Development and Validation of a Modular, Multi-point Phi Meter for Measurement of Global Equivalence Ratio

Abstract

The majority of fire deaths are due to the toxic products of a fire such as carbon monoxide. To better understand the production of these toxic gases, particularly in compartments, fire safety scientists can use phi meters, which take in samples from a fire and report the equivalence ratio, the mass ratio of fuel to oxidizer in the fire, which relates to the production of toxic products. To make phi meters more useful for fire research, a design was built that focuses on modularity, portability, and the ability to process more than one sample at the same time. The phi meter is composed of three module types: the furnace, treatment, and sensing. The furnace module houses a combustor that completes the combustion of all unburnt fuel in the four sample lines. It is contained in a portable case and uses four stainless steel ½” tubes which are heated using a Kanthal A-1 heating wire combustor. The module also contains a temperature controller for the furnace, heaters on each sample line to prevent condensation, and sheet metal enclosures to hold the insulation and prevent the electronics from overheating. Each line also has a supplemental oxygen supply, controlled with its own mass flow controller, to ensure all fuel is combusted in the furnace. The treatment module measures the humidity in the combusted sample before drying it to prepare it for the sensors. This drying uses Nafion technology. The sample passes through flow controllers and pumps that drive the sample flow. The sample then reaches sensing modules that each use paramagnetic and NDIR sensors to measure the O2, CO2, and CO concentrations for each of the sample lines. These values, along with humidity, are used to find the equivalence ratio. The design was then tested by flowing known mixtures of fuel and air into a mixing container. Samples were pulled from that container, run through the system, and equivalence ratio was extracted and compared to the expected equivalence ratio for the mixture. The results indicate that the device is capable of accurately calculating the equivalence ratio of the sample. Opportunities for future experiments exist to apply this design to full scale compartment fire experiments.