Study On The Exergy Loss Mechanism Of Combustion Of Natural Gas Under The Control Of Thermodynamic Boundary

With the increasingly serious problems of energy crisis and climate change,natural gas,as a low-carbon energy with abundant global reserves,has attracted extensive attention.The irreversibility produced in the combustion process of engine hinders the conversion of fuel chemical exergy to work,and it is difficult to identify through the analysis of the first law of thermodynamics.Based on the local equilibrium hypothesis and chemical reaction kinetics,this paper makes an in-depth study on the mechanism of exergy loss in the combustion process of natural gas by using the methods of numerical simulation and theoretical derivation.In this paper,the calculation model of irreversible loss in the non-equilibrium natural gas combustion process is established,the irreversible loss sources in the combustion process of natural gas are grouped,and the distribution of irreversible loss sources is clarified.Under different thermodynamic boundaries,the distribution characteristics of each reaction group relative to time and loss rate remain basically unchanged.On this basis,it is found that the total combustion loss is mainly affected by irreversible combustion loss and incomplete combustion loss.Among them,the irreversible loss is affected by the inherent irreversibility of combustion and the thermodynamic state of combustion.The incomplete combustion loss is mainly affected by dissociation and the degree of combustion completeness.The combustion chemical reaction process can be affected by adjusting the thermodynamic boundary.Adjusting the initial thermodynamic boundary of combustion can reduce the total loss of combustion process,and the minimum total loss can be reduced to about 17.8% at 6MPa initial pressure;Under the limit condition of 40 MPa,the total combustion loss of natural gas can be further reduced to 15.6%.In addition,this paper also studies the distribution of total exergy loss of different fuels.It is found that the influence law of thermodynamic boundary on exergy loss ratio is similar of different fuels.In addition to the influence of thermodynamic boundary on exergy loss,the composition of fuel also has a great influence on exergy loss.In this paper,the diesel natural gas dual-fuel combustion process is analyzed with the exploration of the influence of initial fuel composition on the combustion irreversibility.The change of initial fuel composition mainly affects the ratio of fuel low heat value to chemical exergy(heat / exergy ratio).The research shows that the heat / exergy ratio has a strong correlation with the combustion irreversibility,and changing the heat / fuel ratio can significantly reduce the combustion irreversibility.The total exergy loss of combustion plays a leading role in the transformation from initial chemical fuel to thermal fuel and mechanical fuel.Changing the compression ratio,specific heat ratio and other methods improve the conversion efficiency from thermal and mechanical to work,and finally the high thermal efficiency of the engine can be realized.