Interferometric spark calorimetry

Abstract

 We present a technique based on interferometry for the measurement of the quantity of energy transferred from a spark to the gases surrounding it. The primary advantage of this new technique is that it can be used to make accurate measurements not only in stagnant, but also in flowing gases. It has been used to make measurements with an estimated accuracy of better than ±5% in gases flowing at up to 6 m/s. We present the interferometric measurement technique, a simple phase-stepping holographic interferometer for making the measurement, and measurements made using a standard automotive ignition system. Measurements in flowing air at 1 bar show that the amount of energy transferred from a spark to the air doubles when the flow speed is increased from 0 to 2.2 m/s.