Abstract
This paper describes the improvement in combustion efficiency achieved using streamwise vorticity and fuel injections when using hypermixer struts at high Mach numbers. The effects of fuel injection conditions on combustion were investigated using numerical simulations of chemical reactive flows with a detailed reaction mechanism. Hydrogen fuel was injected from the trailing edges of a separation-resistant strut. Fuel injection at sonic speeds led to an enhancement in efficiency with an increased injection angle at Mach number 2.5, but this improvement was not observed at Mach number 3.5. It was found that hydrogen accumulated in the vortex core because of the strong circulation generated from the strut at high Mach numbers. With fuel injection at speeds exceeding the sonic speed, the efficiency increased, and it improved further with an increasing injection angle. From the results, an important indicator for combustion enhancement was derived from the streamwise vortex circulation, fuel injection velocity, and inflow Mach number. To increase the combustion efficiency using the strut, the indicator value should exceed a threshold. This is crucial for ensuring effective fuel consumption during combustion. These findings provide useful insights into a good design of hypermixer struts in supersonic combustion.
Highlights
A fundamental understanding of supersonic combustion is important to realize supersonic combustion ramjet engines for airbreathing hypersonic aircraft.1–3 High-speed airbreathing vehicles require stable combustion reactions within the engine to achieve reliable thrust and high propulsion efficiency over a wide range of flight Mach numbers
Little is known about the effect of the fuel injection condition on combustion efficiency
To improve the combustion efficiency at a high Mach number, we focused on fuel injection conditions, namely, the angle and injection speed
Summary
A fundamental understanding of supersonic combustion is important to realize supersonic combustion ramjet (scramjet) engines for airbreathing hypersonic aircraft. High-speed airbreathing vehicles require stable combustion reactions within the engine to achieve reliable thrust and high propulsion efficiency over a wide range of flight Mach numbers. A fundamental understanding of supersonic combustion is important to realize supersonic combustion ramjet (scramjet) engines for airbreathing hypersonic aircraft.. High-speed airbreathing vehicles require stable combustion reactions within the engine to achieve reliable thrust and high propulsion efficiency over a wide range of flight Mach numbers. Since the flow residence time in a scramjet combustor is very short (0.1–1.0 ms), the rapid mixing of fuel and air is essential to realize stable combustion in supersonic flows. The growth rates of the mixing layers decrease with an increasing Mach number in the combustor because of compressibility effects.. Swirling flows with streamwise vorticity are known to relieve compressibility effects.. To enhance the mixing efficiency by reducing the compressibility effects, introducing streamwise vorticity into the combustor flow may have potential in terms of improving supersonic mixing and combustion performance. Turbulent mixing can be adopted to promote combustion at relatively low flight Mach numbers. the growth rates of the mixing layers decrease with an increasing Mach number in the combustor because of compressibility effects. Swirling flows with streamwise vorticity are known to relieve compressibility effects. To enhance the mixing efficiency by reducing the compressibility effects, introducing streamwise vorticity into the combustor flow may have potential in terms of improving supersonic mixing and combustion performance.
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