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An optical measurement named the “transmissive light extinction method” was carried out to investigate soot behavior in a diesel combustion chamber. First, the theoretical principle was discussed, and some preliminary experiments to examine the applicability of the method were performed. The method was applied successfully to the measurement of actual soot density in an experimental engine with a facility to observe the inside of the combustion chamber. However, some limitations were noticed in the method, as it was essentially a matter of local measurement. Then a simple but unique optical arrangement was made to enable simultaneous highspeed photographing of shadowgraphs and direct images of the combustion flame. As a result, a total picture of the combustion process, though it was not sufficiently quantitative yet, was obtained, including fuel spray, flame and soot behaviors.

The authors designed and produced a new dual fuel injector that allows two different kinds of fuel to be injected. This injector contains both a throttle type nozzle and a hole type which are located coaxially. The injection timing as well as the fuel quantity can be controlled individually. The running test using two lines of gas oil brought a good reduction of NOx and exhaust smoke. The experiment using gas oil and alcohol also brought a satisfactory reduction of exhaust emission.