Exhaust Recirculation and Spark Control - A Speed Governed and Vacuum Modulated System

Published test results have established that the recirculation of a portion of an engine's exhaust gas is an effective means of reducing oxides of nitrogen in the exhaust. Many methods of flow control have been tried; some require extensive revisions to the carburetion system. A retrofit system in which recirculation and spark advance are selectively controlled by vehicle speed and vacuum level has been tested on various cars to give 30-70% reductions in NO_x as well as significant reductions in HC and CO. Revisions to the existing power train are minimal, while changes in driveability and fuel economy are hardly noticeable.