Ethanol Effect On Biodiesel/n-Heptane Auto-Ignition Characteristic

With the development of energy crisis and the conscience of environment friendly of humans,looking for a clean,renewable diesel alternative fuel has become the key for sustainable development of diesel engine.Biodiesel,n-heptane and ethanol is as the popular alternative diesel fuel nowadays,which are rarely used independently considering technology,cost and application restriction.Blending any two or three kinds of fuel is the usual way.In this paper,the effect of the addition of ethanol on the combustion behavior of biodiesel/n-heptane blends has been studied.Auto-ignition characteristics of the biodiesel/n-heptane/ethanol BHE blends were studied in two experiment systems: a modified cooperative fuel research(CFR)engine and a constant-volume combustion chamber(CID 510).And then chemical kinetic were studied via CHEMKIN PRO to do the zero-dimension simulation.The observations of ignition behavior include critical compression ratio and heat release profile,which were assessed using the CFR engine.While the physical and chemical ignition delays were measured by the CID 510 under a wide range of air temperatures and oxygen dilution levels.According to the experiment result,critical compression ratio increases with the addition of ethanol.And the onset of low temperature heat release(LTHR)of BHE15 and BHE20 is very close at both equivalence ratios at the same compression ratio.Furthermore,with the increase of ethanol in the blend,the total ignition delay and physical ignition delay at different temperatures are increased.BHE5 has the highest chemical ignition delay time at 853.15 K.With the Exhaust Gas Recirculation(EGR)increased,the total ignition delay is decreased.As for the chemical kinetic study,firstly,based on methyl decanoate(MD),methyl-9-decanoate(MD9D)and n-heptane(H)as alternative blends,it builds a 3324 components,the 11053 elementary reactions blend alternative fuels detailed chemical kinetic mechanism.It verifies the ignition delay time of the detailed mechanism in the experiment conditions is reasonable.Via the analysis of the reaction path of MD,MD9 D and ethanol,the three mainly through dehydrogenation of dehydrogenated radical oh,o and oxygen process consumed.MD and MD9 D will produce MP2 D and finally dehydrogenated as CH2 O.Furthermore,R4(O+H2O=OH+OH)and R228(CH2CHO+O2=CH2O+CO+OH)are the key reactions which will influence on the ignition delay and heat release.According to the simulation result,rate of BH blends in CID 510 is the highest,however,with the development of ethanol,the rates are decrease.The reactors of BHE5 has the highest rate among the ethanol blend.In addition,the intermediate substance of KHP in CFR engine combustion,with the ethanol addition,the rate of KHP decreases.However,the rate of KHP of BHE15 and BHE20 is very close,which caused the closed onset of LTHR.The rate of R2358,R2368 and R2378 are the key reactions which effet the chemical ignition delay of blends in the CID 510 experiment.