Numerical Study on Thermal Choke Behaviors Driven by Various Rocket Operations in an RBCC Engine in Ramjet Mode

Lei Shi; Da Gao; Liangliang Xing; Fei Qin; Guoqiang He

doi:10.1515/tjj-2019-0012

Article

Numerical Study on Thermal Choke Behaviors Driven by Various Rocket Operations in an RBCC Engine in Ramjet Mode

Lei Shi , Da Gao , Liangliang Xing , Fei Qin and Guoqiang He

Published/Copyright: May 25, 2019

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From the journal International Journal of Turbo & Jet-Engines Volume 37 Issue 3

Abstract

Thermal choke is commonly employed in a fixed geometry RBCC combustor to eliminate the need for physically variable exit geometry. This paper proposed detailed numerical studies based on a two-dimensional integration model to characterize thermal choke behaviors driven by various embedded rocket operations in an RBCC engine at Mach 4 in ramjet mode. The influences of different embedded rocket operations as well as the corresponding secondary fuel injection adjustment on thermal choke generation process, the related thermal throat feature, and the engine performance are analyzed. Operations of embedded rocket bring significant effects on the thermal choke behaviors: (1) the thermal throat feature becomes much more irregular influenced by the rocket plume; (2) the occupancy range in the combustor is significantly lengthened; (3) the asynchrony of the flow in different regions accelerating to sonic speed becomes much more significant; (4) as the rocket throttling ratio decreases, the thermal choke position constantly moves upstream integrally, and the heated flow in the top region that is directly affected by the rocket plume reaches sonic speed more rapidly. Finally, we can conclude that appropriate secondary fuel injection adjustment can provide a higher integration thrust for the RBCC engine with the embedded rocket operating, while the thermal choke is stably controlled, and the increased heat release and combustion pressure are well balanced by the variations of pre-combustion shocks in the inlet isolator.

Keywords: rocket based combined cycle (RBCC) engine; ramjet mode; thermal choke; embedded rocket; secondary fuel injection

PACS: 590.25; 130.2564

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China through grant 51606156.

Nomenclature

H: Height, km/mm
D: Height of different parts in RBCC engine, mm
M: Mach number
σ: Total pressure recovery coefficient of RBCC inlet
MR: Mixture ratio (oxygen-to-fuel, O/F) of embedded rocket
TR: Throttling ratio of embedded rocket
P: Pressure, MPa
x: X-value along engine flowpath, mm
ER: Equivalence ratio
△: Throttle degree of two dimensional supersonic inlet for numerical validation
A_r: Pre-exponential factor
β_r: Temperature exponent
E_r: Activation energy
I_s: Specific impulse of engines, s
F: Thrust, N
m: Mass flow rate, kg/s
Subscripts
∞: Free incoming flow
c: Air capture; entrance of RBCC combustor
rkt: Embedded rocket
t,0: Total
ab: RBCC engine operating in pure ramjet mode
tot: Integration thrust of RBCC engine with embedded rocket operating
ideal: Physical combination of RBCC engine operating in pure ramjet way with an equivalent propelled rocket engine

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Received: 2019-04-30

Accepted: 2019-05-07

Published Online: 2019-05-25

Published in Print: 2020-08-27

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Articles in the same Issue

https://doi.org/10.1515/tjj-2019-0012

Keywords for this article

rocket based combined cycle (RBCC) engine; ramjet mode; thermal choke; embedded rocket; secondary fuel injection