The major parameters that affect spark ignition engine performance, efficiency and emissions are compression ratio, injection timing and mixture composition. To prevent the knock, the compression ratio of gasoline engine cannot be increased beyond 12:1. For the same engine volume increasing the volumetric efficiency raises fuel economy and engine power output. An extensive research work was focused on air fuel ratio and injection timing of a gasoline direct injection engine to evaluate its influence on lean operating limit and performance features of the engine on stratified charge mode operation. A modified engine and a customized fuel injection module were developed for the proposed task. A test matrix of variable spark timing from 14 to 20 degree bTDC, air fuel ratio beyond stoichiometric and variable injection timing from 60 to 140 bTDC at compression stroke was implemented. The experimental results showed that the maximum brake torque timing, air fuel ratio and injection timing were implied significant influence on lean limit operation, fuel economy and exhaust emission reductions. The test report revealed that the developed engine attained lean limit at air fuel ratio 16.7 without affecting speed fluctuations. A module of air fuel ratio 16.7, SOI 100 degree with MBT 18 degree bTDC was identified as a most suitable operating variable for stratified charge gasoline direct injection operation. Reduction of fuel consumption, HC, CO and NOx was observed 15.62%, 83.33%, 14.28%, and 31.08% respectively with reference to the SOI 100 degree bTDC at AFR 16.7 compared with baseline PFI engine operating AFR 14.7.

Full text: IJEIR_1137_Final.pdf