Abstract
Keywords - Gasoline HCCI, Combustion Switching, VEL, Internal EGR, A/F
In this paper, SI-HCCI combustion switching is investigated, which is one of the issues of a gasoline HCCI engine. The main challenge in switching combustion is how to change in-cylinder conditions (for example, A/F, internal EGR, etc.), because the conditions of HCCI are different from those of SI. The performance of one switching method that changes the in-cylinder conditions by changing the target set values of engine parameters (for example, throttle angle and valve timing) at the same time is investigated. For this investigation, an in-line 4-cylinder gasoline engine is used, which has the variable valve systems and the direct injection system. From experimental results from SI to HCCI, the incylinder condition becomes different from desirable SI and HCCI. The different condition is SI under superfluous lean A/F. So, misfire the variance amount of BMEP are occurred. Therefore, it is clear that A/F and internal EGR need to be precisely controlled during the switching period. To solve the problem mentioned above, we propose a new switching method. In switching from SI to HCCI, the concept of the proposed method is as follows. At the first step, the in-cylinder condition is changed to the particular SI in which A/F is kept stoichiometric and internal EGR is increased. At the second step, the condition mode is switched from the particular SI to HCCI by making A/F lean and increasing internal EGR. The proposed method controls in-cylinder conditions during the switching period precisely by operating throttle and variable valve systems in cooperation. From experiments, it is made clear that the proposed method is also valid for the reverse combustion switching. In addition, the optimal in-cylinder gas behavior during combustion switching is investigated by using the engine cycle simulator, in order to clarify the transient phenomena. As a result, the transient control of the amount of intake air is important to keep the combustion stability, and the method for controlling it optimally is figured out.