Gasoline flammability limits

Note 1. When loading volatile products such as gasoline, whose vapor concentration can be shown to rapidly exceed the upper flammable limit during tank filling, the velocity-diameter product may be increased to 0.50 mVs- This is consistent with API RP2003 [3]. Similarly, shorter wait periods of 1-2 min can be used. 

The flash-point is a measure of the ease of ignition of the liquid. It is the lowest temperature at which the material will ignite from an open flame. The flash-point is a function of the vapour pressure and the flammability limits of the material. It is measured in standard apparatus, following standard procedures (BS 2000). Both open- and closed-cup apparatus is used. Closed-cup flash-points are lower than open cup, and the type of apparatus used should be stated clearly when reporting measurements. Flash-points are given in Sax s handbook, Lewis (2004). The flash-points of many volatile materials are below normal ambient temperature for example, ether —45°C, petrol (gasoline) —43°C (open cup). 

Flammability limits for methane, hydrogen, and gasoline. (Courtesy of Air Products and Chemicals, Inc., Allentown, PA.)... 

A critical safety issue of using diesel-ethanol blends relates to flashpoint and flammability. E-diesel blends containing 10-15% ethanol have the vapor pressure and flammability limits of ethanol. This means that ethanol concentrations in enclosed spaces such as fuel storage and vehicle fuel tanks are flammable over the temperature range 13-42 °C. Thus, there are higher risks of fire and explosion than with diesel fuel, or even gasoline. Other vehicle performance-related concerns are (a) a decreased maximum power (b) an increased incidence of fuel pump vapor lock and (c) a reduced fuel pump and fuel injector life due to the decreased lubricity of ethanol. 

Table 4.12 shows a comparison of safety-relevant thermo-physical and combustion properties of hydrogen with those of methane, propane and gasoline [26]. The flammability limits are affected by temperature, as shown in Figures 4.9 and 4.10, so that a preheated mixture has considerably wider limits for coherent flames [27]. An increase in pressures up to lOkPa has only a small effect. Water vapor has a strongly inhibiting influence on the oxyhydrogen reaction. 

An important issue when handling hydrocarbon/steam/air mixtures are the flammability limits. Auto ignition temperatures were determined for reformulated gasoline by Ellis et al. [75], The auto ignition temperature of the air/fuel mixture was determined to be 360 ° C. Addition of steam increased this value to at least 500 ° C at O/C 1.0 and S/C 1.5. 

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