s a result of concern over exhaust gas emission from mobile sources, much research is currently being directed towards alter-A native fuel systems for use in road vehicles. One such alternative is the natural gaddiesel dual fuel engine, which offers an alternative to the standard diesel fuel compression ignition engine. In the dual fuel configuration, the primary fuel i s natural gas, replacing as much as 90% of the diesel fuel, with a small amount of diesel fuel required to ensure effective ignition. The main constituent of natural gas is methane, which has a high combustion efficiency. Compared to a conventional diesel engine, dual fuel engines offer the promise of lower NO, emissions and fewer particulates. At moderate engine loads, however, a lower fuel combustion efficiency has been observed (Karim, 1991), which results in significant amounts of hydrocarbon (HC) and carbon monoxide (CO) being present in the exhaust gas. It i s therefore necessary to use a catalytic converter in the exhaust system to reduce these emissions to an acceptable level.Catalytic converters have been widely used on gasoline engines since 1976, with the most commonly used catalyst a t present being the threeway catalyst W C ) , which oxidizes CO and HC, and reduces NO, . Many experimental and modelling studies have been reported for automotive catalytic converters, some of which are summarized in Table 1. The performance and operating conditions of a catalytic converter for the natural gas/diesel system have not been widely studied. Compared to a gasoline engine running at conditions close to stoichiometric, dual fuel engines provide higher exhaust gas oxygen levels and lower exhaust gas temperatures. The high oxygen concentrations, in excess of 4% and up to 10% or more, are a consequence of lean combustion and the high compression ratios used in the engine. This paper reports on the development and implementation of a numerical model for a dual fuel engine catalytic converter. The model is validated against experimental results for both transient and steady state operation.
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