Effect of Lean Pre-Mixture on the Combustion in Diesel Engine : 2nd Report, Consideration from Combustion Photographs

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The high-speed photography was used to make clear the influences of lean pre-mixture on the combustion in the cylinder. In this attempt, a 2-hole nozzle was used for main injection, main sprays were deflected in two directions at an angle of 50°. The pre-mixture was intentionally concentrated in one of the two main sprays, so that two different combustion processes with and without the pre-mixture could be compared under the same condition.The results obtained are summarized as folloes : (1) Under the existence of the pre-mixture, ignition nuclei can break out all over the main spray core and even outside of it. The area of breaking out of them is so widened that the flames can rapidly spread over the chamber, and the flaming duration can be reduced.(2) For the favourable results shown in (1), n-paraffins and methyl alcohol are most effective as the auxiliary fuel. Acetone and cyclohexane are not effective at the compression ration of 12. Increasing the ratio to 18,these fuels have the same effectiveness as n-paraffins. In general, it defeats its own purpose to use the aromatics having simple side chains as the auxiliary fuel. Aromatics seem to ignite later than the main fuel.
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