Abstract:
In maintaining performance of a dedicated natural gas engine to be the same as original Diesel one, it can be done by using a turbocharging system and enhancing combustion process. From this idea, it led to a research work of enriching natural gas fuel by hydrogen in a turbocharged dedicated natural gas engine. The objectives were to examine effects of hydrogen on combustion characteristics, engine performance and emissions. All test runs were carried out using a modified 2.5L, 4-cylinder, natural gas engine. The amount of hydrogen added into natural gas was in the range of 0-11 percent. All tests were done at steady state conditions. The results show that adding hydrogen 0-11 percent into natural gas gives rise to increasing of the engine performance of 23.0 - 44.4 percent, thermal efficiency of 27.6 - 31.4 percent and oxides of nitrogen of about 0.6 - 13.0 times while brake specific energy consumption, carbon monoxide and hydrocarbon are decreased by 27.6 -31.4 percent, 0.3 -0.4 times and 0.1 - 0.8 times respectively. From analysis of cylinder pressure data, it shows that hydrogen helps increasing combustion velocity in the form of burning times. The burning times from the start of ignition to 5, 10, 50 and 90 percent mass burned fractions are reduced by 0.37,0.38, 0.44 and 0.48 times respectively. The values of COV of IMEP and COV of Pmaxa re decreased by 64 percent and 9.0 - 56.9 percent respectivelywhen more than 5 percent of hydrogen is added. For a hydrogen-natural gas engine, the effect of spark timing shows that changing timing slightly affects to engine performance, carbon monoxide and hydrocarbon. However, oxides of nitrogen are affected significantly. The analysis of cylinder pressure data shows that retarded ignition timing increases COV of Pmax and combustion duration while COV of IMEP is almost unchanged. It is also found that adding hydrogen of 9-1 1 percent in the mixture extended lean operating limit of the engine from 0.60 to 0.44. However, at lean operating limit the values of burning time, COV of IMEP and COV of Pmax are increased. In conclusion, adding hydrogen in the range of 5 - 7 percent into natural gas is recommended for use in practice.