A general calorimetry framework for measurement of combustion efficiency in a suppressed turbulent line fire

The present study seeks to measure suppression effects in a canonical experimental configuration, featuring the exposure of a buoyant, turbulent, methane or propane-fueled diffusion flame to a co-flowing oxidizer diluted with nitrogen gas. Species-based calorimetry measurements, using either oxygen-consumption (OC) or carbon-dioxide-generation (CDG) based methods, are derived and applied to this configuration. Traditional OC models, which cannot account for oxidizer-dilution, are found to significantly overpredict total heat release rate in the present configuration, while traditional CDG models coincidentally give accurate results. Only the present calorimetry formulation, with full accommodation for oxidizer dilution, provides accurate results for both methods. In both methane and propane flames, global combustion efficiency is found to remain close to unity over a wide range of oxidizer dilution, decreasing abruptly only at the onset of global extinction. Similar trends are noted in the net combustion yields of oxygen, carbon-dioxide, and water-vapor. Net yields of carbon-monoxide remain close to zero for both fuels, but increase slightly near the extinction limit. These measurements reveal that despite visible suppression effects in all of the present flames, until the extinction limit is reached, nearly all of the fuel continues to react and combustion products are produced in stoichiometric proportions.