An Experimental Investigation of Spark Plug Temperature in Bi-fuel Engine and Its Effect on Electrode Erosion

Temperature is one of the effective parameters in erosion of spark plug electrodes. In this research, temperature of spark plug was measured in engine's different operation conditions with two types of fuels: compressed natural gas and gasoline. Test results showed that, temperature of center electrode is lower than ground electrode and maximum difference between them is 110ºC that occurs at 2500 rpm and full load conditions. Maximum temperature of spark plug occurs with CNG under full load conditions and 6380 rpm. In these conditions, ground electrode’s temperature reaches to 960ºC which is very prone to pre-ignition. On the other hand, center electrode’s temperature is 195ºC higher than the same condition with gasoline as a fuel which cause more electrode erosion rate. This temperature rise lead to cold type spark plug selection because of its better heat transfer. Spark plug erosion was studied after endurance tests with CNG as a fuel. Electrodes have non uniform wear patterns and consequently gap growth is not uniform. The average gap growth for two sets of spark plugs after two similar 200 hr endurance tests is 49.6%