Monitoring of Gasoline Fuel Distribution in a Research Engine

Abstract
Fuel distribution in gasoline engines has significant influence on the cyclic stability of charge ignition and combustion, and hence on engine performance parameters related to the variation of combustion and heat release. There are numerous ways to influence in-cylinder fuel distribution by means of mixture preparation systems, engine aspiration or by combustion chamber geometry itself. However, methods to observe in-cylinder fuel distribution are scarce, and very often charge distribution—homogeneous or highly stratified—is just heuristically assessed, based on engine performance data. Therefore, a method has been devised which allows observation of vaporized fuel in the cylinders of optically accessed engines. The method, based on the absorption of infra-red laser light radiation by hydrocarbon molecules, needs optical access to the combustion chamber to transmit a laser beam of appropriate wavelength and to monitor the attenuation caused by absorption and scattering. The paper describes the concept of the measurement technique and its application to an optically accessed single-cylinder research engine. The engine is equipped with a transparent cylinder liner to allow investigation of the entire cylinder volume. In order to evaluate the feasibility of the method, the response of the line-of-sight absorption measurements to various engine operating modes was investigated. A comparison with actual engine data showed that fuel distribution, as governed by the injector operating mode, can have significant influence on combustion and cycle-to-cycle stability.