Multiple Injection and Boosting Benefits for Improved Fuel Consumption on a Spray Guided Direct Injection Gasoline Engine

The combination of turbocharging and direct injection offers a significant potential for SI engines to improve fuel consumption, specific power output, raw emissions and transient behavior. To realize the full benefit of this combination Ricardo uses spray guided lean stratified operation with multiple injections. The Ricardo T-SGDI concept has already been presented at various international conferences and is constantly being developed using modern optimization techniques. This paper shows the latest results of the T-SGDI engine with a maximum brake thermal efficiency about 41 % and a BSFC of about 278 g/kWh at 2000 rpm and 2 bar BMEP. Additionally, the stabilization of combustion through the multiple injections allows EGR rates of up to 35 % in order to reduce NOx raw emissions. Further, this engine achieves 30 bar BMEP and 100 kW/l. These outstanding values are possible by combining different mechanisms such as charging, multiple injection, high Exhaust Gas Recirculation (EGR) rates plus the appropriate charge motion and combustion chamber design. At low loads, the multiple injections ensure stable combustion, even with residual gas fractions of up to 35 %. At medium loads the Ricardo Multiple Injection Variable Injection Separation (MIVIS) Strategy, through the distribution of the injection processes during the intake and compression strokes, in combination with boosting means that the lean operating range can be up extended to BMEP of 15 bar. At WOT, injection during both the induction and compression strokes leads to higher knock mitigation and, above 30 bar BMEP, to 50 % MFB at the thermodynamic optimum. The Ricardo T-SGDI concept thus achieves the efficiency of modern direct injection diesel engines whilst retaining the positive characteristics of a gasoline engine, such as a wide engine speed range and spontaneous power response.