Research of the influence of design parameters of a 400 N-thrust low-thrust liquid rocket engine on its energy efficiency

Computational and experimental work to select optimal design parameters of a fuel injector in order to obtain high-energy characteristics of low-thrust liquid rocket engines (LTLRE) with a deflector-centrifugal mixing scheme with 400 N thrust was carried out. A centrifugal atomizer is installed coaxially with the combustion chamber in the deflector-centrifugal mixing scheme. The engine thrust increases with the diameter of the combustion chamber and, consequently, the length of the free span of the fuel film in the cone of the fuel spray of the centrifugal injector also increases before hitting the inner wall of the combustion chamber. Thus, it is necessary to determine the parameters of the injector which provide the stability of the fuel film (absence of the film decay) along the span before it gets to the wall of the combustion chamber. For efficient organization of liquid-phase mixing of fuel components on the inner wall of the combustion chamber the design parameters of the centrifugal nozzle (the diameter of tangential holes, the length and diameter of the vortex chamber, the length and diameter of the injector nozzle) that would ensure the stability of the fuel film all along the free span up to the inner wall of the combustion chamber, as well as the speed, the film thickness and the angle of the atomization cone were calculated. In case of the optimal choice of parameters the films of oxidizer and fuel interpenetrate each other through their thickness. Thus, complete conversion of the fuel components takes place, which ultimately provides higher power characteristics of the engine. The article presents the results of firing tests of a 400 N LTLRE with different design parameters of an injector with the deflector-centrifugal mixing scheme. It follows from the test results that as the nominal pressure drop across the centrifugal nozzle decreases to a certain limit the value of the specific impulse increases. If the inlet pressure is considerably reduced and, as a consequence, there is a significant reduction in the pressure drop across the centrifugal nozzle, the amplitude of the pressure oscillations in the engine’s combustion chamber is increased. The analysis of the test results made it possible to optimize the design parameters of the fuel swirler for a regular 400N LTLRE.