Influences Of The Mixture Reactivity On Combustion Process In A N-butanol/Diesel Dual-fuel Engine

With the environmental deterioration and energy shortage crisis,engine researchers are forced to seek renewable clean energy.The oxygen element in the molecular structure of oxygen-containing fuel plays a postive role in solving the problem of inhomogeneous distribustion of mixture in combustion chamber during the combustion process,which has a great application prospect to improve the emission and thermal efficiency of the engine.Among the existing oxygenated fuels,butanol is considered to be a next generation renewable fuels due to its excellent physical and chemical properties.In this paper based on a modified high pressure common rail diesel engine which the first cylinder installed with an independent intake and exhaust system.The n-butanol / diesel compound combustion mode(n-butanol PFI and diesel DI)is adopted on the condition of speed at 2000r/min,air intake temperature 75?and inlet pressure constant at 0.13 MPa.The variation trend of the heat release rate in the cylinder,as well as the combustion characteristic parameters and the indicator performance under each combustion process,is deduced from the heat release rate curve.The conclusions are as follows:The relationship between the combustion of the high activity layer and the low activity layer is relatively "independent".When ?0 < 0 ° ATDC,the compound combustion is mainly triggered by the self-ignition of the high reactivity layer.The increase of the high reactivity layer concentration magnifies the energy released by the diesel self-ignition,and the combustion can be more widespread in the combustion chamber,then a higher heat release rate in the compound combustion is promoted.Due to the multi-point pilot ignition of diesel fuel and the premixed compression ignition of n-butanol,the compound combustion shows a shorter combustion duration and higher indicated thermal efficiency as the n-butanol concentration increases.When ?0 > 0 ° ATDC,n-butanol premixture spontaneously burns under certain temperature and pressure conditions before diesel injection timing,which further increase the temperature and pressure in the cylinder.The compound combustion duration shows an increasing trend due to more diesel fuel to tend to be burn in diffusion combustion mode.There is a trigger condition for the premixed compressive ignition of n-butanol premixed gas.This triggering condition is mainly determined by the temperature in the cylinder,the pressure in the cylinder and the concentration of the mixture gas.With the increase of diesel concentration,both the ?Q and ? is increased,and the curve of n-butanol premixed combustion is more similar to the parabolic curve.Under the same diesel injection timing,with the increase of diesel fuel concentration,the ?Q increases greatly and ? reaches 91.61% at Md=12mg.Due to the higher-octane number and latent heat of evaporation of n-butanol,it will act as an inert substance at the early stage of compound combustion.With the increase of the concentration of n-butanol and diesel injection timing,the degree of coincidence between the n-butanol premixed compressive ignition and the dieseldiffusion combustion increases,which accelerates the heat release rate.