Abstract
The paper presents some results regarding the identification of a turbojet engine’s optimal combustion chamber geometry, characterized by small dimensions, with enhanced possibilities for air and fuel mixture circulation in the primary combustion zone in order to obtain good residence time in the flame tube, higher turbulence and optimal radial temperature distribution. Also, it deals with the identification of some solutions of the differential equation for reduced temperature under imposed initial conditions. Some models of combustion numerical computations have been applied, as presented by the specialized documentation, to establish the combustion rate and flame speed for laminar combustion. The geometry of a combustion chamber, with twenty-four injectors and size comparable to a real combustion chamber, has been created in order to obtain the speed and temperature flow field within the flame tube. The major conclusion of the current research is that the distribution of holes within the liner does not need to be symmetric, which means that they have to be positioned in such as a manner as to ensure a higher degree of turbulence in the combustion primary zone and a helical shape of stream lines in the proximity of the walls of the flame tube.
Highlights
The combustion chamber is one of the most important constructive elements of an aircraft engine and has an important role in the conversion of energy from chemical to kinetic
The current flame tubes are based on experimental data and less so on theoretical, analytical and CFD calculation because the old models of the combustion chamber were improved slowly due to their complexity, and the advanced combustion algorithms being developed are based on powerful computers
The prototype of the flame tube with asymmetric distribution of holes on its surface ensures a higher turbulence in the secondary area
Summary
The combustion chamber is one of the most important constructive elements of an aircraft engine and has an important role in the conversion of energy from chemical to kinetic. The curve of adiabatic temperature, regarded as a function of the equivalence ratio, φ, has a maximum value at φ = 1, but the actual temperature falls below the theoretical prediction, starting around an equivalence ratio of 0,4-0,5, due to the dissociation reactions [1] This range of equivalence ratio corresponds to a fuel-to-air ratio of 2,53,5 and, taking into account the fact that gas temperature decreases after the point where φ = 1, a burner exit temperature can be reached from either the fuel-lean or the fuel-rich side of the stoichiometric point. The burning of liquid droplets requires the liquid to evaporate and for the fuel and air to diffuse together to form locally a near stoichiometric mixture [4] This process is much slower than the main chemical process of combustion. The content of this study is based on the mathematical approach presented in reference [1]
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