Abstract
Abstract Nitrogen oxides (NOx) poses a direct threat to human health during peak pollution and is mainly emitted from vehicles powered by spark ignition (SI) engines, especially in which liquid fuel is used such as gasoline, and is mostly responsible for air pollution, therefore, this destructive phenomenon of the environment must be addressed and reduced by improving the performance of spark-ignition engines. In this paper, the focus was on the emissions of nitrogen oxides (NOx) from the spark-ignition engine, a computer program was developed using a FORTRAN language, the simulation based on the thermodynamics relations of piston internal combustion engines, so the aim of the present paper intends to study the performance and emission rates of a spark-ignition engine (Single-cylinder high-speed engine was selected from previously published research in order to make some comparison and verification of the results of the simulation) by changing some of operating conditions of the engine. The formation of nitrogen oxides (NOx) have been investigated under different conditions; including the effect of the intake air temperature (Ti) naturally aspirated into the engine cylinder, the effect of the ignition timing (θig) of the spark plug, and also the effect of the equivalence ratio of air to fuel (ϕ) on the formation of nitrogen oxides. The results showed that the intake air temperature (Ti) has a strong effect on the reduction of nitrogen oxides (NOx) formation when the intake air temperature decreased from 350K to the temperature of 283K, the emission of nitrogen oxide decreased by about 20%. Also, the spark ignition angle has a strong effect on the formation of NOx, that is because of the high temperature of gases produced from the combustion inside the cylinder, in this case, an early spark ignition angle may not provide a good performance of the engine because of occurring the maximum pressure in the cylinder at the top dead center (TDC), which causes a decrease in thermal efficiency, high temperature, and a decrease in power. Also, the ignition angle delay causes a drop in the maximum pressure inside the cylinder at a very late angle After Top Dead Center (ATDC). The results show that by changing the ignition from 40o to 20o Before Top Dead Center (BTDC), the formation of NOx decreased by 74%. The effect of air-fuel ratio, on the formation of NOx, significantly decreased on the formation of NOx when the engine was operated with a very lean mixture because the temperature of the gas at very lean is very low. Nitrogen oxide formation decreased from ϕ ൌ 0.85 to ϕ ൌ 0.6 by 96%. KEYWORDS: Air Pollution; NOx; Spark Ignition Angle; Ignition Timing; Air to fuel Ratio.