The Influence Of Ethanol And Bio-esters On The Combustion Progress And Emissions Of Diesel Engines

The energy crisis and the deterioration of the environment makes it increasinglyconcerned about alternative of the petroleum fuel. Ethanol and bio-esters as therenewable and easy-degradation fuels has attracted widespread attention. Ethanol andbio-esters blends can significantly improve the diesel engine soot emissions, andeffectively reduce CO and HC emissions.Experiments were conducted on a4100QBZL-2diesel engine test benchplatform with different blend ratio of ethanol and methyl esters to study the NOxemission and particulate emissions of diesel engines. The results showed that: whenusing ethanol blends, NOx emissions increased under the heavy load, the total totalparticulate mass emissions dropped significantly and the particle size distributionchange significantly, the total number concentration decreases while the GMD of theparticles redcued, and the nuclei particles will increase with increase of ethanol in theblended fuel. The methyl ester blended fuel will make NOx emission of the dieselengine increased slightly in all tested conditions, and the total particle mass emissions,the number of accumulation mode particles, particle geometric mean diameter,particle surface area and volume concentration will be reduced.Then, a combinated mechanism model was builded based on ethanol andn-heptane mechanisms, and then the combined chemical kinetic model was coupledwith diesel three-dimensional CFD combustion model to simulate in-cylindercombustion process and analysis the effects of ethanol blends on important reactionsof combustion and harmful emissions. The results show that: the ethanol blendsleaded to the higher temperature of the combustion process, and promoted theformation reaction of CO, prompted the PAH formation and the oxidation reaction.Due to the difficults of simulate the combustion of methyl ester blends directly,this paper studied the effects of methyl ester’s chemical characteristics on it’scombustion. A combined chemical kinetic model was builded based on methyldecanoate reaction mechanisms. The combined model contains PAH and NOformation reaction mechanisms and was applicated to analysised the effects ofunsaturated methyl esters on the combustion and emissions of diesel engine. Theresults show that: the carbon-carbon double bond in the methyl esters will make the increase in the maximum heat release and advance the starting point of combustion.The PAH and thermal NO formation increased with the the increase of unsaturatedesters. The prompt NOx formation was also indirectly show increases. The carboncarbon double bonds will cause the CO formation amount reduction, and more likelyto be oxidized to CO₂. Meanwhile, the formation of formaldehyde in the combustionprocess will be reduced with the unsaturated ester proportion increased, and theimportant reactive radical such as OH radical will be promoted with the increase inthe proportion of unsaturated ester which accelerated the high temperature reactions.In order to better understand the combustion process of methyl esters and uncoveredthe effects of ester moiety in methyl esters on the combustion process and andharmful emissions formation, a combined methyl butanoate and a combined n-butaneoxidation chemical kinetics model were builded. The PAH and NOx formationreaction mechanism were added to the combined models. The simulation results showthat: the ester moiety in methyl esters will change its combustion reaction path andlead to more oxygenated product formation such as CO, CO₂, CH₂O and so on. Theoxygen atoms in the ester moiety will drag one carbon atom from the the carbon poolwhich could be form PAH precursor and consequently reduce the PAH formation.The ester moiety will increase the local oxygen concentration and correspondentlyincrease the thermal NOx formation which is consistent with experimental results.