Comparisons of Computed and Measured Results for a HSDI Diesel Engine Operating Under HCCI Mode

As engine researchers are facing the task of designing more powerful, more fuel efficient and less polluting engines, a large amount of research has been focused towards homogeneous charge compression ignition (HCCI) operation for diesel engines. Ignition timing of HCCI operation is controlled by a number of factors including intake temperatures, exhaust gas recirculation (EGR) and injection timing to name a few. This study focuses on the computational modeling of an optically accessible high-speed direct-injection (HSDI) small bore diesel engine. In order to capture the phenomena of HCCI operation, the KIVA computational code package has been outfitted with an improved and optimized Shell autoignition model, the extended Zeldovich thermal NO_x model, and soot formation and oxidation models. With the above named models in place, several cases were computed and compared to experimentally measured data and captured images of the DIATA test engine. The selected cases utilized both single and multiple injection schemes with output ranging from 3 to 7 bars IMEP. Results show that the computational code was able to match both pressure and heat release rates for all cases accurately. Ignition timing and peak combustion pressures were precisely predicted and successful attempts were also made for image comparison of spray penetration along with flame luminosity generated within the experimental optical engine. NO_x emissions were shown to be produced primarily in regions in excess of 2500 K whereas soot formation occurred primarily along the piston bowl wall. Soot oxidation was suppressed as a lack of in-cylinder flow prevented soot to reach areas of high oxygen concentration within the squish region.