Study On The Quantitative Mapping Relationship From Fuel Structure Molecular To Combustion Characteristic Parameters

Alkane occupies large proportion in the composition of gasoline,which are always used as a characterization of gasoline fuel.It has been becoming a hot topic in recent years that whether alcohol fuel could be the alternative fuel for gasoline.In order to study systematically the two types of fuel combustion process,the research determined by fuel molecular structure was studied in this paper.The premixed combustion mode experiment of single component fuel was carried out on a constant volume bomb platform.During the experiment,the combustion parameters and emission indexes of harmful pollutants were monitored.And the macroscopic combustion characteristics of fuel were analyzed in detail based on research results of microcosmic kinetics mechanism.Subsequently,the model of mapping from the fuel molecular structure to combustion characteristic parameters was established by widely accepted and used machine learning algorithm.It provided a reference method for simplifying the kinetic model and directly predicting the combustion process based on fuel molecular type.The main research contents of this paper include that:In the first part,the fuel with different carbon chain length,different number of branched chains and isomers were experimented by using homogeneous mixed gas constant volume bomb platform with fuel type as the main variable.The reasons for influence of fuel molecules on combustion characteristics under different classification criteria were discussed.The results showed that:?1?Under the condition of initial pressure P=19bar and in the straight-chain alcohol fuel with carbon atom less than or equal to 4,the law of ignition temperature is n-butanol<ethanol<methanol.Because?-carbon atoms of n-butanol have lower bond energy and are easier to dehydrogenate for chain excitation reaction.Because the reaction path of n-butanol is long and the reaction type is complex.The combustion speed of n-butanol is slow and incomplete.It is difficult for methanol to present a large number of core-mode particles through chain growth reaction.The non-uniform mixture of n-butanol and the slow combustion rate lead to transition of the nuclear mode particles to the aggregates,resulting in a large number of particles of large size.?2?Under the condition of the initial pressure P=19bar,n-heptane has higher reactivity than n-pentane in the C₅-C₁₀ straight-chain alkanes experiment.Because the elemental reaction of n-pentane promoting the combustion process in the low-temperature combustion process has a slower reaction rate than n-heptane.N-pentane could enter the NTC region earlier than n-heptane.With the decrease of the equivalent ratio,the combustion rate gradually slows down,which leads to the transformation of the nuclear mode particles discharged to the aggregates.So the mass concentration of the aggregates increases under the condition of low equivalence ratio.?3?Under the condition of the initial pressure P=19bar,the ignition temperature of linear alcohols is higher than that of n-alkanes.The combustion reaction path of alcohols is relatively simple and the elemental reaction types of alkanes vary with the external conditions.So the reactivity of straight chain alcohol fuel is low.?4?Under the condition of the initial pressure P=15bar and maximum combustion temperature is less than 1000K,n-butanol has lower ignition temperature in the three isomers of butanol.Sec-butanol could not initiate intramolecular dehydration.So chain excitation and chain propagation reactions are performed for the three butanols to make no obvious difference on ignition temperature between sec-butanol and iso-butanol.Iso-butanol burns faster and more efficiently because it is mixed with air more evenly.The emission of iso-butanol particles is mainly distributed in the nuclear mode region.Although n-butanol emitted fewer particles,its mass concentration was larger.?5?Under the condition of the initial pressure P=15bar and maximum combustion temperature is less than 900K,iso-octane is less reactive with the same number of main chain carbon atoms but different number of branch chains.Some of the dehydrogenation reactions inhibit the combustion process which belong to chain excited elementary reactions.And partial oxidation products of isooctane dehydrogenation still hinder the combustion process in the process of isomerization.The presence of three methyl branched chains in the iso-octane molecule increases the stress of the transition ring compared to n-pentane and 2-methylpentane.So activation energy is increased and the reaction rate is decreased.In the second part,the quantitative mapping model of fuel molecule to combustion characteristics was constructed with BP neural network.Its input parameters were composed of molecular structure descriptors and initial boundary conditions and its output parameters were combustion characteristic values obtained from experiments.The quantitative mapping model was trained and tested through experimental samples.The error analysis of combustion output parameters was carried out and the generalization ability of the model was evaluated.The results showed that:?1?The correlation coefficients of quantitative mapping model in the training,validation and testing on combustion characteristic parameters are all greater than0.965,such as ignition temperature,peak pressure and maximum combustion temperature.It can be concluded that the quantitative mapping model has good applicability for the fitting prediction of combustion characteristic parameters in this experiment.It can be seen from the phenomenon that the correlation coefficient of the verification process of instantaneous heat release rate is smaller than that of the training and testing process that the quantitative mapping model has a strong sensitivity to the original error of the sample.So the quantitative model is reliable in predicting combustion parameters.?2?The quantitative mapping model evaluates the generalization ability of the three molecular structure characteristics which could include carbon chain length,isomer,and number of branched chains.And the evaluation index is the deviation percentage of the fitting value relative to the experimental value.The proportion of samples the three molecular structure characteristics corresponding to with combustion parameters?except peak heat release rate?within the range of 0-10%deviation percentage is over 66%.Therefore,the quantitative mapping model can be considered to have a good generalization effect on the molecular characteristics.