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The effect of changing catalyst precious metal ratios and loadings on close coupled catalytic converter efficiencies has been studied. The three precious metals were platinum, palladium and rhodium. The specific matrix used for the development of response surface models is a central composite design and provides the capability of visually optimising the precious metal loadings. Catalysts were evaluated using perturbed scans. lightoff curves from the dynamometer aged, and vehicle emission tests. These scans show percent conversion efficiencies of the three legislated gases; HC, CO and NOx, over a range of Air Fuel Ratios (λ). Whilst lean and rich lightoff curves provide indications of conversion efficiencies at varying temperatures. Prior to testing the catalysts were aged, using an accelerated dynamometer ageing process, to 80K simulated kilometres. The catalysts were then fitted to a vehicle and chassis roll emission tests conducted.

The rapid heating of an under-body catalyst after cold start by combustion of rich engine products with added secondary air is described. The results of initial durability studies including spark plug fouling, oil dilution and thermal shock are presented, together with emissions performance and a mileage accumulation study. Also discussed are failure mode assessment and the system tolerance to anticipated open-loop errors and real-world driving scenarios.