Technical Paper
Studies of Knock in a Spark Ignition Engine with “CARS” Temperature Measurements and Using Different Fuels
1995-02-01
950690
A “CARS” System using a modeless dye laser has been extensively calibrated and shown to give average temperatures of acceptably good accuracy. It has been used to measure temperatures in the end-gas of a single-cylinder E6 engine under knocking conditions using propane, commercial butane, iso-octane and a primary reference fuel made up of 90% iso-octane and 10% n-heptane by volume. These measurements show that there is significant heating of the end-gas because of pre-flame chemical reactions for all the fuels except propane. Propane has to be compressed to a much higher pressure compared to the other fuels studied in order to make it knock. At a given engine operating condition, there is significant cycle-by-cycle variation in both combustion and knock.
