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Two-stroke engines have to face the problems of insufficient charge for short intake time and the loss of intake air caused by long valve overlap. In order to promote the power of a two-stroke poppet valve diesel engine, measures are taken to help optimize intake port structure. In this work, the scavenging and combustion processes of three common types of intake ports including horizontal intake port (HIP), combined swirl intake port (CSIP) and reversed tumble intake port (RTIP) were studied and their characteristics are summarized based on three-dimensional simulation. Results show that the RTIP has better performance in scavenging process for larger intake air trapped in the cylinder. Its scavenging efficiency reaches 84.7%, which is 1.7% higher than the HIP and the trapping ratio of the RTIP reaches 72.3% due to less short-circuiting loss, 11.2% higher than the HIP.

A concept of high density-low temperature combustion (HD-LTC) is put forward in this paper, showing potential of its high thermal efficiency and very low engine-out emissions by engine experimental and CFD modeling study. A single cylinder test engine has been built-up equipped with mechanisms of variable boost pressure and intake valve closing timing (IVCT). By delaying IVCT and raising boost pressure to certain values according to engine loads, the in-cylinder charge density is regulated much higher than in conventional engines. It is found that the high charge density can play the role of rising of heat capacity as exhaust gas recirculation (EGR) does. Thereby low temperature combustion is realized with less EGR (about 18~19% oxygen concentration) to achieve very low NOx and soot emissions, which is extremely important at high and full loads.

This paper presents a compound combustion technology of Premixed Combustion and “Lean Diffusion Combustion” for realizing the concept of HCCI combustion in a D I diesel engine. The premixed combustion is achieved by the technology of multi-pulse fuel injection. The start of pulse injection, injection-pulse number, injection period of each pulse and the dwell time between the injection pulses are controlled. The objective of controlling the pulse injection is to limit the spray penetration of the pulse injection so that the fuel will not impinge on the cylinder liner, and to enhance the mixing rate of each fuel parcel by promoting the disturbance to the fuel parcels. The last or main injection pulse is set around TDC. A flash mixing technology is developed from the development of a so-called BUMP combustion chamber, which is designed with some special bump rings.

Combustion control strategy for high efficiency and low emissions in a heavy duty (H D) diesel engine was investigated experimentally in a single cylinder test engine with a common rail fuel system, EGR (Exhaust Gas Recirculation) system, boost system and retarded intake valve closing timing actuator. For the operation loads of IMEPg (Gross Indicated Mean Effective Pressure) less than 1.1 MPa the low temperature combustion (LTC) with high rate of EGR was applied. The fuel injection modes of either single injection or multi-pulse injections, boost pressure and retarded intake valve closing timing (RIVCT) were also coupled with the engine operation condition loads for high efficiency and low emissions. A higher boost pressure played an important role in improving fuel efficiency and obtaining ultra-low soot and NOx emissions.

In this study, experimental and simulation investigations on the roles of charge density (ρtdc), temperature (Τtdc) at the top dead center and oxygen concentration (φO2) on the combustion paths, emissions and thermal efficiency of a high load operation diesel engine were conducted. Experimental engine was a modified single-cylinder engine equipped with variable mechanisms of boost, exhaust gas recirculation (EGR) and intake valve closing timing (IVCT) to regulate the Ptdc, φO2 and Τtdc. Simulations of engine combustion processes were performed with an ECFM-3Z combustion model. The results revealed that higher Ptdc, leading to lower overall fuel/oxygen equivalence ratio (Φm), enhanced the rate of mixing and chemical reaction and benefited improvement of the thermal efficiency.

In this study, Partially Premixed Combustion (PPC) on a modified heavy-duty diesel engine was realized by hybrid combustion control strategy with flexible fuel injection timing, injection rate pattern modulation and high ratio of exhaust gas recirculation (EGR) at different engine loads. It features with different degrees of fuel/air mixture stratifications. The very low soot emissions of the experiments called for further understanding on soot formation mechanism so that to promote the capability of prediction. A new soot model was developed with highlight in effects of surface activity on soot growth for soot formation prediction in partially premixed combustion diesel engine. According to previous results from literatures on the importance of acetylene as growth specie of PAH and soot surface growth, a gas-phase reduced kinetic model of acetylene formation was developed and integrated into the new soot model.