Numerical Simulation Of Oxygen-enriched Combustion Mechanism And Emission Characteristics In Diesel Engine

Oxygen-enriched combustion technique can not only improve the mechanical efficiency, the indicated power, the indicated specific fuel consumption and CO, Soot etc, but also it can decrease the fuel ignition point, widen the application range of poor quality fuel and recover the power of engine running at altitude. This combustion technique has attracted considerable attentions due to its outstanding performance. Because of this, this paper investigated the influence of intake air oxygen concentration on combustion mechanism and emission characteristics in diesel engine.Firstly, this paper studied the influence of oxygen concentration on the stoichiometric air-fuel ratio, calorific value of theoretical mixture gas, the ignition delay, the indicated power, the effective power, the mechanical efficiency, the indicated specific fuel consumption by using logical reasoning method in diesel engine. The result of the theoretical analysis indicate that with the increasing of oxygen concentration, the stoichiometric air-fuel ratio, calorific value of theoretical mixture gas, the indicated power, the effective power, the mechanical efficiency were enhanced, the stoichiometric air-fuel ratio and the indicated specific fuel consumption were declined, and the ignition delay got short apparently. But the effects on them got smaller and smaller along with the growing of the oxygen concentration.Next, this paper used the IC Engine single-zone model of CHEMKIN-PRO to simulate the oxidation process of n-heptane, aim at analyzing the effects of oxygen concentration on some important reaction paths which happened at low temperature, middle temperature and high temperature. The formation mechanism of CO, CO2and NO were also studied in this paper.Finally, giving the effects of in-cylinder working fluid flow and the inhomogeneity of mixture on the combustion and emission performance of diesel engine, a single cylinder135diesel text engine was simulated with the application of Three Dimensional simulation program KIVA-3V to study the effects of oxygen-enriched intake air on the combustion and emission performance of diesel engine. The simulation results showed that under the equal amount of the total intake air, the averaged cylinder temperature and pressure both increased with the rise of intake oxygen concentration, while the moment of the in-cylinder peak temperature and pressure happened in advance. The combustion heat release rate and accumulated heat release of the fuel increased, the moment of the combustion heat release rate is advanced, the ignition delay and the combustion duration got short, but the influence of the increased intake oxygen concentration on accumulated heat release and the ignition delay was no longer apparent. At the same time, the emissions of Soot and CO were inhibited, but the NO emission increased remarkably.This paper studied the combustion process and emission characteristics of Oxygen-enriched combustion in diesel engine from three aspects of logical reasoning method, mechanism analyzing and Three Dimensional simulation. It is helpful to understand Oxygen-enriched combustion and emission characteristics of diesel engine in different ways, laying a solid theoretical foundation for the future experiment research.