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The characteristics of smokeless low temperature diesel combustion in various fuel-air mixing was investigated by engine tests with high rates of cooled exhaust gas recirculation (EGR), three compression ratios, and fuels of various cetane numbers, as well as by computational fluid dynamics (CFD) simulation of the in-cylinder distributions of mixture concentration and temperature. The results show that besides combustion temperature, fuel-air mixing is also vital to efficient, smokeless, and low NOx diesel combustion. Smokeless and low NOx diesel combustion can be realized even with insufficient fuel-air mixing as long as the combustion temperature is sufficiently low. However low combustion temperature and insufficient oxygen due to ultra-high EGR cause very high UHC and CO emissions, and a severe deterioration in combustion efficiency.

The thermal cracking and polyaromatic hydrocarbon (PAH) formation processes of dimethyl ether (DME), ethanol, and ethane were investigated with chemical kinetics to determine the soot formation mechanism of oxygenated fuels. The modeling analyzed three processes, an isothermal constant pressure condition, a temperature rising condition under a constant pressure, and an unsteady condition approximating diesel combustion. With the same mole number of oxygen atoms, the DME rich mixtures form much carbon monoxide and methane and very little non-methane HC and PAH, in comparison with ethanol or ethane mixtures. This suggests that the existence of the C-C bond promotes the formation of PAH and soot.

Direct injection of various ignition suppressors, including water, methanol, ethanol, 1-propanol, hydrogen, and methane, was implemented to control ignition timing and expand the operating range in an HCCI engine with induced DME as the main fuel. Ultra-low NOx and smoke-less combustion was realized over a wide operating range. The reaction suppressors reduced the rate of low-temperature oxidation and consequently delayed the onset of high-temperature oxidation. Analysis of the chemical kinetics showed a reduction of OH radical in the premixed charge with the suppressors. Among the ignition suppressors, alcohols had a greater impact on OH radical reduction resulting in stronger ignition suppression. Although water injection caused a greater lowering of the temperature, which also suppressed ignition, the strong chemical effect of radical reduction with methanol injection resulted in the larger impact on suppression of oxidation reaction rates.

The combustion characteristics in a partially premixed charge compression ignition (PCCI) engine with n-hexane were compared with ordinary diesel fuel to evaluate combustion improvements with lower distillation-temperature fuels. In the PCCI engine, a lean mixture was formed reasonably with early stage injection and the additional fuel was supplied with a second stage fuel injection after ignition. With n-hexane, thermal efficiency improved while simultaneously maintaining low NOx and smokeless combustion. A CFD analysis simulated the mixture formation processes and showed that the uniformity of the mixture with the first stage injection improves with lower distillation-temperature fuels.

Ammonia-selective catalytic reduction (SCR) systems have been introduced commercially in diesel vehicles, however catalyst systems with higher conversion efficiency and better control characteristics are required to know the actual emissions during operation and the emissions in random test cycles. Computational fluid dynamics (CFD) is an effective approach when applied to SCR catalyst development, and many models have been proposed, but these models need experimental verification and are limited in the situations they apply to. Further, taking account of redox cycle is important to have better accuracy in transient operation, however there are few models considering the cycle. Model development considering the redox reactions in a zeolite catalyst, Cu-ZSM-5, is the object of the research here, and the effects of exhaust gas composition on the SCR reaction and NH3 oxidation at high temperatures are investigated.

Ultra low emissions and high performance combustion was achieved with a combination of high EGR, a three-way catalyst, and a highly oxygenated liquid fuel, neat dimethoxy methane (DMM), in an ordinary DI diesel engine. The smokeless nature of neat DMM effectively allowed stoichiometric diesel combustion by controlling BMEP with EGR. NOx, THC, and CO emissions were reduced with a three-way catalyst. At lower BMEP with excess air, the EGR effectively reduced NOx. High-speed video in a bottom view type engine revealed that luminous flame decreased with increased fuel oxygen content and almost disappeared with DMM.