Flammability limit is a significant safety issue for industrial processes. A certain amount of flammability limit data for pure hydrocarbons are available in the literature, but for industrial applications, there are conditions including different combinations of fuels at standard and non-standard conditions, in which the flammability limit data are scarce and sometimes unavailable. This research is two-fold: (i) Performing experimental measurements to estimate the lower flammability limits and upper flammability limits of binary hydrocarbon mixtures, conducting experimental data numerical analysis to quantitatively characterize the flammability limits of these mixtures with parameters, such as component compositions, flammability properties of pure hydrocarbons, and thermo-kinetic values; (ii) Estimating flammability limits of binary hydrocarbon mixtures through CFT-V modeling prediction (calculated flame temperature at constant volume), which is based on a comprehensive consideration of energy conservation. For the experimental part, thermal detection was used in this experiment. The experimental results indicate that the experimental results fit Le Chatelier’s Law within experimental uncertainty at the lower flammability limit condition. At the upper flammability limit condition, Le Chatelier’s Law roughly fits the saturated hydrocarbon mixture data, while with mixtures that contain one or more unsaturated components, a modification of Le Chatelier’s is preferred to fit the experimental data. The easy and efficient way to modify Le Chatelier’s Law is to power the molar percentage concentrations of hydrocarbon components. For modeling prediction part, the CFT-V modeling is an extended modification of CAFT modeling at constant volume and is significantly related to the reaction vessel configuration. This modeling prediction is consistent with experimental observation and Le Chatelier’s Law at the concentrations of lower flammability limits. When the quenching effect is negligible, this model can be simplified by ignoring heat loss from the reaction vessel to the external surroundings. Specifically, when the total mole changes in chemical reactions can be neglected and the quenching effect is small, CFTV modeling can be simplified to CAFT modeling.

Flammability limit is a most significant property of substances to ensure safety of chemical processes and fuel application. Although there are numerous flammability literature data available for pure substances, for fuel mixtures these are not always available. Especially, for fuel mixture storage, operation, and transportation, inert gas inerting and blanketing have been widely applied in chemical process industries while the related date are even more scarce. Lower and upper flammability limits of hydrocarbon mixtures in air with and without additional nitrogen were measured in this research. Typically, the fuel mixture lower flammability limit almost keeps constant at different contents of added nitrogen. The fuel mixture upper flammability limit approximately linearly varies with the added nitrogen except mixtures containing ethylene. The minimum added nitrogen concentration at which lower flammability limit and upper flammability limit merge together is the minimum inerting concentration for nitrogen, roughly falling into the range of 45 plus/minus 10 vol % for all the tested hydrocarbon mixtures. Numerical analysis of inert gas dilution effect on lower flammability limit and upper flammability limit was conducted by introducing the parameter of inert gas dilution coefficient. Fuel mixture flammability limit can be quantitatively characterized using inert gas dilution coefficient plus the original Le Chatelier's law or modified Le Chatelier's law. An extended application of calculated adiabatic flame temperature modeling was proposed to predict fuel mixture flammability limits at different inert gas loading. The modeling lower flammability limit results can represent experimental data well except the flammability nose zone close to minimum inerting concentration. Le Chatelier's law is a well-recognized mixing rule for fuel mixture flammability limit estimation. Its application, unfortunately, is limited to lower flammability limit for accurate purpose. Here, firstly a detailed derivation was conducted on lower flammability limit to shed a light on the inherent principle residing in this rule, and then its application was evaluated at non-ambient conditions, as well as fuel mixture diluted with inert gases and varied oxygen concentrations. Results showed that this law can be extended to all these conditions.

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