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A compact transient mini-tunnel (multi-tube type) inducing only a part of the exhaust gas, has been newly developed as a device for measuring the quantity of regulated exhaust emissions in the exhaust gas from diesel engines. This device allows measurement of exhaust emissions even for transient mode operating conditions of the engines, such as U.S. EPA FTP transient mode (FTP mode). The size of this mini-tunnel can be reduced to approximately twenty percent of the dilution tunnel (full-flow tunnel) specified by EPA and the flow rate in the mini-tunnel is a few percent thereof. The results have been demonstrated that the mass emissions of particulate, CO, NOx and HC measured with the mini-tunnel have good agreement to that measured with the full-flow tunnel under FTP mode and also steady state operating conditions of the engines (correlation coefficients of particulate, CO, NOx and HC are not less than 0.97).

To reduce exhaust emissions and fuel consumption, the effect of high pressure fuel injection was investigated with in-cylinder fuel spray observation and single cylinder engines. Spray impingement on the cavity wall promotes mixing with air and reduction in the nozzle area extends this wall impingement as a result of increasing both fuel injection pressure and injection period. There exists an optimum range for the injection period. Increased injection pressure by modifying injection rate of fuel pump and nozzle area, improves smoke and fuel consumption at low and medium speeds in particular. To extend these effects of high pressure injection, more optimized combustion system and minimized injection equipment drive torque must be required. To resolve the problem of high pressure injection such as higher combustion noise and increase in NOx emissions, the combination with pilot injection must be one of the most effective ways.

A premixed compression-ignited (PCI) combustion system, which realizes lean combustion with high efficiency and low emissions, was investigated and its effects and problems were ascertained. With PCI combustion, fuel was injected early on the compression stroke and a premixed lean mixture was formed over a long mixing period. The test engine was operated with self-ignition of this premixed lean mixture. From the results of combustion observation and numerical simulation, a need to prevent the fuel spray from adhering to the cylinder liner and combustion-chamber wall was identified. Consequently, an impinged-spray nozzle with low penetration was made and tested. As a result, an extremely low nitrogen-oxide (NOx) emission level was realized but fuel efficiency was detracted slightly. Also, the engine operating range possible with PCI combustion was found to be limited to partial-load conditions and PCI combustion was found to cause an increase in hydrocarbon (HC) emission.