Effects of Exhaust Throttling on Engine Performance and Residual Gas in an SI Engine

Combustion in engines can be controlled by the amount of residual gas, which has high temperature and heat capacity compared with fresh charge. Residual gas also acts like a dilution gas during combustion period. Accordingly, combustion duration increases, while the peak combustion temperature and nitrogen oxides (NOx) decreases. Amount of residual gas is affected by pressure difference between exhaust and intake, valve timing and engine speed.

The main objective of this work is to identify the effects of exhaust throttle, valve timing and load conditions on residual gas fraction and engine performance. The intake valve open timing was varied freely under fixed exhaust valve close (EVC) timing. Additionally, exhaust throttle has been installed in the exhaust manifold to build up the exhaust back-pressure allowing extra amount of exhaust gases to be admitted into the cylinder during the valve overlap duration.

Operation of exhaust throttle also increases exhaust gas temperature and pumping loss. However, it reduces NOx and hydrocarbon (HC) emissions. The results show that the variation of valve overlap duration with exhaust throttle provides a wider range of residual gas fraction (RGF) without much influence on engine performance.