Recombination and Condensation Processes in High Area Ratio Nozzles

Abstract

D or evaporated species that do not recombine or condense to equilibrium values during expansion in the nozzle of a rocket or air breathing engine may represent a large thrust loss. Data and understanding on recombination and condensation rates are needed for predicting engine performances such as hypersonic ramjets, chemical rockets, and nuclear rockets. Trends to higher operating temperatures, expansion to lower pressures, and use of metals or their compounds in fuel lead to the increasing importance of the chemical and physical processes in nozzles. This paper summarizes information on nozzle processes for certain systems of current interest; essentially it brings Ref. 1 up to date. In particular, the effect of recombination on performance, some implications to design, and data and analyses are presented for hydrocarbon-air, hydrogen-air, hydrogenfluorine, hydrogen-oxygen, jet fuel-oxygen, metallized propellant, and heated hydrogen systems. Not all available information in the field is treated, but the grosser aspects of the problem are highlighted. The systems discussed are examples of the three types of study that can be considered for evaluating nozzle performance. First, applying rate data to evaluate nozzle performance can be accomplished by solving a set of equations relating the flow, thermodynamics, and kinetics of the system. One difficulty in this rigorous approach is the mathematical complexity of including a number of processes. For example, assume that the hydrogen-air system requires consideration of four elementary reactions and seven species as follows: