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A second-generation phi meter for global equivalence ratio and gas species concentration measurements



Ryan Falkenstein-Smith, Thomas Cleary


This work presents a second-generation phi meter capable of making simultaneous real-time measurements of the global equivalence ratio and combustion product concentrations (i.e., water vapor, carbon dioxide, and oxygen). The fuels initially examined are methane, propane, and propene. Fuel is mixed with predetermined air concentrations to create a broad spectrum of fuel-air ratios. The global equivalence ratio of a sampled mixture is measured by the phi meter via lean combustion. Water vapor concentrations are made using a thermal electric cooler and supplemental drying unit placed between a high-temperature mass flow controller and ambient temperature mass flow meter. The difference between the flow units provides the water vapor concentration measurement. Carbon dioxide and oxygen concentration measurements are made using IR and paramagnetic sensors, respectively. The ability to measure combustion product concentrations provides additional insight into the sampled gas, specifically, carbon to hydrogen ratio calculations and total mass balance. The measured and expected global equivalence ratios for all gas mixtures are observed to be in fair agreement. The expected values and estimated water vapor concentration measurements are consistent within the experimental uncertainty. The uncertainty of the calculated carbon to hydrogen ratio of incoming gas mixtures is within the parent fuels' ratio, thus validating the instrument's ability to measure gas species concentrations of the combustion products.
Proceedings Title
12 U.S. National Combustion Meeting
Conference Dates
May 23-26, 2021
Conference Location
College Station, TX, US


Gas extractive sampling, Lean combustion, Mass balance, Phi meter


Falkenstein-Smith, R. and Cleary, T. (2021), A second-generation phi meter for global equivalence ratio and gas species concentration measurements, 12 U.S. National Combustion Meeting, College Station, TX, US, [online], (Accessed July 23, 2024)


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Created September 23, 2021, Updated November 29, 2022