Scramjet and combined cycle propulsion Flashcards
Why is designing and controlling the combustion process in a scramjet more difficult than in a rocket combustor?
The flow speed in scramjet combustor is much higher than a rocket, meaning lack of sufficient time for reacting and mixing
What makes SABRE look so appealing?
Pre-cooler; Rapidly cools incoming air from 1000 deg to ambient, enabling operations at higher speeds than existing engines
Nacelle; advanced materials designed to withstand extreme temperature conditions
How would you arrange turbine, ramjet, scramjet, and rocket propulsion systems based on specific impulse and why?
Turbine, Ramjet, Scramjet, Rocket, based on specific impulse. Air-breathing engines (Turbine, Ramjet, Scramjet) have higher specific impulses due to atmospheric air utilisation for combustion and bypass, unlike rockets.
Why can’t an inlet designed for Mach 10 flight be used for Mach 5?
Inlets designed for Mach 10 are unsuitable for Mach 5 due to the sensitivity of shock wave structures to Mach number. Inlet geometry must be matched to flight speed for optimal air compression and shock wave management.
What changes occur in a supersonic flow when heat is added?
Adding heat in supersonic flow decreases Mach number, velocity and total pressure, while increasing pressure, temperature, and total temperature.
In a scramjet engine, which is larger: combustion enthalpy or freestream enthalpy?
In scramjets, the combustion enthalpy is typically lower than the freestream enthalpy. This reflects the higher kinetic energy of incoming air compared to the energy released from fuel combustion.
Why do hypersonic vehicles usually use blunt leading edges?
Hypersonic vehicles use blunt leading edges to dissipate heat into the flow, reducing thermal stress. This contrasts with sharp edges that concentrate heat, and the detached shockwave from blunt edges aids in thermal management.
How do scramjet engines differ from traditional jet engines?
Scramjets operate at hypersonic speeds without moving parts, unlike traditional jet engines which use turbines for compression.
What is a combined-cycle engine ?
It’s an engine that combines multiple propulsion systems, like turbojets and scramjets, to operate efficiently over a broad range of speeds and altitudes.
How does thermal choking affect scramjet performance?
Thermal choking can limit the maximum achievable speed of a scramjet by restricting airflow due to heat addition in the combustion process.
What is the role of shock waves in scramjet operation?
Shock waves compress and heat the incoming air, a key process for fuel combustion in scramjets operating at supersonic speeds.
What advancements have been made in scramjet technology?
Advancements include improved materials for thermal management, more efficient fuel injection and mixing techniques
How does a rocket-based combined cycle (RBCC) work?
An RBCC system combines air-breathing jet propulsion with rocket propulsion, allowing operation in the atmosphere and in space.
What are the key considerations in supersonic inlet design for scramjets?
Design must account for efficient air compression, shock wave management, and minimizing drag at varying speeds and altitudes.
