Numerical analysis of the effect of fuel injection position and angle on the air-fuel mixing process in strut- and cavity-based scramjet engines

The development of high-speed aircraft has necessitated significant technological advances in propulsion systems. Especially for vehicles that can reach hypersonic speeds, conventional jet engines have proven inadequate and therefore air-breathing engine systems such as ramjet and scramjet have begun to be developed. In studies aimed at improving combustion efficiency and increasing thrust in air-breathing engines, strut and cavity-based designs stand out. In this thesis, the effects of the position and angle of fuel injection on the air-fuel mixture in strut and cavity-based flame arrester geometries used in scramjet engines have been analyzed by numerical methods. The contributions of different spray strategies to the mixture efficiency and combustion performance have been investigated in detail through parametric analyzes. Within the scope of the study, fuel injection was carried out from different points in cavity-based flame arresters, from the vertical, inclined and bottom surfaces; and from the upper, middle and lower regions of the strut surface in strut-based configurations, and ±30°, ±60° and 90° spray angles were applied at each point. In the analyzes performed; velocity vectors, streamlines, pressure and temperature distributions and water vapor concentration contours were evaluated for flow and combustion structures. The findings showed that the spray position and angle have decisive effects especially on flame stabilization, backflow formation and turbulence characteristics. In the strut-based design, a regular, symmetric and dense mixture was formed along the axis in 90° angle sprays, especially when sprayed from the top point. The highest water vapor concentration of 5.13% was obtained during spraying from the top point and the combustion efficiency increased. In the cavity-based flame holder, the highest water vapor concentration (13.35%) was obtained in the spraying made from the left side surface at 60° angle. The results were supported by indicators related to combustion efficiency such as water vapor concentration, and it was revealed that this parameter is an important indicator in determining the optimum spray strategies. It is anticipated that this thesis study may be an important resource for injection strategies in scramjet engines.