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One of countermeasures for exhaust emissions from a diesel engine, especially, DI diesel engine, is the use of a super high pressure injection system with a small hole diameter. However, the system needs greater driving force than that with normal injection pressure, and its demerit is increase in NOx, although soot is decreasing. Then, authors propose the new concept on the simultaneous reduction of NOx and soot. The concept is that the utilization of flash boiling phenomenon in a diesel engine. The phenomenon can be realized by use of the injection of fuel oil with CO2 gas dissolved. Flash boiling facilitates the distinguished atomization of fuel oil and CO2 gas contributes to realizes the internal EGR during combustion. Fundamental information on the characteristics of a flash boiling spray of n-tridecane with CO2 gas dissolved is described in this paper, as a first step.

The concept of oxygen enriched charging (OEC) was exploratively examined as a means of reducing particulate emissions from a direct injection (DI) diesel engine. A single cylinder DI engine was operated with intake gas oxygen concentrations of 21% to 29%, under a constant engine speed of 40 Hz, and several load conditions. It was found that OEC reduces particulate emissions from a DI diesel engine for all operating conditions tested. Insoluble particulate is especially suppressed by OEC at high load conditions. Oxygen enriched charging has little effect on particulate size distribution at high loads when the mass fraction of extractables is low. Fuel consumption, at constant injection timing, is improved a little by OEC. Emissions of NOx increase exponentially with increasing oxygen concentration. Ignition delay is decreased by OEC and this allows injection timing to be retarded to reduce NOx emissions without increasing the specific fuel consumption.