Using catalytic heat recovery to improve efficiency of gasoline spark ignition engines

Exhaust gas recirculation is a widely used technology on conventional vehicles, primarily for lowering emissions of local pollutants. Here we use chemical models to show that an exhaust-gas recirculation loop can be converted into a heat-recovery system by incorporating a catalytic reformer. The system is predicted to be particularly effective for gasoline-fuelled spark ignition engines. The high temperature and low oxygen-content of the exhaust gas mean that endothermic reactions will predominate, when some of the gasoline is injected into the recirculation loop upstream of the reformer. The output of the reformer will, therefore, have a higher fuel heating value than the gasoline consumed. Chemical efficiency calculations, based on the predicted reformer output at chemical equilibrium, indicate that the direct improvement in fuel economy could be as high as 14%. Initial tests using a rhodium reforming catalyst suggest that much of the heat recovery predicted by the thermodynamic models can be achieved in practice, which together with a reduction in throttling may allow a gasoline spark ignition engine to match the fuel economy of a diesel engine.