Ultrasonic Temperature Measurement in Internal Combustion Engine Chamber

A method and apparatus for measuring the velocity of propagation of sound in the gases within the combustion chamber of an operating internal combustion engine are described. Two barium titanate crystals are used to generate and receive transient acoustical signals of approximately 2 Mcps. A calibrated commercial oscilloscope is the time base of the system. From the value of the velocity of sound it is possible to compute the temperature of the portion of the engine gas which lies in the measuring path, provided it is permissible to assume that the gas mixture behaves like a perfect gas, that it is of known composition, and that thermal relaxation effects are negligible. The maximum error is estimated at 4.7 percent and experiments indicate a dispersion of results less than 1 percent.