Experimental Study on Ignitability of R290/Air Premixture by an Arc Discharge at the Gap of Electric Contacts

Abstract

The ignitability of the R290/air mixture by arc discharge at the gap of the electric contacts was experimentally examined. A series of ignition tests were conducted by opening and closing a pair of electric contacts, and the voltage between the anode and cathode, and the current through the circuit were measured. The varieties of electric load, power consumption of the circuit, and composition of the R290/air mixture were varied under the experimental conditions. The ignition frequency showed an upward convex curve against the equivalence ratio, and it was taken maximum value near ϕ = 1.3 (approximately 5 vol% of C₃H₈). It was easier to ignite when the electrical contacts were opened than when they were closed. It was also observed that ignition occurred more easily with increased power consumption. The minimum energy generated at the gap of the electric contact in the case of ignition (E_{arc_m} ) was much larger than the minimum ignition energy (E_min). This was because the contribution rate of energy available for ignition was much smaller than in the case of capacitive spark ignition. The net energy contributing to ignition (E_cont) is less than 6% of the E_{arc_m} at most because go or no-go of ignition can be distinguished well by comparing and Econt(=0.006E_{arc_m}). This almost coincides with the data reported in the literature.