Catalyst light-off behavior of a spark-ignition LPG (liquefied petroleum gas) engine during cold start

The effects of the length of the gas flow path from the exhaust outlet in the cylinder head to the catalyst inlet in the exhaust line, the ignition timing and the engine idle speed on the three-way catalyst light-off behavior in an electronically controlled inlet port LPG (liquefied petroleum gas) injection SI (spark-ignition) engine during cold start were investigated experimentally. The results showed that these factors affect the catalyst light-off behavior significantly during cold start. The reduction of the gas flow path length upstream the catalyst reduces the heat loss from the exhaust gases, increases the temperature of the catalyst, and results in faster catalyst light-off. Retarding the ignition timing from 0 to 15°CA ATDC decreases 22 and 8 s catalyst light-off time for HC and CO respectively. Increasing the engine idle speed from 1400 to 1800 rpm decreases 19 and 15 s the light-off time for HC and CO respectively.

Research highlights
► The evaluation methods of the temperature and conversion efficiency are essential for catalyst light-off.
► We adopt HC and CO emission to explain the catalyst light-off during cold start.
► The reduction of the gas flow path length upstream, retarding the ignition timing and increasing the engine idle speed can reduce the catalyst light-off time during cold start.
► We concluded that improving methods for catalyst light-off are essential for the catalyst light-off behavior during cold start.