Experimental Study On Macroscopic Spray Characteristics Of Diesel At The Elevated Temperatures And Back Pressures

The significant advantages of diesel engines in terms of fuel economy and utilization rate help reduce the energy burden of transportation industry,but the formal implementation of the emission regulation(China VI)has put forward higher requirements for diesel engine emissions performance.The existing theory of combustion path control shows that the atomization of fuels after the injection in conventional diesel engines directly determines the subsequent combustion path direction and the concentration of pollutants.Therefore,controlling and optimizing the fuel injection process to form good spray characteristics is the key factor to improve combustion and reduce emissions.At present,most spray researches on diesel fuels have focused on the spray at the normal temperature and pressure or just high back pressures,which is different from the actual conditions of spray generation in the diesel engines.Therefore,in this paper,a spray test platform using high-speed photography technology and the constant volume combustion chamber is developed to study the macro spray characteristics under different injection pressures and back pressures,where the high temperature and high back pressure environment is established by preburning combustible mixtures.The main contents are as followed:Firstly,the experiments are carried out at different initial temperatures(358,388,418 K),fuel types(ethanol,ether,ethyl acetate,acetone,butanone),equivalent ratio(0.7 ~ 1.4),and initial pressures(1,3,4,and 5 bar)to study the temperature and pressure characteristics of premixed combustible gas.The variation of the pressure peak,combustion duration and adiabatic flame temperature are compared and analyzed,and the relatively optimal pre-burning conditions are gradually selected.Secondly,the high-speed camera was used to capture the entire spray process under different injection pressures(110,130,150 MPa)and ambient back pressures(15,20,25 bar).The corresponding data processing program of spray images is developed to calculate the spray penetration and the spray cone angle based on Python and OpenCV.Combined with the spray images,the change patterns and reasons of spray morphology,spray penetration and spray cone angle under different test conditions are analyzed.The results show that the spray penetration increases over the time and the growth rate at BP = 15 bar is a constant value,but at higher back pressures,the growth rate gradually decreases to zero;the spray cone angle descends over the time and finally stays between 10 ° ~ 12 °.In addition,as the ambient back pressure increases,the peak value of the spray penetration decreases,while the spray cone angle increases;the injection pressure has a smaller effect on the peak value of the spray penetration and the stable spray cone angle but enhancing the injection pressure can advance the time when the spray cone angle stabilizes.