Upper explosive limit estimation

Evaluation of the above equations with normal alkanes disclosed favorable agreement of estimates and data. For lower explosive limit, very favorable agreement was experienced for small, intermediate and large size alkanes. For upper explosive limit, rough agreement was experienced for small and large size alkanes. More favorable agreement was experienced for intermediate size alkanes. 

When a combustible substance is mixed with air, the mixture will explode only when it is neither too rich nor too lean. The lower explosion limit (LEL) is the minimum volume percent of the substance in air with flammability, which is separated from the upper explosion limit (UEL) by the explosive concentration range. The tabulations in handbooks are based on experimental data, and sometimes derived from estimation methods based on the elemental composition of the fuel as CmEtxOy. Figure 6.11 shows the LEL for the series of normal paraffins and of 1-alcohols versus the number of carbon atoms. There are two ways to plot the results, which show that, for paraffins, the volume percent shows a steeply declining trend, but the weight percent shows a mildly increasing trend. One may conclude that a smaller volume percent of higher paraffin... 

The results for lower (LEL) and upper (UEL) explosive limits in air are presented in Table 3-1. The LEL and UEL values are the lower and upper concentrations (expressed as volume %) for flammability. The tabulation also provides the freezing and boiling point temperatures which are helpful in determining whether the substance is a gas, liquid or solid at ambient conditions. The tabulation is based on both experimental data and estimated values. 

Example 2 Estimate the lower (LEL) and upper (UEL) explosive limits in air for the gas mixture below ... 

Experience tells that this estimate agrees fairly well with the measured values of the lower explosion limit for similar flammable gases. The upper limit shows larger deviations. The equations should be applied with care to safety technological questions, since the deviations may lie on both the safe and the unsafe side [4]. 

M the mass of gas between the lower and upper flammability limits. The quantity is needed for estimating the explosive contents of the cloud. 

The shock wave calculation of NO production does not take into account the fact that air within the fireball center contains approximately one-sixth of the initial explosion energy, having been heated by the radiative growth mechanism described earlier. This air cools on a time scale of several seconds by further radiative emission, entrainment of cold air, and by expansion as it rises to higher altitudes. These mechanisms are sufficiendy complex that one can only estimate upper and lower limits to the quantify of NO finally produced. 

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