Assessing the Efficiency of a New Gasoline Compression Ignition (GCI) Concept
A practical Gasoline Compression Ignition (GCI) concept is presented that works on standard European 95 RON E10 gasoline over the whole speed/load range. A spark is employed to assist the gasoline autoignition at low loads; this avoids the requirement of a complex cam profile to control the local mixture temperature for reliable autoignition. The combustion phasing is controlled by the injection pattern and timing, and a sufficient degree of stratification is needed to control the maximum rate of pressure rise and prevent knock.
With active control of the swirl level, the combustion system is found to be relatively robust against variability in charge motion, and subtle differences in fuel reactivity. Results show that the new concept can achieve very low fuel consumption over a significant portion of the speed/load map, equivalent to diesel efficiency. The efficiency is worse than an equivalent diesel engine only at low load where the combustion assistance operates. In this work, a detailed, dynamic longitudinal simulation model was created that allows accurate CO2 emission and fuel consumption predictions for a typical C-segment vehicle in the New European Drivecycle (NEDC), Worldwide Harmonized Light-Duty Test Cycle (WLTC) and Real Driving Emissions (RDE) driving cycles.
Modelling and simulation were performed in the GT-Suite simulation environment. The vehicle simulation for the NEDC with its low load demand shows that the outstanding fuel consumption at higher engine loads is more than compensated by the poor efficiency at lower engine loads. For the WLTC and RDE cycles, the fuel consumption improves relative to the NEDC due to the higher average load. In order to take better advantage of the GCI concept’s performance at high loads, a virtual engine map for a 4-cylinder engine was also created that is capable of running in cylinder deactivation mode. Avoidance of low-load operating points in this way leads to a significant improvement in cycle efficiency.