Water injection (NOx)

Water injection is a NOx-control method that lowers peak combustion temperature, cutting thermal NOx formation, to help meet MARPOL Annex VI Reg 13. Direct water injection sprays water into the cylinder through a separate nozzle near the fuel injector. Fuel-water emulsion premixes water into the fuel before injection. The Humid Air Motor (HAM) instead saturates the charge air with hot water vapor. All three add water mass that absorbs heat and slows the Zeldovich NOx-forming reactions, giving roughly a 30 to 50% NOx reduction depending on water ratio, less than SCR but without a catalyst or urea supply.