Enhancing the phi-meter by incorporating carbon dioxide measurement

Abstract

This paper describes the development, calibration and experimental application of an enhanced equivalence ratio measurement apparatus, or ‘phi-meter’. The original phi-meter developed by Babrauskas et al. used only an oxygen analyser and chemically removed the CO2. In this study, an enhanced phi-meter was developed to measure the equivalence ratio from experimental enclosure fires by O2 and CO2 measurements. As with all combustion calorimetry, the accuracy of the results increases with the number of species being directly measured and removing the need for chemical removal of the CO2 is an advantage. This is of practical importance as scrubbing agent required to remove CO2 from the combustion products requires careful handling and increases test costs. Moreover, in severely under-ventilated conditions, the production of CO significantly increases, and its measurement by phi-meter provides real-time validation of the occurrence of complete combustion within the phi furnace. The original equations derived for the phi-meter incorporated the depletion of oxygen, whereas the phi-meter equations developed in this paper incorporate O2 and CO2 measurements. The equivalence ratios measured in compartment fires for heptane, LPG and timber crib fuels ranging from 0.2 for oxygen-rich to 3.0 for fuel-rich conditions are found to agree with theoretical values.