Effects of the throttle opening ratio and the injection timing of CNG on the combustion characteristics of a DI engine

We investigated the effects of the fuel injection timing — both for early and late injection — in conjunction with the throttle opening ratio on the fuel-air mixing characteristics, engine power, combustion stability and emission characteristics of a DI CNG spark engine and control system that had been modified and designed according to the author’s original idea. We verified that the combustion characteristics were affected by the fuel injection timing and that the engine conditions were affected by the throttle opening ratios and the rpm. The combustion characteristics were greatly improved for a complete open throttle ratio with an early injection timing and for a partial throttle ratio with a late injection timing. The combustion duration was governed by the duration of flame propagation in late injection timing scenarios and by the duration of early flame development in cases of early injection timing. As the result, the combustion duration is shortened, the lean limit is improved, the air-fuel mixing conditions are controlled, and the emissions are reduced through control of the fuel injection timing and vary according to ratio of the throttle opening.