Effects of intake and exhaust manifold water injection on combustion and emission characteristics of a DI diesel engine

Abstract

Water injection is a technique that has been used for decades to control the combustion and emissions in diesel engines. The effects of water injection at the intake and exhaust manifolds on the combustion and emission characteristics of a direct injection diesel engine are studied in this work. Water injection in the intake manifold increases engine heat losses. Therefore, waste heat in exhaust gases is used to vaporize water before combustion and prevent the water-cooling effect. The injection of 40 mg/cycle of water into the intake and exhaust manifolds were tested with exhaust gas recirculation (EGR) ratios of 10% and 25%. The fuel injection timing, quantity, and engine speed were maintained at constant values to keep the cylinder combustion condition constant. The results show that the exhaust manifold water injection improves engine performance and combustion characteristics and reduces emissions compared to intake manifold water injection. The peak improvement is achieved at exhaust manifold water injection at 25% EGR where the reduction in the brake specific fuel consumption (bsfc) is about 5%, while the increase in the indicated mean effective pressure (IMEP) and the indicated thermal efficiency (ITE) is by 7% and 3%, respectively. On the other hand, the maximum reduction in soot was obtained with exhaust manifold water injection at 10% EGR ratio with reduction ratios of 55%. The intake manifold water injection gives the lowest NOx emissions with a 88% reduction ratio. The exhaust manifold injection is the recommended technique for water injection to improve engine performance and reduce emissions to avoid the disadvantages of the previously applied techniques.