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.
THERMODYNAMIC ANALYSIS OF COMBUSTION PROCESSES FOR PROPULSION SYSTEMS
A key issue in conceptual design and analysis of proposed propulsion systems is the role of the combustion mode in determining the overall e‐ciency of the system. Of particular recent interest are detonations and the e‐ciency of detonation-based propulsion systems as compared to more conventional systems based on low-speed ∞ames. Our goal is to understand, based on thermodynamics, the merits of detonative combustion relative to de∞agrative combustion characteristic of conventional ramjet and turbojet engines. After reviewing detonation thermodynamics, we analyze the merits of detonations for steady ∞ow systems and highlight the importance of the irreversible portion of the entropy rise in steady ∞ow analysis. The conventional analysis of steady combustion waves is reformulated to obtain solutions at a flxed stagnation enthalpy. The implications of this analysis are that detonations are less desirable than de∞agrations for a steady air-breathing combustion system since they entail a greater entropy rise at a given ∞ight condition. This leads us to consider the situation for unsteady, i.e., intermittent or pulsed, combustion systems which use various modes of operation. For unsteady detonation waves, we consider a notional cyclic process for a closed system (the Fickett-Jacobs cycle) in order to circumvent the di‐culties associated with analyzing a system with time-dependent and spatially inhomogeneous states. We use the thermodynamic principles for closed systems to compute the maximum amount of mechanical work produced by a cycle using an unsteady detonation process. This ideal mechanical work is used to compute a thermal e‐ciency for detonations. Although this e‐ciency cannot be precisely translated into propulsive e‐ciency, the results are useful in comparing detonations with other combustion modes. We flnd that the e‐ciency of cycles based on detonation and constant-volume combustion are very similar and superior to a constant-pressure combustion (Brayton) cycle when compared on the basis of pressure at the start of the combustion process.
Regional strategies for the minerals industries of the states of the SADCC
The SADCC has been in existence for eleven years but little progress has been made in regional coordination of the minerals sector even though this sector is the most important exporter of the region. There is however scope for minerals development at the regional level.