Exhaust-Port Fuel Injection for Chemical Reduction of Nitric Oxide

Nitric oxide can be chemically reduced in a vehicle exhaust system if hydrocarbons are supplied to high-temperature exhaust gas near the engine exhaust valves. Ethane was injected into the exhaust ports of engines equipped with either stainless steel or ceramic thermal reactors. Thermal decomposition of the ethane provided hydrogen and hydrocarbon radicals for the gas phase chemical reduction of nitric oxide formed in the engines.

Although significant reductions of nitric oxide were achieved, severe spark retard was required to attain the elevated exhaust temperatures required to effect the nitric oxide reduction. Furthermore, carbon monoxide, hydrogen cyanide, and ammonia were formed, especially with the stainless-steel reactors. In view of these findings, this scheme for reducing nitric oxide emissions is not felt to be practicable for automotive application at this time.