The development of two low emission combustors for an automotive Rankine cycle engine is described. Emphasis has been placed on low emissions, fast response, compactness, and low parasitic power. Air atomization and rotary atomization of fuel have been incorporated, leading to two different combustor configurations. Emission characteristics of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) are described for both concepts. HC and CO emissions have been generally found to be well below 1976 federal standards for automotive emissions. Fine atomization of fuel and thorough air-fuel mixing have been found to be the keys to low NOx emissions. The use of exhaust gas recirculation reduced NOx emissions significantly. Effects of excess air and cooled primary zone are also shown.