Structure of gaseous detonation. IV. Induction zone studies in H 2-O 2 and CO-O 2 mixtures

Abstract

The density structure of the flow behind shock waves in H 2 −O 2 and in CO−O 2 mixtures has been examined interferometrically. In the former case it is shown that the oxygen is vibrationally excited before observable exothermic reaction. At least for very rich mixtures and probably for all mixtures, the hydrogen is also, since the vibrational relaxation time for H 2 (as well as for D 2 ) is found to be less than 2×10 −6 atm sec at 1400°K. The induction time for exothermic reaction has been measured for 0.0075≤[H 2 ]/[O 2 ]≤100 and the data may be fit to better than a factor of two for 2200> T >1100°K by log 10 ([O 2 ][H 2 ]) 1/2 ti =3100/ T —9.8, where concentrations are in moles/liter and time in seconds. Induction times in 2 H 2 +5 Air are also found to be represented by this equation. The observed density profiles in the region of rapid exothermic reaction have been analyzed for a number of very rich and very lean mixtures, assuming heat evolution to be due to three-body recombination processes, and termolecular rate constants of reasonable magnitude have been deduced. In 8 CO+O 2 , it is shown that both reactants become vibrationally equilibrated prior to reaction, and that the vibrational relaxation time is significantly less than for pure CO implying that vibrational exchange with excited O 2 is an important process in excitation of the CO. Addition of up to 1% H 2 is shown to reduce the relaxation time and accelerate the reaction, but not to affect the maximum density. With the thinner reaction zone due to added H 2 , the detonation is observed to develop spin and to acquire the characteristic “turbulent” appearance due to the transversely propagating shocks behind the main shock front and the consequent shear layers in the flow.