Poetry therapy

Abstract

The gas explosion test facility (GETF) previously used to study detonability of natural gas (NG)–air mixtures was modified for studies of flame acceleration and deflagration-to-detonation transition (DDT). The 73-m-long by 1.05-m-diameter tube was equipped with 15 baffles of varying blockage ratio (BR) = 0.13, 0.25, or 0.50, placed near the closed end of the tube and spaced 1.52-m apart. The remaining part of the tube was smooth. Experiments used mixtures between 5.1% and 15.0% NG–air.Ignition was achieved in NG–air mixtures over the composition range 6.1–14.1%. After passing the 15 baffles, both flame and pressure wave velocity were more than 300 m/s over this range. Flame velocity was increasing over the range 6.2–12.8% NG–air, and it reached the sound speed in the burned gases (800–1000 m/s) over the composition range 8.0–10.8% NG–air. Pressure wave velocity was increasing over the composition range 6.1–14.1% NG–air and had reached sonic velocity over the composition range 6.2–12.6% NG–air. Shock waves with magnitude greater than 1 MPa were measured in all tests over the composition range 6.5–12.4%. DDT within the baffled section of the tube and sustained detonations beyond the baffles in the smooth part of the tube were observed over the composition range 8.0–10.8% NG–air. The observed run-up length to sonic flame velocity normalized by the tube diameter, Xru/D, ranges from 16 to 23 at BR = 0.13, 10 to 21 for BR = 0.25, and 13 to 21 for BR = 0.50. The observed run-up length to DDT normalized by the tube diameter, XDDT/D, ranges from 19 to 23 at BR = 0.13, and 16 to 23 for BR = 0.25 and 0.50.Coal mine safety regulations in the US require mine seals to resist an explosion pressure–time curve that rises instantaneously to 0.8 MPa and remains at that level for 4 s. Pressure–time curves measured in these experiments show that shock waves with near-instantaneous rise time and magnitude greater than 1 MPa can develop from weak spark ignition after passing 15 turbulence-generating obstacles in test mixtures ranging from 6.5% to 12.4% NG–air.