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Supersonic Combustion Ramjet Technology
Published in Debi Prasad Mishra, Advances in Combustion Technology, 2023
The scramjet engine is uniquely suited for hypersonic propulsion. Though there are no moving parts like turbo machines, the system becomes very complex as the processes are controlled by aerodynamics and thermodynamics. External vehicle drag and heat loads are varying as a function of square and cube of flight speed respectively. This implies that a lot of drag has to be overcome and a lot of heat flux has to be handled during the flight. Therefore, getting a thrust margin and choosing materials for airframes and engines are the real challenges in this system. The design methodologies are well proven with the advent of maturity in CFD and availability of high-power computers. However, the ground tests and flight tests are very complex due to huge investments and limitations of the facilities in their inability to simulate the actual flight corridor. In addition, as scaling laws are not known, there is a need to do tests on the full-scale engine. A cost-benefit analysis is needed to embark on the scramjet technology development program as the investments on test facilities, test article realization, test facility and test article instrumentation, quality control and safety are huge. But, in a single program a lot of challenges are to be overcome in terms of scramjet development and the launch vehicle development and their integration and successful separation during flight and sustained scramjet flight acquiring thrust margin. This is truly a frontier area of aeronautics and there is an urgency to conquer it.
Hypersonic Aircraft
Published in G. Daniel Brewer, Hydrogen Aircraft Technology, 2017
Scramjet mode — Supersonic combustion ramjet (scramjet) operation is used to accelerate the vehicle from the ramjet transition point to high hypersonic flight speeds. Thrust and specific impulse both decrease as speed increases. At some point, as dictated by vehicle configuration and trajectory requirements, fuel-rich operation (equivalence ratio >1) must be initiated to both augment thrust and enhance engine and vehicle cooling capabilities. At the point in the trajectory where the combination of scramjet mode-effective specific impulse and thrust level produces less velocity increment per quantity of fuel burned than would rocket operation, a shift to hydrogen/oxygen rocket mode is performed. Estimates vary as to what the realistic upper limit of scramjet operation might be; the consensus seems to be in the vicinity of Mach 12 to 16. More analytical and experimental effort is required before a firm choice can be made.
Supersonic Diffusers
Published in George Emanuel, Analytical Fluid Dynamics, 2017
Both the PM and L‐A approaches are relevant to the inlet diffuser of ramjet and scramjet engines. The needs and challenges associated with a scramjet engine, however, are different from alower Mach number inlet, such as for a ramjet or a gaseous laser. A scramjet engine has three major components: a supersonic inlet that directly feeds air into a combustor, which then feeds a thrust producing nozzle. In a scramjet engine, as compared to a ramjet engine, the combustion process is supersonic, not subsonic. This necessitates an inlet Mach number of 7, or higher, with a diffuser outlet/combustor inlet Mach number of about 4. To maximize thrust, the fuel/air mixture ratio is near stoichiometric. To further maximize thrust, the combustor outlet/nozzle inlet Mach number needs to be supersonic, but close to unity A scramjet (or ramjet) thrust nozzle is the topic of Section 20.14, where the near unity Mach number assertion is established.
Thermal stress stability of hydrocarbon fuels under supercritical environments
Published in Chemical Engineering Communications, 2023
Sundaraiah Konda, Madhavaiah Nalabala, Srikanta Dinda
In recent years, heat management in a hypersonic engine has received significant attention from the research fraternity. A supersonic combustion ramjet (SCRAMJET) engine works at high Mach numbers and provides power to a hypersonic air-breathing vehicle. A scramjet engine requires efficient cooling to manage its severe heat load (Bunker et al. 2018; Edwards 2006). Cooling of engine structure using onboard fuel could be an effective way of thermal management (Gascoin et al. 2010; Jin et al. 2017; Li et al. 2018a). In a regenerative cooling method, the fuel temperature increases gradually due to heat exchange, and it reaches a temperature that can cause endothermic chemical reactions (Jiang et al. 2013; Li et al. 2018b; Wu et al. 2018). The sensible heat sink of fuel can provide the cooling demand of an engine up to Mach-3 speed (Dinda et al. 2021; Jackson et al. 2004; Konda and Dinda 2022; Lisa et al. 2008). In high heat loads, hydrocarbon tends to break into smaller molecules. The cracked products would be injected into the combustor to fulfill the combustion requirement (Feng et al. 2018; Ma et al. 2016).
Heat Transfer Enhancement of Regenerative Cooling Channel with Pyramid Lattice Sandwich Structures
Published in Heat Transfer Engineering, 2023
Jiawen Song, Yunfei Yuan, Jian Liu, Shibin Luo, Bengt Sunden
Hypersonic vehicles are the strategic development direction for military and civil application in the future, with the characteristics of high speed, light weight, wide speed range and wide airspace operation [1]. Scramjet is a key technology for the development of hypersonic vehicles, and it is one of the hot fields in the world since the 21st century [2]. However, the high enthalpy of the scramjet engine and combustion heat release make the combustion chamber an extremely harsh thermal environment where the temperature can reach as high as 3000 K in the combustion chamber. Even the most advanced high temperature resistant materials cannot withstand such a harsh thermal environment. The combustion chamber cannot meet the long-term operation needs of the engine so accordingly it must be actively cooled [3, 4].
Bayesian Model Calibration Using High-Fidelity Simulations of a Mach 8 Scramjet Isolator and Combustor
Published in Combustion Science and Technology, 2023
Supersonic combustion ramjets (scramjets) are air-breathing hypersonic propulsion devices that use shock-based compression to generate thrust. The complex physical phenomena in these devices – namely, supersonic combustion, turbulence-chemistry interactions, and shock-boundary layer interactions – have made them difficult to study since their conception (Curran 2001; Gaitonde 2015; Liu, Baccarella, and Lee 2020; Smart 2007; Urzay 2018). In general, high-fidelity studies at relevant flight conditions are preferred because they give the greatest insight into the relevant physics. However, these studies pose many challenges in both computational and experimental contexts. Direct numerical simulations (DNS) of scramjets are infeasible with current computing architectures, and comparatively cheap large-eddy simulations (LES) can still incur great computational cost (Fulton et al. 2014; Larsson et al. 2015; Nordin-Bates et al. 2017). On the other hand, ground-based experiments tend to be expensive and short-duration, with test conditions that are specialized to the facility (Abul-Huda and Gamba 2015; Baccarella et al. 2017; Gruber and Nejad 1994; Hannemann et al. 2018; Stalker et al. 2005). As a result, high-fidelity scramjet data sets are generally sparse, which makes design sensitivities and performance envelopes difficult to ascertain. This poses major challenges for developing scramjet designs that are robust under a range of possible flight conditions.