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This work experimentally investigates how the dwell time between pilot injection and main injection influences combustion characteristics and emissions (NOx, CO, THC and Smoke) in a single-cylinder DI diesel engine. Additionally, results from diesel injection are compared with those shown in dimethyl ether (DME) injection under the identical injection strategy to demonstrate the sensitivity of the combustion characteristics and emissions to changes of the fuel type. Two fuel injection systems are applied for this experiment due to the differences of fuel characteristic with regard to physical and chemical properties. The injection strategy is accomplished by varying the dwell time (10°CA, 16°CA and 22°CA) between injections at five main injection timings (-4°CA aTDC, -2°CA aTDC, TDC, 2°CA aTDC and 4°CA aTDC). It was found that pilot injection offers good potential to lower the heat-release rate with reduced pressure traces regardless of the dwell time between injections and fuel type.

This study experimentally investigates the control system and the algorithm after constructing a HCCI combustion control system for the development of a small HCCI engine fuelled with Dimethyl Ether (DME). This system can control four throttles for the mixing ratio of three gases of in-cylinder (stoichiometric pre-mixture, hot EGR gas and cold EGR gas). At first, the combustion behavior for combustion phasing retarded operation with cold and hot EGR was examined. Then, the potential of model-based and feed back control for HCCI combustion with change of the demand of IMEP was investigated. In the end, the limit of combustion-phasing retard for IMEP and PRR was explored. Results shows that to get high IMEP with acceptable PRR and low coefficient of variation of IMEP, crank angle of 50% heat release (CA50) should be controlled at constant phasing in the expansion stroke. CA50 can be controlled by changing the ratio of pre-mixture, hot EGR gas and cold EGR gas with throttles.

Auto-ignition, which is observed in homogeneous and premixed charge compression ignition engines, allows expansion of the lean flammability limit of engine operation and realization of stable ignition and combustion over a range of ultra-lean conditions, where NOx emissions are very low. In this study, the basic combustion mechanism of auto-ignition and combustion was studied with initial mixture temperatures and compression speeds for n-butane and dimethyl ether. A single-mode type heat release process was observed with n-butane in the homogeneous charge compression ignition test engine.

ATAC (Active Thermo-Atmosphere Combustion) is autoignition combustion in two stroke engines, which occurs by diluting trapped Fuel-Air mixture with residual gas to maintain a high temperature at low load operation. In this study, two-stroke ATAC engine testing was carried out to obtain fundamental knowledge for controlling the autoignition and combustion characteristics in this premixed charge compression-ignition combustion engine. The influences of delivery ratio, equivalence ratio and enginespeed (i.e. compression speed) on autoignition timing, autoignition temperature and combustion duration were investigated. It was found that the ATAC autoignition temperature and combustion duration did not depend on the delivery ratio and equivalence ratio, but were determined by the individual fuel characteristics. Increasing the compression speed reduced the ATAC autoignition temperature a little.