A Computational Investigation of Water Injection Strategies for Nitric Oxide Reduction in Large-Bore DI Diesel Engines

Computational investigations have been conducted to study the reduction of nitric oxide formation by means of water injection into the combustion chamber of large-bore diesel engines using a KIVA-based code. The main objective has been the development of an optimal fuel/water injection strategy which minimizes the nitric oxide formation for the same amount of injected water. The investigated water injection techniques include the injection of water via separate injectors, the injection of fuel/water mixtures and the stratified injection of fuel/water packages via specially designed nozzles. Both, the stratified and the emulsified injections yield best NO_x reductions per injected water mass for the same power outputs and at identical cylinder peak pressures, depending on the particular injection configuration.

The computational tool is a KIVA-based code where the nitric oxide formation is modeled with a variation of the extended Zeldovich mechanism. This code has been adapted to accommodate the simulation of multiple liquid species in such a way that collisions have been limited to droplets of the same species. Comparative studies have shown that this restriction of the collisions does not significantly influence the spray behavior.