Abstract
Keywords Catalyst warmup, Cold start, Variable exhaust valve timing, Spark timing, Exhaust gas temperature
Abstract - The effects of spark timing and exhaust valve timing change on exhaust gas temperature during cold start period of an SI engine are studied through engine bench tests. Optimal spark timing and exhaust valve timing are investigated to find the best conditions for rapid warmup of catalysts. The exhaust gas temperature increases when the spark timing or valve timing are retarded individually, due to late combustion or slow flame speed. Therefore, exhaust gas temperature shows a large increase when the two timings are retarded simultaneously, with the cost of COVimep. Combustion stability during cold start deteriorated under these retarded conditions. To increase exhaust gas temperature for fast warmup of catalysts while maintaining combustion stability, an optimal condition for spark and valve timing retard should be appied for the cold start period.