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.

The numerical results obtained from high-speed photography are examined in order to determine the frame rate best suited to a given phenomenon. Procedures for optimum frame rate determination are shown for deterministic and random space-time functions with emphasis on error reduction in velocity measurements. Characteristics of the random errors of a typical high-speed camera are given.

The possibility of measuring gas temperatures in internal combustion engines during actual operation has been studied at the Sloan Laboratories for Automotive and Aircraft Engines under the supervision of Professor C. F. Taylor. Barium titanate transducers are used at 2 mcps to produce short ultrasonic pulses in the combustion chamber through metallic coupling rods. The transit time of the sound signal is measured electronically and related to the absolute temperature of the gas mixture. The accuracy of temperature measurement in the unburned charge at about 1500°F is about 20°F. No complete evaluation of the accuracy has yet been made inside of the flame region. Sonic temperature measurements are expected to be particularly useful in studies of the antiknock properties of fuel. Real-gas behavior and thermal relaxation are the limiting factors in other applications. [This work was initiated by the Coordinating Research Council, Inc. and has been carried out with the support of the U. S. Army Ordnance.]

No abstract