Controllability Of Variable Composition Of Intake-air And Combustion Control

The study on controllability of variable composition of intake-air and combustion research as an active control technology aims at sloving the problems of combustion and emissions in engine. In the combustion process of an internal combustion engine, the control mode and effectively organize intake-air of air components of variable density stratification play an important role in improving the cold start combustion and emissions,also play an active role in improving the problem of combustion imbalance in cylinder on different conditions. The variable density distribution and stratification of oxygen-enriched not only reduce the combustion adverse effect of cool-wall and flame-failure, but also reduce the oxygen-enriched degree in the high temperature field, inhibit the negative effect on the increase in NOx emissions. Finally achieve a more effective regional combustion control.Numerical simulation of variable composition of intake-air in intake,compression and combustion process was performed in this paper with CFD software.This paper uses dynamic mesh to simulate engine working process continuously, and uses the Finite-Rate/Eddy-Dissipation model to simulate the engine combustion process. This study mainly divided into two parts:oxygen-enriched variable composition and nitrogen-enriched variable composition. Not only include variable composition control, but also include preliminary analysis on the effects of the combustion. This paper mainly controls injection pressure of enriched gas, injection position, injection angle, injection pulse width and injection mode etc, which takes the basic point of in-cylinder analysis though using the mixture of enriched gas and air, such as researching the variable composition and distribution characteristic in the end of compression process, and achieves the aim of combustion control.In the simulation of the controllability of concentration field in cylinder with variable composition of oxygen-enriched intake, this paper systematic researches the influence characteristic of injection pressure of oxygen-enriched flow, injection position, injection angle, injection pulse width and injection mode etc.As the result show, At low speed, in a certain position (positionⅠ) andα=55°, which can form variable density distribution of oxygen by center thick edge thin in cylinder at the end of compression process. Two-stage injection is better than three-stage injection in variable density distribution of concentration field. The concentration distribution and oxygen-enriched degree by using the strategy of injection later on two-stage injection is better than which uses the strategy of injection first on two-stage injection. The better oxygen-enriched injection time is 30℃A ATDC. With oxygen concentration increases 2% by oxygen-enriched intake, the mean concentration of oxygen improves around 1.2% in sylinder. Therefore, from the economy, we can choose appropriate oxygen-enriched degree. By increasing the oxygen-enriched injection pressure, it is easy to form variable density distribution of oxygen by center thick edge thin in cylinder, and 2-3atm is appropriate.In the simulation of the controllability of concentration field in cylinder with variable composition of nitrogen-enriched intake, this paper also systematic researches the influence characteristic of injection pressure of oxygen-enriched flow, injection position, injection angle, injection pulse width and injection mode etc. As the result show, at medium speed, in a certain position (positionⅢ) andθ=45°, which can form variable density distribution of oxygen by center thick edge thin in cylinder at the end of compression process. Two-stage injection is better than three-stage injection in variable density distribution of concentration field. The better nitrogen-enriched injection time is 90℃A ATDC on two-stage injection. With nitrogen concentration increases 2% by nitrogen-enriched intake, the mean concentration of oxygen declines around 0.3% in sylinder. Therefore, from the economy, we can choose appropriate nitrogen-enriched degree. The injection pressure is unfavorable and exorbitant, and 2-3atm is appropriate.In addition, the study simulates oxygen-enriched combustion of different intake-air mode at low speed. When use the mode of controllable composition distribution of oxygen-enriched intake, combustion pressure and combustion temperature are higher, generation of CO is lower than natural oxygen-enriched intake which has the same oxygen degree. With the higher temperature of intak-air, the combustion pressure and combustion temperature become higher in degree, which can reduce the generation of CO.The study also simulates nitrogen-enriched combustion of different intake-air mode at medium speed. The mode of controllable component distribution of nitrogen-enriched intake-air can improve combustion performance. The generation of CO is lower than natural nitrogen-enriched intake. As intake temperature increases, combustion temperature increases, the generation of CO does not change significantly.Throughout researching variable components distribution control of intake-air, enriched gas injection can realize variable density distribution control of concentration field of intake in engine, and improve combustion performance, provide the basis for enriched gas control. Thus, through more efficient regional combustion control, realize the combustion chamber regional combustion balance and combustion temperature uniformity, reduce the maximum combustion temperature, slove high combustion temperature and NOx emissions which are caused by conventional region-wide oxygen-enriched. Inhibite the negative impact of the increase of NOx emissions due to oxygen-enriched in the combustion exuberant area.Therefore, it is the key technology of application of oxygen-enriched and nitrogen-enriched combustion in-depth development though organizing regional oxygen-enriched degree in an internal combustion engine intake process, combining the difference of combustion region in engine, reforming composition of variable density distribution and controling layering.