Ignition Delay Study Of Binary Fuel Blends Of DME/N-butanol Under High Temperature Conditions

Based on dual pressures of environmental pollution and energy consumption,the new combustion technology,which is represented by homogeneous charge compression ignition(HCCI)and alternative fuels draw more attention.However,it has been recognized that a single fuel(or fixed fuel physicochemical properties)can not achieve optimal efficiency and emissions within the full operating range of the engine,the fuel design and management must be used to control the advanced engine combustion process.According to the fuel design method,butanol has a high octane number,which helps reduce knock under high load,and DME has a high cetane number,which contributes to combustion in a wide range.So butanol/DME dual fuel(or mixed fuels)will implement more clean and efficient combustion in a wide range of engine load.But there is not enough detailed research about the chemical kinetics of butanol/DME mixtures.As a result,the ignition delay times of different DME/n-butanol mixtures(DME blending ratios of 100%,80%,60%,40 %,and 0%)were studied behind reflected shock waves at equivalence ratios of 0.5,1.0,and 1.5;pressures of 6.0 bar,10 bar,and 15 bar;and temperatures of 1150 K-1650 K.The effects of a carrier gas(nitrogen or argon)on the ignition delay times of single and blended fuels were also studied.The detailed chemical kinetic mechanism of DME/n-butanol was constructed based on Zhao's DME chemical kinetic mechanism(Int.J.Chem.Kinet 2008;40:1-18)and Sarathy's n-butanol chemical kinetic mechanism(Combust and Flame 2012;159: 2028–2055),which can accurately predict the ignition delay times of both single and blended fuels.Experimental results show that the ignition delay time of DME is longer than that of n-butanol when the temperature is high(>1150 k)and that the ignition delays of blended fuels increase with an increased blending ratio of DME.However,the relationship between ignition delay time and the blending ratio is non-linear.The main factor affecting the blended fuel's ignition delay is temperature,and with every 200°C increase in temperature,the ignition delay times is reduced by an order of magnitude.Additionally,pressure has a large effect on the ignition delay times.The results of reaction path analysis of blended fuels show that with an increasing DME blending ratio,the contribution rate of OH-radicals to H-abstraction decreases during the oxidation of n-butanol,and the contribution rate of H-radicals to H-abstraction of n-butanol increases slightly.However,with increasing DME blending ratios,the pyrolysis of DME decreases,but the contribution rates of CH3 and OH to the H-abstraction of DME increase.