Control of fuel sprays activity in starting and after starting warm-up periods of diesel engine

Abstract

During starting and after-starting warm-up periods of the engine, fuel supplied to the combustion chamber by the injector heats and partially evaporates by means of compressed air exergy. In this case, mainly forms large drops, the amount of which can reach 85…90 % in the cyclic feed. Large drops can not completely evaporate, reach the cold combustion chamber walls, where they condense and don’t participate in combustion, which worsens starting qualities and increases incompleteness of combustion. Clearly that improvement of starting qualities of diesel engine and reducing of combustion incompleteness during after-starting period can be accomplished by the increasing of air charge exergy in the end of compression stroke, or increasing of fuel exergy which sprays in combustion chamber. Experimental research have shown that engines which equipped with traditional fuel system with injection pressure up to 20 MPa, fuel activation provides mainly (on 96,8 %) by means of air charge exergy. The structure of air charge exergy losses is distributed as follows: to heat the fuel to average boiling point - 75 %, evaporation - 12,5 % and 12,5 % - to heat the fuel vapor of total evaporation losses. Thus, a high level of air charge energy supply makes possible to control the quality of fuel mixture formation during starting and after-starting warm-up periods by means of changing the value of thermomechanical part of fuel spray exergy.