COMBUSTION PERFORMANCE AND EMISSIONS CHARACTERIZATION OF METHANE-HYDROGEN BLENDS (UP TO 50% BY VOL.) IN A SPARK-IGNITED CFR ENGINE

Finding alternatives to carbonaceous fuels has become a prime focus to support the global goal of decarbonizing the transportation sector. Hydrogen is a promising alternative fuel given that it is lightweight, and its combustion produces zero carbon dioxide. However, the absence of widespread dedicated hydrogen infrastructure for transportation, distribution and storage greatly limit its potential as the sole source of fuel for future vehicles. Instead, hydrogen can be readily blended with existing low-carbon fuels, such as natural gas, to enhance overall transportability and additionally improve combustion characteristics of operating devices. This manuscript explores the performance and emissions output of various methane-hydrogen blends, from pure methane to 50% hydrogen, by vol., performed over a range of fuel-air equivalence ratios ranging from the lean misfire limit to phi =1.2. Tests were performed on a single-cylinder spark-ignited Cooperative Fuel Research (CFR) engine at a fixed compression ratio and engine speed. Even with hydrogen's lower energy density, initial results show an ability to maintain the same output as the pure methane case over several different blend ratios. A two-phase heat release was observed and attributed to the differences in methane and hydrogen's reactivity. Notably, peak cylinder temperatures and NOx emissions increased as hydrogen blend ratio increased. Lower overall CO emissions were observed with increasing hydrogen blend ratio as the combustion efficiency increased with increasing hydrogen blend percentage. CO2 emissions were observed to decrease in proportion to the amount of carbon displacement in the fuel blend as the hydrogen blend percentage increased. Overall, using hydrogen as a combustion-enhancer for low-carbon fuels is a viable option as both combustion performance improves and emissions are reduced - all while resolving the significant infrastructure issues pure hydrogen faces.