Experimental investigation of the effect of thin-wall substrates and spark timing retard on total hydrocarbon emissions during cold start for super-ultra-low-emission vehicle application

As the basic approach to improve the emission performance under cold start engine operation to meet stringent emission regulations, the effects of thin wall catalysts and spark timing retard on total hydrocarbon (THC) emission characteristics were investigated by engine performance and vehicle emissions tests. From this study, the effects of cell density on back pressure and engine performance were studied for thin-wall catalysts. The light-off time reduction of the thin-wall catalysts was also demonstrated through vehicle emission tests. The effect of spark timing retard from minimum spark advance for best torque on THC emission reduction under the cold-start condition was also studied quantitatively using a fast flame ionization detector and a flame visualization technique. As the spark timing is retarded, THC emission at the exhaust manifold is effectively reduced regardless of the air-fuel ratio. From flame visualization, as the spark timing is retarded, the flame propagation speed becomes slower and the duration of the main flame is longer. It was also found that the reduction in THC emission at the beginning of the engine start is essential to meet the more stringent emission regulations. As a result, the adoption of a high-cell-density catalyst (900 cells/2.0 mil) and the spark timing retard technique (spark advance retard case, after top dead centre 8° crank angle) makes it possible to meet the super-ultra-low-emission vehicle emission regulation if effectively combined along with a metallic catalyst and exhaust gas-flow-optimized exhaust manifold.