Measurements of Unburnt Hydrocarbons in a Spark Ignition Combustion Engine during the Warm-Up Period

New European motor vehicles must comply with emissions regulations which will soon include the exhaust produced during cranking and warm-up, when a catalyst is not active. This paper describes a technique of using rapid acting sampling valves to take measurements from the combustion chamber and exhaust pipe of a spark ignition engine during this period. The samples were analysed for both total hydrocarbons and individual species. Results obtained from an engine operating on propane fuel are presented.

The concept of a storage parameter, developed previously from tests on an engine operating at the cyclic repeating condition (CRC) is used to help interpret the measurements. The total hydrocarbons readings show the behaviour of the engine to resemble that of the fully warmed state 15 seconds after start.

Using the storage parameter indicates this similarity occurs closer to 50 seconds from start.