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[EN] Because of the challenge of meeting stringent emissions regulations for internal combustion engines, some advanced low temperature combustion modes have been raised in recent decades to improve combustion efficiency. Therefore, detailed understanding and capability for accurate prediction of in-flame soot processes under such low sooting conditions are becoming necessary. Nowadays, a lot of investigations have been carried out to quantify in-flame soot in Diesel sprays under high sooting conditions by means of different optical techniques. However, no information of soot quantification can be found for sooting/non-sooting critical conditions. In current study, the instantaneous soot production in a two-stroke optical engine under low sooting conditions has been measured by means of a Diffused back-illumination extinction technique (DBI) and two-color method (2C) simultaneously. The fuels used were n-dodecane and n-heptane, which have been injected separately though two different injectors equipped with single-hole nozzles. A large cycle-to-cycle variation on soot production can be observed under such operating conditions, however the in-cylinder heat release traces were quite repeatable. It is the same with the well-known trends of soot amount to operating conditions that the probability of sooting cycles increases with higher ambient temperature, higher ambient density and lower injection pressure. Both techniques present a pretty good agreement on soot amount when the peak of KL value is close to 1. However, the KL value of two-color method becomes bigger than that of DBI and the difference increases with lower sooting conditions., This study was partially funded by the Natural Science Foundation of China (No. 51876083), China Postdoctoral Science Foundation (2018M642176) and High-tech Research Key laboratory of Zhenjiang (SS2018002)

A decoupling physical–chemical surrogate (DPCS) model was constructed for simulating the multi-component physical and chemical characteristics of practical diesel fuel. In the DPCS model, the physical and chemical characteristics of diesel fuel are surrogated separately, and the physical and chemical surrogates are coupled according to the principles of C/H mass ratio, functional group structure, and carbon balance. By implementing the DPCS model into a Computational Fluid Dynamics (CFD) code, the effect of the multi-component physical and chemical characteristics of diesel fuel on the spray, combustion, and emission characteristics in a constant-volume chamber and an optical diesel engine were explored. The results indicate that the DPCS model can satisfactorily reproduce the diesel vaporization and combustion behaviors under wide operating conditions.

Modeling studies were performed to investigate the methane homogenous charge compression ignition (HCCI) of micro free-piston power device. To ensure the success of combustion in micro power device, mixture gas should be compressed ignition by free-piston with certain amount of initial kinetic energy in the starting phase. Through the modeling studies of methane compression ignition process, a mathematical formula was deduced to predict the critical initial kinetic energy value. Simulation results reveal that a critical initial kinetic energy exists, and the homogeneous gas could not be compressed ignition until the piston obtains more energy than the critical initial kinetic energy. The critical initial kinetic energy is affected by micro-combustor geometric parameters, equivalence ratio and leakage. More important, the formula can be used to guide the design of micro free-piston power device.

A numerical and experimental investigation on gasoline compression ignition (GCI) combustion was performed in a heavy-duty diesel engine using gasoline/hydrogenated catalytic biodiesel (HCB) blends. The effects of HCB blended ratio, initial temperature at intake valve closing ( T IVC ) and start of injection (SOI) on performance of the GCI engine were studied in details. Additionally, the differences between GCI and reactivity controlled compression ignition (RCCI) were also explored. The results show that HCB with high reactivity initiates the combustion of gasoline with lower reactivity, and HCB blended ratio, T IVC and SOI have remarkable impacts on thermodynamic state of the fuel/air mixing and then engine performance. As HCB blended ratio increases, the engine noise, carbon monoxide (CO) and unburned hydrocarbon (HC) emissions can be effectively suppressed with the penalties of the increased nitrogen oxides (NOx) and soot emissions. Retarded SOI results in a stable combustion, lower CO emissions while higher NOx emissions. Overall, the optimized operation range of GCI combustion is mainly limited by the engine noise, which can be relieved by multiple injection. In addition, the RCCI produces much lower engine noise compared to the GCI. However, the RCCI is more sensitive to T IVC with worse fuel economy.

In diesel engines, the cavitating flow in nozzles greatly affects the fuel atomization characteristics and then the subsequent combustion and exhaust emissions. In this paper, with the needle lift curve on the basis of injection rate experimental data, a moving mesh generation strategy was applied for 3D simulation of the nozzle cavitating flow. Based on the third-generation synchrotrons of Shanghai Synchrotron Radiation facility (SSRF), a high-precision three-dimension structure of testing nozzle with detailed internal geometry information was obtained using X-ray radiography for a more accurate simulation. A flow visualization experiment system with a transparent scaled-up vertical multi-hole injector nozzle tip was setup. The experimental data was obtained to make a comparison to validate the calculated results and good qualitative agreement was shown between them. Afterward, the effects of needle movement on development of the cavitating flow and flow characteristics parameters were investigated. Finally, the influence of fuel temperature on development of the cavitating flow was also studied. Research of the flow characteristics for the diesel and biodiesel revealed that the flow characteristics of the biodiesel with a temperature rise of between 50 K and 60 K in injector nozzles will be similar to those of the diesel fuel.