Two-stroke Engine Research Articles

Gas exchange optimization in aircraft engines using sustainable aviation fuel: A design of experiment and genetic algorithm approach

The poppet valves two-stroke (PV2S) aircraft engine fueled with sustainable aviation fuel is a promising option for general aviation and unmanned aerial vehicle propulsion due to its high power-to-weight ratio, uniform torque output, and flexible valve timings. However, its high-altitude gas exchange performance remains unexplored, presenting new opportunities for optimization through artificial intelligence (AI) technology. This study uses validated 1D + 3D models to evaluate the high-altitude gas exchange performance of PV2S aircraft engines. The valve timings of the PV2S engine exhibit considerable flexibility, thus the Latin hypercube design of experiments (DoE) methodology is employed to fit a response surface model. A genetic algorithm (GA) is applied to iteratively optimize valve timings for varying altitudes. The optimization process reveals that increasing the intake duration while decreasing the exhaust duration and valve overlap angles can significantly enhance high-altitude gas exchange performance. The optimal valve overlap angle emerged as 93 °CA at sea level and 82 °CA at 4000 m altitude. The effects of operating parameters, including engine speed, load, and exhaust back pressure, on the gas exchange process at varying altitudes are further investigated. The higher engine speed increases trapping efficiency but decreases the delivery ratio and charging efficiency at various altitudes. This effect is especially pronounced at elevated altitudes. The increase in exhaust back pressure will significantly reduce the delivery ratio and increase the trapping efficiency. This study demonstrates that integrating DoE with AI algorithms can enhance the high-altitude performance of aircraft engines, serving as a valuable reference for further optimization efforts.

The impact of scavenging air state on the combustion and emission performance of marine two-stroke dual-fuel engine

The scavenging process significantly affects the combustion and emission performance of marine low-speed two-stroke dual-fuel engines. Optimizing scavenging air pressure and temperature can enhance the engine's combustion efficiency and emission control performance, thereby achieving more environmentally friendly and efficient operation of dual-fuel engines. This study focuses on marine low-speed two-stroke dual-fuel engines, analyzing the effects of scavenging air pressure (3.0 bar, 3.25 bar, 3.5 bar, and 3.75 bar) and scavenging air temperature (293 K, 303 K, and 313 K) on engine performance and emission products. The results indicate that scavenging air pressure has a greater impact on engine performance than scavenging air temperature. An increase in scavenging air pressure leads to higher thermal efficiency and power. As the scavenging air pressure increases from 3 to 3.75 bar, the indicated thermal efficiency (ITE) increases from 44.02 to 53.26%, and indicated mean effective pressure (IMEP) increases by approximately 0.35 MPa. Increased scavenging air pressure improves nitrogen oxide (NOx) and hydrocarbons (HC) emissions. For every 0.25 bar increase in scavenging air pressure, NOx emissions decrease by 3.53%, HC emissions decrease by 33.35%, while carbon dioxide (CO2) emissions increase by 0.71%. An increase in scavenging air temperature leads to lower ITE and IMEP. As the air temperature changes from 293 to 313 K, the ITE decreases by approximately 1%, and IMEP decreases by about 0.04 MPa. Increased scavenging air temperature improves CO2 emissions. For every 10 K increase in the air temperature, the CO2 emissions decrease by 0.02%, while NOx emissions increase by 4.84%, HC emissions increase by 34.39%. Therefore, controlling scavenging air pressure is more important than scavenging air temperature in the operational management of marine two-stroke engines. Higher power and lower NOx and HC emissions can be achieved by increasing the scavenging air pressure.

Control strategies for mode switching of a large marine two-stroke engine equipped with exhaust gas recirculation and turbocharger cut-off systems

To meet the stringent nitrogen oxides emissions regulations, the recent marine two-stroke engines are equipped with exhaust gas recirculation (EGR) systems. Crossing the boundaries of exhaust control areas requires switching between the engine operating modes associated with the activation or deactivation the EGR system, which imposes challenges to the engine operation. This study aims to develop and numerically test effective control strategies for improving the mode switching of marine two-stroke engines with EGR systems. The investigated engine dynamic model is developed by integrating a zero-dimensional thermodynamic model developed in GT-POWER and the control model developed in MATLAB/Simulink. This model is first validated against the experimentally measured engine performance parameters, and subsequently employed to simulate the engine dynamic operation with mode switching. The simulation results are assessed to quantify the impact of several control strategies on the engine performance. The derived perrformannce parameters time variations demonstrate that the deactivation of the EGR branch and the small engine–turbocharger result in exceeding the manufacturer limits at high loads and increasing the fuel consumption. The proposed load-based control strategies, which employ load thresholds and time delays for the control of the EGR and turbocharging systems activation/deactivation, are proved effective, as the engine performance parameters are retained within their limits and fuel consumption penalties are minimised. This study provides insights for developing the control of the marine engines after-treatment systems, hence contributing towards enhancing shipping sustainability.

Entropy-based environmental analyses of marine fuel preferences for onboard ships

The maritime industry is currently discussing various aspects of alternative fuels, and finding viable and adaptable options for alternative fuels remains a sectoral issue. This study examines the impact of eight alternative fuels on energy and environmental sustainability, based on operating data of a two-stroke diesel engine. Entropy-based thermodynamic analyses were conducted for five different operations using two indices developed to consider the environmental impact, aimed at serving the decarbonization of this sector. Liquid hydrogen led to an 18 % reduction in fuel load, while ethanol resulted in a 5.55 % increase in engine efficiency. In contrast, using hydrogen resulted in a cumulative 27.01 % reduction in CO2 emissions. When evaluating the reduction rate alongside the improvement rate, it indicates a potential of 34.96 %. Additionally, recommendations for alternative fuels during the sector's decarbonization transition were proposed at the end of the study.

Catalytic Advantage in Otto-like Two-Stroke Quantum Engines.

We demonstrate how to incorporate a catalyst to enhance the performance of a heat engine. Specifically, we analyze efficiency in one of the simplest engine models, which operates in only two strokes and comprises of a pair of two-level systems, potentially assisted by a d-dimensional catalyst. When no catalysis is present, the efficiency of the machine is given by the Otto efficiency. Introducing the catalyst allows for constructing a protocol which overcomes this bound, while new efficiency can be expressed in a simple form as a generalization of Otto's formula: 1-(1/d)(ω_{c}/ω_{h}). The catalyst also provides a bigger operational range of parameters in which the machine works as an engine. Although an increase in engine efficiency is mostly accompanied by a decrease in work production (approaching zero as the system approaches Carnot efficiency), it can lead to a more favorable trade-off between work and efficiency. The provided example introduces new possibilities for enhancing performance of thermal machines through finite-dimensional ancillary systems.

Two-stroke engine with constant crank angular velocity

Two-stroke engine with constant crank angular velocity

Design Ideation and Selection of Under-Piston Door for a Two-stroke Marine Engine Using Hybrid TRIZ-biomimetic and MCDM Methods

Design ideation and selection of a two-stroke marine engine under-piston door employing Theory of Inventive Problem Solving (TRIZ), biomimetics, Analytical Hierarchy Process (AHP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) is presented in this paper. The study is motivated by exploring bio-composites as potentially suitable substitutes for conventional steel in engine component manufacture. As bio-composites possess lower mechanical properties compared to steel, the geometrical redesign was deemed necessary for any potential material substitution to take place. New under-piston door designs were ideated through the synergy between TRIZ and biomimetics. Computational models were developed, inspired by the Amazon waterlily, the tortoiseshell and the spider web. Mechanical simulation was performed for maximum stress (von Mises), total deformation and volume. With the simulated results of these designs, AHP and TOPSIS provided the solution’s capabilities to decide the best design overall. The design inspired by the Amazon waterlily proved the best and showed lower stress and deformation values compared to the original by 45.25% and 4.5%, respectively. This research provided conclusive evidence that with refined scrutiny of the TRIZ and biomimetic methods, along with AHP and TOPSIS, potential alternatives to conventional materials that offer environmental friendliness without compromising operational requirements can be realised.

Computational study of gas-dynamic approach for noise reduction in atwo-stroke engine’s exhaust system

BACKGROUND: The traditional approach to designing exhaust mufflers relies heavily on energy dissipation. In the "gas-dynamic" approach, the flow of exhaust gases is equalized by introducing long channel(s) into the muffler to separate impulses and shift them in time. It is assumed that such mufflers will provide noise reduction without creating significant backpressure. AIMS: To evaluate the potential of the "gas-dynamic" approach to reducing the noise level of two-stroke internal combustion engines. MATERIALS AND METHODS: The study was carried out using computational models. The processes in the gas-air tract of the piston engine were calculated using a one-dimensional (1D) model. The noise characteristic was the effective sound pressure at a specified point in the environment, calculated using 2D model of propagation of disturbances in elastic medium. The object of study was a two-stroke gasoline two-cylinder engine RMZ-551i, with a resonator (providing gas-dynamic supercharging) and a muffler. Initially, the parameters and sound pressure level of the engine with the stock muffler at full load and close to nominal engine speed were calculated. Then, the structure of the stock muffler was modified by adding a "tuned" channel between its two chambers. The parameters of the modified muffler were optimized based on the criterion of reducing gas pulsations at the outlet to the atmosphere. The noise reduction of the muffler implementing the gas-dynamic approach was evaluated relative to the stock muffler and expressed in terms of sound pressure levels in dB. Performance and levels of sound pressure were finally calculated over a wide range of engine speeds. RESULTS: According to the computational estimate, the optimal implementation of the gas-dynamic approach in the muffler reduces exhaust noise by 7 dB, while engine power decreases by 2.5%. Calculation of the sound pressure level based on the external speed characteristic showed that at an engine speed of 3000 rpm, the calculated sound pressure exceedsby 8 dB the minimum (99 dB) obtained for the optimally "tuned" muffler at an engine speed of 5000 rpm. It is suggested that the gas-dynamic approach with optimization is also applicable for uniform noise reduction over a wide range of engine speeds, with a more complex structure of the exhaustmuffler. CONCLUSIONS: Theoretical evaluation of a muffler with a tuned channel connecting its two chambers was carried out, with a two-stroke engine RMZ-551i with a stock muffler as a basis for comparison. At the optimum point on the speed characteristic, the exhaust noise was reduced by 7 dB, while the calculated power decrease was insignificant. The authorsnote the suitability of the methodology for rapid assessments and automated computational optimization of mufflers that utilize wave effects. They also point out the limitations of the models used, which require validation or rather calibration based on experimental data, and the need for the development of applied models of acoustic effects and measuring devices for domestic CAE packages.

Numerical simulation of a spark ignition ammonia marine engine for future ship power applications

Given the current state of global carbon emissions, China has proposed the objectives of achieving carbon peaking by 2030 and carbon neutrality by 2060. To meet the requirement of zero-carbon and achieve the application of pure ammonia fuel in low-speed two-stroke marine engines, this paper proposes the Groove Diversion-Assist Ignition (GDAI) combustion system, which can effectively control the temperature, fuel distribution, and flow rate in the spark plug region near the top dead center and finally achieve the spark ignition of pure ammonia without any change in compression ratio and scavenging temperature. At the same time, the boundary conditions for the ignition of ammonia fuel have also been studied. The results show that enhancing the initial temperature can alleviate the requirement for spark ignition energy, and a minimum energy level of 75 mJ remains necessary for effective spark ignition of ammonia. Furthermore, the utilization of spark ignition of ammonia fuel can achieve a maximum thermal efficiency of 51.32%, representing a 2.8% increase in overall thermal efficiency compared to the diesel mode. Additionally, the application of ammonia fuel can relief the NOx emissions compare to diesel fuel, which provides a new and effective utilization way for the application of ammonia fuel on the marine engine.

Selecting lubricating oil for two-stroke gasoline engines: a multi-criteria decision-making approach

Selecting lubricating oil for two-stroke gasoline engines: a multi-criteria decision-making approach

Multi-mode operation of a novel dual-pressure steam rankine cycle system recovering multi-grade waste heat from a marine two-stroke engine equipped with the high-pressure exhaust gas recirculation system

As a promising technology for marine two-stroke engines satisfying the IMO Tier Ⅲ NOx regulation, the high-pressure exhaust gas recirculation (HP-EGR) systems in multi-mode operation significantly redistribute the waste heat, thereby complicating the design and control of the waste heat recovery (WHR) systems. In this paper, a novel dual-pressure steam Rankine cycle (SRC) is proposed to recover multi-grade waste heat from marine engines in multi-mode operation. The HP-EGR system is designed on the 6EX340 engine, followed by the evaluation of waste heat distribution in multi-modes. Detailed thermodynamic and economic analyses of the designed SRC and the combined cycle power plant are then conducted. The results show that the thermal efficiency of the designed SRC is 8.1 %–13.3 % in Tier II mode, increasing to 10.1 %–15.7 % in Tier III mode, attributable to a 16 %–42 % increase in waste heat exergy. Considering typical propulsion profiles, the reduction in weighted average fuel consumption for the combined cycle power plant reaches up to 3.4 % in Tier II operation and 6.1 % in Tier III operation. When 12.5 % of sailing time is spent within ECAs, the combined cycle power plant is expected to yield up to 4 % in annual fuel cost savings.

Analysis of Unburned Methane Emission Mechanisms in Large-Bore Natural Gas Engines With Prechamber Ignition

Abstract Although precombustion chambers, or prechambers, have long been employed for improving large-bore two-stroke natural gas engine ignition and combustion stability, their design predates modern analysis techniques. Employing the latest computational fluid dynamics (CFD) modeling techniques, this study investigates the importance of temperature and chemistry for ignition of the main chamber, with an emphasis on eliminating unburned methane. The sensitivity of the ignition and complete combustion to main chamber air/fuel mixture homogeneity was also explored. This study compares the effect of purely thermal ignition, purely chemical ignition, and how their interplay can influence the complete combustion of methane in typical mixtures and in homogeneous distributions of fuel in the combustion chamber. The CFD results demonstrated that temperature and chemistry are equally important in the ignition mechanism, and combining the two phenomena is effective at igniting the main chamber. Reduction of residual methane in the main combustion chamber (MCC) is most effective when chemical intermediates and thermal ignition are combined. A rudimentary analysis of the effect of fuel/air stratification was also conducted, and it demonstrated that a dramatic reduction in methane emissions is observed for homogeneous mixtures. The flow field in the main combustion chamber was shown to create detrimental stratification of the fuel/air mixture, which inhibited complete combustion of the methane in the main chamber. By contrast, in the extreme case of a perfectly homogeneous distribution of both chemical intermediates and fuel in the combustion chamber, it is possible to completely eliminate unburned methane in the main combustion chamber.

Parameter optimization for two-stroke direct-injection spark-ignition aviation kerosene engine

The type of two-stroke spark-ignition(SI) engine is still the main power sources of small and medium unmanned aerial vehicles. A transition from gasoline to aviation kerosene or light diesel fuel and from carburetor or port-injection equipment to direct-injection(DI) equipment is prevailing. However, the performance of two-stroke DI-SI engine fueled with aviation kerosene is not very good under medium and high loads. Therefore, using the two-stroke DI-SI kerosene engine modified from port-injection SI gasoline engine as the research subject, the effects of different parameters on engine combustion and performance were studied and parameter optimization was also carried out at high loads. Based on the optimal fuel injection parameters, the influences of ignition time, compression ratio, scavenging/exhaust port area and scavenging/exhaust phase on the operating characteristics of two-stroke engine were analyzed. It was indicated that ignition timing, compression ratio and scavenging/exhaust phase have obvious impacts on engine performance, while the scavenging port area shows little impact on engine performance. An optimization calculation with genetic algorithm was made by determining the optimal values of six parameters such as compression ratio, ignition time, scavenging port area, exhaust port area, scavenging phase and exhaust phase. After optimization, the power(P) of the engine was increased by 7.6 % and the thermal efficiency(η) was enhanced by 3.2 % without knock. The results will lay a foundation for further design and research of two-stroke aviation RP-3 SI-DI engine.

Analysis of the interactive effects of scavenge parameters on spark ignition two-stroke diesel engines

The scavenging efficiency of a two-stroke diesel engine affects the formation of the mixture in the engine cylinder, which in turn affects the engine’s performance. A one-dimensional simulation model of a two-stroke diesel engine is established using GT-POWER, and the model with original experimental data is calibrated as boundary conditions. Firstly, the influence of crankcase compression ratio on engine performance of the two-stroke engine was investigated to obtain an appropriate crankcase compression ratio; Then, based on the optimization index of scavenging efficiency, the optimal combination of engine air port structure and timing is obtained through orthogonal optimization calculation method. To achieve higher scavenging efficiency, when the phase of the air port remains unchanged, a scavenging port width ratio of 1.0 and an exhaust port width ratio of 0.8 can achieve a scavenging efficiency of 97.2%; When the air port size remains unchanged, the engine scavenging efficiency reaches 96.44% when the scavenging port timing is 123° CA and the exhaust port timing is 89° CA.

Experimental investigation on the potential of passive prechambers for use in 2S engines

Design improvement of Internal Combustion Engines (ICEs) is required by the continuous update of European exhaust emission standards and vehicle registration protocols. This has pushed research and industry efforts towards the development of Low Temperature Combustion (LTC) systems. Among various LTC technologies, the so called “jet ignition” is claimed to be well-suited for light engines, since it provides a more uniform and rapid combustion while ensuring the mixture ignition process. In this context, the adoption of prechambers was found well-suited for two-stroke engines, for which low-pressure direct injection technologies have been developed in the last decade to reduce the fuel short circuit phenomenon. The present paper experimentally investigates the use of different passive combustion prechambers in a Low-Pressure Direct Injection (LPDI) 2-stroke engine, with the main purpose to understand the relationship between prechamber geometrical parameters and engine performance. A 50-cc single cylinder LPDI motorcycle engine is chosen as the test case and it is re-arranged to run in jet ignition mode. The experimental analysis focuses on the evaluation of benefits provided by jet ignition combustion compared to the baseline LPDI propulsion unit at different engine operating points. Design criteria for prechambers development and the tuning process of engine combustion parameters (such as start of injection, ignition time and throttle valve opening) are described in detail. The results of experimental activity are finally shown and critically discussed, highlighting advantages and disadvantages of this application in terms of engine performance, efficiency and cycle-to-cycle variation.

Low-pressure gasoline direct injection system development and emissions analysis for a reciprocating two-stroke engine

This study presents the design and construction of an electronic low-pressure gasoline direct injection system for two-stroke engines, with the objective to study engine performance and the emission of exhaust polluting gases, maintaining the expectations of this type of engine. The investigation includes a test bench with an incorporated engine and the required control devices for this, as well as a gas analyzer Class 0, a computerized data acquisition and several tools for displaying and process all the electronic signals from the engine in real time. In order to manage this system, a custom electronic injection control unit has been designed and built, which allows to control the fuel injection timing and duration. This unit uses the signal from an inductive sensor installed in the crankshaft as a reference and synchronization point. Additionally, modifications have been made to the fuel feeder circuit and the electronic of the test engine, as well as to some parts of the mechanism in order to adapt them to this technology. The implementation of the engine tests is described, and the performance and operational points of the original system and those of the new injection system are evaluated.

Application of semi-direct fuel injection system to free piston engine generator for better performance: Simulation approach with validation results

This paper explores methods to improve the fuel economy of a two-stroke free piston engine generator (FPEG) with no additional cost. In order to solve the problem of low fuel capture and poor fuel economy of two-stroke FPEG using port fuel injection (PFI), the fuel injection method is optimised in this paper. This fuel injection system is semi-direct injection (SDI). In contrast to PFI, SDI also uses a low-pressure injector, which introduces fuel directly into the ports of the engine. This study explores the feasibility of SDI on a free-piston engine generator through numerical simulation. The results show that SDI can effectively avoid short-circuit losses and improve the fuel capture rate by more than 60 % relative to PFI. Meanwhile, the ISFC is reduced by 42.3 %, and the lowest fuel consumption rate is 259.7 g/(kW·h). The combustion efficiency of SDI is maintained at over 95 % under warm-up conditions. Compared with PFI, the stagnation period is shortened by up to 10.9 % and the centre of gravity of combustion is advanced by up to 16.7 %. SDI effectively reduces HC emissions and has a lower NOx emission level than PFI. At the same time, SDI produces more CO due to stratified combustion.

Investigation on the combustion of ammonia using direct high/medium-pressure-Otto injection approach in a diesel two-stroke marine slow speed engine

The urgent need to reduce exhaust gas emissions has led to increased research activities on the potential of using ammonia as fuel in marine engines. Various researchers have already investigated the combustion of ammonia specifically in two-stroke, slow-speed marine engines, and obtained promising results. In the available literature, both high-pressure direct injection-Diesel (HPDF) and low-pressure direct injection dual fuel - Otto (LPDF) two-stroke engines have been well-researched. This study numerically investigates the potential of using a direct high/medium pressure (Otto) ammonia injection strategy on a marine two-stroke engine. A diesel-fueled engine was retrofitted with ammonia injectors on the cylinder head. The effects of ammonia injection direction, timing, and injection pressure on the combustion efficiency, engine performance, and exhaust gas emissions were investigated to ensure optimum injection parameters. Ammonia substitution rate (ASR) ranging from 40 to 80 % was used in this study. The investigated injection strategy revealed flexibility in achieving the original pure diesel engine power over a wide range of injection pressures (700-200 bar). At 80 %, ASR CO2 emissions were reduced up to 80 % while NOx emissions attained Tier II emission limits. The results of this study are helpful in the development process of ammonia dual-fuel marine two-stroke engines.

Coupling analysis of cylinder block for two-stroke aviation piston engine

The aluminum alloy block is a component of aircraft piston engine, and it is prone to fatigue cracks when working in a thermal mechanical coupling state for a long time. Establish a GT-POWER simulation model for a certain type of engine, verify the accuracy of the model, obtain boundary parameters such as temperature and pressure of the engine block under harsh operating conditions through the model, and divide the cylinder wall into gradients based on the engine operating conditions to obtain the surface heat transfer coefficient of the block, and then obtain the temperature field distribution of the engine body. The coupling analysis of the cylinder burst pressure and temperature field of the engine block under harsh working conditions showed that the maximum stress of the engine block was 292.55 MPa and the maximum deformation was 0.39 mm, with thermal load being the main factor causing deformation. Conduct a complete engine bench test, and under the 1000 h bench durability test, there are no cracks on the engine block, indicating that the design and analysis meet the requirements.

An Innovative Retrofit Design for Energy Efficiency and Emission Reduction: MAN B&W Marine Engine Slide Fuel Injector

Background:: The fuel injector is one of the most essential parts in marine diesel engines. For MAN B&W two-stroke engines, the conventional fuel injector, due to the existence of sac volume, can result in problems such as increased emission and fuel consumption and shortened service life of combustion chamber components. Objective:: The MAN B&W marine engine slide-type fuel injector is a structural retrofit of conventional injectors, improving diesel engine combustion conditions, fuel efficiency, and emission reduction in hydrocarbon, NOx, smoke, and particulate matter by eliminating sac volume with patented technology. Methods:: This study employed a comparative analysis approach to evaluate the performance of conventional fuel injectors versus slide-type fuel injectors in MAN B&W two-stroke engines. Data collection involved practical experiences, onboard operations, and analysis of fuel efficiency, emission reduction, and combustion improvement. The structural differences and operational advantages of both injector types were examined to assess the environmental benefits and economic implications of adopting slide fuel injectors. Recommendations for the gradual replacement of conventional injectors with slide-type injectors were based on empirical data and industry best practices. Results:: Slide fuel injectors obtain a reduction of about 75% of the HC emissions at all loads. The slide fuel injector significantly decreases the smoke emission level at low engine load, at 25% load. A reduction in PM of up to 50% has been confirmed, and slide fuel injectors can reduce NOx emission by approximately 15% on average. result: The smoke emission level at low engine load, at 25% load in particular, is greatly decreased by slide fuel injector. Conclusion:: Slide fuel injectors, with a granted patent, are commonly used in marine low-speed engines due to their advantages.