Research On The Topological Characterization Of Combustion Reaction Zone And Its Mapping Relationship Of Combustion And Emission Characteristics

Fuel consumption regulations and emission regulations are becoming more and more stringent,and further reducing engine pollutant emissions and improving efficiency have become the fundamental requirements for the continued long-term existence and development of internal combustion engines.The progress of internal combustion engine combustion technology and the optimization of vehicle fuel composition are the two main ways to reduce internal combustion engine pollutant emissions and improve efficiency.The coordinated development of them has become an inevitable trend.However,the current researches on fuel diversification and combustion technology are relatively open-loop and qualitative analysis.Fuel optimization is generally characterized in a relative general way such as the blending ratio and content of the components.In addition,the single physical and chemical index of fuel(distillation range,octane number,etc.)has no obvious or non-monotonic correlation with fuel combustion,emission performance or engine performance.The topological index of the combustion reaction zone coupled with the fuel molecular topology and boundary parameters can more accurately predict the combustion effect and harmful emissions of the fuel,so it is of great significance to realize the quantitative characterization of the combustion reaction zone.The topological characterization of the combustion reaction zone includes the quantitative characterization of fuel and the quantitative characterization of the thermal-physical-chemical state of the reaction zone.The quantitative characterization of fuel is realized by using fuel topology index;the thermal-physical-chemical state of the reaction zone is characterized by the equivalent ratio and initial pressure of the constant volume combustion platform,or the compression ratio,operating parameters,and technical parameters of the engine platform.The main purpose of this research is to explore the feasibility of the topological characterization of the combustion reaction zone,and construct reversible quantitative models of two-level indicators of fuel combustion/emission performance(constant volume combustion platform)and engine economy/emission performance(engine platform)based on the combustion reaction zone topology.At the same time,the rapid construction of quantitative models is realized,which provides efficient and fast means for the realization of the fuel-engine collaboration concept based on the phenomenological model.The main contents and conclusions of this research are as follows:1.Topological construction and rationality analysis of the combustion reaction zone.The topology construction method of the combustion reaction zone is introduced.Based on the gray correlation model,it is proved that the topological index has a stronger molecular type characterization ability than simply using the number of carbon atoms.The rationality of fuel quantitative characterization is determined by analyzing the correlation level of fuel quantitative characterization parameters and combustion and emission parameters.1).Topological construction and rationality analysis of elemental alkane combustion reaction zone.The introduction of Balaban central index“B”and Balaban index“J”to construct a binary sequence(B,J)uniquely quantifies the type of alkane molecule.The“B”index mainly contains information about the branching of fuel molecules and the number of carbon atoms;the“J”index mainly contains information about the number of carbon atoms and also contains information about cyclic carbon chains and branching.Introducing the P?variable(product of concentration and pressure)that characterizes the number of reactants and the PT parameter(product of pressure and temperature)that characterizes collision energy to construct a constant volume platform alkane combustion reaction zone topological characterization sequence is(B,J,P?/PT).Based on the grey correlation model,the correlation between combustion emission parameters and the topological index of alkanes is analyzed.It was found that,compared with the simple carbon atom number“CN”,the“B”index and the“J”index,contained two molecular information of branching and carbon atom number,had a better fit with the fuel combustion parameters.The sensitivity of the auto-ignition temperature to the three indices changes with the equivalent ratio showing an obvious law.When the equivalence ratio is 0.8,the local equivalence ratio uniformity is better,which weakens the influence of boundary conditions on the fuel's auto-ignition temperature,and the auto-ignition temperature shows higher sensitivity to the fuel's own characterization parameter;the carbon atom number“CN”is the least correlated with fuel ignition delay among the three molecular characterization parameters.At medium and high temperatures,the“J”index is the most important factor affecting the ignition delay,and the ignition delay at low temperature has the greatest sensitivity to the“B”index;The combustion duration at each equivalent ratio has the greatest sensitivity to the“B”index,which is the most characteristic of fuel molecular branching,followed by the“J”index.The ability of“B”index and“J”index to correlate pressure peaks and peak heat release rates is affected by the equivalent ratio conditions.The peak heat release rates are consistent with the correlation between the two indexs and the pressure peak law.2).The topology construction and rationality analysis of the elemental alcohol combustion reaction zone.On the basis of the quantitative characterization of alkanes,the hydroxyl position information“H”is added,and the unique quantitative characterization sequence(B,J,H)of the elemental alcohol molecule is defined.The“H”index mainly contains the position information of the functional group hydroxyl.The topological characterization sequence of the constant volume platform alcohol combustion reaction zone is constructed as(B,J,H,P?/PT).Based on the grey correlation model,the correlation between combustion emission parameters and alcohol topological index is analyzed.The results show that the hydroxyl position of lower alcohol is the main molecular structure parameter that affects its auto-ignition temperature.The second is the“B”index which tends to characterize the degree of carbon chain branching of alcohol molecules,and the last is the“J”index which tends to characterize the size of the carbon chain of alcohol molecules.In medium and low temperature environments,the“H”index,which characterizes the position of the hydroxyl group,is the leading factor of ignition delay,followed by the“B”index,and the“J”index shows the weakest correlation with the ignition delay.The high temperature environment weakens the advantage of the“H”index in affecting the ignition delay.Then,the degree of carbon chain molecular branching has a strong influence on the ignition delay.Compared to the carbon chain structure and the size of the carbon chain,the position of the hydroxyl group is the dominant factor affecting the combustion rate.The pressure peak and heat release rate peak in the combustion process are the result of the synergy between the fuel type and the combustion environment.The molecular information index has no obvious influence on CO emissions,and the weight of the influence on THC and NO_x emissions is obviously interfered by the equivalent ratio.3).The topology construction and rationality analysis of the multi-component fuel combustion reaction zone.On the basis of the quantitative characterization of elemental components,the characterization value of carbon-carbon bond in aromatic benzene ring was revised,and the characterization sequence of multi-component quantitative characterization(B,J,H)was defined.And with the engine compression ratio“?”as the boundary condition variable,the topological characterization sequence(?,B,J,H)of the combustion reaction zone of the multiple components of the engine platform is constructed.Taking knock intensity as an example,the correlation between the target parameters and the topological variables of the combustion reaction zone is analyzed.It was found that the engine knock intensity and compression ratio showed an approximately linear relationship.There is also a certain correlation between the three fuel indexes and the knock intensity,“B”index has the most obvious influence on the knock intensity.And“J”index mainly contains information about the number of carbon-carbon bonds and the number of cyclic carbon chains.The characterization of“J”index on branching information is not obvious.Therefore,the influence weight of the“J”index on the knock strength is less than the“B”index.“H”index only characterizes the position information of the hydroxyl group,does not include the carbon chain structure and size information,and has the worst impact on the knock intensity.The correlation between the three indices and the octane number and the correlation between the three indices and the knock intensity are consistent,which proves that the molecular structure of the fuel directly determines the octane number of the fuel,further affects the intensity of fuel knock combustion.2.Construction and evaluation of mapping model based on phenomenology.Fuel constant volume combustion,emission performance and engine knock combustion intensity performance are essentially a combustion phenomenon.Data fitting is a fast and core method for the construction of phenomenological mapping models.Therefore,the fuel constant volume combustion,emission parameters,and engine knock intensity are selected as performance indicators,and four regression models with multi-factor and non-linear fitting capabilities are used to perform fitting calculations on performance indicators.To prove that whether it is basic combustion performance or engine performance,there is a mapping relationship between the combustion reaction zone and performance indicators,and the mapping relationship is evaluated by the correlation coefficient.1).Construction of the mapping relationship for the emission parameters of elemental alkane combustion.As for auto-ignition temperature,ignition delay,pressure peak,heat release rate peak and combustion efficiency,the binomial function fitting effect is best.Especially for auto-ignition temperature,pressure peak,heat release rate peak,fitting correlation coefficient is greater than 0.98.For the combustion duration,the exponential function model has the best fitting effect,and the correlation coefficient is as high as 0.9963.The fitting effect of CO in emissions is the worst,with the highest correlation coefficient of 0.9093.The fitting results of NO_x,THC and total particulate mass are good,with correlation coefficients higher than 0.99.2).Construction of the mapping relationship for the combustion emission parameters of elemental alcohols.The fitting effect of the ignition delay exponential function is the best,and the correlation coefficient is 0.9871,while the power function fitting effect of the auto-ignition temperature,combustion duration,pressure peak,peak heat release rate,and combustion efficiency is the best,and the correlation coefficient is above 0.9.The correlation coefficient fitted by the emission parameter function is significantly lower than that of the combustion parameter.Compared with the type of molecules,the combustion process is the dominant factor affecting the emission of alcohol harmful substances.The data series(B,J,H,?)based on molecular characterization information is weak in the quantitative characterization of emission parameters.3).Construction of knock intensity mapping relationship.The power function performs best when(?,B,J,H)is used as the variable parameters,and the correlation coefficient is greater than 0.95;the exponential function model performs best when(?,RON,MON)is used as the variable parameters Good,the correlation coefficient is 0.9282.There is a quantitative mapping relationship between fuel topology and combustion process characteristic parameters and harmful emissions,and the correlation coefficient is higher than0.9.This indicates that in the field of fuel combustion and emissions research,chemical structure related characterizations such as B index and J index are used to quantify the expression of fuel type and Its impact on performance has higher accuracy.3.Rapid mapping construction of combustion reaction zone topology-engine performance based on neural network.The phenomenological quantitative mapping model is obtained based on actual measurement data.It does not reflect the extensive application of the model and the ability to predict"unknown"samples.Therefore,selecting a neural network model with strong generalization ability,taking the topological characterization of the combustion reaction zone(fuel topology index,engine structure and operating parameters)as input,and performance and emissions as the output,can directly realize an engine performance prediction based on the topological characterization of the combustion reaction zone The overall correlation coefficient of the entire training process is R=0.9839,MSE=0.0018,the overall correlation coefficient of the verification process is R=0.9846,MSE=0.0018,and the test process correlation coefficient of the“unknown”sample is R=0.9808,MSE=0.0021.It proves that the prediction model has high accuracy.4.Application and verification of part phenomenological mapping models.Based on the actual engine platform,part phenomenological models are oriented to optimize the fuel product configuration.It is proved that the mapping relationship established in the early stage has a certain parameter value for the estimation of target parameters in the actual engine platform.However,due to the difference between the actual combustion process of the constant volume combustion platform and the engine platform,there are systematic errors between the mapping model and the actual results.In addition,the engine control parameters are extended based on the above conclusions,which proves that the conclusions are still valid when the engine control parameters are adjusted.The engine combustion process can be optimized according to the mapping relationship to guide the refince of aromatics,combined with the adjustment of the ignition timing.