Comparison of central and end spark position for gas explosion vessels with L/D of 2.8 and 2.0

Current explosion vent design correlations and guidance are based on an experimental data base of centrally ignited vented tests. However, there is evidence in the literature that ignition positions other than central produce higher overpressures. The objective of this work was to compare central and end ignition of vented explosions in a 10L and a 200L cylindrical vessels of L/D of 2.8 and 2 respectively, with vent area coefficients of 10.9, 5.4 and 3.1 for free venting. Methane-air (10% v/v) and ethylene-air ( 7.5%) explosion tests were carried out using a 16J spark ignition at the far end wall opposite the vent and half way along the length of the vessel. The results showed that for both vessels and for both gas/air mixtures end ignition produced the highest overpressures. This was attributed to the higher axial flame speed towards the vent with far end ignition, inducing higher vent mass flows and higher external flame speeds and associated overpressures. The present results and other data from the literature show that the vent design guides may not be based on sufficiently conservative data and need to be reviewed.