Study On Auto-ignition Chemical Kinetics Mechanism Of Low-Alcohol/Gasoline Blends Under End-gas Conditions

As high-octane gasoline additives,low-alcohols play an important role in decreasing petroleum usage and reducing pollutant emissions,so this paper selected methanol,ethanol and n-butanol fuel to analyze the auto-ignition characteristics of them and their blending with isooctane fuels under the condition of the end gas.Besides,the effect of the mechanism of promoting and inhibiting of low-alcohols on auto-ignition characteristics of gasoline surrogates was studied based on the detail chemical kinetics mechanisms.Firstly,a constant adiabatic combustion model was established to simulate and calculate ignition delay time of low-alcohols in shock tube and the rapid compression machine by using Chemkin-Pro package,while jet stirred reactor was used to predict species concentration in the fuel reaction process.The most suitable detailed chemical reaction kinetics mechanism of methanol,ethanol and n-butanol were selected by comparing the predicted results of the simulation with the corresponding experimental results under different target conditions of low temperature and high pressure of the end gas.Then,based on the detail chemical kinetics mechanism of selected and verified lowalcohol fuels,a quasi-dimensional single zone model was developed to simulate the autoignition combustion characteristics of low-alcohols.By analyzing the auto-ignition characteristics of fuels,the sensitivity of intake temperature,pressure and speed changes were used to predict the knock tendency of low-alcohols in modern SI engine.In addition,the reactivity of low-alcohol/iso-octane fuels was analyzed by comparing the CA50 contours of different fuels under various intake temperature and pressure conditions.The results show that methanol and ethanol maintain higher anti-knock performance than isooctane and n-butanol fuel.For further explaining the effect of low-alcohols on the anti-knock performance of lowalcohol/iso-octane fuels,the key reaction pathways for the low-temperature reaction of low-alcohol/iso-octane fuels were studied based on the detailed chemical kinetics mechanism of fuels,and the mechanism of promoting and inhibiting of low-alcohols on auto-ignition characteristics of gasoline surrogates were revealed by combining with sensitivity analysis method.Studies show that the low-temperature exothermic reactions rates decrease,which slows down combustion process,when methanol and ethanol fuels are added to isooctane.But the reaction velocity of the system is accelerated,and the ignition time of the blended fuel is significantly earlier than that of isooctane after adding n-butanol in isooctane.