Introduction to "To the Question of Energy Use of Detonation Combustion" By Ya. B. Zel'dovich
Ya. B. Zel’dovich (1914–1987) made numerous contributions [1] to the theory of detonation, beginning with his very well known and widely translated article [2] on detonation structure that first introduced the standard Zel’dovich-von Neumann-Doring (ZND) model of shock-induced combustion. Even at that early stage of detonation research, Zel’dovich was also considering the application of detonations to propulsion and power engineering. He published these ideas in another paper [3] that has been virtually unknown in the West and has apparently remained untranslated until now. We are indebted to Sergey Frolov of the N.N. Semenov Institute of Chemical Physics for first bringing this article to our attention. We believe that the focus of this paper, which is the application of detonation waves to power generation and propulsion, is very relevant to the current activity on pulse detonation engines. In particular, Zel’dovich was apparently the first researcher to consider the questions of the relative efficiency of various combustion modes, the role of entropy production in jet propulsion, and the distinction between unsteady and steady modes of detonation in power engineering and propulsion applications. Even 60 years later, we believe that his results are relevant and can be of value in modern discussions on thermodynamic cycle analysis of detonation waves for propulsion [4]. For these reasons, we have arranged for the paper to be translated and suggested that it be published by the Journal of Propulsion and Power.
THE PERFORMANCE OF STEADY DETONATION ENGINES
Propulsion systems driven by steady normal detonations are studied. The practical di‐culties associated with stabilizing a detonation wave are highlighted. The requirement on the freestream total enthalpy is considered in parallel with efiects such as condensation or auto-ignition of the fuel-air mixture and limitations associated with fuel sensitivity to detonation. A criterion for detonation stabilization is formulated and applied to an analytical treatment of a detonation ramjet and a detonation turbojet, which are the respective analogs of the ramjet and the turbojet using detonative combustion. The performance of these engines is evaluated and compared to the ideal ramjet and turbojet models for hydrogen and JP10. A limitation is placed on the maximum total temperature allowed in the combustor, based on material considerations. The results show that steady detonation engines have a small thrust-producing range, due to the requirements for detonation stabilization. Their performance is always lower than that of the conventional ramjet and turbojet because of the total pressure loss across the detonation.
Doppler interferometry study of unstable detonations
Near-limit detonations are highly unstable and characterized by very large longitudinal velocity fluctuations that can range from 0.4 to 1.8 times the normal Chapman-Jouguet value. The period of the fluctuations also varies over a wide range from a few to a hundred tube diameters. In an attempt to establish a criterion for detonation limits, the velocity fluctuations of near-limit detonations are studied. A novel microwave Doppler technique based on a single coaxial mode has been developed for this purpose to give an unambiguous quasi-continuous velocity measurement of the detonation wave over the entire length of its travel. The near-limit unstable behavior in the detonable stoichiometric mixtures of hydrocarbons (C2H2, C2H4, C2H6, C3H8) with O2, air or N2O, tested in this work, have been characterized by four distinct modes of unstable behavior. This classification allows a qualitative description of the wide range of velocity fluctuations occurring near the detonation limit, including galloping waves.