| With the developing of automobile industry, the number of cars increases so sharply, that environment and energy sources are faced with the highest pressure so far. All the developing and developed countries have established more and more rigorous regulation. In order to release the pressure of energy source and meet the regulation, new style of combustion must be invented, which is more efficiency and clean. Furthermore, the alternative fuel should also be developed for the same purpose.Controlled auto ignition (CAI) is the combusting process of in-cylinder homogeneous charge, combining the advantages of gasoline engine and diesel engine, which have higher efficiency and lower NOx and PM emissions. At the meantime of experiment study, the study on modeling CAI engines have gained plentiful achievement on several aspects, such as combustion model, combustion mechanism and variable parameters, resently this study are focused on more and more concerns. However the problems of entire load and speed range limit the application of CAI combustion. Because CAI are controlled by chemstry kinetics, not by flame spread and turblent, in order to realise CAI combustion, the composition, pressure and temperature of the in-cylinder charge at IVC must be controlled properly. Varialbe vavle timing which is able to change the capatured hot exhaust gas shows the potential of controling CAI combustion.In this paper, AURORA module in the large-scale CHEMKIN, GT-POWER and MATLAB software are applied to set up CAI combustion model. The VVT system model is established by GT-POWER software, gasoline combustion model by CHEMKIN software. The heat release rate and in-cylinder composition concentration are caculated by MATLAB software.The study indicates the following conclusion: 1. Gasoline CAI combusion model are applied to analyse the influence of the different valve timing including exhaust valve close timing, intake valve open timing. The results indicates : EVC of the crank angle from the late change to an earlier, larger EGR rate can achieve CAI combustion, and combustion and gas exchange of the CAI Engine has a strong influence on the engine parameters and the nature of charge significant impact. It can be concluded that the use of valve timing strategy can effectively control the IVC-point nature of charge and thus control of CAI combustion ignition and combustion process. EVC is the main decision to close the residual trapping emissions, engine load and therefore decided to instruct the efficiency of POWER and inflation. Intake valve open timing of the EGR rate and the impact load is secondary. Intake valve is open when the gas pump losses and residual gas in the back of the intake valve has a significant influence.2. There is a certain relationship between CAI combustion ignition (CA10) and the temperature of the mixture (T10) at 10°CA BTDC. This shows that, based on the CAI residual gas internal combustion ignition (CA10) only the main points from the temperature of the mixture before the decision, the only point when the T10 are high, the ignition in advance, on the contrary, he ignition later. Therefore, by controlling the T10, can be achieved on the CAI the effective control of ignition at all times.3. Increasing the negative overlap angle, for CAI combustion EGR rate can change from 38% to 76%.The results indicates : the internal EGR has the dual function to the CAI , one function is to heat fresh air to make it easy to fire;the other function is the heat capacity and the dilution function,which may reduce the chemical reaction speed , postpone the fire, lengthen the burning duration and depressurize elevating rate. When EGR rate is smaller than 54.1% heat function performance to be remarkable. Along with EGR rate increasing, fire beginning spot is ahead of time; When EGR rate is bigger than 54.1%, reducing the chemical reaction rate act to be remarkable role. Along with the EGR rate increasing, the fire beginning spot postpones.4. Through the simulation of Intake heating and found that intake heating increased load up-limit. When in a certain engine speed (1000r/min for example), with the increase in intake air temperature, T10 will be increases, so to determine the corresponding time will also advance the ignition. Therefore, the use of heating control intake T10 is a direct and effective way, and can expand the regional scope of CAI combustion.5. Simulation analysis of a different speed, the negative overlap angle trapped EGR gas distribution. As the speed increased, the air campaign to strengthen the cylinder EGR has a significant impact. In addition, this paper has been calculated under different rotational speed to achieve the lowest CAI combustion temperature and EGR quantity IVC and simulation predicted CAI gasoline CAI combustion engine speed and load range. |
