Browse Topic: Knock

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Optimization Design and Performance Verification Method of Antiaircraft Gun Fuze2026-99-1630To be published on 07/24/2026
In order to ensure that the high-caliber artillery ammunition fuses can successfully complete their combat tasks with high quality, it is necessary to optimize the design of their structure and conduct simulation verification of their performance. Through optimization design, this paper determined that the distance between the antenna plate and the wind cap of the proximity detonation module of the high-caliber artillery ammunition fuse is 6.2mm, and the thickness of the wind cap top is 12.9mm; it also determined that in the coaxial line feeding mode, a circular patch is used as the antenna shape, with the lowest return loss (reaching -38.5244 dB), which is conducive to the emission of electromagnetic wave energy; by introducing the methods and processes of intensity simulation analysis and aerodynamic thermal simulation analysis, as well as the methods of performance verification, this paper provides reference and guidance for the simulation analysis of similar systems.
Liu, Liwen, Sun, Zhangyi, Ning, Quanli, Cai, Canwei
Analysis of the Cause of Knocking Noise in a Marine Dual-Power Dual-Branch Transmission Gear System2026-99-1650To be published on 07/24/2026
This study investigates the knocking noise phenomenon in a marine dual-power dual-branch transmission gear system. Vibration mechanisms are analyzed, and potential failure modes are assessed. System vibration data were evaluated using time-domain and frequency-domain methods. Results show that overall vibration levels remained within acceptable limits, with no indication of imminent failure. Physical inspection confirmed that the shaft, gears, bearings, housing, and installation met specifications, with no observed performance degradation or structural damage. By correlating noise occurrence with vessel loading conditions, a strong relationship was identified among gear transmission torque, the power distribution ratio between high-and low-pressure turbines, and the onset of knocking. Specifically, under low-load conditions, uneven power and torque distribution among the four gear branches led to insufficient loading on the low-pressure side. This light-load state induced instability in the low-pressure gears, resulting in periodic tooth disengagement or back-side tooth contact, which is established as the root cause of the knocking noise.
Gu, Chengzhong, Xu, Hanwei, Luo, Rirong, Ren, Fushan
Numerical Analysis of Pre-Ignition Factors in Hydrogen Engines2026-01-07407/1/2026
Numerical analysis was conducted to investigate abnormal combustion, a major challenge in efforts to improve hydrogen engine efficiency. Focusing on two factors that induce abnormal combustion—surface reactions and lubricating oil—numerical analysis examined the potential for each to trigger abnormal combustion. Furthermore, since it was confirmed that the autoignition prediction using a detailed chemical reaction mechanism deviates from experiments at temperatures around 800K, attempts were made to improve this issue. As a result, it was confirmed that surface reactions affect the chemical species ratio near the wall surface but have little effect on flame propagation. Regarding lubricating oil, two possibilities were investigated: the lubricating oil itself self-igniting and becoming an ignition source for the hydrogen mixture, and deposits generated from the lubricating oil generating heat and becoming an ignition source. The results of these investigations showed that autoignition occurs before top dead center in both cases: when lubricating oil is present in the mixture during the compression stroke and when deposits heated to high temperatures are present. This indicates that engine oil can induce pre-ignition. Furthermore, the effect of water vapor on ignition delay was investigated. Finally, it was confirmed that incorporating corrections for molecules possessing kinetic energy deviating from the Maxwell distribution under low-temperature, high-pressure conditions into the reaction rate calculation improves the prediction accuracy of autoignition around 800 K.
Moriyoshi, Yasuo, Yamane, Taichi, Wang, Zhiyuan, Kuboyama, Tatsuya
Efficient Powertrain Control Using Signal Decomposition: Utilizing Signal Decomposition Constituents for Knock Detection in Internal Combustion Engines2026-01-07377/1/2026
Knocking combustions in an Internal Combustion Engine (ICE) are engine damaging combustions, and reliable detection of each knocking event is very critical. Engines usually rely on piezo-electric knock sensors to monitor structure-borne noise, which outputs a complex, continuous time series signal. Typically, knock combustions have an additional noise component along with the regular combustion signal, but differentiation of knocking vs non knocking signal (signal to noise ratio) based on visual inspection of this signal alone is challenging and requires computationally intense signal processing such as Fast Fourier Transforms (FFT) or Wavelet transforms followed by manual calibration [1]. In this paper, we propose an alternative to replace traditional knock detection with more reliable time-domain alternative signal decomposition technique. Here we decompose the raw sensor signal into seasonality, trend, and residual, and use the residual component as it is seen to retain abnormalities in the signal during knocking combustion. Further, based on the amplitude of the residual, we can easily classify the combustions as low, medium, high or very high knocking events thus providing a precise and reliable detection.
Parulekar, Tushar A., Chilukuri, Sandeep, Mahmood, Haneefa
Investigating the Potential of Two Individually Controlled Injectors per Rotor for a Direct Injection Hydrogen Wankel Engine2026-37-00086/9/2026
Hydrogen-fueled rotary engines offer a promising zero-emission solution for compact commercial powertrains. This study reports experimental results from the further development of a naturally aspirated, direct-injection hydrogen rotary engine by HTM. Initial applications, such as an airport baggage tractor, demonstrated technical feasibility but revealed pre-ignition that limited maximum torque. To address this, mixture formation was investigated using an experimental setup with two independently controlled injectors feeding a single rotor injection channel. The effects on operating behavior, efficiency, and NOx emissions were evaluated. The dual-injector configuration significantly shortens injection duration and improves spatial distribution of hydrogen within the combustion chamber. Enhanced mixture control suppresses pre-ignition and enables higher mean effective pressure. Systematic variation of injection timing under representative steady-state conditions also shows potential for NOx reduction through differentiated injector operation. In-cylinder pressure analysis and exhaust gas measurements provide detailed insight into combustion characteristics and abnormal events. The dual-injector setup increases torque capability and operational robustness without additional mechanical complexity, supporting the use of hydrogen rotary engines in compact hybrid systems and stationary power applications.
Endres, Jonas, Beidl, Christian, Herold, Tim, Lavall, Philipp, Schmidt, Marvin, Hofmann, Silas, Kahl, Jonas
Experimental Study of Knock Resistance Offered by Direct Water Injections in a Single-Cylinder Spark Ignition Engine03-19-02-00114/11/2026
Stochastic end-gas autoignition in spark ignition (SI) engines, commonly called “knock,” limits attainable engine efficiencies. Multiple pathways to extend SI engine operation into knock-limited regions have been studied, including direct water injection (DWI). This study employs single-cylinder engine experiments with a centrally mounted water injector to investigate the knock resistance offered by compression stroke water injections, which, through incomplete mixing, can thermally stratify the cylinder. In SI, thermally stratifying injections are expected to forcibly widen the cylinder temperature distribution by preferentially cooling the cylinder periphery. The end-gas is in the cylinder periphery. A cooler end-gas would result in longer ignition delays, thus providing knock resistance. The difference between intake temperature required to match knock-limited CA50 and a baseline intake temperature at the load of 8 bar IMEPg (gross indicated mean effective pressure) was used to quantify the “effective charge cooling” for the injection timings studied. A higher positive value for the effective charge cooling implies higher knock resistance. Effective charge cooling values for early compression stroke injection timings (−180° to −120° aTDC) were observed in the range of ~35−45 K. Later compression stroke and intake stroke injection timings displayed effective charge cooling values in the range of ~5−35 K and ~0−20 K. A compression stroke injection timing sweep was performed at a load of 6 bar IMEPg while holding the spark timing, intake temperature, and water mass constant to study the effect of injection timing on the combustion process. Although CA50 advanced while delaying the injection timing (−180° to −80° aTDC), post-CA50 burn durations stayed nearly constant, a behavior consistent with the presence of thermal stratification. Thus, it was concluded that injection timings that heterogeneously cool the cylinder provide higher knock resistance compared to bulk cooling.
Datar, Aditya, Vedpathak, Kunal, Gainey, Brian, Lawler , Benjamin
Development and Preliminary Combustion Experiments of a Prototype Engine with Sleeve Valves Based on the Focusing Compression Principle2026-01-02954/7/2026
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
Relative Knocking Intensity to Discuss Similarities and Differences between Low- and High-Speed Knocking Phenomena2026-01-03124/7/2026
Knock intensity, the maximum half-amplitude of pressure oscillation, reaches 1 MPa once in thousands of cycles under a certain boosted high-load condition at the engine speed of 5000 min-1, which is named high-speed super knock. In the present study, a mass-production turbo-charged direct-injection gasoline engine is operated for the indicated mean effective pressure of 1.7 MPa at the engine speed of 1500 to 5000 min-1. Unburned-zone autoignition timing is estimated using Livengood-Wu integral coupled with a small set of ignition delay time equations, which matches that detected from the differential value of net heat release rate, with a difference below 2 degrees in the whole range of engine speed. As unburned-zone autoignition timing advances, ignition delay time in an unburned zone at the autoignition timing shortens. Whenever autoignition occurs at 15 degrees after TDC, the ignition delay time is the period of about 10 degrees, regardless of engine speed. Knock intensity divided by the intensity of pressure oscillation induced by the main combustion, is named relative knock intensity. True heavy knock with an extremely-large relative knock intensity occurs occasionally at the low engine speed of 1500 to 2000 min-1, of which the occurrence rate decreases with the increase in engine speed. The high-speed super knock also has an extremely-large relative knock intensity, which might be a rare occurrence of the true heavy knock. A propagation flame front is visualized at autoignition timing using 20 ion probes mounted on the combustion chamber roof. When the high-speed super knock occurs, a relatively-large volume of unburned zone is located directly below the exhaust valves. However, no remarkable autoigniton heat release is observed.
Zeng, Changzhi, Kuboyama, Tatsuya, Yatsufusa, Tomoaki, Okuyama, Shota, Kuwahara, Kazunari
Investigation of Flame Speed Effects towards Knock Suppression in a Boosted Spark-Ignited Engine Using 1-D Modeling2026-01-03114/7/2026
To combine high efficiencies and low pollutant emissions, engine manufacturers have developed downsized spark-ignited (SI) engines in light- and medium-duty applications utilizing charge boosting and high compression ratio. While these techniques have proven effective, abnormal combustion such as auto-ignition and knock present a challenge and an important limitation towards high efficiencies. In this work, simulations have been utilized for knock onset predictions as well to provide relevant insights and trends of engine and fuel parameters including flame speed on auto-ignition. A one-dimensional (1-D) GT-Power model was utilized in this study with a semi-predictive flame propagation model and kinetic mechanism solver to isolate the flame propagation rate on auto-ignition and knock. This work presents a comprehensive study of the laminar flame speed (LFS) effect on combustion at knocking conditions in a high compression ratio long stroke engine (LSE) fueled by propane. Knock onset and index from GT-Power as well as cylinder pressure were compared, as well as pressure-temperature trajectories and Borghi-Peters diagrams, while changing LFS via a multiplier at fixed ignition timing, fixed combustion phasing and knock-limited spark advance (KLSA). Moreover, cycle-to-cycle variability (CCV) was modeled through GT-Power. Results exhibited consistent trends at each condition, showing a significant importance of combustion phasing on knock onset and index. High flame speed displayed a reduction in knock index at fixed combustion phasing and KLSA conditions as well as a decrease in CCV, even eliminating knock onset at extreme LFS values, thus highlighting the benefits of faster flame speed in SI combustion with respect to engine efficiency and knock avoidance.
Douvry-Rabjeau, Julien, DelVescovo, Dan
Effects of Gasoline Composition and Operating Parameters on the Response of End-Gas Autoignition to Nitric Oxide in a Lean-Burn DI-SI Engine2026-01-03134/7/2026
Lean operation of spark-ignition engines can lead to engine thermal efficiency gains and lower NOx emissions due to reduced combustion temperatures. Yet, lean operation could still face challenges in end-gas autoignition and knock generation due to higher intake pressures and trapped NO in the residual gas. This study evaluates the impact of NO on end-gas autoignition for two gasoline fuels with similar octane rating but different composition: high cycloalkane fuel (HCA) and high olefin fuel (HO). Experiments were performed at stoichiometric and lean (λ = 2) conditions and at two engine speeds of 1400 rpm and 2000 rpm. Accompanying chemical kinetics simulations in CHEMKIN revealed that the mechanisms controlling the effect of NO on autoignition are similar λ = 2 and λ = 1, with NO + HO2 = NO2 + OH being the main pathway for enhancing reactivity by promoting low-temperature heat release (LTHR). The compositionally different fuels reacted differently to NO seeding and engine speed, and differences were augmented at λ = 2 compared to λ = 1 as the end-gas autoignition shifted to the low temperature regime. HO, which has inherent low temperature chemistry, was strongly impacted by engine speed at low NO seeding levels, with no noticeable peak of LTHR detected at 2000 rpm. On the other hand, LTHR of HCA was marginally affected by shortened residence time at higher engine speed as NO + HO2 reaction was not greatly affected by shorter time scales, since HO2 production was sustained even at 2000 rpm to support OH generation from NO + HO2. Contrary to HO, HCA exhibited greater sensitivity to NO seeding, as the increased OH production at higher NO concentrations offset the OH-quenching effect of cyclopentane, which accounts for 28.6% of HCA’s composition. Consequently, a sensitivity analysis revealed that fuels with weak inherent low-temperature chemistry, like HCA, are likely to be more sensitive to variations in NO concentration and charge temperature, whereas fuels with strong low temperature chemistry are more sensitive to variations in end-gas λ and intake pressure.
Kim, Namho, Abboud, Rami, Sjöberg, Magnus, Lopez Pintor, Dario, Saggese, Chiara, Matsubara, Naoyoshi, Kitano, Koji, Yamada, Ryota, Sugata, Kenji
Knock Phenomenon Investigation in SI Engine Fuelled with Ammonia-Hydrogen Mixture2025-01-053211/25/2025
Ammonia has emerged as a compelling carbon-free alternative fuel for applications in sectors such as power generation and heavy-duty transportation, where thermal energy conversion plays a dominant role. Its potential lies in its high hydrogen content, carbon-free combustion, and the feasibility of large-scale storage and transport. However, ammonia’s combustion behavior poses significant challenges due to its low reactivity, characterized by a low laminar burning velocity, high autoignition temperature, and narrow flammability range. These properties hinder stable and efficient operation in conventional internal combustion engines. A common strategy to mitigate these limitations involves blending ammonia with hydrogen—often generated via on-board catalytic cracking of ammonia—which improves ignition and flame speed. Despite these benefits, the presence of hydrogen increases the risk of knock, particularly in high-compression-ratio engines designed to improve thermal efficiency. This research focuses on evaluating knock phenomena associated with ammonia-hydrogen fuel blends in spark-ignition ICEs. First, a Methane Number was obtained for all ammonia-hydrogen blends to quantify the impact of hydrogen on ammonia knock reactivity under conditions close to those of the Motor Octane Number. The second part of this study explores the impact of knock for a fuel mixture consisting of 90% ammonia and 10% hydrogen by volume under varying engine parameters such as combustion chamber design and compression ratio on knock onset and severity. Experiments were conducted at engine speeds of 1000, 1500, and 2000 RPM, across intake pressures ranging from 1.0 to 1.8 bar (in 0.2 bar increments), equivalence ratios between 0.9 and 1.1, and intake temperatures of 60, 65, and 85°C. This study aims to identify the key parameters influencing knock intensity, onset, and distribution, as well as overall combustion properties.
Hurault, Florian, Brequigny, Pierre, Foucher, Fabrice, Rousselle, Christine
Development of a Comprehensive Predictive QD Knock Simulation Model for Hydrogen, Methanol, and an Ammonia–Hydrogen Blend2025-01-052811/25/2025
To support the transition toward climate-neutral mobility and power generation, internal combustion engines (ICEs) must operate efficiently on renewable, carbon-neutral fuels. Hydrogen, methanol, and ammonia-hydrogen blends are promising candidates due to their favorable production pathways and combustion properties. However, their knock behavior differs significantly from conventional fuels, requiring dedicated simulation tools. This work presents a modeling framework based on quasi-dimensional (QD) engine simulation, including two separate knock prediction models. The first model predicts the knock boundary of a given operating point and combines an auto-ignition model with a knock criterion. The overall methodology was originally developed for gasoline and is here adapted to hydrogen, methanol, and ammonia-hydrogen blends. For this purpose, the relevant fuel properties were incorporated into the auto-ignition model, and a suitable knock criterion was identified that applies to all investigated fuels. The model was validated using experimental data from single-cylinder engine tests. In addition, two entirely new modeling approaches were developed to predict statistical knock values, specifically knock frequency and knock intensity. Each model was calibrated once per fuel and subsequently validated across a wide range of conditions. The results show that the adapted knock boundary model and the new statistical model accurately capture the knock behavior of hydrogen, methanol, and ammonia-hydrogen blends. The methodology enables predictive knock analysis using QD simulation and supports the development of robust, high-efficiency ICEs for future carbon-neutral applications.
Benzinger, Steffen, Yang, Qirui, Grill, Michael, Kulzer, Andre Casal, Plum, Lukas, Hermsen, Philipp, Günther, Marco, Pischinger, Stefan, Hurault, Florian, Foucher, Fabrice, Rousselle, Christine
A Combustion CFD Study on the Pre-Chamber Jet Combustion Technology for Large Motorcycle Gasoline Engine2025-32-000111/3/2025
The objective of this study is to enhance the full-load power and the partial-load thermal efficiency of a gasoline spark-ignition engine for large motorcycles. To achieve these goals, it is important to increase the combustion speed and mitigate knocking, so a passive pre-chamber jet combustion system was evaluated. In the specification study, a three-dimensional combustion simulation incorporating detailed chemical kinetics was used to analyze the combustion mechanism, including knocking detection. For full-load conditions, a passive pre-chamber jet combustion system was evaluated. It accelerated combustion by increasing turbulent kinetic energy in the main chamber through jets sprayed from the pre-chamber. By increasing the compression ratio by 2.0, the full-load indicated work increased by 3.6% compared to conventional SI combustion. Under partial-load conditions, the passive pre-chamber jet combustion system faced challenges, such as reduced jet temperature due to increased residual gas in the pre-chamber, heat loss at the holes, and excessive initial jet penetration, which inhibited ignition in the main chamber. To address these issues, the pre-chamber jet 2-plug combustion system was evaluated, where main-chamber side-plug ignition was followed by pre-chamber ignition. The pre-chamber jet 2-plug combustion system enhanced jet ignition through flame interaction in the main chamber, resulting in increased combustion speed. Furthermore, relocating the main-chamber side-plug to a position between the exhaust valves closer to the bore center increased combustion speed and mitigated knocking. As a result, the pre-chamber jet 2-plug combustion system, with the side-plug located between the exhaust valves, enhanced partial-load indicated thermal efficiency by 1.7 percentage points compared to conventional SI combustion.
Ando, Hirokazu, Tanaka, Takumi, Tomizawa, Kengo, Inoue, Yosuke
Computational Investigation on a Boosted Uniflow Scavenged Direct-Injection Combustion Engine (BUSDICE) with Alcohol Fuels2025-32-002711/3/2025
Alcohol fuels, produced from renewable energy sources, are considered a crucial solution for achieving life-cycle carbon neutrality in internal combustion engines. The Boosted Uniflow Scavenged Direct-Injection Combustion Engine (BUSDICE) exhibits significant potential for high thermal efficiency with an aggressive downsizing design. In this study, a computational investigation was carried out to assess the spray mixing and combustion characteristics of BUSDICE fuelled with methanol and ethanol, compared with gasoline, under a high-load condition. The injection duration of methanol and ethanol is significantly longer than that of iso-octane, leading to incomplete evaporation. The mixture exhibits an “outer-rich, central-lean” stratification pattern due to the short mixing time and swirl flow transportation for all three fuels. However, the prolonged injection of methanol induces stronger turbulence, which can enhance the local mixing. The spatial mixture stratification, particularly near the spark-local area, has a strong influence on the initial kernel development and flame propagation. Consequently, methanol exhibits a shorter ignition delay than ethanol under the same spark timing, leading to faster flame propagation attributed to a richer equivalence ratio around the spark plug. Nevertheless, the ignition and combustion performance of ethanol can be improved by advancing the spark timing. The spark timing study reveals that alcohol fuels can operate under high load without knocking, whereas iso-octane requires retarded ignition timing to prevent knocking. As a result, methanol and ethanol provide a better IMEP and ITE than iso-octane under high-load conditions. From an emissions perspective, due to their low carbon-to-hydrogen (C/H) ratio and high oxygen content, unburnt hydrocarbon emissions decrease significantly when using alcohol fuels, especially methanol, for which these emissions are almost zero. However, the soot of ethanol shows a slight increase than iso-octane, due to the highly stratified mixture and incomplete combustion. Additionally, the NOx of ethanol and methanol increases due to the higher combustion temperatures than iso-octane. Overall, the results highlight the strong potential of alcohol-fuelled BUSDICE engines as compact and sustainable solutions for small-displacement powertrains, offering high thermal efficiency and substantially reduced pollutant emissions.
Feng, Yizhuo, Lu, Enshen, Dong, Shuo, Keshtkar, Hossein, Wang, Xinyan, Zhao, Hua
Study on Combustion Detection of a Spark-Ignition Engine with Fuel Variation Using Various Sensors2025-32-005211/3/2025
The use of alternative fuels, such as biofuels and synthetic fuels in small mobility engines has become more common these days. Although these fuels contribute to the carbon neutrality, it is known that they do not have a certain fuel composition, which significantly affects the combustion characteristics of an engine, such as knocking and combustion duration. Therefore, to get the most out of these sustainable fuels, it is necessary to develop engine systems that are highly robust to variations in fuel composition. To achieve this goal, a method to sense fuel characteristics onboard using sensors already widespread in use or can be installed inexpensively is required. Although in-cylinder piezoelectric pressure sensors are useful for research in the laboratory, it is not suitable for the use in commercial engines because of its high cost. Therefore, the use of other sensors should be considered. The purpose of this study is to experimentally analyze what information related to combustion and fuel can be obtained from multiple cost-effective sensors mounted on an engine. For that goal, a linear multiple regression model and Neural Network (NN) model was developed to estimate fuel’s Lower Heating Value (LHV) and combustion duration. Experiments were conducted on a 4-cylinder spark ignition (SI) engine, and combustion characteristics of multiple fuels were investigated while varying engine operating conditions. In addition to gasoline, CH4 gas was introduced into cylinders to simulate the change in fuel composition. Sensors used in this study include intake and exhaust pressure sensors, thermocouples, and in-cylinder ion current sensor. Selection of input variables (sensors) for the regression models were done based on the results of the experiment, and linear multiple regression model and NN model were developed. The prediction errors (RMSE) for LHV were 0.54 MJ/kg with linear regression model and 0.95 MJ/kg with NN model. For CA10-90, prediction errors were 6.15 deg with linear regression model and 14.48 deg for NN model. Since the accuracy of the models were not high enough, hyperparameter tuning was done using Bayesian optimization, and prediction accuracies were improved. However, further work, such as building physical model,increasing sample size, or adding extra sensors, must be done to use these models for engine control.
Hayashi, Kohei, Kim, Jihoon, Yamasaki, Yudai
A Study of Knocking Characteristics in a Hydrogen SI Engine under High Compression Ratio2025-32-006311/3/2025
This study investigated the knocking characteristics of a hydrogen spark ignition engine for the purpose of increasing efficiency and expanding the operating range. In recent years, research focused on carbon neutrality has been vigorously conducted, and hydrogen has attracted attention as a next-generation fuel for internal combustion engines (ICEs). The combustion characteristics of hydrogen are vastly from those of existing gasoline. It is essential to have a sufficient understanding of the combustion characteristics of hydrogen in order to develop next-generation ICEs designed to operate on hydrogen fuel. There are especially many aspects of the knocking mechanisms of hydrogen that are unclear. Consequently, those characteristics and mechanisms must be clarified for the purpose of expanding the operating range of hydrogen engines and enhancing their efficiency. In this study, experiments were conducted using a single-cylinder hydrogen engine that was operated at a high compression ratio of 17:1. High-intensity knocking was observed while operating the engine under various ignition timings and equivalence ratios. The knocking intensity and knocking mode characteristics were examined based on the observed knocking data.
Ishihara, Hiromasa, Kishibata, Shunsuke, Miyake, Shota, Iida, Tomoya, Kuwabara, Kenta, Yoshihara, Shintaro, Miyamoto, Sekai, Iijima, Akira
Knock Sensors for Two Wheelers Applications2025-32-007911/3/2025
This paper describes the design and characteristics of the knock sensor. The sensor is already used as a commodity product for automotive applications and used by all automotive OEMs for spark ignited combustion engines. With the arrival of the electronic fuel injection on the two wheelers, further optimization of the combustion can be obtained. Although there are many publications on the engine knock strategy, little is known publicly about the sensor itself. The knock sensor is an accelerometer based on a piezoelectric component; it provides an analog signal of the engine vibration. The Electronic Control Unit will filter the signal according to a specific strategy and defines the presence and intensity of the engine knock. The ECU will act accordingly on the ignition timing. The inner structure as well as the mechanical and electrical interface are described in this article.
van Est, Jeroen, Prieu, Corentin
Application of MAN Loop Scavenging in a 125 cm 3 Two-Stroke Racing Engine2025-32-002911/3/2025
The use of MAN-type loop scavenging port arrangements in a 125 cc two-stroke racing engine is being investigated. These make it possible to provide larger cross-sections for the transfer ports, but at the expense of the exhaust port cross-section. The investigation is carried out using 1D calculations with GT-Suite. It is shown that significantly higher maximum outputs are possible in this way. However, this requires large exhaust widths, as otherwise the exhaust port is too small and the advantage of the larger transfer cross-section is overcompensated. Mixed forms between the original MAN loop scavenging and Schnürle loop scavenging can represent a good compromise. To improve the power characteristic vs. speed, which is influenced negatively by the higher maximum outputs, optimizations of port heights and exhaust pipe dimensions are carried out. A configuration with the same maximum output as the basis but a wider power band is also shown. One open point is the quality of the scavenging. Results from the literature suggest that similarly good results are possible with MAN-type loop scavenging as with the Schnürle scavenging of the base engine. However, further investigations are required here.
Eilts, Peter
Influence of Twin-Scroll Turbocharging on the Performance of Direct Injection Gasoline Engine2025-01-507010/16/2025
In order to further understand the effect of twin-scroll turbocharging on the engine performance, this paper adopts a combination of one-dimensional numerical simulation and experimental research methods to compare the effects of two-scroll and single-scroll turbocharging on the power and fuel economy of direct injection gasoline engine. The research results show that, compared with the single-scroll turbocharger, twin-scroll turbocharger increased the low-end torque for 16% and 32% at 1000 r/min and 1500 r/min, respectively. However, the average fuel consumption has increased 1.3% at part load with twin-scroll turbocharger due to the pumping loss. Compared with a turbocharged port injection engine with a displacement 1.2 times that of the former, the twin-scroll turbocharged engine saved 11% fuel economy at part loads. The fuel consumption is saved 11% at part loads with twin-scroll turbocharger. This research first establishes the 1D simulation capability in twin-scroll turbocharger, and essentially researches the influence of twin-scroll turbocharger on GDI engine for the first time in China. Twin-scroll turbocharging can increase low-end torque of GDI engine efficiently, take advantage of pulse of exhaust manifolds, eliminate exhaust counter pressure of each cylinder, reduce the residual gas in cylinder so that the anti-knock capability is increased.
Yu, Xiaocao
Impact of Oil Composition on Pre-Ignition in a Hydrogen Engine04-18-03-001810/10/2025
Pre-ignition (PI) is a common issue in internal combustion engines (ICE) with spark ignition. While the various causes have been identified with conventional fuels (such as gasoline or gasoline blends), the causes with hydrogen in ICE are not yet fully understood. This article presents the results of investigations into the influence of seven different lubricating oils on PI in a single-cylinder hydrogen research engine. The variation of two different parameters at two engine speeds were investigated: load and air/fuel mixture. For both variations, the tests start at the same conditions and run until the operating limit of the engine is reached (peak firing pressure, or maximum intake manifold pressure). The PI and knocking PI are investigated, while classifying them according to the peak cylinder pressure. It has been observed that enleanment above λ = 2.4 can lead to higher PI rates, while simultaneously reducing the knocking PI. During the load sweep at 2000 1/min, the highest achievable load among all the oils ranged from IMEP = 19–21 bar, while at 4000 1/min, it ranged from IMEP = 12–15 bar. The performance of the oils showed significantly more disparity at the elevated engine speed. While the impact of different lubricating oils on gasoline engines is rather limited, the outcome of this experiment indicates that in the case of hydrogen engines, oils can have a significant impact on PI. In addition to the oil formulation, different viscosities were also investigated. A lower relative calcium content leads to a much higher PI rate, a lower relative calcium content combined with a higher viscosity did not impact the PI rate. The base oil composition came second in terms of PI influence. The sulfated ash content did not show differences in terms of PI rate. In contrast to gasoline engines, the PI tendency increases with increasing engine speed.
Pehlivanlar, Benjamin, Torkler, Michael, Fischer, Marcus, Göbel, Christoph, Pischinger, Stefan, Maulbetsch, Theo, Nübling, Fritz, Neumann, Stephan
Bridging Fundamental Combustion Analysis and Engine Knock Behavior -1st Report, CFR Engine Test for Various RON Fuels2025-01-039110/7/2025
A collaborative study was conducted to bridge the gap between fundamental combustion research and engine-scale observations of knock in spark-ignition (SI) engines. Using Primary Reference Fuels (PRFs) with Research Octane Numbers (RON) of 80, 90, and 100, experiments were carried out with a Cooperative Fuel Research (CFR) engine at air-fuel ratio, λ = 1.0, focusing on knock onset conditions in terms of unburned gas pressure and temperature. In the engine tests, pressure traces under knocking conditions were analyzed to identify knock onset and to estimate the corresponding unburned gas temperature history. Results showed that the pressure at knock onset varies clearly with PRF value: higher RON fuels exhibited knock onset at higher pressures, likely due to changes in compression ratio applied to match standard RON test procedures. In contrast, the unburned gas temperature conditions showed partial overlap across different PRFs, but with a tendency for higher RON fuels to experience knock onset at slightly higher temperatures. These findings provide a coherent dataset linking engine-based knock behavior with fundamental combustion characteristics, forming the foundation for the reaction-kinetics-based analysis presented in the second report. Additionally, the CFR engine experiments were also conducted at λ = 0.88 to support the comparison with standard RON measurement conditions.
Yasutake, Yuki, Misono, Katsuhiro, Suzuki, Yoshikatu, Naiki, Taketora, Watanabe, Manabu, Moriyama, Hinata, Morii, Youhi, Tsunoda, Akira, Maruta, Kaoru
Bridging Fundamental Combustion Analysis and Engine Knock Behavior - 2nd Report: Detailed Analyses of Knock Behavior Based on Fundamental 1D DNS and Its Relationship with Engine Knock2025-01-039210/7/2025
A collaborative study was conducted to bridge the gap between fundamental combustion research and engine-scale observations of knock in spark-ignition (SI) engines. In the first report, CFR engine tests using Primary Reference Fuels (PRFs) were conducted and knock onset conditions were identified for each fuel. In this study, one-dimensional direct numerical simulations (1D DNS) were performed for stoichiometric PRF80, 90, and 100/air mixtures to investigate fundamental characteristics of knocking with different Research Octane Number (RON) fuels. The 1D DNS reproduced knocking in the constant-volume chamber, and the knock onset conditions in terms of unburned gas pressure and temperature were derived. The 1D DNS results demonstrated that knock onset timing, pressure, and temperature conditions all increased with increasing RON. When comparing 1D DNS and CFR engine tests, differences in pressure-temperature trajectories of unburned gas were observed. However, a key similarity emerged in the relative positioning of knock onset conditions on pressure-temperature diagrams across fuels: higher RON fuels exhibit knock onset at higher pressures and tend to have higher unburned gas temperatures. Additionally, in both 1D DNS and CFR engine tests, knock onset conditions of PRF100 showed higher temperature and pressure values than those of PRF80 and PRF90. These results suggest that even a fundamental 1D DNS can represent knock phenomena in engines and allow investigation of the underlying physical mechanisms of knock onset.
Moriyama, Hinata, Morii, Youhi, Tsunoda, Akira, Yasutake, Yuki, Misono, Katsuhiro, Suzuki, Yoshikatu, Naiki, Taketora, Watanabe, Manabu, Maruta, Kaoru
Advanced Plasma-Based Ignition Strategy for Future Spark Ignition Engines2025-24-00209/7/2025
Internal combustion engines will continue to play an important role in transportation for decades to come because of the high onboard energy density. For present passenger vehicles, efforts have been made to reduce the cold start emissions and improve engine efficiency. To reach such goals, lean and diluted mixtures are needed to reduce the chemical reactivity of the mixture, so a higher engine compression ratio can improve thermal efficiency. The decreased flame temperature of the lean/diluted mixtures is also beneficial for NOx reduction. Strong in-cylinder flow is needed to increase flame propagation speed for efficient and complete combustion process. Strong ignition sources are needed to provide robust ignition to support the combustion process. In this paper, the application of advanced plasma-based ignition strategies was reviewed, with special attention to the on-demand plasma energy profiling, which has flexible control over discharge duration and current amplitudes. The ignition performance of multi-core ignition is compared with on-demand energy profiling under cold start and engine idling conditions. For heavy-duty applications burning low and zero carbon renewable fuels with less chemical reactivity, such as ammonia and natural gas, a novel ignition source with remote chamber and detonation tube is also demonstrated for the first time. The air-fuel mixture in the remote ignition chamber can be ignited, and the flame front can propagate and accelerate along the detonation tube to detonation stage, known as the deflagration-to-detonation transition. The high-speed detonation wave has a much stronger ignition capability to improve combustion efficiency of mixture with low chemical reactivities.
Yu, Xiao, Leblanc, Simon, Reader, Graham, Zheng, Ming
Enabling Near-Zero Emissions and Superior Efficiency in Large-Bore, Medium-Speed Engines with a Hydrogen-Argon Power Cycle2025-24-00019/7/2025
Combustion engines operating on a hydrogen-argon power cycle (H-APC) offer potential for superior thermal efficiency with true zero exhaust emissions. The high specific heat ratio of argon allows extrapolation of the theoretical efficiency of the Otto cycle to almost 90%. However, this potential is significantly constrained by challenges in combustion control, excessive thermal loading, and system integration, particularly regarding argon recovery. This study investigates these trade-offs, within the context of real-world engine-based peaking power plants. An experimentally validated 1D-simulation model of a prototype Wärtsilä 20 DF engine serves as reference for analysis of a retrofit incorporating a closed-loop argon cycle, with dedicated H₂ and O2 injectors, a water condenser and water separator. Engine performance is evaluated at reference operating point of 75% load, considering pre-ignition, peak pressure and exhaust temperature constraints, condenser limitations, and impurity accumulation. Argon emerges as the best monoatomic gas for H-APC. Helium, the second-best candidate, offers superior thermal conductivity and specific heat, but its low density and molecular weight reduce power output. A 90% argon and 10% oxygen mixture offers the optimal trade-off between power output, efficiency, and durability. A compression ratio of 11.90:1 ensures stable combustion within design constraints, while stoichiometric operation and condenser inlet pressure of 3.23 bar enhances performance, achieving the best indicated gross efficiency of 59.10%. This is over 10 percentage points better than the reference engine at 75% load. Nevertheless, practical implementation is limited by pumping losses in a packaging-optimized argon-path layout, reducing extractable efficiency to 56.70%. Furthermore, just 2% impurities in fuel/oxidizer stream causes progressive efficiency decline, falling below the reference threshold after approximately 10 minutes of operation. This highlights the necessity of a membrane-based separator and system volume optimization. The findings establish a validated computational framework for optimizing closed-loop hydrogen combustion and provide valuable insights for progressing demonstrator development.
Ahammed, Sajid, Ahmad, Zeeshan, Mahmoudzadeh Andwari, Amin, Kakoee, Alireza, Hyvonen, Jari, Mikulski, Maciej
Cylinder Balancing Algorithms: Enabling the Transition to Future Fuels in Large-Bore Spark-Ignited Engines2025-24-00179/7/2025
Large-bore spark-ignited engines equipped with individual cylinder injection systems require advanced balancing strategies to achieve optimal combustion performance and mitigate risks associated with abnormal combustion phenomena. The integration of highly reactive fuels, such as hydrogen, introduces additional challenges for high-power-density, low-speed engines. This study investigates closed-loop cylinder balancing strategies utilizing real-time cylinder pressure feedback to optimize engine operation. Key performance metrics were evaluated on a 20-cylinder medium speed stationary gas engine (8.5 MW electrical power) under eight different control strategies. The results indicate that the tested balancing methods reduce average knock intensity and variation of combustion peak pressure across all cylinders compared with original manufacturer control strategy. Furthermore, the study demonstrates that a well-balanced engine offers significant advantages, including enhanced power output, a 0.5% improvement in thermal efficiency, and a 20% reduction in NOx emissions. These findings highlight the critical role of cylinder pressure-based balancing algorithms in improving the performance, efficiency, and environmental sustainability of engines operating on natural gas and hydrogen blends. This research provides a unique experimental campaign with valuable insights into the development of next-generation combustion control systems in large-scale industrial and power generation applications.
Martelli, André, Penaranda, Alexander, Martinez, Santiago, Zabeu, Clayton, Salvador, Roberto
In-Cycle Predictability and Control of Knock in a PFI HD SI Engine Fueled with Methanol2025-24-00199/7/2025
Knock is an anomalous combustion occurrence limiting the efficiency of the spark-ignited engine, hence increasing fuel consumption and emissions. The global aim to cut the emissions from green-house-gases therefore makes knocking combustion a very appropriate research topic of today. This paper explores the possibility to do in-cycle spark timing control of knock, based upon cycle-to-cycle adaptation of the temperature of a hypothesized hot spot. The potential for post-spark timing control is also examined. Experiments were carried out on a single cylinder port fuel injected spark ignited engine fueled with methanol. Knock was quantified by the Maximum Amplitude of Pressure Oscillations metric and predicted by the Livengood-Wu integral. Normalized distributions, together with different σ confidences, of the in-cylinder state such as gas temperature, in-cylinder pressure and Livengood-Wu integral were computed both pre- and post-spark timing. Type I and Type II errors of the computed metrics revealed that knocking cycles cannot be distinguished from normal cycles, and that hot spots are likely not the root cause of auto-ignition in the current engine. Hence, in-cycle control of knock based upon a hypothesized hot spot temperature would be fruitless. A proven method to mitigate knock in-cycle is the use of water injection. Nevertheless, the post-spark timing analysis showed that this control post-spark timing may be counterproductive. The knocking and normal cycle combustions have a large overlap before the knocking occurs. Therefore, in-cycle regulation through water injection can penalize normal cycles, to a degree that the indicated thermal efficiency would drop more than just retarding the spark timing to 1% knocking (regular knock controller). Lubricant oil, instead of hot spots or fuel-rich spots, was demonstrated to be the most plausible cause of knock in the current engine-fuel configuration.
Ainouz, Filip, Lius, Andreas, Cronhjort, Andreas, Stenlaas, Ola
Integrated CFD-Experimental Methodology for Hydrogen-Fuelled Small Loop Scavenged Two-Stroke Engines2025-24-00149/7/2025
This paper presents an integrated methodology for the analysis of hydrogen-fueled 2-Stroke engines, combining experimental data, 1D-CFD simulations, and 3D-CFD combustion calculations. The proposed approach aims to enhance the understanding of scavenging, injection, and combustion processes in a 50 cm3 loop-scavenged engine with low-pressure direct hydrogen injection, experimentally studied on a test bench. The hydrogen-fueled engine was capable of achieving a maximum power output of 3.1 kW, using a slightly lean air-to-fuel ratio (lambda = 1.3). The maximum engine speed for stable combustion without knocking was achieved at wide open throttle at 7119 RPM. The developed 1D-CFD model, based on the engine layout at the test bench, was calibrated using average experimental data and specific full load operating points. 3D-CFD simulations were performed for one full load operating point, focusing on combustion dynamics and fuel distribution within the chamber, with combustion model parameters calibrated to ensure consistency with experimental data. The integrated approach resulted in a good agreement between numerical results and experimental data. The proposed methodology enables accurate model calibration and a deeper understanding of complex physical phenomena, representing a valuable tool for the development of low emission engines.
Caprioli, Stefano, Ferretti, Luca, Scrignoli, Francesco, Fiaschi, Matteo, D'Elia, Matteo, Oswald, Roland, Schoegl, Oliver, Nambully, Suresh Kumar, Rothbauer, Rainer, Mattarelli, Enrico, Kirchberger, Roland, Rinaldini, Carlo
Machine Learning-Enhanced Combustion Modelling: Predicting Ethanol Effects in a Single-Cylinder Research Engine2025-24-00269/7/2025
Recent studies highlight the urgent need to reduce greenhouse gas (GHG) emissions to mitigate the impacts of global warming and climate change. As a major contributor, the transport sector plays a vital role in these efforts. Ethanol emerges as a promising fuel for decarbonising hard-to-electrify propulsion sectors, thanks to its sustainable production pathways and favourable physical and combustion properties, such as energy density, rapid burning velocity, and high knock resistance. This work proposes a methodology to enable the possibility of replicating the combustion behaviour of ethanol in a 1D CFD simulation environment representative of a single-cylinder research engine. Spark-ignition combustion is simulated through the Eddy Burn-Up combustion model previously calibrated for standard fossil gasoline. The combustion model features a laminar flame speed neural network, trained and tested through reference chemical kinetics simulations. The combustion model showed great accuracy in replicating key combustion metrics, highlighting its predictive capability while switching fuel kinds. Eventually, knock occurrence was evaluated by employing the Livengood-Wu induction time integral. The model was adjusted by the induction integral multiplier to align the knock predictions to the normalised experimental Mean Amplitude Pressure Oscillation value. The latest remains always below 1, meaning that the engine can be run at maximum combustion efficiency without knock occurrence even at maximum load.
Ferrari, Lorenzo, Sammito, Giuseppe, Fischer, Marcus, Cavina, Nicolò
Visualization Analysis of Hydrogen Combustion Triggered by Non-Controlled Hotspots Using a Rapid Compression Expansion Machine2025-24-00479/7/2025
Research on hydrogen-fueled internal combustion engines has gained growing attention as a carbon-neutral solution to reducing emissions in the transport sector. However, challenges remain, with the risk of abnormal combustion being one of the major criticalities. This paper aims to clarify the ignition process of a hydrogen-air mixture caused by lubricant oil droplets and soot deposition. To achieve this, high-speed imaging methods were applied with a Rapid Compression Expansion Machine under engine-like conditions. Direct imaging and OH* chemiluminescence were captured simultaneously on the engine head to visualize the ignition point and flame propagation. Different operating conditions were tested to evaluate the influence of lambda, intake pressure, and soot quantity on ignition occurrence. For each test bench configuration, ten successive tests were conducted to assess the probability of ignition. The presence of soot was ensured through a preliminary run with diesel injection. The presence of oil, instead, naturally increases inside the cylinder with each successive run due to the functioning of the modified test bench’s lubricating system. Three typologies of combustion modes were identified – late, weak, and early ignition. These are analyzed using chamber dynamic pressure and heat release rate trends, along with optical analysis. Direct imaging enables the identification of the droplet responsible for ignition, and OH* chemiluminescence allows visualization of the flame front propagation from the ignition point. As expected, an increase in intake pressure, a decrease in lambda, and the presence of soot all raise the probability of early ignition, with lambda having the most significant effect.
Tempesti, Claretta, Yukitani, Takumi, Horibe, Naoto, Romani, Luca, Ferrara, Giovanni, Kawanabe, Hiroshi
Optimization of HEV Vehicle’s Engine Modulated Noise2025-01-00845/5/2025
One 1.5L Miller-cycle turbocharged four cylinder gasoline hybrid engine is installed on a certain hybrid vehicle. When accelerating at low to medium speeds with a small throttle, there is a "da da" knocking noise inside the car, which seriously affects the overall sound quality of the vehicle. By analyzing the vibration and noise data of the engine, it was found that the frequency of the abnormal knocking sound is 200-2000Hz, which presents a half order characteristic in the time domain, that is, one knocking occurs when the engine crankshaft rotates twice. Through Hilbert demodulation analysis of the vibration data in the problem frequency range, it was found that the knocking noise was modulated in the frequency domain, with a modulation frequency of half of the crankshaft rotation frequency. By building a fully flexible multi-body dynamic model of a hybrid powertrain and inputting the engine's cylinder pressure excitation, the combustion excitation is coupled with mechanical vibration noise to simulate the surface vibration of the powertrain. Measures such as optimizing the cylinder pressure curve by adjusting spark angle and scavenging angle, and improving crankshaft stiffness by increasing the overlap between mainbearing diameter and connecting rod diameter, the sound quality issue of this hybrid model has been significantly improved under low speed and low throttle acceleration conditions.
Dan, Kong
Influence of Exhaust Gas Recirculation on Knock in a Spark Ignition Engine Fueled with Ethanol–Gasoline Blends03-18-03-00194/28/2025
Exhaust gas recirculation (EGR) is widely used in spark ignition engines to reduce throttling losses, decrease exhaust gas temperatures, increase efficiency, and suppress knock. However, the effectiveness of EGR as a knock suppressor is dependent on the fuel type and operating condition. In this study, the effectiveness of EGR to suppress knock was tested with E10, E30, E50, E75, and E100 at a moderately boosted condition. It was found that EGR was effective at suppressing knock with E10, but high EGR rates were required to achieve a knock suppression effect with E30 and E50. No knock suppression effect was observed with E75 and E100 across all tested EGR rates. With E30 and E50, EGR that was passed through a three-way catalyst was more effective at suppressing knock at all EGR rates. Chemkin modeling with neat ethanol revealed that nitric oxide enhanced ignition by increasing the hydroxyl radical concentration in the end gas, resulting in earlier auto-ignition. Directly seeding nitric oxide in the intake system with neat ethanol resulted in an increase in knock intensity, which required a knock-limited CA50 retard of 3.5 crank angle degrees with 660 ppm of nitric oxide.
Gandolfo, John, Gainey, Brian, Lawler, Benjamin
Effects of Hydrogen Addition on Spark Knock Suppression under High Engine Speed and Boosted Conditions2024-32-01084/18/2025
The effect of hydrogen addition on spark knock suppression under high engine speed (4800 rpm) was investigated at the intake pressures of 96 kPa and 120 kPa. The experimental results showed that hydrogen addition has a slight effect on advancing the knock limit at 96 kPa, whereas a greater spark knock suppression effect can be achieved by increasing the intake pressure. To elucidate the influences and differences of hydrogen addition on the ignition process under low and high intake pressures, chemical kinetic analyses were performed using a two-zone combustion model. The calculation results showed that the reduction of heat release in the end gas resulting from the consumption of OH radicals by hydrogen can only be achieved at the initial stage of the ignition process. This leads to the smaller knock suppression effect at low intake pressures, where a remarkable heat release at this stage is absent. On the other hand, an increase in intake pressure results in a remarkable heat release at the initial stage of the ignition process due to a higher reaction rate with increased mass in the cylinder, despite the high engine speed with a shortened residence time of the end gas in the low temperature range. This, in turn, leads to the greater spark knock suppression effect with hydrogen addition.
Goto, Jun, Ueno, Yoshito, Kobashi, Yoshimitsu, Shibata, Gen, Ogawa, Hideyuki, Kojima, Kentaro
Impact of Ordinal Proximity of Frequency Components on the Auditory Perception of Engine Knocking2024-32-00324/18/2025
This study examines the acoustic properties of engine-knocking sounds in gasoline engines, arising from misfires during spark ignition that negatively affect driving performance. The aim was to understand the frequency characteristics of acceleration sounds and their connection to the proximity of the order components. The study also explores “booming,” where two different frequencies of sounds occur simultaneously, potentially linked to the unpleasant nature of engine knocking. Using a sinusoidal model, we generated engine acceleration sound models with 5th-, 10th-, and 15th-order components, including engine knocking. Two types of sound stimuli were created: one with the original amplitude (OA) and one with a constant amplitude (CA) for each component order, emphasizing the order-component proximity in CA sounds. Aural experiments with 10 participants in an anechoic room using headphones and the MUSHRA method revealed an inverse relationship between OA and CA ratings as the component order increased. OA typically produced better evaluations, possibly owing to the reduced high-frequency components preventing booming, whereas CA received lower ratings owing to pronounced booming from a constant amplitude. Overall, OA significantly outperformed CA, likely because the reference tone also contained the original amplitude data. This study confirms the significant impact of order-component proximity on auditory perception, such as booming. This suggests that the original amplitude information improves sound quality. We aim to further explore this relationship and analyze engine-knocking sounds in more detail.
Suzuki, Ryuhei, Ishimitsu, Shunsuke, Nitta, Misaki, Sakakibara, Mika, Hakozaki, Tomoyuki, Fujikawa, Satoshi, Iwata, Kiyoaki, Matsumoto, Mitsunori, Kikuchi, Masakazu
Experimental Investigation for the Effect of Cavity Geometry on the Flame Propagation and Auto-Ignition in RCM2024-32-00604/18/2025
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
Prediction of Pre-Ignition Borderline on Supercharged SI Engine by Livengood-Wu Integral2024-32-00084/18/2025
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
Influence of Methanol-to-Gasoline Fuel Formulation on Knock Propensity and Flame Speed2025-01-84004/1/2025
Drop-in gasoline fuels that originate from renewable, low-net-carbon sources, such as methanol-to-gasoline (MTG), are an important bridge in the transition between traditional fossil fuels and electrification of the transportation sector. The composition of these fuels can be tuned by adjusting the settings of the chemical processes used to create them, which can be leveraged to formulate optimized fuels for higher knock resistance or higher flame speed. This study investigated how the distribution of hydrocarbon classes and molecular structure of a renewable MTG gasoline surrogate affected knock and flame speed using chemical kinetic modeling. The original MTG surrogate was modified by increasing the relative amount of a certain hydrocarbon class while the concentration of other hydrocarbon classes is reduced equally. Increasing normal- and iso-alkanes increased reactivity and penalized octane sensitivity, olefins increased octane sensitivity while keeping the research octane number constant, and increasing cyclo-alkanes or aromatics decreased reactivity with the fuel being more sensitive to cyclo-alkanes. To optimize octane rating, short normal-alkanes and long, highly-branched iso-alkanes are preferred, with octane rating being very sensitive to the structure of iso-alkanes. Increased branching also improves octane rating for cyclo-alkanes, olefins, and aromatics. Regarding flame speed, normal-alkanes tend to increase flame speed at engine-relevant conditions because they form radicals that accelerate the flame. However, aromatics and cyclo-alkanes, which are promising octane boosters, showed lower flame speeds. Based on this understanding, an optimized MTG was formulated and compared against the effect of ethanol blending on the original MTG, with the optimized fuel showing similar performance as MTG with 52.5%vol ethanol. Chemical kinetic analyses showed that the chemistry that controls octane rating is different from that that controls flame speed, opening the door to fuels that simultaneously improve both knock and deflagration characteristics.
MacDonald, James, Lopez Pintor, Dario, Matsubara, Naoyoshi, Kitano, Koji, Yamada, Ryota
Experimental and Numerical Investigation of Different Dilution Techniques in a High-Performance H2 - Fueled SI Engine2025-01-84244/1/2025
Nowadays, hydrogen (H2) is rising as a key solution to fuel internal combustion engines (ICE) since it allows carbon free combustion process. At the same time, ICE fueled with H2 can reach similar performance and driving experience of gasoline fueled ones. In stoichiometric conditions, hydrogen shows higher flame speed, lower ignition energy and lower quenching distance than gasoline. Mainly for these reasons, H2 combustion is characterized by a high risk of abnormal combustion (i.e. knock and pre-ignition), relevant NOx emissions and high heat losses. On the other hand, the wide flammability range and high combustion stability of H2 allow the use of different techniques to reduce combustion reactivity. This work presents a combined approach, experimental and numerical, to assess the benefits of three mixture dilution methods. The experimental campaign, in different operating conditions, was carried out on a production derived high specific power gasoline Single Cylinder Engine (SCE) retrofitted to H2 with Direct Injection (DI). Three different dilution techniques were tested: enleanment, cooled Exhaust Gas Recirculation (cEGR) and manifold Water Injection (WI). The impacts on combustion of the different strategies were analyzed in order to evaluate their effectiveness on engine thermal efficiency and NOx emissions. Enleanment has a relevant impact on the size of the turbocharger system, cEGR affects the engine total heat rejection, while WI requires dedicated injection system and tank. Therefore, each dilution strategy requires a dedicated hardware optimization. In this regard, a 1D-CFD simulation model of complete 6-cylinder engine was developed with the aim to assess the above-mentioned techniques in terms of fuel economy and heat rejection at low-medium loads.
Tonelli, Roberto, Medda, Massimo, Gullino, Fabrizio, Silvestri, Nicola, Zaffino, Francesco, Mariconti, Roberto, Rossi, Vincenzo
Impact of Oxygenated Fuel Components on Engine Performance and Particulate Emissions in Gasoline Blends2025-01-84464/1/2025
The challenges with electrification in the automotive industry have led to rethinking the decisions to ban internal combustion engines. Nonetheless, decarbonization of transportation remains a regulatory priority in many countries, irrespective of the energy source for automotive powertrains. Renewable oxygenated fuel components can help with the rapid decarbonization of gasoline fuels in the current fleet. Ethanol is one of the primary renewable components typically used for blending in gasoline primarily at 10% v/v but up to 20% v/v substitution which corresponds to 3.7 to 8.0% oxygen by mass. However, a range of oxygenates could be used instead of ethanol. This study aimed to determine if the engine could discriminate between different oxygenates in gasoline fuels blended at the same octane (RON) and oxygen levels. Oxygenates such as methyl-tert-butyl-ether (MTBE) and ethyl-tert-butyl-ether (ETBE) were considered in this study. Blends were made using a combination of n-heptane, iso-octane, toluene, and oxygenated components. Seven blends with a nominal RON of 98 +/-2 were evaluated in a single-cylinder engine. Four E10 equivalent and three E20 equivalent fuel blends were studied. The engine was operated at a range of test conditions from throttled, low-load points to boosted, high-load points that required knock retard. The results indicated that all blends had minimal differences in engine performance in terms of knocking behavior, spark timing, burn duration, fuel flow, and injection duration which could all be compensated by the engine control unit (ECU). Particulate matter emissions (AVL micro soot sensor, PN10, PN23) were also evaluated at the test conditions. While the fuels had lower PM-generating components compared to commercial fuels, we could demonstrate that the PM emissions largely correlated with the particulate matter index (PMI) (or the toluene content) of the fuels.
Kalaskar, Vickey, Mitchell, Robert, Pourreau, Daniel
Effects of Critical Compression Ratio on Rating Gasoline Knock Propensity2025-01-84514/1/2025
It is common practice in the automotive industry to explore the knock limits of fuels on an engine by a comparison of the knock limited spark advance (KLSA) at threshold knock intensity. However, the knock propensity of gasolines can be rated by changing one of three metrics on a variable compression ratio Cooperative Fuels Research (CFR) octane rating engine while holding the other two variables constant: knock intensity, spark timing, and critical compression ratio. The operational differences between the standard research octane number (RON) rating and modern engine operation have been explored in three parts. The first part focused on the effects of lambda and knock characterization. The second part studied the effects of spark timing. This third part explores the knock ratings of several gasolines by comparing the critical compression ratios at constant combustion phasing and knock intensity. The threshold knock intensity was based on the standard octane rating D1 pickup or by maximum amplitude of pressure oscillations (MAPO) measured by a piezoelectric cylinder pressure transducer. Several Fuels for Advanced Combustion Engines (FACE) gasolines, primary reference fuels (PRFs), and toluene standardization fuels (TSFs) were tested on a CFR octane rating engine with advanced data acquisition equipment and a piezoelectric cylinder pressure transducer. These tests deviated from the ASTM D2699 standard octane rating procedure. For each test fuel, the CFR engine was operated at stoichiometry at a constant combustion phasing (CA50) and the compression ratio was modified until a threshold knock intensity was realized. It was found that the chemical composition of the fuels affected the relationship of critical compression ratios between the D1 knockmeter and piezoelectric pressure transducer knock intensity thresholds, as well as the measured combustion maximum pressure rise rate and spark timing setting for constant CA50. For highly aromatic fuels tested at a constant MAPO knock intensity threshold, it was found that the maximum pressure rise rate was two to three times higher than that of highly paraffinic fuels with similar RON and the spark advance was several crank angle degrees less for constant combustion phasing.
Kolodziej, Christopher, Hoth, Alexander
Knock Assessment in Wankel Rotary Engine Adopting Low Octane Rating Fuels2025-01-84524/1/2025
Series hybrid vehicles with internal combustion range extenders are a promising solution for sustainable transportation. In this application, net zero carbon emissions can be achieved using renewable fuels. Fischer-Tropsch-derived e-gasolines/naptha allow for high energy density and safe liquid fuels. However, Fischer-Tropsch naptha fuel derivatives must undergo several processing stages to reach current engine-grade octane ratings, negatively affecting the synthesis's profitability and energy efficiency. Gasoline engine technologies capable of operating with low-octane fuels could allow the adoption of unprocessed Fischer-Tropsch gasoline. The rotary Wankel engine design suits range extenders thanks to its high power-to-size ratio. In this study, the knocking tendency of homogenous charge spark-ignition rotary Wankel engines is numerically assessed through Chemkin-Pro spark-ignition engine zonal model for knock assessment. Rotary Wankel engines are modeled by providing the corresponding time-dependent profiles of volume, wall surface area, wall global heat transfer coefficient, and burnt gas fraction retrieved from previous experimental work. Different engine load conditions have been investigated spanning engine shaft rotational speeds from 3000RPM to 6000RPM and brake mean effective pressures from 3 bar to 7 bar. Detailed kinetic modeling of normal-heptane/iso-octane primary reference fuels is adopted to describe the autoignition tendency of different octane-rating blends. Simulations show a low knocking tendency under the investigated conditions, therefore suggesting the suitability of rotary engines for the adoption of unprocessed Fischer-Tropsch fuels.
Brunialti, Sirio, Vorraro, Giovanni, Turner, James, Sarathy, Mani
Experimental Investigation between Pre-Ignition, Knocking, Vibration and Performance in an Internal Combustion Engine2025-01-83804/1/2025
Otto cycle internal combustion engines have undergone technological developments that can be fueled by various types of fuels in different mixture proportions. To achieve this, a detailed study of the main factors that influence the engine combustion process is necessary. The objective of this study is to evaluate the effects of varying the ignition advance on the performance parameters and vibration level of the engine operated with regular gasoline, podium gasoline, ethanol and a mixture of ethanol with regular gasoline. The experimental tests consisted of operating an Otto cycle engine on a bench dynamometer under full load conditions, varying rotation and ignition advance by 5, 10 and 20% in relation to the original ignition advance and correlating the levels of pre-ignition, knock, engine vibration levels with engine performance parameters. The results showed that the engine vibration level was influenced by the type of fuel used, engine performance parameters and the presence of pre-ignition and knock. The results also confirmed that fuels with a higher-octane number supported greater ignition advances, presenting lower levels of pre-ignition, knock and vibration in the engine. In all operating conditions, the level of engine vibration, presence of pre-ignition and knock was higher when using regular gasoline, followed by a mixture of ethanol and regular gasoline. This study is relevant because it correlates the vibration level of an internal combustion engine with the type of fuel and the engine's combustion process.
Santana, Claudio
Control Re-Optimization of a Series-Parallel Hybrid Powertrain Fueled with High-Octane Gasoline2025-01-70281/31/2025
High-octane gasoline has the potential to improve engine efficiency but has been reported to marginally reduce and even increase vehicle fuel consumption. The objective of this study is to evaluate the fuel-saving effect of high-octane gasoline on series-parallel hybrid electric vehicles (HEVs) under the re-optimized powertrain control, including engine control and energy management. Firstly, a bench test was conducted on a spark ignition engine fueled with three fuels with research octane numbers of approximately 92, 95, and 98, named 92#, 95#, and 98#. Then the engine control parameter (i.e., spark advance) was re-optimized for maximum engine efficiency and acceptable particle number emissions with the knock constraint. Finally, the energy management was re-optimized for a series-parallel hybrid powertrain equipped with the engine. It was found that 95# and 98# even increased vehicle fuel consumption by 0.2% and 0.6% without the re-optimization of powertrain control compared with 92#, but reduced the fuel consumption by 2.1% and 3.8% with the re-optimization. The results indicated high-octane gasoline can reduce HEV fuel consumption but requires the re-optimization of powertrain control. The engine control re-optimization for high-octane gasoline increased the maximum torque and expanded the high-efficiency area toward higher torque in the engine efficiency map. Then the energy management re-optimization shifted the engine operating points to area with higher engine efficiency and reduced powertrain operation under low-efficiency series mode. The fuel-saving analysis indicated that, under the condition of re-optimizing only the control, high-octane gasoline is suitable for application in parallel or series-parallel HEVs rather than in series HEVs.
Tan, Guikun, Li, Ji, Li, Yanfei, Wang, Changhui, Sun, Yuncai, Xu, Anzhao, Shuai, Shijin, Xu, Hongming
Analysis of the Characteristics of Hybrid Vehicles and Low-Viscosity Lubricating Oil Based on Real Road Tests in Four Extreme Environments04-18-02-00091/7/2025
As countries around the world attach more importance to carbon emissions and more stringent requirements are put forward for vehicle emissions, hybrid vehicles, which can significantly reduce emissions compared with traditional fuel vehicles, as well as low-viscosity lubricating oil, have become significant trends in the industry. In this article, a total of nine vehicles of 48 V mild-hybrid models and full-hybrid models are tested. Using three kinds of low-viscosity lubricating oil and driving a total of 120,000 km in environments with low temperature, high humidity, high temperature, or high altitude, the engines are then disassembled and scored. The effects of the four extreme environments on the engine starts–stops, ignition advance angle, engine power, state of charge (SOC), acceleration performance, and oil consumption characteristics of hybrid vehicles are studied; the oxidation characteristics and iron content change characteristics of low-viscosity lubricating oil are analyzed; and how lubricating oil protects the engine in durability tests are verified. According to the test results, in the low-temperature environment, for full-hybrid models, the number of engine starts–stops and the running time are significantly increased, while the SOC is generally high. In the high-temperature environment, for full-hybrid models, the ignition advance angle of the engine is reduced, which inhibits the risk of pre-ignition; the characteristics of the SOC are similar to those in the high-humidity and standard-temperature WLTC working conditions; the oxidation rate of lubricating oil has almost no effect on full-hybrid models; for mild-hybrid models, oil is prone to oxidation and decay. In the high-humidity environment, the oil consumption rate deteriorates with the increase in relative humidity under the same load and engine speed, and the accumulation rate of iron content in oil increases compared with that in the high-temperature and high-altitude environments. In the high-altitude environment, with the increase in altitude, the engine power of full-hybrid models decreases at the same engine speed, resulting in a decrease in the engine’s charging efficiency to the battery, so that the battery level could not be relatively stable. The acceleration performance of both hybrid models decreases significantly with an increase in altitude. After the engines are disassembled, it is found out that with the protection of low-viscosity lubricating oil, the wear of engine parts is very small, and the deposit control is good.
Zhu, Gezhengting, Hu, Hua, Pan, Jinchong, Luo, Yitao, Hua, Lun, Jiao, Yan, Jiang, Jiandi, Shao, Heng, Xu, Zhengxin, Yan, Jingfeng, Wei, Guangyuan, Zhang, Heng
Experimental Investigation of Performance and Vibration Parameters of an Otto Cycle Engine Operated with Regular Gasoline, Premium Gasoline, Pure Ethanol and Mixture of Ethanol with Regular Gasoline2024-36-000112/20/2024
Otto cycle internal combustion engines have undergone technological developments that can be fueled by various types of fuels in different mixture proportions. To achieve this, a detailed study of the main factors that influence the engine combustion process is necessary. The objective of this study is to evaluate the effects of varying the ignition advance on the performance parameters and vibration level of the engine operated with regular gasoline, premium gasoline, ethanol and a mixture of ethanol with regular gasoline. The experimental tests consisted of operating an Otto cycle engine on a bench dynamometer under full load conditions, varying rotation and ignition advance by 5, 10 and 20% in relation to the original ignition advance and correlating the levels of pre-ignition, knock, engine vibration levels with engine performance parameters. The results showed that the engine vibration level was influenced by the type of fuel used, engine performance parameters and the presence of pre-ignition and knock. The results also confirmed that fuels with a higher-octane number supported greater ignition advances, presenting lower levels of pre-ignition, knock and vibration in the engine. In all operating conditions, the level of engine vibration, presence of pre-ignition and knock was higher when using regular gasoline, followed by a mixture of ethanol and regular gasoline. This study is relevant because it correlates the vibration level of an internal combustion engine with the type of fuel and the engine’s combustion process.
Santana, Claudio Marcio, Santana, Linicker Lopes Bruno, Almeida, Helder Giostri Alves
Fuel Design Concept to Improve Both Combustion Stability and Antiknocking Property Focusing on Ethane2024-01-427611/5/2024
For realizing a super-leanburn SI engine with a very-high compression ratio, it is necessary to design a new fuel which could have low ignitability at a low temperature for antiknocking, but high ignitability at a high temperature for some contribution to stable combustion. C2H6 has a very-long ignition delay time at a low temperature, close to that of CH4, but a short ignition delay time at a high temperature, close to that of gasoline. C2H6 also has a laminar burning velocity about 1.2 times higher than that of gasoline. C2H6 addition to gasoline could be a good example of fuel design to improve both combustion stability and antiknocking property. In the present study, the antiknocking effect of adding CH4, C2H6, or C3H8 with the RON of 120, 115, or 112, respectively, to a regular-gasoline surrogate fuel with the RON of 90.8 has been investigated in an SI engine with a stoichiometric mixture. With the energy fraction of the gaseous fuel of less than 0.35, knocking limit CA50 is advanced further in the order of C2H6 addition > C3H8 addition > CH4 addition, which is conflict with the order of RON of CH4 > C2H6 > C3H8. The effect is dependent on not the RON of the gaseous fuel, but the rate of OH consumption by the gaseous fuel. The effect of adding each gaseous fuel to a premium-gasoline surrogate fuel with the RON of 100.2 has been also investigated. The effect is not dependent on the cool-flame reactions of the liquid fuel.
Kuwahara, Kazunari, Shimizu, Taisei, Okada, Atsuki
Premixed Dual-Fuel Combustion of Camelina sativa Oil and Ethanol03-18-01-00018/6/2024
Dual-fuel (DF) engines enable efficient utilization of a low reactivity fuel (LRF), usually port-injected, and a high reactivity fuel (HRF) provided directly into the cylinder. Ethanol and Camelina sativa oil can be ecologically effective but not fully recognized alternatives for energy production using modern CI engines equipped with a common rail system and adopted for dual fueling. The high efficiency of the process depends on the organization of the combustion. The article describes the premixed dual-fuel combustion (PDFC) realized by dividing the Camelina sativa dose and adjusting its injection timing to the energetic share of ethanol in the DF mixture. The injection strategy of HRF is crucial to confine knock, which limits DF engine operation, but the influence of EGR is also important. The research AVL engine’s dual-fueling tests focused on combustion process modification by the proposed injection strategy and cooled EGR at different substitution rates. For all examined points of the engine run, the volumetric heat release rate diagrams, cylinder pressure, and temperature illustrate changes that resulted from the tested fueling options. Additionally, engine thermal efficiency and emissions are presented. Because of potential application, the tests were confined to one engine speed (n = 1500 rpm). The research confirmed the possibility of efficiently applying raw Camelina sativa oil as an HRF for DF engines and ethanol (LRF) under high-load conditions.
Pawlak, Grzegorz, Skrzek, Tomasz, Kosiuczenko, Krzysztof, Płochocki, Patryk, Simiński, Przemysław
Effects of Dimethyl Ether and Propane Blends on Knocking Behavior in a Boosted SI Engine03-17-07-00566/12/2024
Dimethyl ether (DME) is an alternative fuel that, blended with propane, could be an excellent alternative for exploring the use of fuels from renewable sources. DME–propane blends are feasible for their comparable physicochemical properties; these fuels may be pressured as liquids using moderate pressure at ambient temperature. Adding a proportion of DME with a low octane number to a less reactive fuel like propane can improve the combustion process. However, the increased reactivity of the mixture induced by the DME could lead to the early appearance of knocking, and this tendency may even be pronounced in boosted SI engines. Hence, this study experimentally analyzes the effect of E10 gasoline (baseline) and DME–propane blends, with varying proportions of DME in propane ranging from 0% to 30% by weight, in increments of 5% on knocking tendency, combustion characteristics, gaseous emissions, and particle number concentration, under different intake pressure conditions (0.8, 0.9, 1.0, and 1.1 bar) in an SI engine. The results show that as the proportion of DME in the propane blend rises, the knocking tendency becomes more pronounced. That behavior intensifies with increasing intake pressure, but with 20% DME in the propane blend, reaching the maximum brake torque (MBT) without knocking in the four boosted conditions is feasible. The presence of knock limited the advance of combustion phasing and decreased the gross indicated thermal efficiency (ITEg) with E10 gasoline and 25% and 30% DME in propane blends under 1.0 and 1.1 bar boosted conditions. In these knock-limited circumstances, the NOx emissions decreased due to the retarded phasing, and THC and PN emissions increased due to the lower combustion stability, considerably raising the concentration of accumulation mode particles in the particle size distribution (PSD) compared to the other fuel blends tested.
Soto, Lian, Han, Taehoon, Boehman, Andre L.
Potential Analysis of Defossilized Operation of a Heavy-Duty Dual-Fuel Engine Utilizing Dimethyl Carbonate/Methyl Formate as Primary and Poly Oxymethylene Dimethyl Ether as Pilot Fuel03-17-07-00534/18/2024
This study demonstrates the defossilized operation of a heavy-duty port-fuel-injected dual-fuel engine and highlights its potential benefits with minimal retrofitting effort. The investigation focuses on the optical characterization of the in-cylinder processes, ranging from mixture formation, ignition, and combustion, on a fully optically accessible single-cylinder research engine. The article revisits selected operating conditions in a thermodynamic configuration combined with Fourier transform infrared spectroscopy. One approach is to quickly diminish fossil fuel use by retrofitting present engines with decarbonized or defossilized alternatives. As both fuels are oxygenated, a considerable change in the overall ignition limits, air–fuel equivalence ratio, burning rate, and resistance against undesired pre-ignition or knocking is expected, with dire need of characterization. Two simultaneous high-speed recording channels granted cycle-resolved access to the natural flame luminosity, which was recorded in red/green/blue and OH chemiluminescence. Selected conditions were investigated in more detail with the simultaneous application of planar laser-induced fluorescence of OH and HCHO and recording natural flame luminescence in a cycle-averaged manner. Poly oxymethylene dimethyl ether was used as pilot fuel, building on prior investigations. The mixture of 65 vol% Dimethyl Carbonate and 35 vol% Methyl Formate with prior verification on a passenger-car-sized engine substitutes synthetic natural gas in this study. Thermodynamically, the increased compression ratio up to 17.6 resulted in feasible operation and increased indicated efficiency. On the lower compression ratio of 15.48, a more comprehensive range of applicable air–fuel equivalence ratios and increased degrees of freedom regarding the pilot’s total energy share are observed compared to the base configuration with natural gas and EN590 as pilot fuel. The air–fuel equivalence ratio sweep from λ = 1.0–2.0 revealed predominantly premixed and high-temperature heat release via OH*. The temporal and spatial evolution shifts while leaning out the mixture with increasing gradients on the radial distribution and decouples for lean mixtures from the initial spray trajectory.
Mühlthaler, Markus Sebastian, Härtl, Martin, Jaensch, Malte
Deflagration-Based Knock of Methanol SI Combustion and its Implications for Combustion Noise2024-01-28194/9/2024
Methanol emerges as a compelling renewable fuel for decarbonizing engine applications due to a mature industry with high production capacity, existing distribution infrastructure, low carbon intensity and favorable cost. Methanol’s high flame speed and high autoignition resistance render it particularly well-suited for spark-ignition (SI) engines. Previous research showed a distinct phenomenon, known deflagration-based knock in methanol combustion, whereby knocking combustion was observed albeit without end-gas autoignition. This work studies the implications of deflagration-based knock on noise emissions by investigating the knock intensity and combustion noise at knock-limited operation of methanol in a single-cylinder direct-injection SI engine operated at both stoichiometric and lean (λ = 2.0) conditions. Results are compared against observations from a premium-grade gasoline. Experiments show that methanol’s end-gas autoignition occurs at lean conditions, leading to the typical autoignition-based knock as that occurring with premium-grade gasoline. However, at stoichiometric conditions, knock-limited operation is achieved with deflagration-based knock. Noise of deflagration-based knock has lower variability than that of autoignition-based knock and it does not seem to be an issue at the engine speed tested experimentally in this paper (1400 rpm). However, computational fluid dynamic large eddy simulations show that deflagration-based knock may lead to high noise levels at 2000 rpm. Deflagration-based knock is insensitive to changing spark timings, so new knock mitigation strategies are required, such as adjusting the spark energy and/or adding dilution. Finally, this study shows that deflagration-based-knock may be directly impacted by the flame speed, occurring more frequently with faster-burning fuels or under conditions that elevate flame speeds, like rich-stoichiometric operation. The finding bears implications on renewable e-fuels, such as ethanol, methanol and hydrogen.
Singh, Eshan, Strickland, Tyler, Abboud, Rami, MacDonald, James, Lee, Sanguk, Lopez Pintor, Dario
Effects of Ethanol Blending on the Reactivity and Laminar Flame Speeds of Gasoline, Methanol-to-Gasoline, and Ethanol-to-Gasoline Surrogates2024-01-28174/9/2024
Ethanol blending is one method that can be used to reduce knock in spark ignition engines by decreasing the autoignition reactivity of the fuel and modifying its laminar flame speed. In this paper, the effects of ethanol blending on knock propensity and flame speed of petroleum and low-carbon gasoline fuels is analyzed. To do so, surrogate fuels were formulated for methanol-to-gasoline (MTG) and ethanol-to-gasoline (ETG) based on the fuels’ composition, octane number, and select physical properties; and 0-D and 1-D chemical kinetics simulations were performed to investigate reactivity and laminar flame speed, respectively. Results of MTG and ETG were compared against those of PACE-20, a well-characterized surrogate for regular E10 gasoline. Similarly to PACE-20, blending MTG and ETG with ethanol increases the fuel’s research octane number (RON) and sensitivity. The trends of the ethanol blending effects were slightly stronger with PACE-20 and MTG than with ETG, with 13.6% volume of ethanol necessary to reach a RON of 98 for MTG and 18.4% volume necessary for ETG. 1-D modeling of the flame speed showed that while ethanol has a faster flame speed than gasoline at pressures below 2.4 bar, the flame speed decreases at increasing pressure, with regular gasoline having a higher flame speed at pressures representative of combustion. Sensitivity analyses to identify the reactions and species relevant in controlling laminar flame speed showed that for ethanol, the active radicals in the flame decreased as pressure increased due to increasing methyl recombination leading to a decrease of the flame speed. For regular gasoline, the formation of active radicals increased with pressure due to increasing HCO decomposition leading to an increase in the flame speed.
MacDonald, James, Lopez Pintor, Dario, Matsubara, Naoyoshi, Kitano, Koji, Yamada, Ryota
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