Study of Fuel Injection Systems in Scramjet Engine—A Review

Abstract

The scramjet engine is categorized in air-breathing vehicles, and this engine utilizes the high-speed forward motion of the vehicle to compress the surrounding air for getting forward thrust. Air-breathing engines complete the cycle by using air from the atmosphere. In the scramjet engines, the atmospheric free stream air enters the combustor at supersonic speed. And the process of mixing and combustion both take place at the same speed. Due to the higher speed of incoming air, the residence time is less inside the combustor. This phenomenon leads to poor mixing of fuel and air. As the scramjet engine does not have any moving part, so there is very less way to improve the performance. One of the optimum ways is fuel injection strategies to enhance combustion performance. To incorporate the behavior of the fuel entrance inside the combustor with the performance of the engine, a detailed literature review has been done in three separate sections by their preferences, i.e., parallel, transverse, and combined fuel injection system. A detailed literature review has been performed to understand and explain the impact of the different fuel injection system at supersonic speed. The parallel fuel injection system at supersonic speed gives higher combustion performance when the additional vortices present. These stream wise vortices can be generated with the help of different shapes of a fuel injector. In the transverse fuel injection system, the total pressure recovery is found less nonetheless stable flame can be achieved by using cavities at the walls. The recirculation zone can easily be created near to this zone. As parallel and transverse fuel injection systems give the best performance among all in their own way however fewer research has been performed in the direction of combined fuel injection strategy at supersonic speed. Flame holding capacity with additional vortices formation can only be achieved by using a combined system.