Abstract
Future emission regulations for internal combustion engines require increasingly stringent reductions of engine-out emissions, especially NOx and particulate matter (PM), together with the continuous improvement of engine efficiency. In the current scenario, even though compression-ignited engines are still considered the most efficient and reliable technology for automotive applications, the use of diesel-like fuels has become a critical issue, since it is usually not compatible with the required emissions reduction. A large amount of research and experimentation is being carried out to investigate the combined use of compression-ignited engines and gasoline-like fuels, which proved to be very promising, especially in case the fuel is directly injected in the combustion chamber at high pressure. This work investigates the combustion process occurring in a light-duty compression-ignited engine while directly injecting only gasoline. A specific experimental setup has been designed to guarantee combustion stability over the whole operating range that is achieved controlling boost pressure and temperature together with all the injection parameters of the multijet pattern. The analysis of the experimental data clearly highlights how the variation of the control parameters affect the ignition process of small amounts of directly injected gasoline and the maximum achievable efficiency. In particular, the analysis of the sensitivity to the injection parameters allows identifying an ignition delay model and the key control parameters that might be varied to guarantee a robust control of combustion phasing within the cycle.
