Downsizing of Gasoline Engine: an Efficient Way to Reduce CO2 Emissions
In order to meet commitments in terms of vehicle CO2 emission reduction for the whole fleet of cars for the year 2008, engine research and development is today exploring several fields. From CO2 point of view, gasoline engines suffer from an handicap in comparison to Diesel engines. Reduction of size of gasoline engine (downsizing) appears to be a promising way to improve engine efficiency and is subject to extensive research. Having a look to the long term, the aim should be to reduce by half the engine displacement volume. Calculation results from a vehicle simulation illustrate that even a so extensive downsizing will not be enough to bring the entire gasoline fleet to the requested CO2 levels. It would just be sufficient to reach the targeted levels for year 2008 for a mid-class vehicle powered by a downsized 0.8 l engine instead of a current 1.6 l gasoline engine. Reduction of CO2 emission is in that case about 18% in warm engine conditions. Then, further improvements have to be achieved in terms of gasoline engine specific fuel consumption, especially for bigger cars. IFP has developed an innovative approach combining two energy saving technologies that are gasoline direct injection and turbocharger with renewed definition of valve timing. This has been applied on a 1.8 l engine. An unconventional combustion chamber scavenging process becomes then feasible on a turbocharged engine. Knock resistance and volumetric efficiency are improved. The close interactions between combustion, turbocharger and valve timing have been analysed and optimised. Result is a significant increase in specific engine output in terms of torque and power, while keeping low specific fuel consumption level over the whole range of engine running conditions. Specific torque obtained at 1250 rpm has been progressively increased by 50% and is today close to 1.7 MPa BMEP while maximum power is now 83 kW/l with a specific fuel consumption of about 300 g/kWh. This type of 1.8 l engine would be an interesting competitor to downsize current big gasoline engines with displacement from 2.5 to 3.0 l.