DEFLAGRATION-TO-DETONATION TRANSITION IN STOICHIOMETRIC BINARY HYDROCARBON (METHANE, PROPANE, ETHYLENE) HYDROGENBLENDS IN AIR

Systematic experimental studies of de§agration-to-detonation transition (DDT) in binary hydrocarbon (methane, propane, ethylene) hydrogen air mixtures of stoichiometric composition with hydrogen volume fraction xH2 varied from 0 to 1 are conducted at normal pressure and temperature conditions in a pulse-detonation tube of three geometrical con¦gurations: C1, C2, and C3 (Fig. 1). Contrary to expectations based on the well-known high reactivity of hydrogen, the measured dependences of the DDT run-up distance LDDT and time τDDT on xH2 are shown to be highly nonlinear [1 3]. Thus, in methane hydrogen air mixtures, with an increase in xH2 , the DDT run-up distance changes nonmonotonically: in the range 0.25 < xH2 < 0.65, the dependences LDDT(xH2 ) can have local maxima, i. e., the detonability of such fuel air mixtures deteriorates with the addition of hydrogen (Fig. 2a). In propane hydrogen airmixtures, the measured dependences of the DDT run-up distance appear to be nonlinear and nonmonotonic (in some cases): mixture detonability increases sharply only at relatively large hydrogen content (at xH2 > 0.7) (Fig. 2b). Finally, in ethylene hydrogen air mixtures, hydrogen addition to ethylene at 0 ≤ xH2 ≤ 0.7 results in no variation of mixture detonability in terms of DDT run-up distance (Fig. 2c). However, hydrogen addition to ethylene at xH2 > 0.7 results in a drastic increase of mixture detonability. Since various modi¦cations of tube design do not affect the character of the dependences, these e¨ects are attributed to the physicochemical properties of the mixtures. In general, based on the similarity of the experimental results for methane hydrogen air, propane hydrogen air, and ethylene hydrogen air mixtures obtained using the same experimental facilities and conditions, one can conclude that such unexpected dependences are caused by chemical and physical properties of hydrogen, namely, its temperature and pressure dependent reactivity in terms of the laminar §ame velocity, selfignition delay, etc., as well as its low molecular mass.