PERFORMANCE AND EXHAUST EMISSION CHARACTERISTICS OF A DIESEL ENGINE USING ALTERNATIVE FUELS
JES. Journal of Engineering Sciences
The present work introduces an improvement performance and reduces the exhaust emissions of Diesel engine. The experimental comparative study of the combustion characteristics and exhaust emissions for a single cylinder Diesel engine using LPG-Diesel and CNG-Diesel dual fuels separately are studied. Different ratios of LPG and CNG in Diesel fuel up to 70% were used respectively. The test rig was furnished with a computer-controlled data acquisition system and the necessary measuring instruments
... asuring instruments to measure and record ignition delay, combustion duration, peak cylinder pressure, dual specific fuel consumption and exhaust emissions. The engine was tested at different speeds and loads. The results indicated that the ignition delay of both LPG-Diesel and CNG-Diesel dual fuel are obviously longer than that of Diesel fuel only. The combustion duration for the two cases is slightly reduced with the increase of gaseous fuel ratio at low speeds; however, it increases at high speeds. As gaseous fuel ratio is increased, the peak cylinder pressure is slightly reduced at low loads, however, at high loads; the peak cylinder pressure strongly decreases. The level of NO x emissions under dual fuel operation is lower than normal Diesel operation at different gaseous fuel ratios. CO and HC emissions for the two cases decrease with the increase of gaseous fuel ratio. The dual specific fuel consumption slightly increases with the increase of gaseous fuel ratio. The final results showed that when using CNG dual fuel, the combustion performance increases while the exhaust emissions decrease compared with Diesel and LPG dual fuel. resulting of high CO and unburned HC emissions  . However, at high loads increased admission of LPG can result in uncontrolled reaction rates near the pilot fuel spray and leads to knock [11, 13] . CNG is basically composed of methane whereas LPG is a mixture of propane, butane and other chemicals,  . Another important difference from a physical point of view is that CNG does not liquefy under high pressure, but it remains a gas, unless it is cooled down to at least -164°C  . LPG becomes liquid when it is compressed or when it is cooled down (therefore its name is Liquefied Petroleum Gas). CNG comes directly from a gas field. The only process, which sometimes needs to be done, is the filtering of the gas. But usually, the gas can be used as a fuel right away after the compression process. CNG has a density less than the air, while LPG has twice density of the air. Compressed natural gas (CNG) used in dual fuel engines has been studied from point of view of the combustion duration and ignition delay     . A CNG-Diesel dual fuel engine offers an attractive alternative to both Diesel and spark ignition engines. Also, CNG readily forms homogenous air/fuel mixtures which can be ignited and burned over a wide flammability range [20&21]. This pre-mixed combustion produces lower nitrogen oxides (NOx) emissions and soot emissions compared to Diesel engines. At low engine loads, lower fuel combustion efficiency has been observed  , which results in significant amounts of hydrocarbon (HC) and carbon monoxide (CO) in the exhaust emissions. Using dual fuel engine, Elnajjar et al,  ,have investigated the effects of different engine parameters and their correlation to the overall generated noise. The study was conducted for three different fuels: pure diesel fuel, natural gas and duel fuel of diesel-LPG. The study reported the location (crank angle) corresponding to maximum cylinder pressure and maximum pressure rise rate. Vezir Ayhan et at  investigated the effects of LPG injection during air inlet period on performance characteristics and emissions. The engine has been modified to determine the best LPG substitution for dual operation in order to improve the emissions quality while maintaining high thermal efficiency in comparison to a conventional diesel engine. LPG injection rate were selected as 5, 10, 15 and 25% on a mass basis. Minimum SFC and maximum brake efficiency obtained with 15% LPG between 1400 and 1800 rpm engine speeds. Optimum injection rates is found at 5% LPG in terms of exhausts emissions and performance. In the present work, an experimental study has been conducted to create alternative dual fuel (mixture of gas and Diesel fuel) to improve the performance of diesel engine and reduce the exhaust emission. The combustion characteristics and exhaust emissions (NO x , CO and HC) of Diesel engine using LPG-Diesel and CNG-Diesel dual fuels are experimentally compared at the same operating conditions respectively. Different ratios of LPG and CNG in diesel fuel up to 70% were used at different engine speeds and loads.