Abstract
Abstract Research nowadays has become interested in how to improve alternative fuels to reciprocating internal combustion engines, as it has become necessary due to the high prices of conventional fuels, and also its significant contribution to hazardous pollutants. Natural gas is one of the most promising fuel alternatives for the future, which will help reduce harmful emissions. In this paper, a computational simulation software model of a four-cylinder, 5000rpm natural gas spark ignition engine is developed. The computational program works on the thermodynamic fundamentals of the gaseous cycles of reciprocating internal combustion engines. The effect of different proportions of methane gas in the natural gas mixture on the performance of the engine was studied, where the pressure, temperature and quantities of nitrogen oxide formation inside the cylinder were calculated as a function of crank shaft angle of the engine. The indicated mean effective pressure, indicated power, thermal efficiency, maximum pressure, maximum temperature, amount of nitrogen oxide formation and indicated specific fuel consumption were also calculated at different equivalence ratios of fuel and air, and also at methane gas containment ratios in natural gas fuels. The results showed that the equivalence ratio and methane percentage in the fuel have a strong effect on engine performance. The high percentage of methane presence caused a decrease in the thermal efficiency of the engine, which harmed a decrease in the indicated power of the engine. On the other hand, natural gas contains large proportions of methane gas, causing a decrease in the amounts of nitrogen oxide formation, as well as a decrease in the indicated specific fuel consumption. It has been proven that the proportion of methane gas in natural gas fuels improves combustion, emission and performance, when added by a high percentage, natural gas is usually generally composed of methane (85-96%) and can be used in both reciprocating internal combustion engines as an alternative to gasoline and diesel fuels. Keyword. SI engine; Natural gas; Equivalence ratio, NOx emissions; fuel consumption