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Both in conventional diesel combustion and the low temperature combustion represented by PCCI and EGR-diluted combustion, high mixing rate at the whole combustion history is the key to achieve comparative clean and high-efficiency combustion. In this study, a newly developed combustion chamber, vortex-induced combustion chamber which can enhance middle and late cycle combustion is developed based on BUMP combustion chamber investigated in previous study. And then, the combustion and emission characteristics in the circumstances of diluted combustion are studied. For low oxygen concentration cases, heat release rate goes down and combustion efficiency decreases due to decreased mixing efficiency. The results of chamber design indicate complex structure of flow can be realized by special designed chamber geometry. The velocity difference in the interface of the vortexes will benefit to mixing of fuel and air, therefore combustion and emissions.

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.

A numerical simulation was performed to investigate the pilot ignited natural gas combustion process in a direct injection natural gas engine. Various mixture distribution characteristics were compared in terms of the evolution of mixture equivalent ratio distributions and mixture concentration stratifications around top dead center (TDC). Based on above, the pilot injections were specially designed to investigate ignition core formation and its effects on natural gas combustion process. The result shows that pilot ignition sites have great impacts on pilot fuel ignition process and natural gas combustion process. The pilot ignition site on the region with rich NG/Air mixture is disadvantageous to the pilot fuel ignition due to a lack of oxygen, which is not beneficial to ignition core formation.

This paper investigated the effects of late intake valve closing timing (IVCT) and two-stage turbocharger systems matching based on partially premixed combustion strategy. Tests were performed on a 12-liter L6 heavy-duty engine at loads up to 10 bar BMEP at various speed. IVCT (where IVCT is -80°ATDC, -65°ATDC and -55°ATDC at 1300 rpm, 1600 rpm and 1900 rpm, respectively) lowered the intake and exhaust difference pressure, reducing pumping loss and improved the effective thermal efficiency by 1%, 1.5% and 2% at BMEP of 5 bar at 1300 rpm, 1600 rpm and 1900 rpm. For certain injection timings and EGR rate, it is found that a significant reduction in soot (above 30%) and NOx (above 70%) emissions by means of IVCT. This is due to that IVCT lowered effective compression ratio and temperature during the compression stroke, resulting in a longer ignition delay as the fuel mixed more homogeneous with the charge air ahead of ignition.

Engine experiments have shown that simultaneous reductions of NOx and soot emissions can be achieved by the so called BUMP (Bump-up mixing process) combustion chamber. In order to understand the underlying mechanism of emission reduction, a STAR-CD based multi-dimensional combustion modeling was carried out for a heavy-duty diesel engine with the BUMP combustion chamber. The results from an impingement gas jet experiment were also presented and compared with computer modeling. The results showed that complex air motion with high turbulence was obtained by adoption of the bump ring. The fuel/air mixing rate was promoted greatly. Therefore, for the BUMP combustion chamber, much fuel fell in the optimum equivalence ratio range than that of the baseline chamber.

To explore the exergy loss of engine combustion process, entropy generations were numerically analyzed through detailed chemical kinetics. It revealed that the reformed fuel with simpler molecular tended to produce lower combustion irreversibility. Furthermore, a promising high efficiency RM- HCCI (Reformed molecule HCCI) combustion principle was proposed. In a RM-HCCI engine, hydrocarbon fuels were reformed into small molecule fuels under high temperature and low/no oxygen atmosphere before injection into the cylinder when the exhaust gas enthalpy to a certain extent was recovered, further improving the engine efficiency. The second law efficiency (η2nd) of a RM-HCCI combustion with a CR of 10 can be increased from 36.78% to 45.47% by coordination of multiple control parameters, and to 67.79% by raising CR from 10 to 100.