| The engine clean alternative energy research is very important under the world's severe energy and environmental protection situation.Gaseous alkanes are abundant in natural reserves and widely exist in natural gas fields.They are stable in physical and chemical properties and do not produce harmful gases when completely burned.They are ideal clean energy.However,the slow combustion speed,low flammable limit,low density and unstable composition of natural gas lead to problems such as power decline and cycle change increase in the internal combustion engine in use.The study shows that among C1-C3 gaseous alkanes,ethane burns the fastest,followed by propane and methane the slowest;Ethane,propane and methane mixing combustion can increase methane dilute limit,reduce methane loose change coefficient,improve the problem of methane combustion slower,so the common combustion of methane,ethane,propane,and relatively higher calorific value of ethane,propane as the feasibility of the internal combustion engine fuel and combustion performance improve the possibility of larger significance;From the perspective of combustion science,their molecular weights are less than,approximately equal to and greater than the molecular weights of air respectively,and they are representative gaseous fuels.At the same time,ethane,as a theoretical alternative fuel,has not been fully studied yet due to natural reserves and other reasons.Therefore,the research of this paper not only has great theoretical significance,but also has high practical value.In this paper,laminar combustion,cellular instability and self-acceleration characteristics of methane,ethane and propane are studied in the basic constant volume combustion test system.Firstly,a batch processing program for flame shadow image and schlieren image acquired by constant volume combustion is developed,which can easily identify flame contour,accurately calculate flame radius and center,and can be applied to the calculation of self-accelerating index,greatly improving the accuracy and speed of subsequent experimental data calculation.Then,based on the data processing of flame shadow image calculation,got the mark stein length of three kinds of fuel,and no stretched laminar burning velocity changing with the pressure,equivalent ratio,confirmed that the molecular weight gas fuel instability change regularity of different sizes,three types of fuel is obtained by fitting respectively applied to the initial condition in high pressure and equivalent than changes in the scope of the laminar burning velocity empirical formula;The results of the linear method and the nonlinear methodfor calculating laminar combustion velocity are compared,and the rationality and necessity of the combination of the nonlinear method and the linear method are verified.Next,we combined with the results of density ratio,flame thickness,Lewis number,flame image and critical Peclet number analysis,the variation rules of cellular instability in flame combustion of three fuels with pressure and equivalent ratio are obtained.The empirical formula of the change of critical Peclet number with pressure and equivalent ratio is obtained.At last,the self-acceleration phenomenon is introduced.The reasons of self-acceleration and its subsequent development are analyzed.The contour variation of self-accelerating flame is studied quantitatively.A quantitative study was made on the characteristics of the development of the cell in the front of the flame under self-acceleration,and the internal relationship between the development and the instability of the cell was analyzed.The change rule of flame morphology characteristic during self-acceleration is analyzed,the self-acceleration index and fractal dimension of three fuels are calculated,and the change rule is analyzed.Within the scope of this paper,the maximum self-accelerating index they can achieve is about 1.36 methane,about 1.4 ethane and propane,and the maximum fractal dimension is 2.26 methane,2.28 ethane and propane,respectively. |
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