Effect of electrode erosion on the required ignition voltage of spark plug in CNG spark ignition engine

In this article, the electrode erosion and the gap growth of spark plugs were measured on of a CNG fueled engine after durability tests. Then, the required ignition voltage and the spark quality were investigated by a spark plug test rig. Considering results of measurements, the gap growth increased as the running time increased. Thus, the gap growth of spark plugs with 200 and 280 hours running time were 2 and 4.4 times more than the gap growth of spark plugs with 80 hours running time. Results of the voltage test show that the required voltage is increased with the pressure. The required voltage at 9 bar was 2 times higher than 1 bar. The increase of the required voltage and the adverse effect on the spark quality due to the gap growth are due to more running time. Accordingly, the required voltage was increased 11% at 5 bar while the gap growth was 20%. Comparing results of new and used spark plugs showed that in addition to the gap growth, deposits on the electrodes surface could lead to increase the required voltage.