Natural gas plays an important role as an alternative fuel for gasoline and diesel engines. It has a promising future especially with the world crisis in fuel and the lower prices of natural gas compared to the prices of gasoline and diesel fuels. It can be used as a sole fuel in spark ignition engines because it has nearly similar properties as gasoline, but in diesel engines it is used as a main fuel while the diesel fuel is injected to the combustion chamber as a pilot fuel to be an ignition source.
This paper investigates the performance of a small dual fuel engine where a single cylinder, four stroke water cooled diesel engine is converted to run on a dual fuel of diesel and compressed natural gas (CNG). An exhaust gas recycling system is used to introduce two ratios of EGR (Exhaust gas recirculation) to the engine. Effects of percentage of natural gas content and EGR ratio on engine performance and emissions are investigated for different engine loads.
Based on the obtained experimental results, it can be concluded that the total reduction in engine thermal efficiency increases as the ratio of the used natural gas increases. A maximum reduction of about 5 % in engine efficiency is recorded when 80% of diesel fuel is replaced by natural gas to deliver the same engine power. Also, NOx emissions are decreased while CO is increased with utilization of EGR.
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