The influence of air dissolved in the diesel fuel on the speed of heat release in the combustion process and the compounds in exhaust gases

摘要

The specificity of the combustion process being realized in the direct injection compression-ignition engine (CI) consist in a fact that the liquid fuel in a form of fuel sprays is supplied to the engine combustion chamber right before the piston top dead centre (TDC). Thus a complete process of preparing the mixture for being burnt, i.e. a disintegration of the fuel spray into drops, their evaporation and mixing with air needs to be performed in a very short time. For such a way of fuelling the engine some local and very significant differences of the excess air factor values λ are met (fig. 1). The values met in the combustion chamber range from the infinite high one in the area which is not covered by the fuel spray, throughout λ ≈ 0.8 ÷ 1.5 at the edges of the fuel spray initializing the ignition to λ ≈ 0 being recorded in the spray core. The local deficiencies of oxygen occur despite the high value of the global excess of air the value of which changes with the engine load and ranges from λ ≈ 11 at the engine idle running to λ ≈ 1.4 ÷ 1.3 at the engine full load, i.e. for the operating conditions corresponding to the outer engine operating characteristic.