In recent years, there has been a trend towards an increase in demand for microturbines. The microturbine application area is very wide. These are hybrid power plants for transport and specialized equipment, as well as power plants for providing electricity to homes, towns, businesses. When developing advanced gas turbine units, it is necessary to take into account sufficiently high requirements for economic and operational indicators. To improve the performance of microturbines, it is necessary to optimize and refine the basic elements. In particular, to reduce the emission of harmful substances, it is necessary to develop low-toxic combustion chambers. In this paper, we present the results of optimization and fine-tuning of a low-toxic combustion chamber with the use of numerical modeling of intra-chamber processes. The applied models of flow, combustion, radiation, NOx emission are described. The main parameters of the computational grid built for ¼ of the full-size combustion chamber are given. The boundary conditions necessary for the development of mathematical modeling of the flow and combustion processes are formulated. The results of comparison of the initial and optimized geometry of the combustion chamber in the form of patterns of temperature distribution, velocities, total pressure in the swirler, and the distribution of the mass fraction of nitrogen oxides NOx are presented. According to the results of optimization calculations, it can be concluded that relatively small changes in the size, shape and number of secondary air holes, the shape and dimensions of the flame tube, the diameter of the blade swirler and the shape and size of the nozzles of the gas injector have a significant effect on such indicators of the working process as: form, volume and location of the combustion zone; location and intensity of the mixing zone, which, as a consequence, greatly affects the integral parameters of the combustion chamber.
The article contains the results of development of small-size gas turbine engine with efficiency not lower than top piston engines. It is shown that use of a heat exchanger with an ultrahigh degree of regeneration (95% and above) in microturbines allows to raise the efficiency of small gas turbine engines up to 38-43%.
One of the applications of microturbines is their use as part of a hybrid transmission. This will significantly improve the environmental friendliness of vehicles. One of the problems of microturbines with a radial turbine and heat exchanger is the effective braking of the gas flow behind the turbine in the turbine diffuser. The purpose of this paper is a design study of the flow of gas in diffusers of various designs in order to determine the optimal (for losses of the total pressure and uniformity of the velocity field) structure. For the study, two variants of the layout of the microturbine were taken. In the first case, the axis of rotation of the heat exchanger was located parallel to the axis of rotation of the impeller of the turbine stage, in the second case - perpendicular. In order to minimize losses, the geometry of the output device of the first variant of the arrangement of the microturbine was varied, in particular, the output device without and with deflectors was considered. From the results of calculations it follows that the introduction of deflectors into the geometry of the output device makes it possible to reduce the vortex formation and, correspondingly, the total pressure loss. To determine the loss and the optimal value of the diffuser opening angle, a series of flow computations in the stage of the radial-axial turbine with a variation in the slope angle of the upper generator of the output diffuser α (0.0°, 2.5°, 4.0°, 6.0°, 7.0°) were conducted. A preliminary study was made of the effect of the selected model of turbulence and the size of the grid on the results of the calculation. Analysis of the results of calculations showed that the minimum losses of the total pressure and the maximum increase in static pressure are provided by the diffuser with an angle of inclination of the upper generatrix of 6°. An increase in the angle of inclination of the upper generatrix of 7° leads to developed detachment currents and an increase in losses. A comparative analysis of the obtained data for different versions of the diffuser showed that the second version of the layout of the microturbine (with a straight circular annular baffle diffuser) has significantly lower total pressure losses in the turbine output device.
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