A review of vaporization models as design criterion for bipropellant thrust chambers

Abstract

In the beginning of liquid propellant rocket engine development, the thrust chamber sizes were obtained, mainly, empirically. With the technological advancements over the years, several approaches have been developed in order to optimize its sizes and predict more accurately the performance. Besides the clear contribution in predicting efficiencies, the use of accurate vaporization models to optimize combustion chambers decreases losses and the number of required tests. To increase efficiencies, the chamber must be optimized. In case the chamber is too small, incomplete combustion is achieved and combustion instability may occur. In case the chamber is too large, losses due to weight and heat transfer increase and the vehicle becomes larger (leading to more drag losses). Additionally, the number of tests is reduced since models were experimentally validated and less experimental iterations are required in order to obtain the optimized design. Although there are many models, all of them reach similar conclusions, such as an increase in chamber pressure, a decrease in injected droplet size and velocity, and others, lead to a decrease in the required chamber size. Nowadays, with the advancements in computing budget, more complex and accurate models have be developed. Some of these models account for chemical reactions, turbulence effects, droplet collisions and interactions, two- and three-dimensional modeling, and others. Also, the use of CFD codes provides relevant contributions to the analytical and numerical models, especially in validating them, and, additionally, decreases the amount of required experimental tests. The main propulsive parameter that rules this phenomenon is the characteristic length, which accounts the required chamber size for the propellants to be injected, atomized, vaporized, mixed and combusted. Most of the available models neglect the atomization, mixing and combustion of the propellant, since those phenomena occur much faster compared with the vaporization. This work provides a review of those vaporization models, focusing on the main used models worldwide. Such review is of great importance in order to supply enough information and comparison between models, making possible for the researcher/engineer to choose the model that better fit its necessities, requirements and limitations.

Keywords

• vaporization models
• liquid propellant rocket engines
• characteristic length
• injected droplet size