Inlet Manifold Water Injection for Control of Nitrogen Oxides — Theory and Experiment

Parallel theoretical and experimental studies of the influence of inlet manifold water injection on nitric oxide emission from spark ignition engines have been performed. Theoretical analysis based on chemical equilibrium calculations indicates that the reduction of combustion temperature due to water injection at rates comparable to the engine fuel consumption rate is sufficient to yield significant reductions in nitric oxide emissions. Theoretical results further show that water injection may be accompanied by increased volumetric efficiency due to evaporative cooling of the inlet charge during induction.

Experimental results obtained through modification of a CFR test engine confirm the predicted effectiveness of water injection on nitric oxide control. For a water injection rate 1-1/4 times the engine fuel consumption rate, nitric oxide reductions of over 90%were achieved. While no change was observed in volumetric efficiency with water injection, modest improvements in bmep and bsfc were observed.