Effect of internal exhaust gas recirculation on performance, combustion, and emissions in a PFI camless engine

The internal exhaust gas recirculation (EGR) into the intake manifold has a significant impact on fuel economy and emissions in the spark ignition (SI) engine. In this study, an in-house developed novel electro-pneumatic variable valve actuation (VVA) system was integrated on a PFI conventional engine and modified into PFI camless engine to vary the valve events independently. The potential of the developed VVA system in achieving the internal EGR by varying the intake valve opening (IVO) timings was widely investigated. The IVO timing was varied from 30 degrees CA (crank angle) bITDC (before intake top dead center) to 40 degrees CA aITDC (after intake top dead center). The spark timing was varied from 10 degrees to 30 degrees CA bCTDC (before compression top dead center). A 41% pumping mean effective pressure reduction was achieved with varying the IVO from 40 degrees to -30 degrees CA aITDC. It is due to the internal exhaust gas recirculation into the intake manifold that reduces the differential pressure between the manifold and combustion chamber. The entrapment of exhaust gas in the intake manifold dilutes the fresh charge, which deteriorates the combustion. However, advancing the spark timing from 10 degrees to 30 degrees CA bCTDC at IVO -30 degrees CA aITDC, an 18% gas excahnge efficiency improvement was obtained. The fresh charge dilution forms an inhomogeneous mixture inside the cylinder that results in lower NOx emission. It is concluded that the developed VVA system has the potential to improve part loads efficiency by utilizing the internal EGR in a PFI camless engine.