Turbocharging a Gasoline Direct Injection Engine 2001-01-0736
Gasoline direct injection is one of the best way to reduce fuel consumption of spark ignited engines. Stratified combustion has the advantage of drastically increasing the SI engine efficiency. However, whereas future pollution standards become more restricting, it makes after-treatment of NOx emissions more difficult, especially since NOx traps require very low sulfur level in fuel. Thus, engines working with this type of combustion are expensive to be after-treated and actual consumption benefits on the urban cycles are significantly lower than theoretical expectations without any pollution constraint.
Homogeneous stoechiometric conditions present lots of advantages. After-treatment can be easily achieved without too expensive systems and applications of this combustion mode on current naturally aspirated engines show high volumetric efficiency and compression ratio in comparison with intake port injection. Gasoline direct injection engine has a lower knocking sensitivity, which is a main advantage in supercharging applications which allow to pull down consumption levels by downsizing.
This paper presents a development based on the Renault 2.0 liter “IDE” engine with a new type of turbocharger using twin-scroll housing and fixed turbine geometry. Two high compression ratios and several intake valve timings with early and late valve openings have been considered to study their respective influence on performances, fuel consumption and pollutants emissions levels. The high torque obtained at low engine speeds contribute to reduce vehicle fuel consumption by using longer gear ratio.
Following are the whole results at part and full load of the engine with a reduced engine displacement of 1.8 liter. Thus, this engine with high knock resistance would be able to overtake a typical 3.0 liter naturally aspirated engine performance. It has to be noticed that BMEP higher than 22 bar at 2000 rpm have been reached with a compression ratio of 10.0:1.