Browse Topic: Two stroke engines

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1D and MultiD Modeling Techniques for IC Engine Simulation Second EditionR-5805/29/2026
The internal combustion (IC) engine remains the most widely used thermal machine in the world and will continue to play a central role in global mobility for decades to come. Even as alternative powertrains expand, optimized IC engines—often integrated within hybrid and electrified architectures—are essential to achieving low fuel consumption, near-zero pollutant emissions, and reduced carbon dioxide output. Advances in combustion strategies, synthetic fuels, turbocharging, and aftertreatment systems are driving this evolution. This fully revised and expanded second edition reflects the rapid progress made in engine modeling and simulation over the past two decades. One-dimensional (1D), three-dimensional (3D), and coupled 1D–3D modeling techniques have become indispensable tools in modern engine design, enabling engineers to evaluate performance, efficiency, and emissions through advanced virtual engine environments. Bringing together contributions from leading international researchers and industry experts, this book presents the most significant and recent developments in IC engine simulation. Topics include 0D, 1D, quasi-3D, and full 3D modeling approaches; turbocharging and aftertreatment systems; co-simulation and real-time applications; hydrogen and two-stroke engines; and advanced thermal modeling techniques. Designed for engineers, researchers, and graduate students, this second edition serves as a comprehensive reference for understanding, comparing, and applying state-of-the-art IC engine modeling methodologies in an evolving mobility landscape. Chapter topics include: • state of the art of 1D thermo-fluid dynamic simulation models • virtual engine development: 1D- and 3D-CFD up to full engine simulation • advanced 0D and quasiD thermodynamic combustion models for SI and CI engines • compressor and turbine (turbocharger, supercharger, or turbocompounding device) as boundary conditions for 1D simulations • 3D-CFD combustion models for SI and CI engines • model order reduction for real-time simulation and control applications • modeling of EGR systems •1D engine model in XiL application-a simulation environment for the entire powertrain development process • coupling of 1D and 3D fluid dynamic models for hybrid simulations • extending the 1D approach to the simulation of 3D components: the quasi-3D approach • 1D simulation models for aftertreatment components• 3D simulation models for after-treatment systems • modeling of IC engine silencers and tailpipe noise: 1D and 3D approaches • hydrogen-fueled internal combustion engines • optimization of the gas exchange process in advanced 2-stroke engines • IC engine 0D/1D thermal modeling
Onorati, Angelo, Montenegro, Gianluca
Optimum Bore-to-Stroke Ratio for a Flathead Uniflow Two-Stroke SI Engine and its Impact on Different Fuels2025-32-002411/3/2025
This numerical study investigates a spark-ignited, two-stroke engine employing uniflow scavenging, flathead cylinder head design, and an exhaust valve system to identify the optimal bore-to-stroke (B/S) ratio for maximizing brake efficiency at fixed displacement. A single-cylinder prototype engine was constructed, and its experimental data validated a 1D GT-SUITE simulation model. This validated model was then utilized to simulate a full-scale, 1.5-liter displacement, horizontally opposed four-cylinder engine with supercharger-assisted boosting, intended for small aircraft propulsion. The simulations explored a range of B/S ratios from undersquare (0.7) to oversquare (1.5), maintaining a consistent brake power output of 60 kW at 3000 rpm and lambda 0.9. Results showed that increasing the B/S ratio enhanced brake efficiency from 26.0% at B/S=0.7 to 27.0% at B/S=1.5, largely due to reduced frictional losses attributed to shorter stroke and lower piston speeds, decreased heat transfer losses, and a modest reduction in compressor power demand. Frictional power decreased from 12.7 kW at B/S=0.7 to 9.6 kW at B/S=1.5, while heat transfer losses dropped from 43.5 kW to 40.6 kW respectively. Fuel analyses involving gasoline E27, ethanol (E100), and aviation gasoline (AvGas) revealed ethanol (E100) provided the highest brake efficiency yet increased fuel consumption (BSFC). AvGas presented the lowest BSFC, with gasoline E27 performing intermediately. A key finding is the inverse trend in heat transfer losses, where the undersquare configuration exhibited greater losses than those of the oversquare geometry, contrary to conventional expectations. Combined with improved mechanical efficiency due to reduced friction, the oversquare design emerged as the most efficient configuration. These findings challenge traditional heat transfer assumptions in common two and four-stroke engines and highlight the benefits of higher B/S ratios for improving overall performance in flathead uniflow two-stroke engines. The results will serve as the foundation for the design of the full-scale four-cylinder aeronautical engine.
Zanchin, Guilherme, Hausen, Roberto, Fagundez, Jean Lucca, Lanzanova, Thompson, Martins, Mario
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
Performance Prediction of a Two-Stroke Aviation S.I. Engine by Means 0D/1D Thermo-Fluid Dynamic Simulation Code2025-32-002611/3/2025
Two-stroke engines represent an attractive solution for aviation industry applications (UAVs, VTOL aircraft, and ultralight aircraft) due to their compact size, high power-to-weight ratio, reduced number of moving parts, and the ability to operate with different fuels. This work presents a 0D/1D methodology for simulating the gas exchange, combustion, and unsteady flow of a two-stroke aviation engine. The scavenging and combustion processes, as well as the unsteady flow within the induction and exhaust systems, are investigated using a 0D/1D modeling approach. This study is motivated by the need to assess the accuracy of such models in predicting engine performance. For this purpose, the thermo-fluid dynamic code GASDYN has been applied and enhanced. The proposed 0D model is embedded into a 1D fluid-dynamic code for simulating the entire engine system. To characterize the baseline configuration, which includes tangential ports that facilitate a loop-scavenging process, computed results are compared with available experimental data from a conventional two-stroke spark ignition engine used in aviation applications. Validation was carried out under operating conditions representative of UAV operation at different speeds and full load. The final goal of this study is to modify the exhaust system geometry to increase the maximum power of the same engine architecture. Satisfactory results were achieved, demonstrating that the proposed approach can be applied to design and optimize two-stroke engines with a high degree of accuracy and reduced computational costs.
Cerri, Tarcisio, Giussani, Alessandro, Lucchini, Tommaso, Marinoni, Andrea, Montenegro, Gianluca, Onorati, Angelo
Effect of Plasma-Assisted Ignition on Combustion and Emission Characteristics of Two Stroke Engines with Different Fuels2025-32-003011/3/2025
This study explores the effect of plasma-assisted ignition (PAI) on combustion stability and emissions in two-stroke spark-ignition engines. Two engine platforms were evaluated: a conventional single-cylinder two-stroke engine and a thermodynamically advanced opposed-piston two-stroke (OP2S) engine. The OP2S engine configuration offers reduced heat loss and higher power density due to its uniflow scavenging and favorable geometry, but suffers from high residual gas fraction, which increases ignition difficulty and combustion instability. To address this, nanosecond-pulsed PAI was applied in various spatial arrangements and discharge voltages, using both gasoline and a low-reactivity gasoline/DMC blend fuel. Spark ignition timing was held constant at the minimum advance for best torque across all tests. Combustion stability was assessed via indicated mean effective pressure (IMEP) and its coefficient of variation, while CO and HC emissions were measured as environmental indicators. Results show that PAI significantly enhanced ignition stability, reducing COVIMEP by up to 84% and HC emissions by up to 24%, depending on fuel and engine type. The OP2S engine showed greater responsiveness to ignition configuration and plasma positioning due to its uniflow scavenging method. These findings confirm that PAI is a promising strategy for improving ignition robustness and emission performance in both conventional and advanced two-stroke engine architectures.
Liu, Jinru, Yamazaki, Yoshiaki, Otaki, Yusuke, Kato, Hayato, Kobayashi, Daichi, Umegaki, Tetsuo, Asai, Tomohiko, Iijima, Akira
Study of Combustion Characteristics of a Two-Stroke Opposed Piston Engine using Low-Octane Fuels2025-32-002811/3/2025
Various fuels are being considered as the next generation of carbon neutral fuels, including methanol, ethanol, and SAF. These have widely different ignition properties. Methanol and ethanol are high-octane fuels, so there are no major problems with their use in gasoline engines. However, SAF is a hydrocarbon with a large molecular weight, so it has a fundamentally low octane rating and is not easy to use in SI engines. In order to put carbon-neutral fuels of various properties into practical use, it is effective to develop a technology that allows fuels with low octane to be operated in SI engines. Therefore, in this study, basic research was conducted on the combustion of fuels with low octane using PRF fuel in opposed-piston engines. Opposed piston engines are characterized by their light weight due to the absence of a cylinder head, low S/V ratio due to the ultra-long stroke, reduced cooling loss due to the long stroke, and reduced vibration due to the offsetting of the reciprocating inertial forces of the left and right pistons, resulting in high efficiency and output. In addition, one of the disadvantages of low-octane fuel is that it tends to auto-ignite, but combustion under high residual gas conditions has the effect of suppressing fuel auto-ignition, and by using a 2-stroke engine with a high percentage and high concentration of residual gas and locally high temperatures, auto-ignition is suppressed and low The use of two-stroke engines with high residual gas content and high concentration and high local temperatures can be expected to suppress auto-ignition and allow the use of low-octane fuels.
Yamazaki, Yoshiaki, Okawara, Ikumi, Liu, Jinru, Iijima, Akira
Assessment of E-Fuels Applicability as Gasoline Replacement in a Small Two-Stroke Engine2025-32-005811/3/2025
The push for reducing greenhouse gas emissions has extended to various sectors, including outdoor power equipment. While electrification is a promising solution for low-power gardening tools, the substitution of small two-stroke engines becomes critical for applications requiring higher power and range. Biofuels and e-fuels produced from renewable sources present a viable short-term alternative, leveraging existing engine technologies to minimize dependence on fossil fuels. However, the ability of current engines to operate with these fuels while maintaining performance and emission levels without modifications requires thorough evaluation. This study investigates the feasibility of using e-fuels as sustainable alternatives to gasoline in small two-stroke engines. Preliminary computational fluid dynamics (CFD) simulations were conducted to evaluate the performance of the e-fuel after defining a proper fuel surrogate. Experimental tests were then carried out to assess combustion characteristics, engine performance, and pollutant emissions substituting a commercial E10 gasoline with the synthetic counterpart. The results demonstrate that e-fuels achieve comparable performance and emissions profiles to gasoline, indicating their potential as drop-in replacements for conventional fuels in existing engine technologies. These findings highlight the practicality and promise of e-fuels in advancing sustainable solutions for outdoor power equipment.
Breda, Sebastiano, Fontanesi, Stefano, Merolla, Santo, Gagliardi, Vincenzo, Cicalese, Giuseppe, Pati, Matteo, Dalseno, Luca, Kuschel, Mario
Development of Supercharged Direct-Injection Two Stroke Engine with Intake and Exhaust Valve for Series Hybrid (2nd Report)- To Realize Lean Burn -2025-32-002311/3/2025
The two-stroke engine, known for its small displacement and high performance, is space-efficient when installed in a vehicle. As such, incorporating two-stroke engines into HEVs is an effective way to reduce vehicle weight and optimize engine space. However, one downside is that the amount of unfired elements in the exhaust gas increases due to the air/fuel mixture being expelled into the exhaust system during the scavenging process. Moreover, combustion can become unstable due to the large volume of residual burned gases in the cylinder. To address these issues, we propose a two-stroke engine equipped with intake and exhaust valves that directly inject fuel into the cylinder. In our first report, we presented an engine design and method that enable high scavenging efficiency and stable combustion in a two-stroke engine [1]. In this second report, we share the results of our research aimed at improving fuel efficiency and achieving low emissions, all while maintaining the high performance typical of a two-stroke engine. To enhance fuel efficiency, the amount of burned gas was optimized by adjusting the timing and lifting the intake and exhaust valves. Lean combustion was achieved by leveraging the high temperature in the cylinder, utilizing its excellent ignitability. Additionally, it has been reported that THC emissions—a common issue in two-stroke engines—are reduced by preventing unburned gas from being expelled into the exhaust pipe through the adoption of in-cylinder direct injection.
Sakurai, Yota, Hisano, Atsushi, Saitou, Masahito, Ichi, Satoaki
Clean Cuts, Clear Conscience: Advanced Engines, Optimized Tools, Eco-Friendly Fuels2025-32-008711/3/2025
Handheld outdoor power equipment is utilized globally to shape and maintain the environment, serving as daily assistants in forestry under demanding conditions. In the power tool sector, the transition from petrol to battery-powered products is already well underway, particularly for consumer applications. However, internal combustion engines will continue to be indispensable for professional users of power tools, who place the highest demands on their equipment in terms of performance and energy density. These power tools are often used in remote locations and thus far away from a possible charging infrastructure. To contribute to climate protection, biofuels and RFNBOs are crucial. The continuous optimization of engine technology and its overall system, including cutting tools (such as saw chains and cutting wheels), is a key development goal for STIHL. The optimized interaction between the saw chain, guide bar, and power train is necessary for efficient work progress and ergonomic handling of the products during operation. Consequently, STIHL focuses on the overall system in design and development, supported by the in-house manufacturing of all critical components. The newly developed STIHL Hexa saw chain is an innovative system featuring a new tooth shape, representing a significant milestone. The Hexa sharpening pattern and narrow kerf enhance the cutting performance of the previous standard saw chain by up to ten percent. This improvement is clearly noticeable to professional users during felling, limbing, and cutting to length. The saw chain also remains sharp for a longer period and has an extended service life with optimal cutting performance. This means that the energy used is converted into work progress with higher efficiency. When combined with a highly efficient two-stroke engine and sustainable fuels, not only the energy consumption per cutting surface is reduced, but CO2e emissions are also significantly lowered. This comprehensive package contributes positively to climate protection during sequential timber harvesting.
Beck, Kai W., Maier, Georg, Müller, Matthias, Lux, Thomas, Kölmel, Armin, Lochmann, Holger, Melder, Jens
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
Numerical Analysis of In-Nozzle Flow of Methanol Injectors for Large Marine Two-Stroke Engines2025-24-00699/7/2025
A statistical method for analyzing momentum deflection angles of fuel injectors based on Computational Fluid Dynamics (CFD) simulation of the internal nozzle flow is proposed. This method is especially relevant for large marine two stroke engines where the spray is often deflected due to an eccentric and asymmetric design of the internal injector geometry. Unsteady Reynolds-Averaged Navier-Stokes (URANS) CFD simulations are employed to analyze the internal flow of different cavitating injectors which have four and five nozzle holes, respectively, for a 50 cm bore and a 95 cm bore dual-fuel engine operating on methanol. The in-nozzle flow dynamics vary from one to another significantly. The use of the statistical analysis on the distribution of deflection angles at the fuel nozzle hole exit further assists at explaining differences in measured surface temperatures of the exhaust valve bottom and piston bowl. The corrected spray angles obtained from these in-nozzle simulations also serve as important inputs to the CFD engine combustion simulations for further in-cylinder analysis.
Quist, Nicolai Arent, Matlok, Simon, Pang, Kar Mun, Norman, Thomas Schaldemose, Mayer, Stefan, Walther, Jens Honoré
Design of a New Overhead Two-Stroke Engine Braking Device and Braking Performance Evaluation2025-01-50487/1/2025
The braking safety of heavy-duty vehicles is widely concerned. This paper proposed a new purely mechanical transmitted OHC two-stroke braking device. The rigid–flexible coupled dynamics model of the device and the engine working process simulation model were used for joint simulation. The effects of CR lift, environmental conditions, compression ratio, and braking type on the engine braking performance were comprehensively evaluated. The result shows: good consistency of valve operation is obtained by using pure mechanical transmission. During the braking process, the in-cylinder pressure acts directly on the valves and significantly affects the maximum valve lift of the CR phase, therefore excessive in-cylinder pressure will reduce the reliability of the braking device. When the CR lift increases from 1.9 to 2.8 mm, the braking power per liter increases at low altitude, but first increases and then decreases at high altitude. The decrease in engine speed and compression ratio as well as the increase in altitude lead to the decrease in braking power per liter. A benchmark of braking performance was taken from a high-compression-ratio (17) engine with a four-stroke decompression brake. For the high-compression-ratio (17) engine with two-stroke brake, the maximum in-cylinder pressure was reduced from 6.30 to 3.84 MPa, and the braking power per liter was increased by 24.5%–32.3% at low altitude and 93.2%–110.2% at high altitude. For the low-compression-ratio (11.6) engine with two-stroke brake, the maximum in-cylinder pressure is reduced to 2.83 MPa, and the braking power per liter changes less at low-altitude conditions and increases by 54.8%–67.1% at high-altitude conditions. The two-stroke braking device will greatly improve the braking safety and device components’ reliability on heavy-duty trucks, broaden the operating speed range, and promote the popularization and application of low-compression-ratio engines such as natural gas engines and methanol engines.
Cui, Jingchen, Wang, Bing, Tian, Hua, Tian, Jiangping, Long, Wuqiang
Effect of Ignition Condition and Fuel Octane Number on Knock Intensity in a Small 2-Stroke Engine2025-01-02116/16/2025
Internal combustion engines (ICEs) remain widely used in automotive transportation for their high energy storage system efficiency and economic benefits. The 4-stroke engine has dominated all other forms to date, because the Otto cycle is relatively simple to understand. However, the significant benefits such as less pumping work and friction, lighter construction of 2-stroke engine, are attractive for applications that prioritize the simplicity and power density as well as meet the emission regulations. The disadvantages of the 2-stroke engine are mainly caused by the lack of sufficient scavenging process. Also, the overlap of the intake and exhaust phases results in charge short-circuiting, more fuel consumption and high unburned hydrocarbon emissions. For these reasons, it is difficult for 2-stroke engines to achieve stoichiometric combustion, making them incompatible with three-way catalyst to control emissions. The residual exhaust gas in the cylinder makes the spark ignition application leads to incomplete combustion and a higher coefficient of variation. Hence, it is imperative to investigate the effect of spark ignition strategies (ignition position, ignition timing conditions) on a portable small 2-stroke engine with complex in-cylinder gas flow distribution. In this study, we discussed the effect of spark ignition strategies on a small 2-stroke engine. In-cylinder combustion characteristics, emission characteristics and flame propagation process were observed by an optical 2-stroke engine with loop-scavenging. Additionally, in terms of fuel properties, gasoline, dimethyl carbonate/gasoline blend fuel and primary reference fuel are used to investigate the influence of ignition method on knock intensity with different octane numbers. To analyze the effect of fuel properties on combustion characteristics, the computational fluid dynamic (CFD) simulation using CONVERGE were conducted to predict the flame propagations. Through the experimental and CFD results, the potential for combustion improvement on 2-stroke spark ignition engine was evaluated by the optimization of ignition strategies.
Liu, Jinru, Yamazaki, Yoshiaki, Otaki, Yusuke, Kato, Hayato, Yokota, Takumi, Iijima, Akira
Two-Stroke-Cycle Engine Oil Fluidity/Miscibility ClassificationJ1536_202505 (Current)5/16/2025
This SAE Recommended Practice is intended for use by engine manufacturers in determining the Fluidity/Miscibility Grades to be recommended for use in their engines and by oil marketers in formulating and labeling their products.
Fuels and Lubricants TC 1 Engine Lubrication
Enhancements in Hydrogen Low Pressure Injection on Small Two-Stroke Engines2024-32-00474/18/2025
The use of small 2-stroke crankcase scavenged engines running on hydrogen is very attractive for low power rates, when low cost and compact dimensions are the fundamental design constraints. However, achieving optimal performance with hydrogen fuel presents challenges, including uneven air-fuel mixtures, fuel losses, and crankcase backfiring. This research focuses on a small 50cc 2-stroke loop-scavenged engine equipped with a patented Low-Pressure Direct Injection (LPDI) system, modified for hydrogen use. Experimental results demonstrate performance comparable to the gasoline counterpart, but further optimizations are needed. Consequently, CFD-3D simulations are employed to analyses the injection process and guide engine development. The numerical analysis focuses on a fixed operating condition: 6000 rpm, Wide Open Throttle (WOT), with a slightly lean mixture and injection pressure fixed at 5 bar. A numerical model of the entire engine is set up with the primary objective of improving injection efficiency by modifying the position and orientation of the injector, along with the piston dome shape. Seven configurations under the same operating conditions and injected mass are investigated to assess the impact of these modifications and find the best compromise. The methodology considers the following parameters: fuel trapped within the cylinder, fuel lost through the exhaust, fuel mass in the crankcase, and mixture uniformity before spark ignition. The best-performing configuration, featuring a standard piston dome but with a repositioned injector, achieves a notable reduction in fuel short-circuiting (up to 20%), while ensuring a relatively uniform air-fuel mixture at spark timing.
Caprioli, Stefano, Schoegl, Oliver, Oswald, Roland, Kirchberger, Roland, Mattarelli, Enrico, Rinaldini, Carlo Alberto
Basic Investigation of Thermodynamic Effects on a Hydrogen Two-Stroke Engine2024-32-00394/18/2025
The spark ignited two-stroke engine, as a cost-efficient power unit with low maintenance demand, is used millionfold for the propulsion of hand-held application, motorcycles, scooters, boats and others. The outstanding power to weight ratio is the key advantage for two-stroke engines. However, poor exhaust emissions, caused by high scavenge losses, especially on port controlled two-stroke engines, and a low efficiency are disadvantages of this combustion process. Under the aspect of increasing environment- and health awareness, the two-stroke technology driven with fossil resources, shows no future advantage. The anthropogenic climate change force for sustainable development of combustion engines whereby reduction of fuel consumption or usage of alternative fuels is an important factor. Best way of a decarbonization to fulfil future climate goals is the utilization of non-carbon fuels. In this field of fuels, hydrogen, with its high energy content and close inexhaustible availability, shows a good solution. Four-stroke gasoline engines are developed since many years for the use of hydrogen. Different strategies of mixture preparation, like port- or direct injection with low- or high injection pressure are available and well known. Compared with two-stroke engines, the usage of hydrogen and, therefore, the knowledge about thermodynamic effects, is still at the beginning. Challenges, such as inhomogeneous air-fuel mixture within the cylinder at high speed, short-circuiting of fuel to the exhaust, and backfiring in the crankcase are open points. In the context of this paper basic investigations of the combustion process with thermodynamic limits are presented. Starting with the general layout of the mixture preparation, an overview of the whole system and safety features are shown. The aim of research is to declare the limits of the combustion and gas exchange process with respect to the combustion abnormalities such as self/pre-ignition and knocking. From this, possible optimizations can be derived. To gain knowledge about the combustion specific relations with the focus on high output performance, different basic approaches are tested. In conclusion, a better understanding of limits in terms of temperatures, mixture preparation, spark advance and injection timing is achieved.
Yasuda, Terutaka, Oswald, Roland, Kirchberger, Roland
Research on Basic Characteristics of a Two-Stroke Opposed Piston Engine2024-32-01124/18/2025
This study investigated the performance characteristics of a two-stroke opposed piston engine that is capable of constantly operating with high power output and high efficiency. An investigation was also made of the performance obtained by applying a pseudo uniflow condition as a measure against large hydrocarbon (HC) emissions owing to blow-by of unburned mixture, which is an issue of two-stroke engines. The test engine had a displacement of 127 cm3 and a bore and stroke of 48 x 70 mm. One-point and dual-point ignition systems were used, and regular gasoline was supplied as the test fuel using a carburetor-based fueling system. Experiments were conducted at engine speeds of 1500 and 3000 rpm at ignition timings of 45 deg. and 35 deg. before top dead center. The results showed that large quantities of HC emissions were emitted because stable combustion was not achieved. This revealed that a stronger uniflow condition must be applied as a countermeasure rather than a simple pseudo uniflow.
Fukushima, Shumpei, Uehara, Ryota, Hayashi, Yoshiaki, Igarashi, Ryo, Tokita, Kazuho, Iijima, Akira
Use of Methanol in a High-Power Density Generator13-06-03-00214/2/2025
Increasing global pressure to reduce anthropogenic carbon emissions has inspired a transition from conventional petroleum-fueled internal combustion engines to alternative powertrains, including battery electric vehicles (EVs) and hybrids. Hybrids offer a promising solution for emissions reduction by addressing the limitations of pure EVs such as slow recharge and range anxiety. In a previous research endeavor, a prototype high-power density generator was meticulously designed, fabricated, and subjected to testing. This generator incorporated a compact permanent magnet brushless dynamo and a diminutive single-cylinder two-stroke engine with low-technology constructions. This prototype generated 8.5 kW of electrical power while maintaining a lightweight profile at 21 kg. This study investigates the performance and emissions reduction potential by adapting the prototype to operate on methanol fuel. Performance and emissions were experimentally evaluated under varying operating conditions. In addition, a comparative analysis between methanol fuel and conventional gasoline was performed. It was found that the generator operable on methanol achieved an overall increase in performance with a peak power output of 10 kW when compared to gasoline. In addition, the generator demonstrated significant reductions in carbon emissions. The goal of this research is to adapt and demonstrate the high-power density, low-emission electric power generator from previous work, which was suitable for applications such as, for example, range extenders and UAV propulsion, to use renewable fuel. This research showcases a potential direction for an electrical generator that offers reduced emissions in applications where specific power is critical.
Gore, Matt, Nonavinakere Vinod, Kaushik, Fang, Tiegang
Achieving Ultra-Low NO x and Meeting Full Useful Life Requirement for CARB 2027 NO x and GHG 2027 Phase 2 CO 2 Regulation w/Opposed Piston 2-Stroke Engine and a Conventional ATS2025-01-83914/1/2025
Internal combustion engines are expected to continue to play an important on-going role in the future of transportation, particularly in long haul transit and off-road applications. Substantially reducing criteria emissions of heavy-duty (HD) commercial vehicle engines while also reducing fuel consumption is the quickest way to achieve more sustainable transportation. The opposed-piston (OP) engine developed by Achates Power has demonstrated the ability to meet the most stringent ultralow NOx emissions requirements using only a conventional, underfloor aftertreatment system, offering reduced cost, complexity and compliance risk compared to other diesel engines. This paper is focused on the measurement results of Achates Power heavy-duty engine achieving CARB proposed ultralow NOx emission for 2027 and 2031+ full useful life requirements while also meeting the EPA Greenhouse Gas (GHG) Phase 2 limits with a conventional aftertreatment system (ATS), which was aged to 435k, 600k and 800k equivalent miles. The paper will describe EPA cycle results at each aging step and highlight the challenge of simultaneously meeting both criteria and CO2 emissions.
Kale, Vaibhav, Bako, Zoltan
Experimental Study on Combustion and Emission Characteristics of a Two-Stroke Engine applying PODE/Methanol Blends Direct Injection2025-01-71121/31/2025
In order to realize the Paris Agreement, which aims to strengthen the global response to climate change, conventional internal combustion engines (ICE) need to contribute to reducing carbon emissions and improving thermal efficiency. More importantly, in the face of energy shortages, it is urgent to search for sustainable fuels. Poly-oxymethylene dimethyl ethers (PODE) and methanol are both regard as important low-carbon, alternative fuels due to their high oxygen content. Using PODE can overcome the characteristics of methanol as a low-reactivity fuel with a low cetane number and poor ignition properties. In this study, the combustion and emission characteristics of PODE/methanol blends were investigated in a two-stroke direct injection engine. Firstly, the performance of the engine under pure PODE (P100) and PODE/methanol blends (P50) was compared. The results show that at BMEP of 0.31 MPa and injection timing of -8°CA ATDE, P50 blends have lower CO2, CO, NOX and THC emissions than P100 fuel. However, the start of combustion of P50 is delayed slightly and ITE is lower than that of P100. Then, the effect of injection timing on the performance of the P50 engine was investigated. With the delay of fuel injection timing, NOX emissions decrease, but CO2, CO, and THC emissions increase. Moreover, as the injection timing is delayed, the engine COVIMEP was reduced and combustion stability was improved. The engine indicated mean effective pressure (IMEP) reaches its maximum value of 0.441MPa at -8°CA ATDC and decreases as injection timing is delayed. However, the indicated thermal efficiency (ITE) decreases with the delay of injection timing, reaching a maximum of 41.8% at -8°CA ATDC. This study provides a theoretical foundation for adopting PODE/methanol blends in diesel engines, highlighting their potential to reduce conventional emissions while maintaining operational feasibility. Further research on varying methanol ratios and load conditions is recommended.
Dong, Pengbo, Sun, Zhuohan, Wang, Qingyang, Wang, Yang, Cui, Jingchen, Zhang, Zhenxian, Long, Wuqiang
Lubricants for Two-Stroke-Cycle Gasoline EnginesJ1510_202501 (Current)1/21/2025
The information in this SAE Recommended Practice has been compiled by Technical Committee 1 (Engine Lubrication) of the SAE Fuels and Lubricants Division. The intent is to provide those concerned with the design and maintenance of two-stroke-cycle engines with a better understanding of the properties of two-stroke-cycle lubricants. Reference is also made to test procedures which may be used to measure the chemical and physical characteristics of these lubricants.
Fuels and Lubricants TC 1 Engine Lubrication
A Computational Study of Hydrogen Direct Injection Using a Pre-Chamber in an Opposed-Piston Engine2024-01-30107/2/2024
Combustion characteristics of a hydrogen (H2) direct-injected (DI) pre-chamber (PC)-assisted opposed piston two-stroke (OP2S) engine are investigated by 3D computational fluid dynamics (CFD) simulations. The architecture of the OP2S engine has potential features for reducing wall heat losses, as the DI H2 jets are not directed towards the piston face. To overcome the high resistance to autoignition of H2, a PC technology was implemented in order to enhance the ignition of the mixture by the multiple hot reactive jets. To further investigate the interaction between the H2 plume and the chamber walls, three different piston bowl designs were evaluated and ranked based on a merit function. For the cases under study, the flat piston design was found to be most favorable (compared to the narrow and wide pistons) due to its reduced surface area for lower wall heat losses. The results also showcase that a co-optimization approach considering various parameters is an effective strategy to minimize the flame-wall interaction. The analysis showed that the PC jet must guarantee ignition and also a high-momentum exchange to support mixing-controlled and late combustion stages, while keeping safety limits from being exceeded. Finally, the results highlight that DI-PC H2 combustion exhibits Diesel-like behavior, which can be exploited to achieve high efficiency and low emissions. Similar to conventional Diesel combustion (CDC), DI-PC H2 combustion can provide the control of combustion phasing by adjusting the timing of the hot jet injection. While more work is needed to achieve the same level of efficiency as CDC, the present study demonstrated additional benefits of DI-PC concept as a robust carbon-free engine operation option. Finally, the analysis with respect to the fuel energy distribution and the DI-PC H2 combustion phases shows that it is possible to further optimize combustion, especially in mixing-controlled and late stages.
Menaca, Rafael, Moreno Cabezas, Kevin, Shakeel, Mohammad Raghib, Vorraro, Giovanni, Turner, James W. G., Im, Hong G.
Application of MAN Loop Scavenging in a 125 cc Two-Stroke Racing EngineSAE-PP-003955/8/2024
The use of MAN-type loop scavenging port arrangements in a 125 cc two-stroke racing engi-ne is being investigated. These make it possible to provide larger cross-sections for the trans-fer 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. One open point is the quality of the scavenging. A study found in the literature on the use of MAN loop scavenging on a small engine shows significantly worse results than is known from large engines. There is still a need for further investigation here.
Eilts, Peter
Evaluating the Effects of an Electrically Assisted Turbocharger on Scavenging Control for an Opposed Piston Two Stroke (OP2S) Compression Ignition Engine2024-01-23884/9/2024
Opposed piston two-stroke (OP2S) diesel engines have demonstrated a reduction in engine-out emissions and increased efficiency compared to conventional four-stroke diesel engines. Due to the higher stroke-to-bore ratio and the absence of a cylinder head, the heat transfer loss to the coolant is lower near ‘Top Dead Center.’ The selection and design of the air path is critical to realizing the benefits of the OP2S engine architecture. Like any two-stroke diesel engine, the scavenging process and the composition of the internal residuals are predominantly governed by the pressure differential between the intake and the exhaust ports. Without dedicated pumping strokes, the two-stroke engine architecture requires external devices to breathe. In the unique OP2S engine architecture studied in this work, the external pumping devices present in the air path include an electrically assisted turbocharger (EAT), an electrified EGR pump, and a back-pressure valve (BPv) located downstream of the turbocharger. In this work, various sweeps were experimentally recorded for these actuators to understand their effects on airflow rate, port pressure, and pressure differential. The objective of these experiments was to identify regions with high scavenging efficiencies while evaluating the effect of electrical power consumption as pumping losses on brake efficiency. The results indicated a higher scavenging efficiency was achievable at low engine speeds as less of the fresh intake charge is short-circuited to the exhaust during the blow down process. Also, with the combination of these actuators, an inherent challenge of decoupling airflow control from intake port pressure became apparent, and thus optimizing scavenging at a given port pressure became difficult. However, the EAT provides the flexibility of changing the air flow rate at a constant load but any increase in the brake thermal efficiency is negated by the electrical energy consumed from pumping more air through the compressor.
Bhatt, Ankur, Gandolfo, John, Huo, Ming, Gainey, Brian, Lawler, Benjamin
1D-3D CFD Investigations to Improve the Performance of Two-Stroke Camless Engine2024-01-26864/9/2024
The transportation sector still depends on conventional engines in many countries as the alternative technologies are not mature enough to reduce carbon footprints in society. The four-stroke diesel engines, primarily used for heavy-duty applications, need either high intake boosting or a large bore to produce higher torque and power output. There is an alternative where a four-stroke engine operated in two-stroke mode with the help of a fully flexible variable valve actuation (VVA) system can achieve similar power density without raising the intake boosting or engine size. A fully flexible VVA is required to control the valve events (lift, timing, and durations) independently so that the four-stroke events can be completed in one cycle. In this study, 1D-3D CFD coupled simulations were performed to develop a gas exchange process for better air entrapment in the cylinder and evacuate the exhaust products simultaneously. The intake and exhaust valve closing timings were optimized based on the engine torque. The in-cylinder fresh charge mostly leaves the cylinder through exhaust ports during the gas exchange process even if the valve timings were optimized. Hence, a new design was proposed in which different deflectors (rectangular and semi-circular) were placed near the intake valve seats with the hope of achieving better air entrapment in the cylinder. The deflectors prevented the intake charge particles from being shot-circuited through the exhaust port and helped the charge particles to trap in the cylinder. The semi-circular deflector showed a more promising technique than the rectangular deflector and achieved a 45% higher torque improvement than the baseline design without a deflector.
Tripathy, Srinibas, Dahlander, Petter, Somhorst, Joop, Kuylenstierna, Claes
A Renewable-Fuel 60% Efficient Engine - Insights from the General Cycle EquationSAE-PP-0037011/25/2023
The General Cycle is a thermodynamic cycle that includes all six steps common to engine cycles. Thus it includes other engine cycles as subsets, each of these lacking one or more of the steps. The General Cycle engine, outside the realm of more commonly known thermodynamic cycles, is best suited to attain highest efficiency. Essential strategies for attaining 60% efficiency in an internal combustion engine are: (1) optimize parameters in the General Cycle, (2) reduce friction and heat transfer losses, and (3) preserve combustion efficiency. Obtaining a practical 60% efficient engine is a struggle against engine cost and power density. Add to that the problem of using only a renewable fuel with the intent of satisfying three additional goals: (1) net-zero-carbon emissions, (2) compatible with existing infrastructure and fuel systems, and (3) able to replace all current fossil fuel use. These conditions will require the highest efficiency in order to satisfy market demand given a limited supply of sustainable fuel. The result is a plan for a 60% efficient engine with practically no emissions. Does applying all of these steps provide a vision for the internal combustion engine of the future? This is not an idle question—decision makers should discard the idea to “electrify everything.” Batteries have far less energy density than do fuels, and they have other problems, such as refueling logistics, when used in working machines such as trucks, farm machinery, and earth movers. Modern civilization was built by internal combustion engines. The world will continue to use engines far into the future, and they can be designed to operate sustainably.
Rogers, Ernie, Collett, Glen
ZERO-EMISSION INTERNAL COMBUSTION ENGINESAE-PP-0036811/17/2023
A new concept of internal combustion engine has been developed. The purpose is to have an engine that can burn hydrocarbon fuels without discharging any greenhouse gas or other harmful substances into the atmosphere. The new engine, the zero-emission engine, inducts no air from the environment. Instead, the engine exhaust gas, with added oxygen, is used in performance of the combustion cycle. Carbon dioxide, the main byproduct of combustion is captured, stored, and unloaded during refueling for further storage, sequestration, or recycling. The zero-emission engine displacement can be significantly smaller than in a conventional air-inducting engine of equal power, with a significantly higher power density. The engine is unthrottled and it can operate with a much higher compression ratio without an increase in the cylinder temperature. The above concept also envisions recycling the captured carbon dioxide by using it with water to produce hydrocarbon fuel and oxygen that can be supplied back to the engine. In that case, an automobile and a refueling station form a closed-energy circuit, in which the internal combustion process produces carbon dioxide that is converted back into fuel at the refueling station (or other processing facility), and that fuel is delivered back to the vehicle. The engine operates in a carbon-neutral mode burning fuel that can be repeatedly used, regenerated, and reused again. This paper describes the above concept and reviews its advantages and disadvantages. It also describes an experimental vehicle system that has been built to evaluate and verify the feasibility of the concept and review the test results. The concept was judged to be feasible, and the experimental vehicle equipped with a zero-emission engine is operational. No exhaust gas is discharged into the atmosphere.
Schechter, Michael, schechter, victor
Development of Supercharged Two-Stroke Engine with Intake and Exhaust Valve for Hybrid System2023-01-182310/24/2023
The two-stroke engine has a small displacement and high output, and therefore saves space when the engine is installed in a vehicle. Thus, the application of two-stroke engines to HEVs is a very effective means of reducing vehicle weight and securing engine space. On the other hand, the unfired element increases in the exhaust gas with a two-stroke engine because the air-fuel mixture is blown through to the exhaust system during the scavenging process inside the cylinder. Moreover, combustion becomes unstable due to the large amount of residual burnt gas in the cylinder. To solve these problems, we propose a two-stroke engine that has intake and exhaust valves that injects fuel directly into the cylinder. We describe the engine shape and the method that can provide high scavenging efficiency and stable combustion in such a two-stroke engine.
Hisano, Atsushi, Saitou, Masahito, Sakurai, Yota, Matsuda, Yoshimoto, ichi, Satoaki
On the Effects of Piston Pocket, Intake Port, and Transfer Duct Geometries in a Small Stratified-Scavenging Two-Stroke Engine2023-01-182510/24/2023
The regulatory framework of pollutant emissions concerning non-road small internal combustion engines is becoming increasingly challenging. The upcoming scenario threatens to cut out small two-stroke engines because of the fuel short circuit occurring during transfer and exhaust ports overlap, causing the emission of unburned hydrocarbons and reducing engine efficiency. Despite this challenge, small two-stroke engines are unmatched in high power density applications in which weight and autonomy hinder the diffusion of electric technologies. The continuation of small two-stroke engines in the market will thus depend on the capability of mitigating fuel short circuit. From this perspective, some of the Authors found the low-pressure injection technology fulfilling the purpose at engine full load; however, in addition to system complexity and costs, a lack of mixture homogenization was noted at low load. Another solution concerns the adoption of a pocket milled in the piston skirt, connecting an auxiliary air intake to the transfer ducts by means of additional ports. This feature leads to the filling of the transfer ducts with fresh air only, reducing fuel short circuit during scavenging. Due to the fluid dynamic complexity, stratified-scavenging engines are typically investigated via experimental or CFD analyses, leading to high costs and times. In the present paper, a novel 1-D numerical approach for the study and optimization of a 55 cm3 stratified scavenging engine is introduced. The model, developed in the GT-Suite framework and validated through test-bench data, allows the replication of complex phenomena like air stratification. The effects of pocket volume, phasing of ports, as well as length of transfer channels, in terms of air stratification and fuel short circuit, is discussed in detail in order to provide design guidelines for stratified-scavenging engines and to find the best setup for the present test case.
Ciampolini, Marco, Raspanti, Sandro, Romani, Luca, Ferrara, Giovanni, Merolla, Santo, Gagliardi, Vincenzo
A Study of the Mechanism of High-Speed Knocking in a Two-Stroke SI Engine with High Compression Ratio2023-01-182410/24/2023
Experimental methods and numerical analysis were used to investigate the mechanism of high-speed knocking that occurs in small two-stroke engines. The multi-ion probe method was used in the experiments to visualize flame propagation in the cylinder. The flame was detected by 14 ion probes grounded in the end gas region. A histogram was made of the order in which flames were detected. The characteristics of combustion in the cylinder were clarified by comparing warming up and after warming up and by extracting the features of the cycle in which knocking occurred. As a result, regions of fast flame propagation and regions prone to auto-ignition were identified. In the numerical analysis, flow and residual gas distribution in the cylinder, flame propagation and self-ignition were visualized by 3D CFD using 1D CFD calculation results as boundary conditions and initial conditions. Flame propagation calculated by 3D CFD was found to be directional due to in-cylinder flow caused by scavenging flow. The calculated direction of flame spread was matched with the experimentally measured direction. It was also found that the first auto-ignition occurred in the high temperature region where the concentration of residual gas was high. Finally, numerical analysis was performed for the high compression ratio engine specifications. As a result, the mechanism of knocking was clarified as the first auto-ignition caused by the high-temperature residual gas, followed by the pressure wave inducing continuous auto-ignition. The flow formed during the scavenging process and the subsequent compression process determine the directionality of flame propagation and residual gas distribution at top dead center. Thus, the possibility of knocking avoidance by scavenging air shape and combustion chamber shape was suggested.
Eto, Kuniyoshi, Kuboyama, Tatsuya, Moriyoshi, Yasuo, Yamada, Toshio, Yatsufusa, Tomoaki, Suzuki, Yusuke
The Flathead Valved Boosted Uniflow Two Stroke Engine2023-01-182610/24/2023
Experimental aviation engines face numerous challenges, including the need for energy efficiency, alternative fuel sources, reduced weight and size, greater durability with reliability, emissions reduction, and integration with advanced control and monitoring systems. This study presents the performance of a two-stroke engine with a Uniflow scavenging system with a flathead valve concept, with lower specific fuel consumption than conventional two-stroke aircraft engines. The engine’s maximum speed is limited to 3000 rpm for better cylinder scavenging efficiency, which also eliminates the need for a reduction gearbox, simplifies the design, and reduces the engine’s total mass. 1D simulations were conducted to evaluate combustion and performance parameters using aviation. At the maximum speed of 3000 rpm, the engine achieved a power of approximately 23 kW with boost around 3bar, while at cruise speeds between 2400 and 2700 rpm, the maximum torque is approximately 80 Nm, with specific fuel consumption ranging from 368 to 378 g/kWh. Brake fuel efficiency is around 23%, which is significantly higher than that of conventional two-stroke engines with cross-flow scavenging, with an average efficiency of only 19%. 3D simulations (CFD) showed promising results with swirl and tumble presenting high velocities promoting high turbulence in the combustion chamber. The engine’s high-power density of approximately 90 kW/l makes it a suitable option for equipping experimental aircraft, as it is compact, efficient, and lightweight compared to commercially available options.
Hausen, Roberto Begnis, Martins, Mario, silveira, Juliano, Fagundez PhD, Jean Lucca
Numerical Investigation of Knocking in a Small Two-Stroke Engine with a High Compression Ration to Improve Thermal Efficiency2023-32-00799/29/2023
This study aimed to achieve both a high compression ratio and low knock intensity in a two-stroke engine. Previous research has suggested that knock intensity can be reduced by combining combustion chamber geometry and scavenging passaging design for the same engine specifications with a compression ratio of 13.7. In this report, we investigate whether low knock intensity can be achieved at compression ratios of 14.4 and 16.8 by adjusting the combustion chamber geometry and scavenging passage design. As a result, the mechanism by which combustion chamber geometry and scavenging passage design change knock intensity was clarified.
Eto, Kuniyoshi, Kuboyama, Tatsuya, Moriyoshi, Yasuo, Yamada, Toshio, Yamazaki, Takahiro, Yamaguchi, Shiro
High Performance and Near Zero Emissions 2-Stroke H 2 Engine2023-24-00688/28/2023
The paper presents a preliminary study on a virtual 2-stroke 3-cylinder 0.9 L DI SI supercharged engine running on Hydrogen (H2), able to meet both high performance targets and ultra-low emissions limits (NOx<20 ppm). Combustion is similar to a conventional 4-stroke H2 DI engine, while the design of the cylinder and the actuation law of both intake and exhaust valves are specifically optimized for the 2-stroke cycle. In comparison to a more conventional 2-stroke loop scavenged engine, with piston-controlled ports, the use of poppet valves enables a more flexible control of the gas exchange process and to maintain the same design of a 4-stroke engine for pistons, cylinders block, crankcase and lubrication system. On the other hand, it is more difficult to avoid the short-circuit of the fresh charge, while permeability of the valves becomes quite critical at high engine speed. Therefore, particular care was devoted to the optimization of the intake and exhaust ports geometry, as well as to the valves actuation law. While the development of the scavenging system was mainly supported by CFD-3D simulation, the optimization of the supercharging system is driven by 1D analyses (by GT-Power). Three different supercharging configurations have been analyzed, with different levels of complexity, performance and cost: compact mechanical supercharger, controlled by a by-pass valve; variable geometry turbocharger, assisted by a mechanical supercharger and controlled by a by-pass valve; variable geometry turbocharger, assisted by an electric supercharger. The 1D engine model of the 2-stroke engine is derived as closely as possible from the experimentally calibrated model of a 4-stroke H2 prototype. In particular, the virtual engines share the setup of the predictive combustion and emissions models.
Caprioli, Stefano, Volza, Antonello, Mattarelli, Enrico, Rinaldini, Carlo Alberto
Investigation of Liquid Lignin-Methanol Blends under Realistic Two-Stroke Marine Engines Conditions2023-24-00858/28/2023
With a view to reducing the environmental impact of fossil fuels, advanced lignin-based biofuels could provide a valuable contribute, since lignin is the most abundant biopolymer on earth after cellulose. However, its thermophysical properties would hamper its use as a pure fuel. In this work we investigated the combustion behavior of sprays of a liquid lignin-methanol blend and evaluated its potential as a low-carbon marine fuel for large two-stroke engines. To this end, an experimental campaign was conducted in an optically accessible combustion chamber whose main dimensions correspond to those of a single cylinder for large two-stroke engines. The chamber is provided with optical accesses for optical diagnostics of the combustion process. The combustion of the mixture was ignited using a diesel pilot jet as the ignition source. Two marine injectors are mounted in the chamber, namely “main” and “pilot” injectors. The tests were performed in environmental conditions around 40 bar and 500°C. The lignin-methanol blend was injected at pressure of 500 and 700 bar, whilst the injection pressure of the pilot diesel was kept at 500 bar. Two different relative orientations of the main and pilot sprays were investigated. The results showed that this type of fuel is suitable for durability trials for the assessment of its final use in a marine internal combustion engine.
Lazzaro, Maurizio, Sementa, Paolo, Catapano, Francesco, Tornatore, Cinzia, Iannuzzi, Stefano, Boot, Michael, Kouris, Panos
A Case Study of an Integrated Starter Generator Failure and Benefits of Time Domain Torsional Vibration Analysis2024-01-41258/10/2023
An Integrated Starter Generator (ISG) was integrated between an opposed piston two stroke engine and a 32 speed binary shift transmission for use in the Advanced Powertrain Demonstrator (APD). The initial design of the ISG integration and accompanying frequency domain torsional vibration analysis was performed considering driveline characteristics within the normal operating speed range of the engine. After a short period of time, the ISG suffered a catastrophic failure. The root cause of this failure is analyzed with special attention to the torsional behavior of the system. Multiple methods are employed to assess the torsional behavior including time domain torsional analysis. The time domain torsional analysis revealed that a significant number of torsional vibration cycles were occurring outside of the normal operating range of the engine as the engine accelerated from engine cranking speed to engine idle speed. The cycle accumulation during these short excursions through resonance ultimately lead to ISG rotor failure. The methods and lessons learned are presented.
Srodawa, John
Investigation of In-Cylinder Pressure Measurement Methods within a Two-Stroke Spark Ignition Engine01-17-01-00045/12/2023
This work describes an investigation of measurement techniques for the indicated mean effective pressure (IMEP) on a 55 cc single-cylinder, 4.4 kW, two-stroke, spark ignition (SI) engine intended for use on Group 1 and Group 2 remotely piloted aircraft (RPAs). Three different sensors were used: two piezoelectric pressure transducers (one flush mount and one measuring spark plug) for measuring in-cylinder pressure and one capacitive sensor for determining the top dead center (TDC) position of the piston. The effort consisted of three objectives: to investigate the merits of a flush mount pressure transducer compared to a pressure transducer integrated into the spark plug, to perform a parametric analysis to characterize the effect of the variability in the engine test bench controls on the IMEP, and to determine the thermodynamic loss angle for the engine. The results indicate that as a spark plug, the measuring spark plug is not statistically different from the stock spark plug at the 95% confidence level. The results indicate a statistically significant, 4% difference in the measured IMEP between the pressure transducer in the measuring spark plug and the flush mount transducer. The results also suggest a statistically significant difference in performance between the modified and unmodified engine heads, verifying the suppositions of other researchers who suggested that even a small modification to a combustion chamber this size could measurably affect the engine performance. While run-to-run variation resulted in a 2% to 5% variation in IMEP, a sensitivity analysis determined that 1% to 3% of that variation arose from variability in the control variables, while the remainder was caused by variation in other engine operating parameters. Between 1000 rpm and 2000 rpm, where the engine was typically motored to determine the TDC, the thermodynamic loss angle was 0.3 crank angle degrees (CAD) to 0.7 CAD, larger than loss angles observed in automotive-sized gasoline engines. The results indicate that using tabulated thermodynamic loss angles to set the TDC location of the engine using a mono-directional peak pressure method would lead to a −1% to −2.5% bias in the IMEP.
Ausserer, Joseph K., Polanka, Marc D., Litke, Paul J., Grinstead, Keith D.
Numerical Study on High-Load Performance of a Two-Stage Boosted Poppet-Valved Two-stroke Diesel Engine2023-01-04434/11/2023
Two-stroke cycle is one of the most effective methods to increase the torque and power output of a four-stroke engine due to the doubled firing frequency compared to four-stroke cycle at the same engine speed. As the two-stroke cycle lacks separate intake and exhaust strokes, the positive pressure difference between intake and exhaust ports is required to drive fresh charge into the cylinder, and is affected by intake port structures due to the different amounts of short-circuited fresh charge during scavenging process. To evaluate the effects of intake port structures on the high-load performance of a boosted poppet-valved two-stroke diesel engine, one-dimensional gas dynamic model and three-dimensional computational fluid dynamics model were established and used to predict the high-load performance of the boosted two-stroke diesel engine with top-entry intake ports, inclined side-entry intake ports, and side-entry intake ports, respectively. The results show that the engine with inclined side-entry intake ports has a much higher scavenging quality coefficient than the engine with other intake port structures. The maximum brake power of the 4.1 L four-cylinder two-stroke diesel engine equipped with a two-stage serial boosting system with a turbocharger and a downstream supercharger can reach 1.4 times that of a 5.1 L four-cylinder four-stroke diesel engine in the cases of top-entry and inclined side-entry intake ports, while that of the two-stroke engine with side-entry intake ports can only reach 1.2 times that of the four-stroke engine due to more power consumed by the supercharger resulted by large amount of short-circuited fresh charge. When the brake power of two-stroke engine is equal to 1.2 times that of the four-stroke engine, the intake pressure and mass flow rate of fresh charge are obviously decreased about 37.3% and 39.3% when intake port structure is changed from side-entry intake ports to inclined side-entry intake ports.
Fu, Xue-Qing, Zhang, Yan, Ding, Zhanming, Zhuang, Anbang, Zhu, Wei, Hou, Linlin, cheng, Jianghua, Zhang, Shuyong
Research of Spark Ignition Engine and Internal Mixture Formation Using Single-Zone, Two-Zone and Three-Zone Calculation Model of It Working Process1325110/27/2022
Thermodynamic models based on the volume balance method for calculating the working process of an engine with spark ignition and internal mixture formation are presented. The single-zone model makes it possible to determine the pressure and average temperature of gases in the engine cylinder during the working process. The two-zone combustion model takes into account the change in the volume of the exhaust gases zone and the air-fuel mixture zone. The model makes it possible to determine the pressure of gases in the cylinder and the temperature in the zones under consideration when the air-fuel mixture is distributed over the entire above-piston volume at the moment of ignition. The three-zone combustion model takes into account the change in the volume of the exhaust gases zone, air-fuel mixture zones and air zones when organizing the stratification of the air-fuel charge, allows you to determine the gas pressure in the cylinder and the temperature in the zones under consideration. The results of theoretical studies obtained by single-zone, two-zone and three-zone thermodynamic models of combustion on a two-stroke engine 1D8.2/8.7 with direct injection of gasoline into the cylinder are compared with experimental data. The results of experimental studies are based on indicator diagrams of gas pressure in the engine cylinder in the load characteristic modes at n = 3,000 rpm in terms of the crankshaft rotation angle. The use of a single-zone and two-zone combustion model is preferably used in high load modes, and a three-zone combustion model is used in partial load modes, which corresponds to the smallest discrepancy between the values of theoretical and experimental indicator diagrams. The results obtained in the work allow us to expand our understanding of the use of the volume balance method for calculating the working process, taking into account the peculiarities of the organization and flow air-fuel mixture.
Korohodskyi, Volodymyr
Improving the Performance of Internal Combustion Engines and Reducing Emissions by Injecting Water with the Air Entering the Engines04-16-01-000510/17/2022
The current work experimentally and theoretically studied the effect of water injection on improving the performance of three different types of single-cylinder internal combustion engines. The first engine is a four-stroke diesel, the second is a four-stroke gasoline, and the third is a two-stroke gasoline engine. Different amounts of water were injected relative to fuel consumption for the three engines to find how it affected the performance, exhaust gas temperatures, and emissions. Comparing the experimental and theoretical results was done to determine the effect of spraying water on lowering the temperatures of the exhaust gases, increasing the thermal efficiency, and lowering specific fuel consumption. The experimental results for the various tested engines show that, in general, the exhaust gas temperature and gas emission decreases by increasing the mass of water injection; these differences vary based on the engine and the operating conditions. Water injected at the inlet of the gasoline engine reduces the overall emissions greater than with the diesel engine and the two-stroke engine. The current laboratory experiments have shown and confirmed by theoretical analyses that spraying water at the inlet of engines reduces braking fuel consumption by a maximum of 10% with an increase in thermal efficiency by up to a maximum of 4.5% and reducing emissions of nitrogen oxides (NOx) and exhaust gas temperature by up to 35%.
Hadidi, Haitham M., Hassan, Ahmed S. A.
An Investigation into the Effects of Swirl on the Performance and Emissions of an Opposed-Piston Two-Stroke Engine using Large Eddy Simulations2022-01-10398/30/2022
Opposed-piston two-stroke (OP-2S) engines have the potential to achieve higher thermal efficiency than a conventional four-stroke diesel engine. However, the uniflow scavenging process is difficult to control over a wider range of speed and loads due to its sensitivity to pressure dynamics, port timings, and port design. Specifically, the angle of the intake ports can be used to generate swirl which has implications for open and closed cycle effects. This study proposes an analysis of the effects of port angle on the in-cylinder flow distribution and combustion performance of an OP-2S using computational fluid dynamics engine. Large Eddy Simulation (LES) was used to model turbulence given its ability to predict in-cylinder mixing and cyclic variability. A three-cylinder model was validated to experimental data collected by Achates Power and the grid was verified using an LES quality approach from the literature. The model was used to simulate port angles from 12 to 29 degrees at constant pressure and temperature boundary conditions. Results indicated that the higher bulk swirl ratio generated by larger port angles tends to trap more internal residuals. This effect on the scavenging performance, combined with the larger trapped swirl ratio, also has a significant impact on the combustion performance in a two-stroke engine. It was concluded that there exists a tradeoff of efficiency and emissions that must be considered when increasing the port angle in a uniflow two-stroke engine.
O'Donnell, Patrick Christopher, Gainey, Brian, Vorwerk, Erik, Prucka, Robert, Lawler, Benjamin, Huo, Ming, Salvi, Ashwin
Assessment of the Combustion Process in Ultra-Lean (λ>1.8) Natural Gas Engines2022-01-10618/30/2022
The majority of today’s natural gas fired engines are applying a premixed combustion concept, which is commonly assumed to be based on the turbulence-enhanced propagation of a thin flame separating the burnt and unburnt fractions of the mixture volume. This concept has been confirmed by means of comprehensive experimental investigations on passenger car engines operating at air/fuel ratios close to stoichiometry; however, for larger industrial engines (4-stroke and 2-stroke) designed for ultra-lean (λ >1.8) operation in order to achieve highest efficiencies, this assumption is no longer valid, as will be shown in the following. On these engines, the combustion process is largely controlled by the reaction kinetics of the chemistry and hence exhibits more similarity to homogeneous charge or spark assisted compression ignition (HCCI or SACI) combustion concepts. This is substantiated by a detailed review on theoretical and experimental investigations of ultra-lean combustion processes, a characterization of the combustion regime and by extending the earlier analysis of combustion in ultra-lean medium-speed 4-stroke gas engines to large two-stroke engines, which are run at yet higher air/fuel ratios. Tests have been performed on a lab engine allowing variations of key parameters such as exhaust gas recirculation rate, charge conditions, mixture quality and ignition intensity over a large range. The results obtained clearly support the hypothesis that combustion on such engines is actually governed by volume reaction instead of the propagation of a turbulent premixed flame.
Unfug, Fridolin, Weisser, German Andreas
Research of Spark Ignition Engine and Internal Mixture Formation Using Single-Zone, Two-Zone and Three-Zone Calculation Model of It Working Process2022-01-10008/30/2022
Thermodynamic models based on the volume balance method for calculating the working process of an engine with spark ignition and internal mixture formation are presented. The single-zone model makes it possible to determine the pressure and average temperature of gases in the engine cylinder during the working process. The two-zone combustion model takes into account the change in the volume of the exhaust gases zone and the air-fuel mixture zone. The model makes it possible to determine the pressure of gases in the cylinder and the temperature in the zones under consideration when the air-fuel mixture is distributed over the entire above-piston volume at the moment of ignition. The three-zone combustion model takes into account the change in the volume of the exhaust gases zone, air-fuel mixture zones and air zones when organizing the stratification of the air-fuel charge, allows you to determine the gas pressure in the cylinder and the temperature in the zones under consideration. The results of theoretical studies obtained by single-zone, two-zone and three-zone thermodynamic models of combustion on a two-stroke engine 1D8.2/8.7 with direct injection of gasoline into the cylinder are compared with experimental data. The results of experimental studies are based on indicator diagrams of gas pressure in the engine cylinder in the load characteristic modes at n = 3,000 rpm in terms of the crankshaft rotation angle. The use of a single-zone and two-zone combustion model is preferably used in high load modes, and a three-zone combustion model is used in partial load modes, which corresponds to the smallest discrepancy between the values of theoretical and experimental indicator diagrams. The results obtained in the work allow us to expand our understanding of the use of the volume balance method for calculating the working process, taking into account the peculiarities of the organization and flow air-fuel mixture.
Korohodskyi, Volodymyr, Leontiev, Dmitry, Rogovyi, Andrii, Kryshtopa, Sviatoslav, Gritsuk, Igor, Voronkov, Oleksandr, Prokopiuk, Demian
Effects of Port Angle on Scavenging of an Opposed Piston Two-Stroke Engine2022-01-05903/29/2022
Opposed-piston 2-stroke (OP-2S) engines have the potential to achieve higher thermal efficiency than a typical diesel engine. However, the uniflow scavenging process is difficult to control over a wide range of speeds and loads. Scavenging performance is highly sensitive to pressure dynamics, port timings, and port design. This study proposes an analysis of the effects of port vane angle on the scavenging performance of an opposed-piston 2-stroke engine via simulation. A CFD model of a three-cylinder opposed-piston 2-stroke was developed and validated against experimental data collected by Achates Power Inc. One of the three cylinders was then isolated in a new model and simulated using cycle-averaged and cylinder-averaged initial/boundary conditions. This isolated cylinder model was used to efficiently sweep port angles from 12 degrees to 29 degrees at different pressure ratios. Results indicate that scavenging performance is correlated with the bulk swirl ratio generated by these port angles. Scavenging performance is also sensitive to the pressure ratio across the engine. It was concluded that, for a given pressure ratio, the smallest port angle produces the best scavenging; however, previous work indicates lower bulk swirl ratio during combustion can have an impact on emissions formation.
O'Donnell, Patrick Christopher, Gandolfo, John, Gainey, Brian, Vorwerk, Erik, Prucka, Robert, Filipi, Zoran, Lawler, Benjamin, Hessel, Randy, Kokjohn, Sage, Huo, Ming, Salvi, Ashwin
Usage of 2-Stroke Engines for Hybrid Vehicles13-03-02-00113/24/2022
As the automotive industry moves toward electrification, battery costs and vehicle range are two large issues that will delay this movement. These issues can be partially resolved through the use of series-hybrid vehicles, which can replace a portion of the batteries with a small engine that serves to recharge the battery. Given the size, weight, and operational constraints of this engine, a 2-stroke engine makes sense. Indeed, 2-stroke engines are currently being used for a number of applications including consumer products, small ground vehicles, boats, and drones. The technology has significantly improved to allow for reduced emissions and increased efficiency, especially through the use of direct injection. This article discusses the state of technology for 2-stroke engines and its application in series-hybrid vehicles. In particular, the use of a 2-stroke engine as a range extender provides significant benefit in range and cost over fully electric vehicles. The study found that although there have been numerous gains in terms of efficiency and emissions, more advances are required prior to the widespread usage of 2-stroke engines as range extenders.
Shah, Rajesh, Khan, Muqsit, Mittal, Vikram
Numerical Investigation of the Effect of Engine Speed and Delivery Ratio on the High-Speed Knock in a Small Two-Stroke SI Engine2022-32-00801/9/2022
Knocking occurs within the high-speed range of small two-stroke engines used in handheld work equipment. High-speed knock may be affected by the engine speed and delivery ratio. However, evaluation of these factors independently using experimental methods is difficult. Therefore, in this study, these factors were independently evaluated using numerical calculations. The purpose of this study was to clarify the mechanism by which the intensity of high-speed knocking that occurs in small two-stroke engines becomes stronger. The results suggest that temperature inhomogeneity due to insufficient mixing of fresh air and previously burned gas may induce high-speed knocking in the operating range at high engine speeds.
Eto, Kuniyoshi, Kuboyama, Tatsuya, Moriyoshi, Yasuo, Yamada, Toshio
E-Fuel applications in Non Road Mobile Machinery2022-32-00741/9/2022
Professional users in particular will continue to rely on internal combustion engine drives in the future due to high power requirements and high daily energy consumption. Especially if they have to work in rural areas without the possibility of recharging batteries, such as in forestry or maintenance of road verges or railway lines. For these applications, it must be possible to run sustainable fuels for defossilization and drastically reduced CO2 emissions. This paper provides insights into a possible future fuel market and describes its evolution towards a more sustainable future from the perspective of a handheld equipment manufacturer. As developments in the fuel market are currently difficult to predict, manufacturers of hand-held power tools with combustion engines need to be prepared for changes in the composition of fuels that might become available on the market. This paper presents the engine performance results of both a 2-stroke engine and a 4-stroke engine, each with spark ignition, for typical handheld applications operating on a fuel blend of dimethyl carbonate, methyl formate and ethanol (DMC+) compared to commercially available fuels. Since DMC+ fuel differs significantly in its chemical properties in terms of material compatibility, air demand and energy content compared to regular fuels, changes to the hardware and engine calibration are necessary. In addition, a common 2-stroke engine oil is not miscible with DMC+. Thus, a special newly developed oil had to be used to lubricate the engine. The investigations will show the influence of this fuel and the engine oil on the mixture preparation, the combustion behavior as well as the resulting exhaust emissions.
von Gaertringen, Christoph Hiller, Schwerin, René, Schweiger, Stefan, Kölmel, Armin, Lochmann, Holger, Schmidt, Stephan, Zinner, Christian, Kirchberger, Roland, Gschanes, Dominik
On the Potential of Transfer Port Injection Strategies for a Two-Stroke Engine2022-32-00571/9/2022
The main drawback of an in-cylinder Low Pressure Direct Injection (LPDI) in a two-stroke engine is the difficulty of achieving a satisfactory vaporization level in low load conditions. The liquid droplets are characterized by large diameters and, when the temperature level and the velocity of the scavenging flow field are low, the time needed for the droplet vaporization and the homogenization with fresh air becomes too long to guarantee a suitable mixture formation. A transfer port injection allows a higher flexibility, due to the possibility of performing a mixed injection either directly in the cylinder or indirectly in the crank case, depending on the load request or engine speed. Also, an even lower injection pressure can be adopted with respect to an in-cylinder LPDI injection, which is relevant in case of lightweight and low power applications. On the other hand, the time available for the direct in-cylinder injection is limited to the scavenge phase. In the present work, a detailed numerical analysis has been performed on a 15kW 300 cm3 two stroke engine for evaluating the potential of a transfer duct installation of a low pressure injector. The influence of the injection system positioning has been investigated by means of high fidelity three dimensional CFD simulations of both the scavenge and the spray processes. The engine model has been validated with experimental data acquired at the test bench on the engine operated in a homogenously scavenged configuration, equipped with a standard carburettor. The spray model has been validated with experimental data acquired during both an imaging test campaign for the analysis of the global spray evolution over time and a Phase Doppler Anemometry (PDA) analysis for a detailed sizing characterization of the spray. The paper shows the results of a sensitivity analysis on the fuel vaporization and short circuit, as well as air fuel mixing and homogenization, by varying the following parameters: choice of the transfer port (from first to fifth), injection direction (co-current or counter-flow) and injection timing.
Balduzzi, Francesco, Romani, Luca, Ferrara, Giovanni, Trassi, Paolo, Fiaschi, Jacopo
Impact of Zero CO 2 Fuels on Engine Behaviour of Two-Stroke Engines in Hand-Held Powertools2022-32-00611/9/2022
One possible path to reduce the CO2 emissions of hand-held power tools are fuels with different amount of renewable content. Within this paper test bench measurements on a small two-stroke engine were carried out. We are trying to reduce CO2 emissions by using fuels which absorbed CO2 from the air during its lifetime or production, so called Zero CO2 fuels The focus was set on the investigation of combustion behaviour, performance and emissions of Zero CO2 fuels in comparison to commonly available fuels. For our measurements we chose a 46 cc serial engine, which was slightly modified for scientific research. This paper shows findings on effects of renewable fuels on engine characteristics. Additionally, the chemical properties of each fuel were investigated in order to form a comprehensive picture, together with the performed dyno measurements.
Gschanes, Dominik, Schmidt, Stephan, Kirchberger, Roland
Design and Implementation of An Oxidation Catalyst for A Spark Ignited Two Stroke Snowmobile Engine2022-32-00051/9/2022
The primary goal of this project was to design and implement an oxidation catalyst specific to a high-performance spark ignited two stroke engines to reduce vehicle-out emissions. The primary challenges of two stroke catalysis at high loads include controlling the catalytic reaction temperature as well as minimizing the increase in exhaust back pressure due to the addition of a catalyst. Reaction temperature is difficult to control due to high HC and CO concentrations paired with an excess of oxygen in the exhaust stream. By limiting catalyst conversion efficiency, the reaction temperatures were controlled. Two stroke engines are also inherently sensitive to changes in exhaust back pressure and therefore location and sizing of the catalyst are key design considerations. Because of these challenges significant effort was directed toward developing the two-stroke specific catalyst design process. Through these efforts several key outcomes were reached including a better understanding of how to size and locate a catalyst in an existing two stroke exhaust system while maintaining minimal performance losses as well as insight into the wash coat development process and methods to promote catalyst durability. In total three actively coated catalyst samples were successfully tested over a range of engine speeds and loads. The catalyst samples showed significant HC reductions ranging from 30 to 96 percent across the engine operating range and CO reductions ranging from 10 to 97 percent in a significant portion of the operating range. Peak power loss also remained less than 1.5 percent for all catalyst samples.
Squires, Noah, A. Miers, Scott
Describing the Auto-Ignition Quality in Small, Air Cooled, Two Stroke Engines2022-32-00631/9/2022
Auto-ignition quality is one of the most important properties in gasoline. Auto-ignition quality is today described by the Motor Octane Number (MON) and the Research Octane Number (RON). For modern, light duty, gasoline engines it has been quite well established that RON is the most accurate number. However, no study has been performed on hand held forest and garden products, such as chainsaws. Is the auto-ignition quality best described in the same way for these engines as for light duty engines? In this paper, a matrix of six different fuels with different combinations of MON and RON values were tested on a Husqvarna 550 XP Mark II, a modern air cooled, sequential stratified scavenging 2-stroke chainsaw engine. Ignition timing sweeps were performed and knock limited spark advance (KLSA) were calculated. Then the data has been analyzed with a multi-variate analysis of KLSA against both MON and RON to try to determine how MON and RON should be combined to best describe the anti-knock quality on this specific engine. The results show that neither MON nor RON describes the anti-knock quality well on this product. The AKI (the average of RON and MON) described the anti-knock quality best of the conventionally recognized anti-knock quality measurements. From the multivariate analysis the K-value was determined to be 0,59. Using a fuel with a more ideal combination of MON and RON on this type of products without knock control can limit the maximum cylinder pressure and cylinder top temperature. This is likely to extend the life time of the forest and garden equipment significantly. Small engine gasoline fuel, also known as alkylate gasoline, has a good combination of RON and MON that makes it outperform other market fuels from an Anti-knock quality perspective on the tested engine. At the same time small engine gasoline has other benefits, such as less health hazardous exhaust emissions, that can improve the work environment for loggers. This tailor made forest and garden fuel remain mysteriously anonymous outside of Europe.
Risberg, Per, Elm, Thomas, Bergman, Mikael, Hellquist, Fredrik, Karvo, Anna, Tripathi, Rupali
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