Abstract
Keywords - Diesel, HCCI, External Mixture Formation
Abstract - Diesel HCCI (Homogenous Charge Compression Ignition) is a combustion technology showing great promise for the reduction of oxides of nitrogen and particulate matter from Diesel engines. Our proposed implementation of HCCI is a mixed-mode concept, which relies on a direct-injection system that is optimized exclusively for direct-injection. To accomplish HCCI, an external fuel atomizer is used. By decoupling the direct-injection from the HCCI mixture formation, the injector and combustion chamber can be optimized much more aggressively for DI (Direct-Injection) operation. This system allows efficient high load operation in DI mode without compromising performance, low to mid-load operation in HCCI mode, and a region in between where both systems operate together.
External mixture formation for Diesel fuel has largely been abandoned in favor of internal mixture formation using the DI system. This is partially due to previous attempts at Diesel HCCI requiring intake air heating in the range to 100 °C to 200 °C and low compression ratio engines. Using a highly effective atomization device, Diesel HCCI operation with external mixture formation has been demonstrated at a compression ratio of 18:1, intake temperatures in the range of 15 °C to 60 °C, and up to a maximum load of 4.7 bar IMEP. With this technique, the traditional problems of external Diesel mixture formation, such as high intake heating, low compression ratio, wall wetting, and soot formation, are largely avoided.
This HCCI mode operation has been demonstrated on a single-cylinder engine (1/4 of a recent production 2.2L engine) in a collaboration between Ohio State University and the FKFS (Research Institute of Automotive Engineering and Vehicle Engines Stuttgart). The concept has demonstrated extremely low levels of nitrogen oxides (< 4 ppm) and smoke (< 0.03 FSN) over a large range of operating conditions. The combustion technique has shown good insensitivity over a wide range of operating conditions such as engine speed, load, boost pressure, intake temperature, and EGR rate. Experimental results for these parameter sweeps as well as for mixed-mixed mode combustion are presented and discussed.