Study On Laminar Combustion Characteristics And Chemical Kinetics Of Pentanol Isomers

The insufficient energy supply and serious environmental issue push the research on the new alternative fuels.Compared to the gasoline,alcohol fuels show many advantages when used on the engine.Until now,ethanol and butanol are the most popular fuels in the alcohol fuel research area,which are always blended with gasoline and used in the SI engine.However,the two alcohol fuels both have lower heating value and the hygroscopicity always bring the problem on transportation and storage especially for ethanol.Pentanol is five carbon alcohol fuel.Compared with butanol,pentanol has much closer heating value to that of PRF,insoluble in water and better self-ignition performance.The engine studies of pentanol on SI engine,diesel engine and HCCI engine all show pentanol is an promising alternative fuel.However,there are few researches on pentanol fuels because of the high cost,especially the fundamental study on the effect of isomers on the laminar combustion.In the recent years,a lot research have been conducted on propanol,butanol and octane isomers.But a very comprehensive study can not be developed with these fuels,as the carbon chain of propanol and butanol are not so long and there are just C-H groups in octane.Petanol has eight isomers with both hydroxyl group and C-H groups,and is very suitable to be conducted as isomers.There are two sections in this study covering six pentanol isomers.The first part is the laminar combustion study*,and the second part is the chemical kinetics study.There are two sections in this study.The first section is experimental study of the laminar combustion characteristics on six pentanol isomers with constant volume chamber and spherical propagating flame at different initial temperatures and pressures.Laminar flame speeds of the six pentanol isomers were measured and flame instability characteristics were analyzed.Because of different structures of the isomers,laminar flame speeds of the isomers are different.The isomers were divided into two groups according to the structure and comparisons were made.Results show that laminar flame speeds of the pentanol-air mixtures increase with the increase of initial temperature,and decrease with the increase of initial pressure,and give the peak value between equivalence ratio of 1.0 and 1.1.For six pentanol isomers,laminar flame speed of 1-pentanol-air mixture is the fastest,following by 2-pentanol,3-pentanol,2-methyl-1-butanol and 3-methyl-1-butanol which all have one branched chain of methyl or hydroxyl group,and the values for the four pentanol isomers are very close.2-Methyl-2-butanol-air mixture has two branched chains with one methyl group and one hydroxyl group attaching to the same carbon,and laminar flame speed is the lowest.Results indicate that the more branching chain,the slower the laminar flame speed.The hydroxyl and methyl group show similar effect on the laminar flame speed when working as the branched chain.Six pentanol isomers-air mixtures show similar flame instability characteristics at the same initial conditions.The second section in this paper is the chemical kinetics studies on the pentanol isomers.Mechanisms have been developed for the n-pentanol and 2-methyl-1-butanol,which were improved in this study with different experimental results,like laminar flame speed obtained in this study,JSR data and ignition delays.A new high temperature mechanism of n-pentanol was developed in this study with the open software,RMG,including both pyrolysis and oxidation mechanism.Pyrolysis experiments were conducted with the pyrolysis experimental setup in Ghent uinversity.With the available experimental results and the new pyrolysis experimental data,the RMG model were improved.Finally,the new developed mechanism(RMG mechanism)were compared with two recently developed oxidation mechanisms of 1-pentanol(NUI mechanism and Li mechanism),and comparsion were analyzed on the differences between the isomers.Two recently developed oxidation mechanisms of 1-pentanol(NUI mechanism and Li mechanism)were compared with the new developed mechanism(RMG mechanism).Results show that the three mechanisms can well predict the experimental data of laminar flame speed,while large discrepancy between the prediction of Li model and the experimental data is presented for ignition delays.RMG model can well predict the ignition delays at high temperature,while over-predict the ignition delays when T< 850 K.According to the analysis of the reaction pathway on laminar flame speed,the pentanol isomers are all initial consumed through H abstraction reactions,and the hydroxypentyl and the pentoxy radicals are mostly consumed through the b siccison and produce small molecules.N-butene mainly produces in 1-pentanol-air flames,2-butene mainly produces in 2-methyl-1-butanol-air flames and iso-butene mainly produces in 3-methyl-1-butanol-air flames,which indicate their differences in chemical structures and reaction pathways of pentanol isomers.