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According to previous papers on the combustion process in LHR diesel engines the combustion seems to deteriorate in LHR diesel engines. However it has been unclear whether this was caused by the high temperature gas or high temperature combustion chamber walls. This study was intended to investigate the effect of gas temperature on the rate of heat release through the heat release analysis and other measurements using a rapid compression-expansion machine. Experiments conducted at high gas temperatures which was achieved by the employment of oxygen-argon-helium mixture made it clear that the combustion at a high gas temperature condition deteriorated actually and this was probably due to the poorer mixing rate because of the increase in gas viscosity at a high gas temperature condition.

Diesel combustion and exhaust gas emissions under transient operation (when fuel amounts abruptly increased) were investigated under a wide range of operating conditions with a newly developed gas sampling system. The relation between gas emissions and piston wall temperatures was also investigated. The results indicated that after the start of acceleration NOx, THC and smoke showed transient behaviors before reaching the steady state condition. Of the three gases, THC was most affected by piston wall temperature; its concentration decreased as the wall temperature increased throughout the acceleration except immediately after the start of acceleration. The number of cycles, at which gas concentrations reach the steady-state value after the start of acceleration, were about 1.2 times the cycle constant of the piston wall temperature for THC, and 2.3 times for smoke.

Nitrogen oxide (NOx) and particulate matter (PM) emissions of diesel vehicles are regarded as a source of air pollution, and there is a global trend to enforce more stringent regulations on these exhaust gas constituents in the early years of the 21st century. On the other hand, the excellent thermal efficiency of diesel engines is certainly a welcome attribute from the standpoints of conserving energy and curbing global warming. Recently, many research institutes around the world have been using high-efficiency direct-injection (DI) diesel engines to research emission control technologies. The authors have also been engaged in such research [1,2]. As a result of this work, we have developed a new combustion concept, called Modulated Kinetics (MK), that reduces NOx and smoke simultaneously due to low-temperature and premixed combustion characteristics, respectively, without increasing fuel consumption [3,4].