after-running - the continued running of a spark-ignited engine after the ignition is turned off; also known as dieseling. There are two basic causes of after-running; surface ignition and compression ignition. In surface ignition, the surfaces of the combustion chamber remain hot enough to provide a source of ignition after the spark ignition is terminated. In compression ignition, the conditions of temperature, pressure, fuel composition, and engine idle speed allow ignition to continue. See compression ignition.