Limiting oxygen concentration evaluation in flammable gaseous mixtures by means of calculated adiabatic flame temperatures

The limiting oxygen concentration (LOC) of fuel-air-inert premixed gaseous systems are usually determined from measurements of explosion limits at progressive dilution with inert gas of fuel-air mixtures, which is a long and cumbersome procedure. An alternative procedure to evaluate LOC would be of great interest for all fields of activity involving the use of flammable mixtures, especially when less characterized fuels are used. The paper describes a new procedure (algorithm) meant to estimate the LOC of fuel-air-inert premixed systems, using the values of lower explosion limit (LEL) of the fuel-air mixture and the calculated adiabatic flame temperature (CAFT) both at LOC and LEL when nitrogen is used as an inert gas. It is based on an empirical correlation established between the CAFT computed for fuel-air-nitrogen mixtures at LOC and CAFT at LEL, for a large number of flammable gases and vapors. This requires only the measurement of LEL. The correlation was derived from flammability data taken from literature sources (German and American recommended values). The method is based upon the assumption that mixtures at LOC have an equivalence ratio psi = 1.250, which is close to the equivalence ratio of the most reactive fuel-air systems. Inverse calculations made with this new algorithm for nine fuel-air-ilitrogen mixtures allowed the determination of LOC with a relative deviation of 2-22%. (C) 2003 Elsevier B.V. All rights reserved.