Combustion Approach for Downsizing: the IFP Concept

Individual transport is facing more and more constraints. In the past decade regulations and car manufacturers have focused above all on decreasing pollutant emissions. Even though it has always been a major part of research, fuel economy has now become the number one priority because of the CO2 greenhouse effect. In the long term, hybridisation presents the best potential but in the short term, downsizing will allow for a substantial reduction in gasoline engine fuel consumption. To obtain the full benefits from downsizing, IFP has developed a combustion concept based on high knock resistance and high low-end torque potential due to scavenging. This approach has initially been developed by combining gasoline direct injection (GDI) variable valve timing and twin-scroll technologies (for 4-cylinder engines). This technology is used to develop lambda one partly stratified combustion due to split injection. These stratified mixtures improve engine knock resistance but with conventional injection systems they induce severe drawbacks on pollutant emissions. IFP's answer to this problem has shown very high potential according to the 1.89 MPa at 1500 rpm reached by a 2 litre engine with compression ratio of 11.2. In the car industry, cost is one of the most restrictive criteria. IFP has taken this into account when proposing 2 concrete solutions to reduce the cost of turbocharged gasoline engines. The first step was to replace twin-scroll turbine housings by mono-scroll turbines. Then the challenge was to maintain scavenging on 4-cylinder engines. Results have shown that this approach seems to be a very good trade-off between cost and performance. The 1.8 litre engine performs either 2.4 MPa BMEP at 2000 rpm and 90 kW/l or 2.4 MPa BMEP at 1400 rpm and 83 kW/l. In the latter case, the engine has also been evaluated in full lambda one operation with maximum upstream turbine temperature of 1050°C. Even if limited by lambda one combustion, maximum power density reaches 73 kW/l with a very attractive 260 g/kWh specific fuel consumption. As the cost of small gasoline engines is critical, IFP has started to develop the scavenging process in the case of port fuel injection. Current results show that it is possible to avoid fuel by-pass with a specifically designed engine that points the way to very interesting prospects