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ENCIT 2020
18th Brazilian Congress of Thermal Sciences and Engineering
EVALUATION OF SMD EFFECTS ON CHARACTERISTIC LENGTHS OF LIQUID ROCKET ENGINES USING ETHANOL/LOX AND RP-1/LOX
Submission Author:
Maurício Sá Gontijo , DF
Co-Authors:
Maurício Sá Gontijo, Gustavo Alexandre Achilles Fischer, FERNANDO DE SOUZA COSTA
Presenter: Maurício Sá Gontijo
doi://10.26678/ABCM.ENCIT2020.CIT20-0794
Abstract
Liquid propellant rocket engines are used in many aerospace applications, since they show higher performance than solid propellant motors and allow thrust control. The characteristic length (L*) is an important parameter for the combustion chamber design, and is related to the stay time required for propellants to fully atomize, mix and react within the rocket chamber. Injector design is also an important factor once it affects directly the droplet Sauter mean diameter (SMD), impacting on L*. Pressure swirl injectors are widely used in propulsion applications because they can yield efficient atomization within a small volume. The swirl motion inside the injector creates a hollow cone spray, particular characteristic of this type of injector, decreasing L*. Ethanol/LOx and RP-1/LOx are propellant combinations used historically in several liquid propellant rocket engines. This work presents a theoretical study of the L* for these mixtures, based on Spalding model for droplet vaporization and combustion and the SMD models of Radcliffe and Jasuja. The algorithm was validated with data of three engines for chamber pressures from 10 to 250 bar and mixture ratios from 1 to 7. The Radcliffe model has predicted better the SMD for the L* comparing with actual engines, and SMD has affected in about 58 % the L*. Also, the concept of the characteristic equivalence ratio (Φ*), which is the equivalence ratio (Φ) required to reach the minimum L*, was presented. The results showed that, besides the thermo-physical properties of each fuel, the L* decreases with the increase in chamber pressure, reduction in propellant mass flux and closer to characteristic equivalence ratio. In general, the L* of the Ethanol/LOx is higher than the RP-1/LOx and it is reached with Φ* of about 0.779 and 1.632, respectively, which are values compatible to actual engines.
Keywords
characteristic length, Sauter Mean Diameter, Liquid Propellant Rocket Engines, Pressure Swirl Injectors
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