Optimization of Dedicated Natural Gas (High Comp.) Spark Ignition Engine for Maximum Efficiency and Minimum Emission

Abstract

All around the world the number of automobiles has increased many folds (about ten times) in the last fifty years which resulted in an enormous increase in urban pollution level especially in developing countries. Pakistan has been considered as the most urbanized country in South East Asia with about 36% of Pakistan‟s total population is residing in towns & cities. It has been estimated that an average vehicle in Pakistan emits 20 times more unburned hydrocarbons (UHCs), 24 times as much carbon monoxide (CO) & about 3.6 times more oxides of nitrogen (NOx) when compared to an average vehicle in U.S. Furthermore the scarcity of conventional fuels also propelled the world to explore alternative fuel options with same or preferably less environmental implications. Natural gas is rated as high octane alternative fuel with octane rating of 120~130 and exhibiting clean burning characteristics. It is possible to attain increased efficiency from natural gas because of its high octane value with the increase of the compression ratio of the engine. Further the improved combustion efficiency of natural gas fuel also reduces the tail pipe pollutant emission. The focus of this research is to suggest the optimum compression ratio at which the performance of dedicated natural gas engine can be optimized. A 2.5 L Diesel Engine was selected and converted to run solely on natural gas as dedicated mode by incorporating spark plugs, electronic ignition control system, and CNG fuel metering system. Different piston sets were modified to obtain selected compression ratios. Based on the literature review, compression ratios were 11, 12, 13 & 14 had been selected. The temperature gauges were installed in the cooling water circuit and exhaust manifold to measure the water & exhaust gas temperatures. The engine was then tested on dynamometer for performance & exhaust emission. The readings of NOx, CO, UHCs at 1000, 1500, 2000, 2500 and 3000 rpm at selected compression ratios were taken by using 5-gas exhaust gas analyzer. For emission testing, steady-state test profile was generated. Exhaust gas temperatures were also recorded at different rpm settings at selected compression ratios. The results have been plotted and normalized by power. Based on the engine performance, the compression ratio of 13 has been selected as optimum compression ratio for dedicated CNG engine. For further reduction of engine exhaust emission Three-Way Catalytic simulation through Chemkin software has been carried out and the performance parameters were also predicted through simulation using single-zone thermodynamic model.