Applied Energy 113 (2014) 1068–1076                          

Experimental study of the performance and emission characteristics of an adapted commercial four-cylinder spark ignition engine running on hydrogen-methane mixtures

Abstract

The use of hydrogen/methane mixtures with low methane contents as fuels for internal combustion engines (ICEs) may help to speed up the development of the hydrogen energy market and contribute to the decarbonization of the transportation sector. In this work, a commercial 1.4 l four-cylinder Volkswagen spark-ignition engine previously adapted to operate on pure hydrogen has been fueled with hydrogen/methane mixtures with 5-20 vol. % methane (29.6-66.7 wt. %). An experimental program has been executed by varying the fuel composition, air-to-fuel ratio (, spark advance and engine speed. A discussion of the results regarding the engine performance (brake torque, brake mean effective pressure, thermal efficiency) and emissions (nitrogen oxides, CO and unburned hydrocarbons) is presented.

The results reveal that  is the most influential variable on the engine behavior due to its marked effect on the combustion temperature. As far as relatively high values of  have to be used to prevent knock, the effect on the engine performance is negative. In contrast, the specific emissions of nitrogen oxides decrease due to a reduced formation of thermal NO_x. A clear positive effect of reducing the spark advance on the specific NO_x emissions has been observed as well. As concerns CO and unburned hydrocarbons (HCs), their specific emissions increase with the methane content of the fuel mixture, as expected. However, they also increase as  increases in spite of the lower fuel concentration due to a proportionally higher reduction of the power. Finally, the effect of the increase of the engine speed is positive on the CO and HCs emissions but negative on that of NO_x due to improved mixing and higher temperature associated to intensified turbulence in the cylinders.