Investigation On The Combustion Chemistry Of Two Typical Hydrocarbon And Bio-derived Fuels With Isomeric Structures

The development of human society is highly dependent on energy,and in the foreseeable future,traditional fossil fuels,which is mainly composed of hydrocarbons,will still be the key drivers of global economic growth.Butanes,as the smallest alkanes with isomeric structures(n-butane and iso-butane),are not only the major components of liquefied petroleum gas(LPG),but also widely used as model fuels for longer-chain alkanes components in gasoline,kerosene and diesel.In addition,investigations on butane isomers combustion are crucial to study the isomeric effect in terms of alkanes.On the other hand,fossil fuels are unable to regenerate and cause a series of serious ecological problems during burning,which has been a challenge to energy security and environmental protection.Thus,bio-derived fuels,with renewable characteristic and low pollution emissions,have been used in transportation fields.More and more attention was paid to the alcohol for its excellent performance in engines,and it has been extensively researched.Propanols are the smallest alcoholic fuels with normal and branched isomers(n-propanol and iso-propanol),which bridge the small molecule alcohols(methanol,ethanol)and higher alcohols(such as butanol and pentanol).In this work,the combustion experiments and kinetic models of two typical hydrocarbons and alcohols with isomeric structures were investigated,with the aim to explore the influence of molecular structure on combustion process as well as mechanism.In addition,these fuels play a significant role in the C0-C4 core mechanism.The development,validation and optimization of butane and propanol kinetic models contribute to the improvement of core mechanism accuracy.A laminar flow reactor apparatus combined with synchrotron vacuum ultraviolet photoionization mass spectrometry(SVUV-PIMS)was used to study the butane isomers and propanol isomers pyrolysis.Butane isomers pyrolysis were performed under temperatures ranging from 700 to 1500 K and pressures at 30,150 and 760 Torr to research the fall-off effects of unimolecular reactions of alkanes.Pyrolysis experiments of propanol isomers were conducted at the temperatures of 1000-1400 K and the pressure of 10 Torr to ensure the detection of unstable species like radicals and enols.Laminar flame speeds of both n-butane/air and iso-butane/air mixtures were also measured at 298 K and pressures of 1-10 atm to study the isomeric effects in combustion.Two sets of spherically propagating flame apparatus were used.One was single cylindrical combustion apparatus in Shanghai Jiao Tong University,and the other was dual-chamber combustion apparatus in Princeton University.The flame speed results obtained from the two different apparatus agree well.On the basis of experimental studies,detailed kinetic models of butane isomers and propanol isomers were developed and validated against the new experimental data in present work.Rate of production(ROP)analysis and sensitivity analysis were conducted to reveal the main decomposition pathways of butane isomers and propanol isomers as well as formation pathways of products.For butane isomers,it is recognized that the initial decomposition temperature of iso-butane was slightly lower than that of n-butane mainly due to the lower C-C bond dissociation energies of iso-butane.Compared with n-butane flames,iso-butane flame speeds are slower under identical conditions,which can be explained by the fact that vinyl and allyl radicals are produced respectively in normal and branched butane flames.Furthermore,a stronger pressure dependence in iso-butane flames than n-butane was confirmed because of the high sensitivity of methyl radical recombination reaction.Reaction pathways towards C2 and C3 species pool are also emphasized in n-and iso-butane respectively.In propanol isomers pyrolysis,it is also observed that branched alcohol owns lower dissociation temperature than the normal species.For iso-propanol,dehydration is the most sensitive to primary consumption and controls production of hydrocarbons,while the a-C-C bond dissociation reaction contributes to abundant radicals.Hydrogen abstraction reactions are another pathways to iso-propanol pyrolysis,contributing to the formation of most oxygen species.While in n-propanol pyrolysis,hydrogen abstraction reactions show larger contributions to fuel consumption than these of dehydration and C-C bond dissociation reactions.Meanwhile,the present model of butane isomers was validated against experimental data available in the literature,which broadens the scope of model application for longer-chain fuels under engine conditions.