Availability of Lubricating Oil in Internal Combustion Engines

2025-01-0302

7/2/2025

Reduced raw emissions from internal combustion engines (ICE) are a key requirement to reach future green-house-gas and pollutive emissions regulations. In parallel, to satisfy the need for increased engine efficiencies, the friction losses of ICEs gains attention. Measures to reduce parasitic drag inside the piston assembly such as reduced piston-ring pretension or thinner grade engine oils may increase oil ingress into the combustion chamber. The oil ingress is known to imply increased particle emissions directly counteracting the raw emission reduction target of engine development. To resolve this target conflict, the transport mechanisms of oil into the combustion chamber are the topic of current research. Specially developed research engines featuring a vertical optical window come with big potential to visualize the phenomena of the oil behavior inside the piston assembly group. Such ‘glass-liner’ engines play a pivotal role in identification and quantification of local and global phenomena and their correlating operating parameters. The objective of this study is to develop and investigate a novel approach facilitating active control over the amount of oil available in the piston group assembly under varying operating parameters. The mechanical incorporation into the engine relies on ports embedded into the cylinder wall. These ports facilitate accessing the ring-land areas to realize fluid flow out of the piston group assembly using either vacuum or compressed air. The system is investigated in both a ‘glass-liner’ as well as a thermodynamic engine. Optically, the amount of oil present at the piston surface as well as residual oil on the cylinder wall is evaluated. A reduction of up to 40 percent of the indicated LIF-intensity from the residual oil on the cylinder surface can be shown. Similar results from tailpipe measurements are also demonstrated.

Stark, Michael, Fellner, Felix, Härtl, Martin, Jaensch, Malte

Flame Developments of Pilot Diesel Ignited Hydrogen Jet in an Optical Dual Direct Injection Engine

2025-01-0237

6/16/2025

This study aims to characterise the flame development for hydrogen-diesel dual direct injection (H2DDI) in an optically accessible heavy-duty engine through high-speed imaging of the natural combustion luminosity. A single hole, side mounted injector was used to inject H2 at 35 MPa in addition to a centrally mounted eight-hole diesel injector providing the ignition source for the H2. Firstly, the diesel pilot flame was examined without H2 to establish the combustion characteristics of the pilot flame. The pilot fuel energy was reduced from 1200 J to 120 J until the minimum repeatable diesel flame was found, which showed a flame distribution that transitioned from an initial quasi-steady diesel flame at peak load (1200 J), to a piston bowl wall-centric flame distribution (840 J) and then to an injector centric flame (120 J). The minimum pilot fuel quantity of 120 J was then used to investigate the ignition process of hydrogen main fuel mixtures supplying 90% energy and only 10% energy from diesel. The images showed three distinct stages of flame development. Firstly, the ignition of diesel pilot fuel occurs prior to interaction between the two fuels, as the H2 requires time to penetrate to the centre of the cylinder where the diesel pilot flame forms. Prior to ignition, the H2 jet penetrates towards the ignition source whilst it is simultaneously spread clockwise by the swirl flow. The second stage of flame development commences as the ignition of this H2 jet occurring after a period of interaction with the burnt products of the diesel pilot. Upon ignition, the H2 flame propagates upstream through the partially premixed H2 mixture and towards the H2 injector. Following the initial flame propagation, the combustion rate reduces as the transition into a diffusion mode occurs, i.e. the third stage of the flame development, with continued steady reaction zone growth, aided by the swirl flow. This three-stage ignition and flame development does not change with varied diesel pilot injection timing as evidenced by the flame images with only delayed phasing for later diesel pilot injection timing. However, the diesel pilot flame merges with the newly propagating H2 flame and thus the later diesel pilot injection timing leads to higher peak flame size and intensity.

Heaton, Alastar, Chan, Qing Nian, Kook, Sanghoon

Effects of Injection and Intake Timing on Atomization and Combustion in a Hybrid Gasoline Direct Injection Optical Engine under the Low-Speed Low-Load Condition

2025-01-0203

6/16/2025

With the growing trend of hybridization in modern engines, hybrid gasoline direct injection (GDI) engines are typically designed for high load at BMEP of 6 to 10 bar, low-to-mid speed of 2000 to 3000 rpm to achieve optimal fuel economy. However, these engines inevitably operate under low-speed, low-load conditions, such as during engine startup and low-speed cruising, where insufficient intake air often leads to poor air-fuel mixing and weak turbulence, resulting in suboptimal combustion. Adjusting intake and injection timing presents a simple and effective approach to optimizing the combustion process in hybrid GDI engines. In this study, an optical engine with a combustion system geometry identical to that of an advanced hybrid GDI engine was used. The engine featured a compression ratio of 15.0:1 and was equipped with a variable timing camshaft for intake timing control and an electronically controlled system for injection timing. High-speed color imaging, using transparent pistons and cylinder liners, captured the in-cylinder spray development and combustion processes. The interaction between the airflow, spray, and piston was analyzed to better understand its effects on combustion. The results showed that advancing the intake timing, relative to the baseline intake and injection settings, enhanced the interaction between the airflow and the fuel spray, improved flame kernel development and reduced pool fires caused by fuel films on the piston. In contrast, delaying the injection timing reduced pool fires by decreasing spray impingement on the piston; however, the delay prevented proper evaporation of the fuel droplets, causing the formation of a sooty yellow flame on the intake side due to the accumulation of fuel in the tumble region. This study demonstrates that careful tuning of intake and injection timings can optimize in-cylinder combustion, improve fuel-air mixing, and reduce emissions in hybrid GDI engines operating under low-speed, low-load conditions.

Cui, Mingli, Fu, Jinhong, Man, Xingjia, Nour, Mohamed, Zhang, Weixuan, Li, Xuesong, Xu, Min

Analysis of Combustion Characteristics of a Small 2-Stroke Opposed Piston Engine Using an Optically Accessible Engine and Numerical Analysis

2025-01-0223

6/16/2025

As global warming becomes more serious, decarbonization of internal combustion engines, which emit a large amount of carbon dioxide, is being promoted. It is predicted that many vehicles will still be equipped with engines in 2035, and a variety of powertrains will be required in the future. Therefore, we focused on the opposed-piston engine as an internal combustion engine specialized for power generation applications. The opposed-piston engine is characterized by its light weight due to the absence of a cylinder head, low S/V ratio due to the ultra-long stroke, reduced cooling loss due to the long stroke, and reduced vibration due to the offsetting of the reciprocating inertial forces of the left and right pistons. We believe that the engine for power generation can achieve the required high efficiency operation and vibration reduction. Therefore, in this study, combustion analysis of a two-stroke opposed-piston engine with features of low vibration, high efficiency, and high output was conducted using numerical analysis to solve the vibration problem, which is a demerit of engines for power generation, and to further improve thermal efficiency. In this study, a prototype opposed-piston engine with a displacement of 126.6 [cc] was built and used as an experimental device, but it is difficult to visualize the inside of a cylinder of an opposed-piston engine. Therefore, an experiment was conducted using a 63.3[cc] an optically accessible single-cylinder engine with the same bore and half the displacement and stroke, and the results were compared with the numerical analysis results of the an optically accessible single-cylinder engine, and the validity of the numerical analysis was confirmed. Therefore, we considered that the combustion analysis of an opposed-piston engine was also valid, and we conducted a combustion analysis of an opposed-piston engine using CONVERGE.

Yamazaki, Yoshiaki, Watanabe, Sou, Okawara, Ikumi, Otaki, Yusuke, Liu, Jinru, Iijima, Akira

Development of a High-Frequency Measurement Apparatus for Evaluating Piston Friction in a Small Gasoline Engines

2024-32-0100

4/18/2025

Efforts to enhance fuel efficiency in small gasoline engines, vital for reducing CO2 emissions, are concentrated on minimizing piston friction losses. Achieving this balance while addressing concerns such as piston seizure prevention and minimizing oil consumption presents challenges, particularly in small gasoline engines operating at higher speeds where the risk of piston seizure is significant. Hence, there is a critical need for accurate methods to measure piston friction. This study introduces the development of a measurement apparatus employing the floating liner method, initially devised by Takiguchi [1] and further adapted by Yamasaka for a mono-cylinder air-cooled gasoline engine [2, 3]. Yamasaka’s research successfully investigated the correlation between the apparatus’s natural frequency and the maximum engine speed measurable, achieving piston friction measurement up to 5000 rpm. Expanding on this achievement, this research aims to broaden the application of the floating liner method to a mono-cylinder water-cooled gasoline engine, enabling precise piston friction measurement up to 6000 rpm. The developed apparatus effectively captured piston friction forces at high engine speeds, offering insights into friction force generation characteristics during each engine stroke. In conclusion, the newly developed measurement apparatus proves to be a valuable tool for piston development aimed at enhancing fuel economy. The findings from this study contribute to ongoing endeavors to improve the efficiency of small water-cooled gasoline engines, thereby reducing their environmental footprint.

Honda, Riku, Ito, Akemi, Saika, Santa, Yamase, Ryouta, Hasegawa, Tatsuhiko, Sakioka, Takeru, Suda, Naoyuki, Ninomiya, Yoshinari

CFD Analysis of Pintle-Nozzle Spray for Swirl Chamber Type Small Diesel Engine -Application of Hole-Nozzle Atomization Model to Pintle-Nozzle

2024-32-0109

4/18/2025

Swirl chamber combustion system is commonly used for IDI (In-Direct Injection) diesel engine. It is characterized by swirl combustion chamber arranged in cylinder head, main combustion chamber with shallow piston recess and connecting throat where fuel spray and flame mixture is ejected out from the swirl chamber to the main chamber [1]. Fuel is supplied in the swirl chamber and a pintle type nozzle is often used in this type engine as its simple structure and robustness for operating condition. In this paper, numerical simulation of a pintle nozzle spray was focused on and simulated results were compared with high speed photo data obtained in a constant volume vessel (CVV). Spray angle and tip penetration were mainly evaluated, but simulated angle and penetration could not be matched simultaneously to these characteristics of the pintle nozzle spray when conventional spray models were used for the simulation. To overcome this mismatch, “Multi-hole replacement model” was newly introduced. In this model, annular liquid sheet was treated as a circular bundle of liquid columns and hole-nozzle breakup model is applied to each liquid column. Fundamental concept of “Multi-hole replacement model” and practical application procedure were explained here. This proposed spray model will be applied actual engine model for the next step and contribute to expand the scope of application of IDI engines.

Okazaki, Tadao, Fujiwara, Tsukasa

Development of Pistons Suitable for Compact Air-Cooled Engines

2024-32-0030

4/18/2025

For the realization of carbon neutrality, we are working on research to improve the thermal efficiency of engines for motorcycles. Friction losses in the cylinder bore account for about 40% of the total friction losses of the engine (Figure 1), which is directly related to thermal efficiency improvement [1]. Air-cooled engines are suitable for motorcycles due to their simplicity and light weight, but it is difficult to achieve both efficiency and reliability. Friction in the cylinder is generated by piston scuffing. The oil film distribution of the piston-skirt(=skirt) is thin at the center of the skirt and thick at the edge. To reduce piston friction, it is effective to make the thin oil film at the center of the skirt thicker. On the other hand, to reduce oil consumption, the oil film must be thinned. However, air-cooled engines, which are difficult to keep the cylinder temperature constant, cannot make the clearance between the cylinder bore and the piston small. An increase in clearance is a cause of increased oil consumption. To achieve both high efficiency and reliability of air-cooled engines, optimal control of the oil film thickness on the scuffing parts of the piston is necessary. We developed a piston capable of solving this difficult problem by combining CAE and laboratory tests and visualization technology. The excellent performance of the developed piston was proved by friction tests using a small air-cooled engine and oil consumption measurement results.

Suda, Naoyuki, Hihara, Taiki, Ninomiya, Yoshinari

Experimental Investigation for the Effect of Cavity Geometry on the Flame Propagation and Auto-Ignition in RCM

2024-32-0060

4/18/2025

In this experiment, we investigated the auto-ignition and flame propagation behavior by using flat piston and cavity pistons which has different geometries, depth, and width of the cavity. In this study, flame behavior inside the cavity is visualized with the ion-probes, which is embedded every 3mm radially from the center of the piston. We also used the pressure sensor in the combustion chamber and high-speed camera through the quartz window near the cylinder wall. Flame appearance obtained with high-speed camera shows that the flame propagation of the cavity piston is faster than that of flat piston. This is considered because of the outward induced flow in the squish area. That is, the flame propagation inside the wide cavity area pushes the unburned gas outwardly and induced the outward flow in the squish area. This induced flow promotes the flame propagation. As a result, unburned gas is consumed rapidly, and thus, it is also found that the intensity of Knocking is reduced by using cavity piston compared with flat piston. The combined analysis using the ion-probe and pressure data indicates that in the cavity piston auto-ignition occurred in the cavity area immediately after auto-ignition in the squish area and the knocking.

Yamaguchi, Riki, Esaki, Daigo, Tateishi, Tokua, Osaf, Ali Hassan, Miyoshi, Akira, Shimokuri, Daisuke, Yatsufusa, Tomoaki, Terashima, Hiroshi, Hara, Takaya, Honda, Yuya, Tadokoro, Tadashi, Kawano, Michiharu

Research on Basic Characteristics of a Two-Stroke Opposed Piston Engine

2024-32-0112

4/18/2025

This study investigated the performance characteristics of a two-stroke opposed piston engine that is capable of constantly operating with high power output and high efficiency. An investigation was also made of the performance obtained by applying a pseudo uniflow condition as a measure against large hydrocarbon (HC) emissions owing to blow-by of unburned mixture, which is an issue of two-stroke engines. The test engine had a displacement of 127 cm3 and a bore and stroke of 48 x 70 mm. One-point and dual-point ignition systems were used, and regular gasoline was supplied as the test fuel using a carburetor-based fueling system. Experiments were conducted at engine speeds of 1500 and 3000 rpm at ignition timings of 45 deg. and 35 deg. before top dead center. The results showed that large quantities of HC emissions were emitted because stable combustion was not achieved. This revealed that a stronger uniflow condition must be applied as a countermeasure rather than a simple pseudo uniflow.

Fukushima, Shumpei, Uehara, Ryota, Hayashi, Yoshiaki, Igarashi, Ryo, Tokita, Kazuho, Iijima, Akira

Prediction of Pre-Ignition Borderline on Supercharged SI Engine by Livengood-Wu Integral

2024-32-0008

4/18/2025

The LSPI (Low Speed Pre-Ignition) is one of the consecutive abnormal combustion cycles of supercharged SI engine with direct injection fuel supply system [1]. The LSPI occurs when the engine is running at low speed and high load condition. It is important for the SI engine to control essentially with alternative fuel, e-fuel and hydrogen in the future. It is considered that the LSPI would be caused by the autoignition of the deposit, the lubricating oil from ring crevice, the lubricating oil from piston crown and so on [2, 3, 4, 5]. Among of these causes, this research focuses on the scattering lubricating oil from piston crown. The previous our research has reported on the two points. One is about the frequency and quantity of the lubricating oil scattering from piston crown [6]. Another is about the frequency of abnormal combustion by the engine test [7]. As the result, it has been cleared that the frequency of abnormal combustion is 1/10 of scattering frequency of the lubricating oil from piston crown. Moreover, it has been evaluated in-cylinder condition by the Livengood-Wu integral when the autoignition occurred. The LSPI would occur suddenly, continue several cycles and return to the normal combustion cycle again. However, it is difficult to find the borderline that the LSPI would occur or not for each engine and operating condition. This research will try to define the borderline of the occurring LSPI or not. The experimental data show the autoignition timing has three patterns. The autoignition timing advances from ATDC to BTDC when the consecutive abnormal combustion cycles proceed, it delays from BTDC to ATDC and all abnormal combustion cycles appear at ATDC. It is proposed that the borderline of LSPI is defined by the analysis of those autoignition with the Livengood-Wu integral.

Omori, Takaya, Tanaka, Junya

Detecting Piston Ring–Cylinder Liner Metal–Metal Contact in a Fired Large Marine Diesel Engine Using Piezoelectric Transducers

03-18-03-0017

4/9/2025

Shear-polarized ultrasonic sensors have been instrumented onto the outer liner surface of an RTX-6 large marine diesel engine. The sensors were aligned with the first piston ring at top dead center and shear ultrasonic reflectometry (comparing the variation in the reflected ultrasonic waves) was used to infer metal–metal contact between the piston ring and cylinder liner. This is possible as shear waves are not supported by fluids and will only transmit across solid-to-solid interfaces. Therefore, a sharp change in the reflected wave is an indicator of oil film breakdown. Two lubricant injection systems have been evaluated—pulse jet and needle lift-type injectors. The needle lift type is a prototype injector design with a reduced rate of lubricant atomization relative to pulse jet injectors. This is manifested as a smaller reduction in the reflected ultrasonic wave, showing less metal–metal contact had occurred. During steady-state testing, the oil feed rate was varied; the high flow rate case was shown to reduce the amount of piston ring–liner contact, while no changes in the lubricant film thickness had previously been detected using traditional longitudinal ultrasonic sensors. This displays the increased sensitivity of shear sensors relative to longitudinal sensors in respect to the quantity of lubricant present. Piston ring oil film breakdown was also studied at a range of steady-state loading levels and engine slow down, showing the amount of contact decreased as engine load decreased, providing a real-time indication of the lubrication regime of the piston rings. When the load was further decreased, into total shutdown of the engine, the amount of contact increased until the engine had stopped rotating. The study has demonstrated the capability of shear ultrasonic sensors to detect changes in solid contact caused by injector design, oil feed rate, engine load, and engine shut down.

Rooke, Jack, Li, Xiangwei, Dwyer-Joyce, Robert S.

Impacts of Injection Pressure on Split-Injection Energy-Assisted Compression-Ignition Combustion of Low Cetane Number SAFs with a Gaussian-Shaped Ribbed Piston Bowl Design

2025-01-8350

4/1/2025

The impact of injection pressure on a split-injection energy-assisted compression-ignition (EACI) combustion strategy was studied in an optically accessible engine with a custom ribbed piston bowl design. Three injection pressures (600, 800, and 1000 bar) were investigated for three split-injection dwells (1.5, 2.0, and 2.5 ms) with a fixed second injection timing of -5.0 CAD. The Gaussian-shaped ribbed piston bowl design was employed to position hot combustion gases from the first injection near the centrally located injector to enable rapid ignition and mixing-controlled combustion of the second injection. At 600-bar injection pressure, as injection dwell was shortened, relocation of hot combustion gases near the injector became increasingly more difficult due to less available time for relocation and due to the higher in-cylinder densities at the start-of-injection (SOI) for the first injection. Increased injection pressure (800 and 1000 bar) improved the relocation of the first injection combusted gases and increased the number of fuel jets rapidly igniting and undergoing mixing-controlled combustion during the second injection. Injection pressures of 800 and 1000 bar for a 2.0-ms injection dwell resulted in a greater number of fuel jets rapidly igniting than for the 600-bar injection pressure with a 2.5-ms injection dwell. These results suggest there is potential to achieve EACI operation at more application-relevant engine speeds through the utilization of custom piston bowl designs which allow for stable engine operation with higher injection pressures.

Amezcua, Eri, Stafford, Jacob, Kim, Kenneth, Kweon, Chol-Bum, Rothamer, David

3D Design and Analyses of an IC Engine Piston under Fatigue Test Conditions Using CNTs for the Next-Generation of Motorcycles

2025-01-8359

4/1/2025

CNTs play an important role in modern engineering projects, especially in engine pistons design for the next-generation of motorcycles. This work presents a comprehensive analyses proposed project using finite element method under actual operating conditions purpose performance evaluation of a motorcycle engine piston design, investigating the suitability of four distinct materials. Precise material properties adhering to linear elastic isotropic behavior were defined within the software environment and proposed advanced nanomaterial ensuring accurate representations of the proposed under the prescribed loading scenarios. The primary objective was to identify the optimal material choice for the piston, ensuring superior strength, minimal deformation, and lightweight characteristics essential for high-performance engine applications. Moreover interpreting and understanding the dynamic behavior of common and advanced engineering materials. Through a comprehensive evaluation of the simulation results, incorporating factors such as material strength, surface deformation characteristics, and lightweight considerations, the Aluminum alloy reinforced with Carbon Nanotubes (Al-CNTs) emerged as the most favorable choice for the motorcycle engine piston design. This advanced composite material offers an exceptional combination of high strength, minimal deformation, and reduced weight, making it an ideal candidate for high-performance engine components subjected to substantial mechanical stresses and thermal loads. The study provides valuable insights into material selection strategies and design optimization techniques for critical automotive and aerospace components, ensuring reliability, efficiency, and adherence to stringent performance standards. Furthermore, the deformation patterns were analyzed, with maximum displacements of 0.01057 mm for AISI 1020 steel, 0.01006 mm for Alloy Steel, 0.01810 mm for Al-CNTs, and 0.02836 mm for 2618-T61 aluminum alloy. Al-CNTs composite demonstrated one of the two lowest surface deformations with significant improvement in high compression tolerance of 265.9 MPa achieved a safety factor of 2.25 with significant reduction in piston weight, further enhancing its suitability for the high-performance piston application. Eventually, the study result and analysis provides valuable insights into material selection strategies and design optimization techniques for critical motorcycle, automotive and aerospace components, ensuring reliability, efficiency, and adherence to stringent performance standards. In conclusion, this research presents an unprecedented innovative step in the use of carbon nanotubes in the design of engine pistons for next generation motorcycles.

Ali, Salah H. R., Ahmed, Youssef G. A., Ali, Amr S.H.R.

Comparative Evaluation of Untextured and Textured Surfaces for Wear, Wettability and Friction Characteristics

2025-01-8331

4/1/2025

Reduction of frictional losses by changing the surface roughness in the form of surface textures has been reported as an effective method in reducing friction in the boundary regime of lubrication. Laser-based micro texturing has been mostly used to create these texture patterns and it is reported that it can reduce the frictional resistance by ~20-50%. However, the use of laser-based techniques for texture preparation led to residual thermal stress and micro cracks on the surfaces. Hence, the current study emphasizes using conventional micromachining on piston material (Al alloy Al4032) to overcome this limitation. Three variations of semi-hemispherical geometries were prepared on the surface of Al alloy with dimple depths of 15, 20 and 40 μm and dimple diameters of 90, 120 and 240 μm. Prepared textured surfaces with untextured surfaces are compared in terms of wear, wettability, and friction characteristics based on Stribeck curve behaviors. Results of this investigation demonstrated that the use of textures limited three-body abrasion wear, reduced wettability and extended the mixed regime of Stribeck curve for improved tribology behavior. Textured surfaces had effectively reduced mean coefficient of friction up to 12.6% for boundary regime of lubrication.

Sahu, Vikas Kumar, Shukla, Pravesh Chandra, Gangopadhyay, Soumya

Experimental Study of Direct-Injection Compression-Ignition Hydrogen Combustion in an Opposed-Piston Two-Stroke (OP2S) Engine

2025-01-8430

4/1/2025

The future heavy duty powertrain market is expected to be more diverse, with a gradual shift towards cleaner and more sustainable alternative fuels. Among various options, the hydrogen Internal Combustion Engine (ICE) holds the promise of significantly reducing carbon emissions while leveraging existing ICE technology. However, it also faces substantial challenges related to engine performance, fuel storage and delivery, infrastructure development, economic feasibility, safety and market acceptance. This paper focuses on performance challenges of hydrogen engine, including knock and pre-ignition, as well as low thermal efficiencies, and introduces the Opposed-Piston Two-Stroke Hydrogen ICE (OP2S-H2ICE) as a potential solution. The study demonstrates that OP2S-H2ICE can operate using direct injection, compression-ignition (CI) combustion solely with hydrogen, under various low-load to partial load conditions. Specifically, as the load increases, the combustion transitions from partial-premixed controlled CI combustion towards mixing controlled CI combustion, resulting in thermal efficiency and power density comparable to those of diesel on the same OP engine platform. Compared with conventional four-stroke engine, the OP2S offers the flexible control of trapped temperature through scavenging by retaining more internal residual inside the cylinder. This feature enables the OP2S-H2ICE to overcome the high autoignition temperature, achieving CI combustion even at low load conditions. Initial tests demonstrated that ITE up to 47% can be achieved at these conditions with hydrogen CI combustion.

Huo, Ming, El-Hannouny, Essam, Longman, Douglas

Three-Body Abrasive Wear Surface Characterization of Military Diesel Engine Piston Rings and Cylinder Bores

2025-01-8346

4/1/2025

Two 50-hr engine dynamometer tests were conducted on 12-cylinder diesel military engines with differing piston ring sets. Engine A exhibited more than double the oil consumption over engine B. An investigation was conducted to explain why the oil consumption differed by employing several posttest analytical techniques including cylinder bore geometry measurements, surface metrology, wear characterization, and chemical analysis on the piston rings and cylinder wall coatings. The 3D colormaps of cylinder bore deformation showed uneven volumetric deformation through the piston stroke instead of 2D plane deformation. It was found that the primary reason of high oil consumption was direct loss of sealing between the piston, piston ring and cylinder bore due to predominately abrasive wear, three-body abrasive wear and bore polishing. Furthermore, the compromised sealing of the combustion chamber led to blow-by. Carbon deposits, corrosive byproducts, surface abrasives, loss of desired surface finish, and insufficient lubrication contributed to severe wear on the running face of the compression rings and cylinder wall near top dead center. The piston rings of Engine B appeared to reduce oil consumption by having a superior barrel contour of the running face as well as being softer by roughly 30%. It was also noted that the cylinder walls were not plateau honed for either engine.

Thrush, Steven, Chen, Aijie, Foley, Michael, Sebeck, Katherine, Boufakhreddine, Ziad

High-Speed Optical Diagnostics of Misfire Limits in a Spark-Ignited Heavy-Duty Hydrogen Engine

2025-01-8401

4/1/2025

This study investigates the ignitability of hydrogen in an optical heavy-duty SI engine. While the ignition energy of hydrogen is exceptionally low, the high load and lean mixtures used in heavy-duty hydrogen engines lead to a high gas density, resulting in a much higher breakdown voltage than in light-duty SI engines. Spark plug wear is a concern, so there is a need to minimise the spark energy while maintaining combustion stability, even at challenging conditions for ignition. This work consists of a two-stage experimental study performed in an optical engine. In the first part, we mapped the combustion stability and frequency of misfires with two different ignition systems: a DC inductive discharge ignition system, and a closed-loop controlled capacitive AC system. The equivalence ratio and dwell time were varied for the inductive system while the capacitive system instead varied spark duration and spark current in addition to equivalence ratio. A key finding was that spark energy correlated well with ignitability, as long as the spark was sufficiently stable. In the second phase of this study, we employed an intensified high-speed camera to directly view the early flame development process. Two distinct types of misfires were identified: flame kernels could be quenched as they were convected away from the spark plug, or by the spark plug shell and ground electrode. Flame kernels were typically extinguished within 300 μs after the end of the spark, but their lifetimes varied with spark duration in a way that suggests that flame kernels can be extinguished even during an ongoing spark. Furthermore, the heat release of fired cycles could be delayed both by unusually slow flame development and due to quenching effects of the spark plug.

Hallstadius, Peter, Saha, Anupam, Sridhara, Aravind, Andersson, Öivind

Topology Optimization of Multibody Systems Undergoing Dynamic Loading Using an Equivalent Static Displacement Method

2025-01-8655

4/1/2025

Structural topology optimization for vehicle structures under static loading is a well-established practice. Unfortunately, extending these methods to components subjected to dynamic loading is challenged by the absence of sensitivity coefficients: analytical expressions are unavailable and numerical approximations are computationally impractical. To alleviate this problem, researchers have proposed methods such as hybrid cellular automata (HCA) and equivalent static load (ESL). This work introduces a new approach based on equivalent static displacement (ESD). The proposed ESD method uses a set of prescribed nodal displacements, simulating the resultant reaction forces of a body subjected to dynamic loading, at different simulation time steps to establish the boundary conditions for each corresponding model—one model for each simulation time. A scalarized multi-objective function is defined considering all the models. A gradient-based optimizer is incorporated to find the optimal topology. Then, a new dynamic analysis is performed, the new ESD is defined for each model, and a new topology is obtained. The iterative process continues until convergence. Furthermore, this work also demonstrates the extension of the proposed ESD method in the topology optimization of multibody systems. To this end, the result shows an internal combustion engine's iterative topology optimization of the connecting rod and piston. Additionally, results from multiple load case problems have been presented to prove the effectiveness of the ESD methodology.

Gupta, Aakash, Tovar, Andres

Experimental Analysis of Piston Surface Temperature in a Heavy-Duty Compression Ignition Engine

2025-01-8383

4/1/2025

The heat transfer processes occurring in a compression ignition engine are complex, especially considering flame-wall interaction on the piston crown from impinging jets. To study the heat flux occurring on the piston in a heavy-duty diesel engine, a piston was instrumented with fifteen thermocouples and a wireless telemetry system. Eight of the thermocouples are high speed surface thermocouples placed primarily in regions with significant flame-wall interaction, providing crank-resolved surface temperature data. This work presents the first experimental datasets collected with this instrumented piston, describing in detail the thermocouple location selection process as well as data processing and uncertainty quantification for the high-speed surface thermocouples with a particular emphasis on cyclic variability and sensor-to-sensor variability. With this methodology established, data from this piston can be used for modeling and simulation studies as well as for studying the impact of operating conditions on heat flux and flame-wall interaction. The analysis showed that there were significant differences in observed cyclic variability of transient heat flux among the different surface thermocouples that did not appear physical. The sensors did appear able to capture phenomenological aspects of the heat flux process of mixing controlled combustion though the magnitude of transient heat flux appeared higher than expected and further work, including repeatability tests with additional instrumented pistons, is required to form stronger conclusions.

Gainey, Brian, Datar, Aditya, Ravikumar, Avinash, Bhatt, Ankur, Vedpathak, Kunal, Kumar, Mohit, Gingrich, Eric, Tess, Michael, Korivi, Vamshi, Lawler, Benjamin

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