Combustion nonsteady

CA 68,61103 (1968) Nonsteady burning of solid propints is being investigated both theoretically and exptly with attention to combustion instability, transient burning during motor ignition, and extinction by depressurization. 

Nonsteady Burning and Combustion Stability of Solid Propellants, Hrsg. De Luca, L., Price, E. W., Summerfield, M., Progress in Astronautics and Aeronautics, Vol. 143, AIAA, Washington, DC, USA, 1992... 

A monograph of Shchelkin Troshin (Ref 11) is based on studies at the Institute of Chemical Physics, Academy of Science, Moscow during the period 1952-1962, of theoretical analyses of detonation, deflagration, flame acceleration, nonsteady-state double discontinuities, and high-frequency oscillations in forced-combustion chambers. The book has been translated into English (See Ref 11a)... 

Despite intensive theoretical and experimental research on the combustion wave over the past decade, a universally accepted concept of the phenomenon has not been achieved. This is particularly true with respect to the nonsteady state phenomena of limits of inflammability and ignition. 

Frequently in theoretical work on the subject, whether dealing with the steady or nonsteady state, the mathematical development of an adopted model is followed by a descriptive summary of the results which is rarely traced back clearly to the assumptions inherent in the model. This has often resulted in extravagant identification of the model with the actual phenomenon and has been an obstacle in the task of reconciling conflicting views. There is need, therefore, of a purely descriptive exposition, stripped as completely as possible of mathematical language, to clarify the physical concepts of the combustion wave phenomenon. 

A reaction at the initial temperature changes the characteristics of an explosive mixture before the flame front and introduces an element of nonsteadiness into the process of propagation of the combustion wave. The method proposed in [1] to describe this effect consists in replacing the original non-steady problem by a quasi-steady one with adiabatically increasing initial temperature Ta(f) and an effective source of heat release which takes this increase into account. We test this method below by comparing it directly with the results of a numerical solution of the original non-steady problem. 

In the case of combustion of condensed substances, consideration of nonsteady processes, accounting for the non-adiabatic nature of combustion, which we do not present here, leads to the following conclusions ... 

A Model for the Nonsteady Ignition and Combustion of a Fuel Droplet... 

Of the many extensions of the classical quasi-steady droplet combustion models, most have dealt with the nonsteady eflFects which take place during droplet ignition and combustion (3-9). Using Greens function techniques to evaluate the nonsteady heat and mass transfer equations... 

The present theoretical model is used here to analyze the entire ignition and combustion process for a single droplet and to examine the eflFects of nonsteady droplet heating and droplet motion relative to the hot gas environment. The computations pertain to a 300 fx furfuryl alcohol droplet with an initial droplet temperature of 295 K, and the conditions for the hot gas environment are taken to be = 1400 K and iVo) = 0.1355 g 02/g air. The rate constants used for the ignition criterion are those determined in Ref. 7. The eflFect of droplet relative motion on ignition and combustion is illustrated in Figures 2-6 as a function of the gas-phase heat and mass transfer mode namely, pure diflFusion, free convection, and forced convection with the droplet relative velocity taken as Vd — Voo = 25 cm/sec. 

Numerical Procedure. This section describes an iterative numerical procedure for evaluating the mathematical model presented in this chapter for the nonsteady ignition and combustion of a fuel droplet The key step of this procedure is to match or couple the analytical equations for heat and mass transport at the liquid/gas interface by establishing the droplet surface temperature for a series of successive short time intervals. The numerical procedure for each time consists of the following steps ... 

If the pressure in a rocket motor changes during the time interval x, the pressure transient is considered to be steady state combustion when x > xc, and is nonsteady state combustion when x < xc. 

Kentfield JAC. Pulse combustors. In Kentfield JAC, ed. Nonsteady, One-Dimensional, Internal, Compressible Flows. New York Oxford Univ. Press, 1993,pp 191-235. King CJ, Clark JP. System for freeze-drying. U.S. Patent No. 3,453,741, 1969. Kitchen JA. Pulse combustion apparatus. U.S. Patent No. 4,697,358, 1987. 

The first mechanistic KDIE correlation of the thermal decomposition process with explosive sensitivity was accomplished with the thermally initiated nonsteady—state thermal explosion event. The HMX thermal explosion event has been discussed and represents an intermediate temperature/pressure regime between the less drastic combustion event and the high order steady—state detonation event. Mechanistic KDIE detonation investigations recently have been conducted and provide the first correlation between the thermochemical decomposition process and shock—induced detonation using an exploding foil driven flyer plate test. i ... 

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