Experimental Research Into The Influence Of Fuel Physicochemical Properties On The Spray Combustion Characteristics In A Constant Volume Combustion Chamber

The spray and combustion process is the fundamental factors affecting performance and emission of diesel engine,while the physical and chemical characteristics of the fuel directly determine the spray combustion characteristics.The discovering of various renewable and clean alternative fuel,which showed great potential of energy saving and emission reduction when applied to the diesel engine,makes studying on the influence of fuel physicochemical properties on the spray combustion characteristics very essential.In this paper,the effects of fuel physical and chemical properties on the spray combustion characteristics of diesel engine were studied by using 6 kinds of fuels,which were mixed with the catalytic hydrogenation biodiesel,which has a high cetane number(CN),and traditional diesel in a constant volume combustion chamber.The effects of fuel physicochemical properties on the spray liquid length(LL)with different ambient density under combustion and evaporation conditions were studied based on the laser Mie scattering technic.The results showed that the spray LL under combustion conditions is shorter than the spray LL under evaporation conditions,and the difference became little when the ambient density is higher.In addition,the study of LL under combustion conditions showed that the LL decreases with the increase of fuel density and ambient temperature,while the ambient oxygen concentration and injection pressure have little effect on the spray LL.The study on the fuel properties affect the instantaneous OH*,CH*,ignition delay and flame lift-off length(LOL)of diesel combustion showed that the ignition delay and flame lift-off decreased with the increase of cetane number.The instantaneous CH* is more close to the flame downstream than the instantaneous CH* and there is an overlap region on the flame surface between them.With the increase of CN,the instantaneous OH* and the instantaneous CH* distribute more uniformly on the flame surface.By using laser Mie scattering technology and chemical fluorescence visualization method innovatively,the spray LL under combustion and LOL was studied simultaneously,studying the interaction between them showed that the combustion LL and LOL can be in a stable state simultaneously,before the end of the injection if the injection duration is long enough.With the increase of ambient density and ambient temperature,the LOL and combustion spray LL decreases,the influence of ambient temperature on the flame lift-off is greater than the effect on the LL.For the conditions where the combustion LL is shorter than the LOL,there will be more interspace for the mixing of air and fuel,the fuel vaporization has completed before the fuel reaches the combustion region.For the conditions where the combustion LL is longer than the LOL,there will be an overlap between liquid phase fuel and combustion flame.The flame and liquid fuel will interact with each other at these conditions.The vaporization of the liquid fuel is enhanced by the heat of the combustion and the combustion rate is reduced by the vaporization cooling.In addition,with the increase of cetane number of fuel density,the difference between lift-off length and liquid length became smaller and the decrease of LOL is greater than the decrease of LL.The physical and chemical properties of fuel have little effect on the difference between LOL and LL,when the injection pressure is low and the ambient oxygen concentration is high.This study revealed the mechanism of fuel physicochemical properties,especially CN,influenced on the spray combustion process,which provided the theories foundation for the application of the catalytic hydrogenation biodiesel and other fuels with different physicochemical properties on the engine.