Three-Way Conversion Catalysts on Vehicles Fueled with Ethanol-Gasoline Mixtures 790428
Three-way conversion catalysts systems which provide control of three emission components - hydrocarbons, carbon monoxide, and oxides of nitrogen - generally require the use of closed-loop feedback control of the air/fuel metering system to provide a near stoichiometric exhaust gas composition. As an alternate fuel such as ethyl-alcohol is added to gasoline, the stoichiometric air/fuel ratio is altered. Conventional air/fuel metering systems do not compensate for this change. This paper studies the ability of the Volvo closed-loop control fuel injection system, now in use on vehicles in the United States, to maintain the stoichiometric air/fuel mixture needed for optimum emission control and to compensate for the change in fuel stoichiometry encountered in gasoline/alternate fuel mixtures. The system was found to have the ability to completely compensate for gasoline/ethyl alcohol mixtures up to 30% ethyl alcohol with no loss in emission control. Gasoline/methyl alcohol blends were also tested successfully.
There is definite potential for the three-way conversion catalyst/closed-loop systems to provide our nation with flexibility in fuel formulation not otherwise found in conventional fuel metering systems. With proper planning and engineering, non-petroleum derived fuels can be blended with gasoline without requiring engine adjustments or compromising emission controls.