Fuel Injection Strategies to Increase Full-Load Torque Output of a Direct-Injection SI Engine 980495
Fuel-air mixing in a direct-injection SI engine was studied to further improve full-load torque output. The fuel-injection location of DI vs. PFI results in different heat sources for fuel evaporation, hence a DI engine has been found to exhibit higher volumetric efficiency and lower knocking tendency, resulting in higher full-load torque output . The ability to change injection timing of the DI engine affects heat transfer and mixture temperature, hence later injection results in lower knocking tendency. Both the higher volumetric efficiency and the lower knocking tendency can improve engine torque output. Improving volumetric efficiency requires that the fuel is injected during the intake stroke. Reducing knocking tendency, in contrast, requires that the fuel is injected late during the compression stroke. Thus, a strategy of split injection was proposed to compromise the two competing requirements and further increase direct-injection SI engine torque output. The proposed strategy was tested in a single-cylinder direct-injection SI engine with different injection pulse-width ratios and injection timings. The best split injection strategies were identified, and the results showed that IMEP at full load increased 2 ∼ 3% versus single-pulse direct injection.