In-cylinder Combustion Process Research Articles

Collaborative effects of fuel properties and EGR on the efficiency improvement and load boundary extension of a medium-duty engine

EGR dilution combustion has problems such as weakened anti-knock capability at high load, slow combustion speed and poor combustion stability, which results in limitations in the thermal efficiency improvement and load boundary extension of medium-duty highly-downsized engines. It is necessary to combine EGR dilution and other measures to collaboratively control the in-cylinder thermodynamic state and combustion process. The experimental investigations in this study isolate the effect of the ethanol blending ratio in ethanol gasoline on the anti-knock performance, combustion performance and thermal efficiency, and verifies the potential of collaborative optimization of fuel properties and EGR in improving the thermal efficiency and extending the load boundary for a medium-duty highly-downsized engine. The results show that as the load increases, the improvement effect of increasing the blending ratio of ethanol in the anti-knock performance, combustion speed, and the turbine inlet temperature reduction will become more obvious. At high load, using E20 fuel can improve the EGR tolerance, advance the spark timing and CA50, and thus increase the BTE. As the speed decreases, the thermal efficiency improvement effect of E20 fuel gradually increases, and the improved load range extends. The collaborative optimization of E20 fuel and EGR can further extend the high thermal efficiency area of the engine. And the Max. achievable load is 0.11 MPa higher than that of E10, which effectively extends the upper load limit during the stoichiometric combustion.

Identification, prediction and classification of hydrogen-fueled Wankel rotary engine knock by data-driven based on combustion parameters

Hydrogen-fueled Wankel rotary engine has excellent power density and low backfire possibility, however, as well as the severe knock. The knock is closely related to the in-cylinder combustion process, therefore, the present work is conducted to identify, predict and classify the knock by data-driven based on combustion parameters in the hydrogen-fueled Wankel rotary engine. The results show that: Knock type can be identified well according to knock intensity and crank angle of peak knock pressure through the Gaussian Mixture Model. There are 141 strong knock cycles and 809 weak knock cycles in test data. Compared with Support Vector Machines and Back-propagation Neural Networks, Multiple Linear Regression has a better global performance in knock-level prediction based on combustion parameters. The maximum pressure rising rate and CA50 have more significant impacts on knock, the partial of regression coefficients of which is about 0.42 and −0.58, respectively. In particular, due to different formation mechanisms, the prediction models of two types of knock are recommended to be established separately. In addition, the Support Vector Machine can be applied to conduct knock classification. Among kernel functions in Support Vector Machine, the linear kernel function can achieve optimal mean test accuracy, about 88.66 %.

Numerical Simulation on the Spray Angle of the Dual-layer Hole Nozzle in a Partition Combustion System of the Diesel Engine

To study the effect of the spray angles of the dual-layer hole nozzle on the combustion and emissions performance in the partition combustion system, the in-cylinder spray, mixture formation and combustion processes of the new combustion system were simulated and investigated using AVL FIRE software. The results show that, compared with the variation of the lower-layer spray angles, the change of the upper-layer spray angles has a great influence on the instantaneous heat release rate. The increasing spray angles of the lower-layer holes lead to reduced peak values of the heat release rate in the cylinder. In all the spray angle cases, the first fire area of the cylinder is in the B zone of the combustion chamber. Compared with lower-layer spray angle, the upper-layer spray angle has a greater impact on the airflow disturbance in the combustion chamber. Appropriately increasing the upper-layer spray angle facilitates the mixing of fuel and air in the combustion chamber and reduces the unburnt fuel equivalence ratio. When the spray angles of the upper- and lower-layer holes are 157° and 112°, respectively, the combustion indicates power has the largest value of 12.18 kW. At the same time, the Soot emission is also the smallest, with a value of 0.52 g/kW·h.

Numerical Investigation of In-Cylinder Combustion Behaviors in a Medium-Speed Diesel Engine

Abstract This study aims to advance understanding of in-cylinder combustion processes in medium-speed diesel engines, which are extensively employed in heavy-duty applications where electrification proves inefficient yet remains insufficiently examined in the literature. By modeling a four-stroke engine with dimensions of 210 mm bore and 310 mm stroke, operating at 900 rpm under full load, this research identifies distinct combustion characteristics that differentiate medium-speed engines from their high-speed counterparts. Key findings illustrate that super turbocharging in medium-speed engines enhances the combustion of the fuel–air mixture under elevated temperatures and pressures. Moreover, an increased stroke length promotes gas velocity and turbulence, facilitating fuel atomization and mixing. Notably, rapid fuel ignition occurs near the nozzle due to the high temperature of compressed air, reducing the ignition delay. As a result, the premixed combustion stage nearly disappears, with diffusion combustion dominating, especially pronounced with long-duration injection, a characteristic of medium-speed engines. The study also reveals a more uniform but elevated distribution of nitrogen oxide emissions in medium-speed engines, attributed to prolonged high-temperature conditions that both facilitate their formation. Early stages of diffusion combustion show high concentrations of incomplete combustion products. However, as the combustion process progresses, the conditions favor the complete oxidation of these products at high temperatures, resulting in decreased carbon-based pollutions. In addition, the larger combustion chamber and enhanced turbulence characteristic of medium-speed engines support efficient fuel and air mixing without necessitating the swirl effect required by high-speed engines, diminishing the dependence on wall impingement dynamics for air utilization. Consequently, efficiency optimization strategies for medium-speed engines, emphasizing adjustable injection parameters, encounter fewer constraints than those inherent to the spatial limitations of high-speed engines.

Effect of key structure parameters of passive pre-chamber on in-cylinder combustion processes and emissions within a gasoline engine

Due to increasingly strict global emission regulations and energy conservation policies, gasoline engines are facing significant challenges. Achieving high efficiency and ultra-low emissions in gasoline engines has become a critical technical challenge that requires attention. Pre-chamber (PC) Turbulent Jet Ignition (TJI) is a highly promising technology for improving thermal efficiency and reducing emissions in gasoline engines. This study employs a three-dimensional flow simulation analysis combined with a detailed chemical reaction mechanism. The investigation is based on eight distinct passive PC structural configurations. The effects of various structural parameters, including the orifice number (ON), orifice axis angle (OAA), orifice diameter (OD), and volume ratio (VR), on the in-cylinder combustion process and emission characteristics are investigated, in which the formation of the fire nucleus and the propagation of the flame are intensively involved. The investigation is conducted under equivalence ratio working condition. Among these, the ITE of the best configuration is relatively 5.46% higher than the baseline engine. The combustion duration decreased by 55.95% to 7.4 °CA compared to the baseline engine, while particulate soot emissions also decreased by 51.22%.

Experimental investigation on in-cylinder working process and thermal efficiency of ammonia/diesel low-carbon engine with pre-injection strategy

Ammonia, as a zero carbon and sustainable fuel, combined with traditional diesel fuel can provide a promising solution for reducing the engine environmental impact. However, ammonia/diesel dual-fuel (ADDF) engine has the significant drawback of low combustion efficiency and poor combustion stability at low loads, which seriously hinders its development. Therefore, this study explored the potential of pre-injection strategy in improving the performance of ADDF engine, comprehensively evaluating the effects of four pre-injection parameters (main injection timing (MIT), pre-injection timing (PIT), pre-injection quantity (PIQ), and diesel injection pressure (DIT)) on in-cylinder combustion process, incomplete combustion emissions, and energy efficiency. The results indicate that MIT has the most significant impact on combustion process. Advancing MIT can significantly increase in-cylinder combustion pressure and reduce CO, HC and unburned NH3 emissions. At MIT = -12 °CA ATDC, the highest brake thermal efficiency (BTE) of 32.3 % is obtained, while simultaneously generating high combustion noise. The advance of PIT has adverse effects on combustion stability. When PIT is advanced from −24 °CA ATDC to −36 °CA ATDC, COVIMEP increases from 2.61 % to 4.44 %, unburned NH3 emission increases by 23.5 %, and the BTE of ADDF engine decreases. Adjusting the PIQ and DIP can improve the reactivity distribution of fuel and reduce incomplete combustion emissions. However, the decrease in main injection quantity would increase the cycle fluctuation. At low loads, shortening the pre-main injection interval and increasing PIQ and DIP can enable the engine to achieve higher BTE while reducing pollutant emissions. This study elucidates in detail the influence of four pre-injection parameters on the operation characteristics of ADDF engine. It can offer insights and practical references for expanding the operating range of ammonia fuel engine.

Cross-interface computed tomography applied in flame propagation detection of an optical engine

With the development of compression ignition (CI) engines, a detailed investigation of the in-cylinder combustion process is needed under strengthened regulation on the emission. The development of a tomographic algorithm makes it possible for further investigation of the 3D structure of the in-cylinder flame. In this study, the Full-field Cross-Interfaces Computed Tomography algorithm (FCICT) is utilized to reconstruct the 3D chemiluminescence distribution of the in-cylinder flame in an optical engine. The reconstructed flame provides 3D information on exhibiting flame equivalence radius variation, as well as clarifying the effect of injection pressure on flame development. The study reveals the 3D structure of the in-cylinder flame and makes it possible for further investigation of the 3D information of the in-cylinder combustion process in the future.

Experimental investigation of the influence of pre-chamber structural parameters on combustion and emission characteristics of a high compression ratio SI engine

The passive pre-chamber exhibits great potential for practical applications in the internal combustion engine due to its simple structure. However, it faces difficulties in scavenging process, making optimization of pre-chamber structure particularly important. In this study, the effects of pre-chamber ignition systems with different structures and original spark ignition were conducted on a high compression ratio direct-injection SI engine to investigate the combustion, performance, and emission characteristics. The results show that the increase in pre-chamber volume weakens the in-cylinder combustion process and engine performance, while increasing the pre-chamber orifice diameter can enhance the combustion stability at medium to high loads, but will weaken the engine performance at low load. Compared to spark ignition, pre-chamber ignition results in an earlier 50% combustion position, a shorter combustion duration and lower COVIMEP, with these effects becoming stronger as load increases. At high load, the pre-chamber ignition (PC1) advances the 50% combustion position by 5.6°CA and shortens the combustion duration by 16.7%. In addition, the indicated thermal efficiency of the pre-chamber ignition achieves an increase of 0.84% at the optimal point and 2.5% at high load. Overall, using the smaller orifice diameter and volume in the pre-chamber can improve in-cylinder combustion process and increase thermal efficiency across the load range. For emission analysis, the pre-chamber ignition leads to an increase in NOx and HC emissions due to the influence of in-cylinder combustion temperature and quenching effect, while the CO emissions are similar to spark ignition.

Effects of ammonia energy fraction and diesel injection parameters on combustion stability and GHG emissions characteristics in a low-loaded ammonia/diesel dual-fuel engine

Ammonia, as a zero-carbon and widely sourced hydrogen carrier fuel, will play an important role in the decarbonization process of internal combustion engines, and the dual-fuel RCCI mode is a potential ammonia combustion technology route. In this study, ammonia/diesel dual-fuel (ADDF) combustion mode was implemented on a modified common-rail diesel engine, and the effects of ammonia energy fraction (AEF), diesel injection pressure (DIP), and diesel injection timing (DIT) on in-cylinder combustion, pollutant emissions and greenhouse effect of dual-fuel engine were investigated. The results indicated that the combustion process of ADDF was limited by the inert combustion and inhibitory effects of ammonia fuel. With the increase of AEF, the dual-fuel combustion process was delayed, the peak in-cylinder pressure decreased, and the ignition delay and combustion duration significantly increased, which was not conducive to the improvement of brake thermal efficiency (BTE). The introduction of ammonia fuel significantly reduced NOx, Soot and CO2 emissions, while unburned NH3 and N2O emissions sharply increased. At AEF = 60 %, CO2 emission decreased by 50.2 %, however, the in-cylinder combustion process deteriorated severely, with cyclic fluctuations reaching 5.06 %. Both increasing DIP and advancing DIT enhanced the chemical reactivity of in-cylinder mixture of ADDF engine, leading to earlier combustion heat release phase and shorter ignition delay, and reducing the variation of combustion cycle. Meanwhile, there was still a trade-off relationship between NOx and Soot emissions. When DIP increased from 100 MPa to 130 MPa, NH3 emission decreased by 20.8 %. Further increasing the DIP to 140 MPa would result in serious “wet wall” problems, leading to an increase in the incomplete combustion area and a decrease in BTE. When DIT was advanced from −4 °CA ATDC to −12 °CA ATDC, CO, HC and NH3 emissions decreased by 71.3 %, 52.7 % and 57.6 %, respectively, while N2O emission increased by 19.9 %, resulting in an increase in equivalent CO2 emissions. Under the optimized diesel injection strategy, the BTE of ADDF engine was 31.9 %, significantly higher than the original engine operating condition (BTE = 30.2 %).

Engine combustion modeling method based on hybrid drive

Accurate and comprehensive reconstruction of in-cylinder combustion process is essential for timely monitoring of engine combustion state. This article developed a method based on the zero-dimensional (0-D) physical model integrated with big data. The traditional 0-D prediction model based on cumulative fuel mass is improved, the factor of in-cylinder temperature is introduced to adjust the heat release rate, which solves the problem of difficulty in calibrating the heat release rate. Then, convolutional neural network-gated recurrent unit (CNN-GRU), as a deep neural network, including a special convolutional layer and a gated recurrent unit (GRU) neural network is designed for the parameters to be calibrated in the model. The 0-D predictive combustion model is constructed by combining the physical model with CNN-GRU, the combustion process is simplified and reconstructed. The fitting results show that the 0-D physical model based on improved cumulative fuel mass approach is an effective method to reflect the heat release law. Under non-calibration conditions, the root mean square error (RMSE) value of peak firing pressure (PFP) based on CNN-GRU prediction model is 0.5862. The prediction model is a promising method to realize online fitting and optimization of combustion process.

Numerical modelling of a heavy-duty diesel-hydrogen dual-fuel engine with late high pressure hydrogen direct injection and diesel pilot

Direct gaseous fuel injection in internal combustion engines is a potential strategy for improving in-cylinder combustion processes and performance while reducing emissions and increasing hydrogen energy share (HES). Through use of numerical modelling, the current study explores combustion in a compression ignition engine utilising a late compression/early power stroke direct gaseous hydrogen injection ignited by a diesel pilot at up to 99% HES. The combustion process of hydrogen in this type of engine is mapped out and compared to that of the same engine using methane direct injection. Four distinct phases of combustion are found which differ from that of pure diesel operation. Interaction of the injected gas jet with the chamber walls is found to have a considerable impact on performance and emission characteristics and is a factor which needs to be explored in greater detail in future studies. Considerable performance increase and carbon-based emission reductions are identified at up to 99% HES at high load but low load performance greatly deteriorated when 95% HES was exceeded due to a much reduced diesel pilot struggling to ignite the main hydrogen injection.

Numerical investigation of the effect of altitude on diesel engine combustion and soot emissions

It is increasing concerned that the plateau environment will potentially increase fuel consumption in engines. Despite this, the current state of research on high altitude engines is still inadequate in providing sufficient and detailed information to counteract the decrease in engine efficiency. In addition, one of the novelty of this study was that the investigated altitudes is up to 4500 m, of which the previous studies was limited. Therefore, this study aims to investigate the effect of altitude on in-cylinder spray, combustion, and soot formation processes in diesel engines. A calibrated three-dimensional (3D) computational fluid dynamics (CFD) model of a single-cylinder, four-strokes, direct injection (DI) compression ignition, intake boost research diesel engine is established. The numerical CFD model used in this study has been validated through comparison with experimental data. It effectively investigates the in-cylinder activities and provides insights into the causes behind combustion and soot emission deterioration. The simulation is operated at altitudes of 0, 1500, 3000, 4500 m with corresponding intake pressure. It has been observed that engine performance and soot emissions deteriorate as altitude increases, and a sharp drop occurs when the altitude exceeds 3000 m, which can be attributed to the dramatic decline in combustion efficiency. The extended spray leads to a decrease in air utilization, which ultimately results in a sudden drop in combustion efficiency at altitudes above 3000 m. Overall, this study has identified that the extended penetration of the spray, caused by reduced pressure and air density, leads to poor air utilization, resulting in decreased performance and increased emissions. Hence, it is recommended that optimization of the combustion chamber geometry and injection strategies of diesel engines operating at high altitudes be undertaken to improve air utilization and combustion quality. This will serve as an avenue for further research in the future.

Performance optimization of radiator engine parameters during hard conditions by control charts monitoring and evaluating

Recently, engine design and control systems have been developed using data-driven modeling techniques to specify the in-cylinder complicated combustion process. The cooling fan performance is highly influenced by several factors that are determined based on what is called (DOE) «design of experiments». These factors include blade tip clearance, pitch angle, distance from radiator. This work presents a method to improve a cooling fan performance of an engine by designing a Six Sigma technique using Control, Improve, Analyze, Measure, and Define (CIAMD). First, let’s assess the existing cooling fan performance and define its problem. Then, let’s specify the parameters that affect on fan performance to be optimized. Next, let’s conduct sensitivity analysis and evaluate manufacturing control of the developed cool Fan. The primary fan does not distribute air enough by the radiator to maintain the machine cool throughout hard circumstances. First, the work demonstrates how to develop an experiment to examine the influence of three performance elements: blade pitch angle, blade-tip clearance, and fan distance from the radiator. In order to improve the performance of the cooling fan, Box-Behnken design is adopted for testing quadratic (nonlinear) effects. It then indicates how to predict optimal quantities for every element, to produce a technique that makes airflows above the objective of 1486.6 m3/h when utilizing experimental measurements. Finally, it reveals how to operate simulations to confirm that this method creates airflow based on the specifications with more additional fans manufactured performance of 99.999 %. The results of S and X-bar control charts indicate that the manufacturing process is statistically under control

Experimental and numerical studies of thermal power conversion and energy flow under high-compression ratios of a liquid methane engine (LME)

To improve the performance of a liquid methane engine (LME) under universal characteristics, the in-cylinder combustion process and thermal power conversion under different compression ratios were studied by experiment. The experimental results show that increasing the compression ratio results in a linear increase in EEE (effective expansion efficiency) and EER (effective expansion ratio). Moreover, the thermal efficiency varies significantly with the compression ratio only at low and medium loads. The effective thermal efficiency can reach up to 48.69%. For high-speed conditions, it is recommended to reduce friction losses and pump gas losses. Furthermore, a 1-D simulation model was developed to simulate the in-cylinder energy flow with a compression ratio of 12.6. The simulation results show that exhaust timing has a more pronounced effect on the in-cylinder energy flow (thermal balance) than intake timing. When the engine speed is 800 rpm, advancing the exhaust timing by 20°CA can increase the effective thermal efficiency by about 1%.

Characterization of in-cylinder spatiotemporal flame and solid particle emissions for ethanol-gasoline blended in gasoline direct injection engines

Stricter regulations for internal combustion engines have necessitated the inclusion of eco-friendly fuels with conventional ones to reduce gas and solid emissions. Gasoline direct injection (GDI) engines, however, have been found to produce more particle number and mass emissions than port fuel injection engines. To address this, bioethanol fuel has been selected as an additive eco-friendly fuel for gasoline, with the aim of reducing particle emissions. In this study, we quantitatively characterize in-cylinder spatiotemporal flame to feature combustion performance and particle emissions for ethanol fuel in the GDI combustion chamber. We examined three engine combustion modes differed in equivalence ratio and injection strategy to produce various combustion results to quantify combustion performance and particle emission characteristics. Using an eight-channel non-intrusive flame luminosity sensor in one cylinder, we measured the flame front and its propagation direction. At the tailpipe, we measured particulate emissions using an engine exhaust particle sizer and a micro soot sensor coupled with a catalytic stripper that removed semi-volatile compounds. Our study found that increasing ethanol fuel content for different combustion modes resulted in distinct combustion and flame development. The particle size distribution also showed different patterns at each combustion mode, depending on the ethanol content. Lean combustion modes yielded high diffusion flame intensity compared to stoichiometric combustion mode, which resulted in a larger amount of particle formation. The physical properties of ethanol fuel were found to predominantly determine the fuel-air mixture quality, combustion process, and flame development at each combustion mode. An increase in ethanol fuel content at lean-homogeneous mode resulted in higher diffusion flame intensity and larger particle emissions. Our comparative study of flame and solid particles for ethanol fuel content improves the understanding of in-cylinder combustion processes and their correlations.

Effects of ambient density and injection pressure on ignition and combustion characteristics in diesel spray under plateau cold-start conditions

Gaining insights into the multi-parameter coupling dominated in-cylinder combustion process takes on critical significance to controlling and enhancing the performance of diesel engines under plateau cold-start conditions. In this study, the effect of varying injection pressure and ambient density on ignition and combustion characteristics of No. -50 diesel spray was investigated through high-speed direct photography and the two-color imaging technique, respectively. Regarding ignition characteristics, the increase of the ambient density led to the variation of the non-monotonic trend of ignition delay time with the rise of the injection pressure to a monotonous decrease, whereas the correlation between the axial ignition location and the injection pressure remained unaffected. Under three different ambient densities, the transition modes of the flame structure varied with the increase of injection pressure, subsequently impacting combustion characteristics. For combustion characteristics, the average level of flame temperature and soot were inversely proportional to the injection pressure for all three ambient densities. Higher ambient density facilitated the heat release from combustion chemical reactions, influencing the impact of increasing turbulence intensity on the ignition and combustion processes of diesel spray. The overall temperature level of the flame displayed an inflection point with the rise of the injection pressure, and this inflection point is delayed with the increase of the ambient density. The local high-temperature regions in flames (＞2300 K) were identified under higher ambient densities, such that soot generation and oxidation were subjected to significant competition. At ρam = 16.6 kg/m3, the oxidation dominant time gradually decreased with the rise of the injection pressure, leading to the integral KL factor maximum at Pinj = 80 MPa case. The optimal fuel injection pressures for cold starting at different altitudes were determined by considering the ignition and combustion characteristics of the flames.

Evaluation and Simulation Analysis of Mixing Performance for Gas Fuel Direct Injection Engine under Multiple Working Conditions

Gas fuel direct injection (DI) technology can improve the control precision of the in-cylinder mixing and combustion process and effectively avoid volumetric efficiency reduction in a compressed natural gas (CNG) engine, which has been a tendency. However, compared with the port fuel injection (PFI) method, the former’s mixing path and duration are shortened greatly, which often leads to poor mixing uniformity. What is worse, the in-cylinder mixing performance would be seriously affected by engine working conditions, such as engine speed and load. Based on this situation, the fluid mechanics software FLUENT is used in this article, and the computational fluid dynamics (CFD) model of the injection and mixing process in a gas-fueled direct injection engine is established. A quantitative evaluation mechanism of the in-cylinder mixing performance of the CNG engine is proposed to explore the influencing rule of different engine speeds and loads on the mixing process and performance. The results indicate that phase space analysis can accurately reflect the characteristics of the mixture mixing process. The gas fuel mixture rapidly occupies the cylinder volume in the injection stage. During the transition stage, the gas fuel mixture is in a highly transient state. The diffusion stage is characterized by the continuous homogenization of the mixture. The in-cylinder mixing performance is linearly dependent on the engine’s working condition in the phase space.

Effect of spark timing on the pre-chamber jet ignition in a lean-burn natural gas engine

An enhanced combustion concept, pre-chamber jet ignition can provide high ignition energy and a wide dispersion of ignition sources, thus improving combustion performance and realizing stable lean combustion. However, the ignition performance of the pre-chamber jets depends strongly on the pre-chamber combustion process and is sensitive to many factors. Therefore, this paper will explore the impact of spark timing on the pre-chamber combustion, turbulent jet characteristics, and main chamber combustion performance by CFD simulation based on an active pre-chamber natural gas engine. The in-cylinder flow and combustion processes of the engine are calculated with the fuel-air equivalence ratio of the main chamber maintained at 0.5, and the spark timing varied from 684°CA to 708°CA with a step of 3°CA (compression top dead center is 720°CA). The results show that, in the present engine operating point, the pre-chamber combustion heat release rate is improved when the spark timing is retarded from 696°CA to 705°CA, and the injection velocity of the pre-chamber jet accordingly increases. As the spark timing continues to be delayed until 708°CA, the pre-chamber combustion deteriorates, and the injection velocity of the pre-chamber jet decreases. Under the combustion phase CA50 no more than 725°CA and the combustion duration CA5-90 fixed around 30°CA, the IMEP will maintain a relatively stable value when the spark timing is delayed from 693°CA to 705°CA, in the meantime, the NOx emission decreases with the delay of spark timing. Therefore, on the premise of ensuring engine power performance, it is a feasible scheme to delay spark timing to reduce NOx emission for the natural gas engine with an active pre-chamber.

Study of Scavenging and Combustion Processes for Small Two-Stroke Aviation Heavy Fuel Direct Injection Engines

Heavy-fuel aviation piston engines (HF-APEs) are widely used in general aviation and unmanned aerial vehicle (UAV) due to their safety and fuel economy. This paper describes a numerical and experimental study of scavenging and combustion processes on a 2-Stroke Direct Injected HF-APEs for light aircraft, with its cylinder specifically designed as cross scavenging. A 3-Dimentional transient model of in-cylinder flow and combustion process is established by the Forte platform, and the engine test system is set up. By comparing the simulation results to the experimental results, it showed that multi-ports cross scavenging can generate unbalanced aerodynamic torque in the cylinder. In the compression process, the swirl ratio (SR) gradually increases, and the peak SR reaches 15. Moreover, approximately 25% of exhaust residual gas in the cylinder is conducive to the fuel atomization and evaporation process in a high-altitude environment. When the injection timing is between −8 °CA and −16 °CA, the engine has the optimal power and economy performance at different altitudes. Finally, when the injection advance angle moves forward by 4 °CA, the maximum pressure increases by 2 MPa, with the rising rate decreasing gradually. The results have important significance for the development of the combustion system of small 2-Stroke Direct Injected HF-APEs.

Effects of EGR on combustion and emission characteristics of PODE/methanol RCCI mode at high load

In order to extend the high-load operation range of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel reactivity controlled compression ignition (RCCI) combustion mode, a numerical model of in-cylinder combustion was established by coupling PODE/methanol chemical reaction kinetics with CONVERGE software. And then the influence mechanism of exhaust gas recirculation (EGR) addition on in-cylinder combustion process, combustion stability and pollutant formation of the RCCI engine under high load and pilot injection strategy were investigated. The results show that with the increase of EGR ratio, the peak values of the first heat release formed by PODE pilot injection combustion and in-cylinder pressure decrease, the combustion start timing and CA50 phase are gradually delayed. While the peak value of the second heat release formed by PODE main injection combustion at low EGR ratio and the combustion duration remain unchanged. Meanwhile, as the EGR ratio increases from 0 to 30 %, the brake thermal efficiency (BTE) decreases from 46.54 % to 44.40 %. And the in-cylinder equivalent ratio and temperature field distributions become uniform, and both high-temperature region (above 1800 K) and NOx generation area are reduced, which decreases NOx emissions by 42.6 % without increasing soot emissions. The methanol mixture at squish zone is subjected to the high-temperature and high-pressure of pilot injection combustion, resulting in obvious pressure oscillation. While EGR addition decreases the generation of HCO and OH active radicals, ignition points and reaction rate, which effectively inhibits methanol spontaneous combustion and knock phenomenon, and decreases the ringing intensity from 2.82 MW/m2 to 1.50 MW/m2. The pilot injection strategy coupled with 18 % EGR can extend the indicated mean effective pressure to 1.22 MPa. However, the load further extension is mainly limited by the sharp decline of BTE.