Research and optimization of valve curve parameters for homogeneous charge compression ignition based on variable valve actuation

Abstract

Homogeneous charge compression ignition (HCCI) can improve engine emissions and fuel consumption. HCCI based on variable valve actuation (VVA) benefits from the wide application of VVA technology, which makes it easier to popularize. However, most VVA mechanisms are based on cam drive and inherit from spark ignition (SI) engine, the valve lift and duration can only be increased or decreased simultaneously. Therefore, the above VVA mechanisms cannot give full play to the performance of HCCI. The control parameters of valve curve are simplified into maximum valve lift and duration. At different speeds, this paper uses GT-POWER to first study the influence of the matching relationship between maximum valve lift and valve duration on HCCI combustion economy, and then study the design strategies of HCCI valve curve with fuel economy as the target. At same speed, multiple valve curves can achieve almost the same load range, however, among those valve curves, under the condition that the pumping loss and temperature in the cylinder are almost identical, the valve curve with lower cylinder volumetric efficiency can achieve lower indicated specific fuel consumption (ISFC). For low and medium loads, there is a better matching relationship of valve curve for each speed. For high loads, large maximum valve lift combines with large valve duration is easy to obtain lower ISFC in most situations, but the ISFC deteriorates significantly for low and medium loads. The fixed valve curve can obtain a smaller IMEP range or a higher ISFC; the optimized valve parameters combine with SI valve control strategy and VVT of 110°CA can only optimize the load range of partial speeds, the load range of other speeds will attenuation and the ISFC is higher; the newly designed valve curve scheme in this paper can achieve the maximum IMEP range and relatively low ISFC.