Experimental investigation of the effect of fuel injection timing on the combustion regime of the direct-injection internal combustion engine – Transition from conventional compression ignition combustion to low temperature combustion

The application of the low temperature combustion (LTC) technology improves the performance and emission characteristics of the engine. However, the most important challenges regarding the integration of this technology in mass-production engines are the limited operating range and uncontrollability. To get the utmost from LTC advantages it is possible to use the diesel combustion in load points undeliverable by LTC. Experimental study in this research on a diesel engine reveals that the change in fuel injection timing from 176 to 2 CAD, bTDC (crank angle degrees before top dead center) leads to the combustion regime change. Fuel injection near top dead center from 11 to 2 CAD,bTDC, resulting in the dependence of the injection and combustion processes, leads to the diesel combustion. In this region, the combustion sensitivity as a measure of fuel injection timing on combustion timing is between 1.2 to 1.3. Advancing the injection to early timings in the compression stroke from 86 to 176 CAD, bTDC and providing enough time for the complete mixing of the fuel and air, yields HCCI combustion having almost zero combustion sensitivity. The fuel injection timing between these ranges, resulting in a mixture which is neither fully homogeneous nor fully stratified, leads to the PPC. In this region, the combustion sensitivity is between 0.1 to 0.2.