1. A process for reducing noxious exhaust emissions from a spark-ignition engine comprising the steps of providing an infrared reflecting surface highly reflective to infrared radiation in the 1 to 5 micron range to the walls of the combustion chambers of said engine while operating said engine at air-fuel ratios greater than 17 but less than 22.

2. A spark-ignition internal combustion engine having combustion chambers comprising coating means on the surfaces of said combustion chambers of an infrared reflecting material highly reflective in the 1-5 micron range for preventing a relatively large proportion of the nitrogen oxides, which are conventionally developed, from being formed at combustion and to cause them to revert to molecules of nitrogen and oxygen prior to exhaust to the atmosphere, and control means providing an air-fuel mixture to said chambers at an air-fuel ratio greater than 17 but less than 22.