Assessment of atomized water injection in the intake manifold of a heavy duty diesel engine for NOx reduction potential

Abstract

Diesel engines, since many years, have found their own market with their robustness, low manufacturing cost and high efficiency. Although diesel engines have so many advantages, they are being blamed for their high pollutant emissions. Main pollutants from diesel engine are NOx, CO, CO2, HC and PM. Out of these pollutants, CO, CO2, HC, and PM can be reduced using some after treatment system in the tail pipe. But NOx needs to be addressed within the cylinder which would reduce the cost of after treatment system. Since NOx formation is the function of high combustion temperature, this temperature should be reduced by some means. In this study, atomized water injection system was employed to reduce in-cylinder combustion temperature there by reducing NOx formation. Here, water was injected into the air-intake pipe along with the EGR stream. 1-D simulation model of the study engine was created using AVL BOOST. Three full load operating points were considered and simulations were performed for 2.8mg, 4mg and 6mg of water injection at each operating points. Performance and emission parameters were then validated with the test data. Results showed that increase in water injection quantity reduces NOx emission but increases the smoke value. 2.8mg of water injection was chosen to be optimum, which reduces about 90°C of in-cylinder temperature, 8-10% of NOx reduction and increases smoke by about 20% from base value.