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Four different diesel particulate filter (DPF) systems for city buses have been studied on an engine bench, and based on the results, their practicalities are discussed. On road data of buses operating in Tokyo were collected, and a city bus driving pattern for engine bench test was prepared. Evaluation tests were carried out on an engine bench using an 11-liters engine, used on city buses. The test engine equipped with a DPF system was operated on cyclic test of the city bus driving pattern for the accumulated loading time of 400 hours. Each of the DPF systems has a wall flow monolith filter. A diesel fuel burner or an electric heater with or without catalyst-coated filter is used for regeneration. It is possible to remove about 90% of particulates from the exhaust gas by the use of DPF systems for diesel engines. Soluble organic fraction (SOF) is reduced by about 30%. It is difficult to sufficiently remove SOF.

Four urea SCR systems were developed and evaluated on a C/D and on the road to investigate their potential for Japanese emission regulations in 2005 and beyond. Test results showed that NOx conversion ratios were 50 to 70% during the Japanese D13 mode cycle, and the ratios under the transient driving cycle were lower than those tested during a steady state. Unregulated emissions, such as benzene, aldehyde and benzo[a]pyrene, existed either at a trace level using the oxidation catalyst, or lower than a base diesel engine, when no oxidation catalyst was used. The health effects of particulate matter emitted from the SCR system were almost the same as those from conventional diesel engines, as evaluated by the Ames test and in vitro micronucleus test. Thermal degradation products, such as cyanuric acid and melamine, were two to four figures lower compared with the toxicological information of Safety Information Resources Inc. (SIRI).

Schlieren and direct cine photography have been used in conjunction with the gas sampling method to investigate three dimensional combustion phenomena in a DI diesel engine cylinder. Gas movement, dispersion of fuel-air mixture after fuel impingement on the cavity wall and the combustion process under continuous running conditions were observed. Gas concentrations of NOx, THC, CO, CO2, O2, H2 and decomposed hydrocarbons were analyzed. The distribution of equivalent fuel concentration and the decomposition process of fuel are presented. Air swirl accelerates the homogeneity of fuel-air mixture after spray impingement on the cavity wall. It is concluded that a combined measurement by photography and gas sampling method is a useful one to combustion study of diesel engines.

A diesel engine with a dual-fuel (methanol-diesel) injection system has been developed, and the practicality of a prototype bus equipped with the developed engine has been confirmed. This study showed that methanol could be substituted for diesel fuel at the rates of 86 vol. percent in transient mode operation and 94 vol. percent in steady-state operation. Driving performance was equivalent to that of a conventional bus. Fuel economy of the dual-fuel injection engine was the same as that of a conventional diesel engine in steady-state operation, and decreased by about 9 percent in transient mode operation. The dual-fuel injection engine met the Japanese regulations on exhaust emissions stipulated in 1979. Exhaust smoke and particulate emissions were extremely reduced to the level of smoke-free operation.

Ignition and combustion of methanol in a spark-assisted methanol diesel engine were studied for the purpose of developing such an engine that is practical for actual vehicles. It became clear through investigations on combustion of methanol in a spark-assisted methanol diesel engine that methanol combustion proceeds mainly by flame propagation. Based on this finding, effects of such parameters as the injection direction, ignition position, ignition energy, compression ratio, injection timing and ignition timing were studied to obtain optimal conditions for methanol combustion. It was found through such studies that it is effective to form the mixture upstream of the spark, plug relative to the swirling direction and increase the inductive component of the ignition energy to achieve a high ignition stability.