Experimental analysis of NOx reduction through water addition and comparison with exhaust gas recycling

Highlights: • Effects of adding water into the intake manifold with a flow-blurring injector. • NOx reduction on a current technology diesel engine with multiple injection. • The NO_x emission was reduced by adding water in comparison to the EGR. • A reduction of NOx emissions around 60–70% was achieved with water injection. • The minimum attainable NOx emission and the thermal capacity are related. -- Abstract: The diesel engine requirements regarding the reduction of exhaust emissions, especially nitrogen oxide (NO_x) and particulate matter (PM) are becoming more stringent year by year. A current method used for NO_x control is exhaust gas recirculation (EGR). However, this approach significantly increases the production of soot for medium and high rates. Water addition can also be used for NO_x control, achieving 50% NO_x reduction rates in relation to EGR with a lower production of soot and without additional carbon monoxide (CO) and hydrocarbons (HC) substantially. This paper analyses the weaknesses and the strengths of adding water into the intake manifold with a flow-blurring injector for NOx reduction on a current technology diesel engine with multiple injection thorough a proprietary tool for heat release rate that considered real gas properties. A reduction of NO_x emissions around 60–70% was achieved with water injection at different loads and speeds. Besides, a clear relationship was established between the minimum attainable NO_x emission and the thermal capacity of the load (air plus water), this result stablish the hard relationship between NO_x formation and combustion chamber temperature and therefore shows the strong dependence of the Zeldovich mechanism.