Problems with identifiying a standard procedure for determining KG values for flammable vapors

Assessing the effect of potential confined fuel–air explosions involves the examination of several essential parameters. These include the limits of combustion, maximum pressure and the deflagration index or K_G. Accurate measurement of these parameters can be influenced by numerous experimental conditions. This paper describes the sensitivity of one of these parameters (K_G) to several experimental influences. The deflagration index, K_G, is important since it is the main design parameter for explosion protection systems. These studies used a highly automated 20 liter combustion sphere, with a 10 mm fuse wire igniter. Our results for methane combustion show that the deflagration index, K_G, is very sensitive to

• •the gas composition; a 1% change in nitrogen composition changed the index value by 12 bar-m/s along the stoichiometric line. Our studies also identified some problems with mixing gases to the desired composition.
• •the moisture content of the gas, which can change the index by 13 bar-m/s.

For some combustion gas compositions, it was difficult to describe a K_G value due to significant fluctuations in the pressure vs time data. Finally, an extensive study of fuse wire igniter dynamics identified a means to provide a consistent energy delivery to the igniter. All of these problems contribute significantly to specifying a standard procedure for determining the deflagration index.