Assessment of Knock Characteristics of Alternative Gas Fuels through Methane Number Measurement
Numerous alternative gaseous fuels are currently being considered to supplement our natural gas supply. These consist of synthetic gas (coal gasification, reformed natural gas) and biomass derived gases (anaerobic manure digestion, bio-mass pyrolysis gasification, landfill methane collection). Published combustion characteristics for alternative gas fuels are limited. A key combustion characteristic for gaseous fuels is the methane number, analogous to the octane number for liquid fuels. Fuel with a high methane number has good knock resistance, while a fuel with a low methane number has poor resistance to knock. More data is needed for alternative gas fuels so engines operating on these fuels can be designed for high efficiency and low pollutant emissions. For this work, methane number measurement is performed utilizing a single cylinder, F-12 Cooperative Fuel Research (CFR) engine, modified for gaseous fuel operation. A fuel blending system is used to simulate documented alternative fuel compositions. A mobile gas collection system is developed for field gas samples of previously untested alternative gas fuels. Methane number measurements of blended alternative gas fuels show an extremely wide range of methane numbers, from 24 (coal gas) to 140 (landfill gas). By comparison, the typical range for natural gas is approximately 80-95. The implications to engine design are discussed. This work was funded by the California Energy Commission.