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Effects of fumigated fuel on the initial combustion stage of a diesel spray were studied by measuring an ignition delay period and rate of heat release, clarifying a self-ignition limit of a fumigated fuel. Combustion experiments on both fumigated diesel fuel and methanol in a direct injection diesel engine gave the following results; a rapid combustion occurs with the methanol fumigation, while, the diesel fuel fumigation slightly changes the combustion of the main spray of diesel fuel injected directly into the combustion chamber. Regarding the rate of heat release, the maximum rate in the initial combustion stage increases rapidly with an increase in methanol fumigation, while for the fumigated diesel fuel, the maximum rate changes only slightly. The ignition delay period affected by fumigated diesel fuel is shorter than that affected by methanol at the same fumigation equivalence ratio and intake temperature.

A high-speed photographic study is presented illustrating the influence of engine variables such as an introduced air swirl, the number of nozzle holes and the piston cavity diameter, on the combustion process in a small direct-injection (D.I.) diesel engine. The engine was modified for optical access from the under and lateral sides of the combustion chamber. This modification enabled a three-dimensional analysis of the flame motion in the engine. The swirling velocity of a flame in a combustion chamber was highest in the piston cavity, and outside the piston cavity it became lower at the piston top and at the cylinder head in that order. The swirl ratio of the flame inside the cavity radius attenuated gradually with piston descent and approached the swirl ratio outside the cavity radius, which remained approximately constant during the expansion stroke. Engine performance was improved by retarding the attenuation of the swirl motion inside the cavity radius.