Aerospace Research - ISTC Funded Projects 1994-2009

128
Aerospace Research. Volume 1
Background
Development of a high­temperature combustion
chamber is one of the most important
problems as the increase of gas temperature
in air­breathing engine improves engine
performances. A high­temperature annular
combustion chamber with minimum emission
can be designed based on principles which
are quite different from conventional. If the
air­fuel ratio in the combustion chamber
with standard operation process decreases
to the level of α < 1.8...1.5, the combustion
efficiency decreases abruptly whereas the
value of harmful emissions in the exhaust
increases (primarily NOx).
At present, considerable progress in
theoretical and experimental investigations
of complex flows in combustion chambers
has been achieved. The research team of this
Project has also got a rich experience in such
investigations, in particular those related
to the operation process of combustion
chamber components. Team’s previous works
were aimed at providing stable operation of
combustion chambers and other elements in
the flow path such as frontal devices ensuring
air­fuel mixture preparation.
Project Objectives
The primary objective of this Project was
to develop recommendations towards a
design of pollutant­free high­temperature
combustion chamber for gas turbine
engine.
Description of the Work
The Work Plan included:
• literature review on low­emission combustion
chambers with particular attention to design
of swirl vanes and their experimental and
theoretical investigations, as swirl vanes
determine mixing quality and flame holding;
• experimental investigations of swirl bur ners;
• experimental investigations of the combustion
chamber operation process; and
• recommendations on operation process
organization in a low­emission combustion
chamber.
At the Moscow State Aviation Institute,
a scheme of an annular combustor with
fuel supply through a large number of fuel
injectors placed in the front section of the
combustor is being considered as a possible
solution for a low­emission combustor
with reduced nitrogen oxide formation in
combustion products of hydrocarbon fuels.
The frontal device of such a combustor has
two parts (Fig. 60):
– a row of combined flame devices (CFDs)
in the combustor central part and two axial
vane swirlers (AVS); and
– encircling of the row of CFDs from top
and bottom.
Fuel is fed to the frontal device, both to
the CFDs and AVS. In this scheme, the
CFD is the snail fuel swirler, a tangential
air swirler, and a cone branch duct with
a reverse­flow zone inside. In an annular
combustor, the number of such CFDs
depends on the combustor diameter and
in a first approximation can be selected
as the number of injectors for common
combustors. The role of the AVS in the
annular combustor is played by AVS.
The main characteristics of such a combustor
are listed below:
Fig. 60: Schematic of the CFD: 1 – input
branch duct; 2 – fuel vortex generator;
3 – mixing chamber; 4 – air vortex generator;
5 – exit duct; 6 – spray nozzle;
and 7 – swirl-type burner