Experimental Study on Fuel-Air Mixture Formation and Ignition Process in Diesel Combustion

Abstract

The purpose of this study is to investigate fuel-air mixture formation during the ignition delay period and to clarify its effect on the initial combustion process. Thermal decomposition of fuel injected into hot compressed air or nitrogen was studied by detecting gaseous hydrocarbons, with a rapid compression machine and a total gas sampling device. The results show that the ambient temperature is a very important factor affecting the fuel decomposition process. If the temperature is sufficiently high, a considerable amount of injected fuel can be gasified even in the delay period when much oxygen is not yet supplied into the spray. When fuel is injected into very low-temperature air, the ignitability deteriorates because an adequate mixture to ignite exists in only the limited area in the combustion space. At very high temperature, residual fuel in the later stage of combustion is severely cracked into unburned gas and soot, because of the insufficient mixing until ignition. © 1991, The Japan Society of Mechanical Engineers. All rights reserved.