Variables Affecting Flame Speed in the Otto-Cycle Engine 370184

IN the investigations reported in this paper flame-trace photographs were taken on a moving film through a glass-window slot in an engine cylinder to show the effects of various operating conditions on the rate of flame travel across the combustion-chamber. The tests were made with a small L-head single-cylinder engine in the Sloan Automotive Laboratories at the Massachusetts Institute of Technology. The technique is similar to that used by Withrow and Boyd in flame studies reported in 1931.
This investigation covers a considerable range of operating conditions, including altitude, with and without supercharging, inlet temperature, humidity of the intake air, engine speed, ignition timing, and fuel-air ratio.
In general, the results show that flame speed decreases with increasing altitude in an unsupercharged engine. Either supercharging or reducing the exhaust pressure with inlet pressure constant, tends to increase flame speed. The flame speed decreases with increasing inlet temperature and with increasing humidity. Observations of the effects of revolutions per minute, fuel-air ratio, and spark-advance confirm the results of previous investigations.


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