Scramjet aerothermal properties

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Scramjets operate by first slowing down supersonic inlet flow to low subsonic speeds before accelerating it again in the diverging section for combustion. This process allows for supersonic combustion, which is essential for scramjet efficiency. The initial slowdown is necessary to achieve optimal conditions for combustion before re-accelerating the flow. The discussion highlights a common confusion regarding the efficiency implications of this flow management. Ultimately, combustion begins in the diverging section, clarifying the scramjet's operational mechanics.
yangshi
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Doing my undergrad thesis on a ramjet and am confused about scramjets. A ramjet's diffuser slows down supersonic inlet flow to low subsonic to allow combustion. But a scramjet's diffuser first slows the flow down, then speeds it back up in the "diverging" section for supersonic combustion. Why would you slow the flow down only to speed it back up? Wouldn't this result in more total pressure loss (thus efficiency) than if you just slowed the flow down slightly?
 
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Nevermind, figured it out. Combustion starts in the "diverging" section.
 

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