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The Flammability Limits of Lean Fuel-air Mixtures--thermochemical and Kinetic Criteria for Explosion Hazards.
20th Ann Mtg Anal Instr Symp Isa Pittsburgh, Pennsylvania, 5/12-15/74 Reprint No Aid 74414 Pp 61-69 (Aid):61-69
The present state of knowledge of the flammability limits of lean fuel-air mixtures is reviewed concisely in terms of the experimental methods used, the effect of apparatus size, accuracy of data, methods of data presentation, and the sensitivity of the limits to initial temperature and pressure. The heat of combustion per mole of gas mixture at the lean limit is a reliable thermochemical criterion for the flammability of organic fuels with comparable reactivities. [the limit calorific value for the heavy paraffins is 11.5 +/- 0.1 Kcal/mole. However, kinetic effects strongly influence this value.] highly reactive fuels (hydrogen, acetylene) require lower energy contents, whereas less reactive fuels (ammonia) require higher values. Hydrogen-starved fuels (carbon monoxide, cyanogen) show marked anomalies and are sensitive to impurities that can provide h-atom chain carriers. [these kinetic effects are reflected in the experimentally measureable burning velocity of the fuel.] this parameter is a key ingredient in the theory of flammable limits, which is briefly sketched. Five competing processes dissipate power from the combustion wave and quench it at some characteristic limit velocity. The prevalant consensus that the limits are controlled by natural convection is clearly demonstrated, and the complex interplay of kinetics and thermochemistry follows logically therefrom.
20th Ann. Mtg., Anal. Instr. Symp., Isa, Pgh., Pennsylvania, 5/12-15/74, Reprint No. Aid 74414, Pp 61-69
Page last reviewed: March 11, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division