Research into thermal efficiency of film cooling along combustion chamber wall of low-thrust rocket engine

1 / 10

RESEARCH INTO THERMAL EFFICIENCY OF FILM COOLING
ALONG COMBUSTION CHAMBER WALL OF LOW-THRUST
ROCKET ENGINE
A.A. Kozlov, . Bogacheva, I.N. Borovik
Moscow Aviation Institute (National Research University),
Moscow, Russian Federation
e-mail: ;
The paper focuses on experimental study of the film cooling efficiency in combustion
chambers of liquid propellant low-thrust engines. A completeness rate of the research
into different parameters affecting the thermal efficiency of film cooling is analyzed.
The thermal efficiency proves to be mostly influenced by such factors as a coolant
mass flow-rate, a coolant feed slot design, and flow parameters of both the main flow
and a cooling component. Combustion chamber pressure produces slight effect on
the film cooling thermal efficiency. Guidelines for film cooling in low-thrust rocket
engines are presented. The authors use the results of both Russian and foreign studies,
which are publicly available.
Keywords: low-thrust rocket engines, thermal efficiency of film cooling, chamber wall
temperature.
One of the most important current trends in rocket propulsion enginee-
ring is the design of reliable and highly efficient low-thrust rocket engines
(LTRE) powered by environmentally friendly nonhypergolic propellant
components.
High efficiency (high specific impulse) can be obtained in case the
propellant composition is close to the stoichiometric ratio. At this ratio
the temperature of combustion products is about 2800. . . 3500 K (at
pk = 1 MPa chamber pressure and the excess oxidizer ratio α = 1
for a propellant component, kerosene + О2, kerosene + Н2О2 , Н2 + О2,
СН4+ О2) [1–3]. Therefore, when high-energy propellants are used, the
problem of the reliable thermal protection of LTRE remains relevant.
The most frequent method of protecting LTRE combustion chamber
walls from high-temperature combustion product gases (convective and
radiative heat flows) is so called internal cooling (also referred to as film,
barrier, curtain or spray cooling).
Film cooling occurs along the low-temperature near-wall gas or liquid
layer (depending on the aggregate state of the propellant components).
This paper focuses on gas films. The propellant component creating the
film (oxidizer or fuel) is fed onto the inner surface of the combustion
chamber wall through holes or slots of various configuration. Film cooling
in LTRE results in significant losses of specific impulse. The lower the
near-wall layer temperature is, the greater the losses are. The near-wall
layer is formed when two flows are mixed: the film and the flow from the
periphery row (which is closest to the chamber wall) injectors. The near-
wall gas temperature in its turn depends on such factors as the equivalence
ratio of the components in the injectors of the closest to the wall row (when
80 ISSN 0236-3941. HERALD of the BMSTU. Series “Mechanical Engineering”. 2014. No. 1