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.

In present paper, the potential of auto-ignition of heavy oil during in-situ combustion (ISC) process was studies. Kinetic studies were carried out using Thermo Gravimetric Analyzer (TGA), Differential Scanning Calorimetry (DSC) and Accelerating Rate Calorimetric (ARC) techniques. Effects of oxygen partial pressure, reservoir pressure and clay on auto ignition condition were investigated on a number of different heavy oil samples fro south west Iran mixed with silica sand or crushed carbonate rock and clay. Based on the experimental results obtained by TGA runs, the kinetic equation was derived for different oil samples in the presence of different sands. Effect of partial pressure of oxygen in the injected air was studied. Results showed that at atmospheric pressure, the peak of low temperature combustion (LTC) by producing CO was initiated at 300°C when air was injected. Also, enriching the injected air by oxygen lowers the LTC by up to 50°C. When the experiments were extended to reservoir pressure (1300 psi), it was found that activation energy in the LTC region was lowered. As a result, initiation of LTC was started at 115°C when air was injected. The DSC experiments, under non-isothermal condition showed that increasing the oxygen partial pressure resulted in more heat being evolve during the high temperature combustion reactions. Also, effect of clay as a catalyst was studied and it was found that the activation energy decreases considerably when clay is present in the system. The decrease in activation energy was from 359 to 149 kj/gmole for one sample.