Development of a Lean Burn Methane Number Measurement Technique for Alternative Gaseous Fuel Evaluation

A wide range of fuels are used in industrial gas fueled engines. Fuels include well-head gas, pipeline natural gas, producer gas, coal gas, digester gas, landfill gas, and liquefied petroleum gas. Many industrial gas fueled engines operate at high power density and at ultra-lean air-fuel ratios for low NOx emissions. Engines operate in a narrow air-fuel ratio band between misfire and knock limits. To utilize this wide range of fuels effectively it is important to understand knock properties. Methane number determination for natural gas blends is traditionally performed with research engines at stoichiometric conditions where the onset of knock is identified through subjective audible indication. The objective of this paper is to develop a process to determine knock onset through direct indication from pressure transducer data at lean operating conditions characteristic of lean-burn industrial gas engines. Validation of the method is provided with methane number determination and comparison of pipeline natural gas. A Waukesha F2 Cooperative Fuel Research (CFR) engine is modified to incorporate piezoelectric pressure transducers at the cylinder head and conversion from natural aspiration to boosted intake and variable exhaust back pressures (to simulate turbocharger operation). The new pressure sensors enable Fast Fourier Transform calculation of pressure data to calculate amplitude at characteristic knock frequency.