Investigation on the chemical equilibrium products for CnHmOlNk type fuels using equilibrium constants database

Abstract

As international concern that regards NOx emissions from the shipping industry increases, it is challenging and urgent to reduce ships’ NOx emissions. According to the extended Zeldovich, the determination of the equilibrium concentration of combustion products is crucial for the prediction of NO formation in internal combustion engines. In the present work, an equilibrium constants database of related chemical reactions is established based on the theory that the total Gibbs energy reaches its minimum when a reaction achieves equilibrium. Afterward, a combustion product equilibrium model with twelve species considered is established based on the equilibrium constants database. The accuracy of the model is significantly improved compared with the commonly used ones which calculate the equilibrium constants through fitting function. The errors of the model are within 2% compared with STANJAN which is widely used for chemical equilibrium analysis. The model results are comparable to STANJAN. Afterward, the effects of the temperature, pressure, fuel–air equivalence ratio, O2 concentration, N2 concentration, Ar concentration and fuel type on the equilibrium mole fractions of the combustion products are investigated. The equilibrium concentration of combustion products is significantly affected by the temperature, O2 concentration and fuel–air equivalence ratio, but slightly influenced by the pressure and Ar concentration. The existence of O and N in the fuel slightly reduces the NO equilibrium mole fraction of the combustion products at the same temperature, pressure and fuel–air equivalence ratio. However, the ratio of molar carbon hydrogen in the fuel and the existence of O and N in the fuel have a significant impact on the CO2 mole fraction of the combustion products.