| This paper proposes the study of variable intake-air composition effect on combustion and emission characteristics of diesel engine, this technology can improve the combustion characteristics and reduce the emission of many harmful gas, what’s more, it can improve a series of problems, such as ignition difficulty at high altitude area, loss of power, low heat efficiency and incomplete combustion. But this technology is still in the stage of research, lots of technical problems still exist.This paper consists of two main parts, one part is oxygen-rich intake-air combustion, the other part is nitrogen-rich intake-air combustion. In order to realize the purpose of this research, this paper carry out relevant simulation analysis by the software of Chemkin-pro and AVL-Fire. First, establish the chemical reaction mechanism of n-heptane by Chemkin-pro. In order to better predict the effect of variable intake-air composition on the emission characteristics of diesel engine, on the basis of the original chemical reaction mechanism, the mechanism model of NO formation was added,a new chemical reaction mechanism was established.In this paper, during the study of the process of combustion with oxygen-rich intake-air, 4 different concentrations of oxygen were set, respectively is 23%, 25%, 27% and 29%. Study on the change trend of temperature,heat release rate, total heat release rate, pressure, pressure rise rate and other related parameters compared with natural intake state. It was found that with the increase of oxygen concentration, these parameters are increase. So oxygen-rich intake-air can effectively increase the dynamic performance of diesel engine. During the study of the effect of oxygen-rich intake-air on the emission characteristics of diesel engine. Low temperature and hypoxia are the main factors that lead to the formation of CO. So oxygen-rich intake-air can reduce the emissions of CO effectively. During the study of the effect of oxygen-rich intake-air on the emission characteristics of HC, select CH3、CH4、CH3O、CH2O、C2H5 and C3H6 six kind of main products as research objects. we found that HC decreased with the rising of oxygen by simulation analysis. Studying shows that the higher of oxygen concentration, the more NO produces,and the growth range and growth rate are larger and larger, the moment of NO began to generate also gradually advance. In order to study the effect of fuel injection timing on NO formation, there different injection duration were set up, which are 15°CA, 20°CA and 25°CA. There different injection advance angles were set up, which are 3°CA, 7°CA and 11°CA. Through the study found, under the condition of the same oxygen concentration, the emission of NO decreased with the shortening of the duration of fuel injection and injection advance angle, so we can optimize the emission of NO by changing the fuel injection timing.In this paper, during the study of the process of combustion with nitrogen-rich intake-air, 2 different concentrations of oxygen were set,respectively is 81%and 83%. The result of the study show that nitrogen-rich intake-air will lead to the decrease of peak temperature and pressure compared with natural aspiration. Nitrogen-rich intake-air have great effect on the emission characteristics at the same time, it will increase the fuel’s incomplete combustion, lead to the increase product of CO and HC. In the study of the effects of different rotational speed on the formation of CO and HC, with the decrease of engine speed, the production of CO and HC were decreased. At the same time, the effect of nitrogen-rich intake-air on NO emission was studied, the production of NO will be lower and lower with the increase of nitrogen due to its fire retardant effect. |
PDF Full Text Request