Investigation of intake manifold water injection to reduce NOx emission of lean burn natural gas engine

Abstract

Nitrogen oxide (NOx) is the main emission released from lean burn natural gas engine (LBNGE). In order to satisfy the stringent emission standards, NOx emission of LBNGE must be decreased. One of the known methods for reduction NOx emission is to apply water injection (WI) to engines, which has been widely researched on conventional fuel engines. However, effects of WI on NOx emission and combustion characteristics of LBNGE are not yet quite certain. In this study, effects of variable intake manifold water injection (IMWI) rates on NOx emission and combustion characteristics of LBNGE were investigated by a quasi-dimensional two-zone combustion model and a kinetic model for NOx emission prediction. The results demonstrate that, due to the decrease of in-cylinder temperature with IMWI, NOx emission of LBNGE is reduced by 45.7% with 2g/s IMWI rate in comparison with that without IMWI. However, with IMWI, the peak in-cylinder pressure of LBNGE and rate of pressure rise is decreased as well as peak pressure crank is increased, while the ignition delay and combustion duration are prolonged. Thus, the deterioration of in-cylinder combustion will be caused by the large IMWI rate.