Intelligent coolant control – a potential technology to improve controlled auto ignition combustion

Controlled Auto Ignition (CAI) uses compression heat to auto ignite a homogeneous air/fuel mixture in an internal combustion engine. Using internal exhaust gas recirculation (IEGR) as an indirect control method, CAI offers superior fuel economy and pollutant emission reductions. Practically, this can readily be achieved by a method of early exhaust valve closure and late inlet valve opening to trap a large quantity of exhaust gas residuals within the cylinder from one cycle to the next. However, it has been found that the IEGR promoted CAI combustion largely depends on the quantity and quality of the IEGR, which in turn depends upon the combustion quality of previous cycle, engine speed, load, etc. At low loads, where the overall engine temperature is low, although an extra large amount of IEGR has been used, CAI becomes difficult to achieve. At high loads, the IEGR is much hotter. The CAI combustion is so strong that it may potentially be converted into detonation combustion. It is difficult to control the CAI combustion quality without external interferences. Engine coolant controls engine heat transfer performance. By physically adjusting its temperature, it was found in this research that IEGR promoted CAI combustion can be significantly extended by increasing engine coolant temperature.