Experimental Investigations on the Influence of Valve Timing and Multi-Pulse Injection on GCAI Combustion 2019-01-0967

Gasoline Controlled Auto-Ignition (GCAI) combustion, which can be categorized under Homogeneous Charge Compression Ignition (HCCI), is a low-temperature combustion process with promising benefits such as ultra-low cylinder-out NO_x emissions and reduced brake-specific fuel consumption, which are the critical parameters in any modern engine. Since this technology is based on uncontrolled auto-ignition of a premixed charge, it is very sensitive to any change in boundary conditions during engine operation. Adopting real time valve timing and fuel-injection strategies can enable improved control over GCAI combustion. This work discusses the outcome of collaborative experimental research by the partnering institutes in this direction. Experiments were performed in a single cylinder GCAI engine with variable valve timing and Gasoline Direct Injection (GDI) at constant indicated mean effective pressure (IMEP). In the first phase intake and exhaust valve timing sweeps were investigated. It was found that the Intake Valve Closing (IVC) timing and Exhaust Valve Closing (EVC) timing have a dominant influence on combustion, performance and emission parameters.

In the second phase of experiments, multiple injection strategies were investigated. Here the influences of combining an injection pulse during the negative valve overlap phase (pilot injection), an injection pulse during the compression phase (pre-injection) and an injection pulse after combustion TDC (post- injection) along with the main injection pulse occurring at the end of IVC were studied. The potential of the valve timing and multi-pulse fuel injection strategies to effectively control combustion instabilities on a cycle-by-cycle basis in real time has also been discussed in the paper. In addition, the possibility of extending the load range through the above strategies has also been explained.