NON-EQUILIBRIUM CHAMBER EFFECTS

if not all, solutions of the nozzle expansion problem have used equilibrium composition chamber conditions as the initial condition for nozzle solution. The feature is common to all of the nozzle flow solutions that is, the equilibrium composition expansion, frozen composition expansion, Bray freezing model, and kinetic rate solutions have all invoked the assumption of equilibrium composition at the beginning of the expansion process. While the failure to obtain equilibrium composition predicted performance, in terms of experimental characteristic velocities, has suggested a departure from equilibrium in the combustion chamber, only recently have non-equilibrium compositions been measured directly (31). 

The existence of non-equilibrium combustion products is important to at least two considerations. Firstly, the observed propellant performance may depart substantially from the predicted level. This departure may result in performance either less than or greater than the equilibrium predicted level. A striking example of greater than equilibrium performance is that of hydrazine monopropellant decomposition, table m-A-1. Another is that of ethylene oxide monopropellant, as mentioned in section n. B. 4., in which the equilibrium quantities of condensed carbon never are formed. Secondly, the non-equilibrium composition may have significant effects on the expansion process. In particular, nozzle kinetic calculations based on an assumed equilibrium composition initial condition may diverge significantly from expansions occurring from non-equilibrium initial conditions. 

Greater than equilibrium concentrations of intermediate species have been observed in the combustion products of several reactant systems. Examples are the concentrations of ammonia in the products of the decomposition of hydrazine (32), the concentration of CH4 in ethylene oxide decomposition (33), nitric oxide and ammonia in the products of the reaction of hydrazine and nitrogen tetroxide (34), and chlorine monofluoride in the products of the reaction of hydrazine and chlorine pentafluorlde (35). 

Direct evidence may be found both in laboratory and rocket engine experiments that the kinetics of the hvHragnnp/nitrogen tetroxide reaction controls the composition of the reaction products. Even early observations of the reaction of hydrazine and nitrogen tetroxide in rocket combustion chambers contain evidence of the role of chemical kinetics in the production of non-equilibrium combustion products (36). 

The results of several rocket engine investigations are summarized as the variation of characteristic velocity with mixture ratio and are compared with the predicted values based on equilibrium combustion in figure m-A-1. Greater than theoretical performance is obtained at fuel rich mixture ratios while considerably less than theoretical performance is reported at oxidizer rich mixture ratios. The results cannot be dismissed as the consequences of poor injection technique, poor mixing, or insufficient reaction time (L ), especially with the observation of greater than theoretical performance. At near stoichiometric mixture ratios and at chamber pressures of about 300 psia, performance in terms of characteristic velocity is near the theoretically predicted value. 

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