Computational and experimental work to select optimal design parameters of a fuel injector in order toobtain high-energy characteristics of low-thrust liquid rocket engines (LTLRE) with a deflector-centrifugal mixingscheme with 400 N thrust was carried out. A centrifugal atomizer is installed coaxially with the combustionchamber in the deflector-centrifugal mixing scheme. The engine thrust increases with the diameter of the combustionchamber and, consequently, the length of the free span of the fuel film in the cone of the fuel spray of thecentrifugal injector also increases before hitting the inner wall of the combustion chamber. Thus, it is necessaryto 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-phasemixing of fuel components on the inner wall of the combustion chamber the design parameters of the centrifugalnozzle (the diameter of tangential holes, the length and diameter of the vortex chamber, the length and diameterof the injector nozzle) that would ensure the stability of the fuel film all along the free span up to the inner wallof the combustion chamber, as well as the speed, the film thickness and the angle of the atomization cone werecalculated. In case of the optimal choice of parameters the films of oxidizer and fuel interpenetrate each otherthrough their thickness. Thus, complete conversion of the fuel components takes place, which ultimately provideshigher power characteristics of the engine.The article presents the results of firing tests of a 400 N LTLRE with different design parameters of an injectorwith the deflector-centrifugal mixing scheme. It follows from the test results that as the nominal pressuredrop across the centrifugal nozzle decreases to a certain limit the value of the specific impulse increases. If theinlet pressure is considerably reduced and, as a consequence, there is a significant reduction in the pressure dropacross the centrifugal nozzle, the amplitude of the pressure oscillations in the engines combustion chamber isincreased. The analysis of the test results made it possible to optimize the design parameters of the fuel swirlerfor a regular 400N LTLRE.