Acetylene detonation cell size

Figure 7.15a, b present, in detail, the effect of hydrogenous mixture composition and pressure on the detonation cell size [18, 19]. Besides, Fig. 7.15b compares HAM cell sizes with the same parameter for propane + air and acetylene + air mixtures. 

Detonation cell size (DCS) Characteristic size of the cellular structure generated by a flow instability on the detonation wave motion. It is measured by using traces on smoky foil placed on the inner wall of a detonation tube. DCS is used for evaluating detonation capability of a combustible mixture. DCS of a sensitive mixture (for example, acetylene + oxygen) is less than 1 mm. A low reactivity mixture DCS (for example, methane + air or lean hydrocarbon + air mixtures) is up to 1 m. 

A deflagration-detonation transition was first observed in 1985 in a large-scale experiment with an acetylene-air mixture (Moen et al. 1985). More recent investigations (McKay et al. 1988 and Moen et al. 1989) showing that initiation of detonation in a fuel-air mixture by a burning, turbulent, gas jet is possible, provided the jet is large enough. Early indications are that the diameter of the jet must exceed five times the critical tube diameter, that is approximately 65 times the cell size. 

---