Power plants – Reaction motor – Method of operation
Reexamination Certificate
1999-08-19
2001-03-13
Freay, Charles G. (Department: 3746)
Power plants
Reaction motor
Method of operation
C060S039821
Reexamination Certificate
active
06199370
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an acoustic igniter and to a method of igniting a propellent mixture in the combustion chamber of a liquid propellent rocket engine.
PRIOR ART
Various types of acoustic igniter are already known for use in space to ignite propellent mixtures fed to the combustion chamber of a liquid propellent rocket engine.
Thus, patent document SU-A-1 255 818 has already described an example of an acoustic igniter as shown in FIG.
2
. In such an acoustic igniter, a cylindrical precombustion chamber
1
has an injection nozzle
3
on one of its main faces with an injector
4
placed inside the nozzle for feeding fuel, with the injector
4
lying on the axis of the injection nozzle
3
. A hollow acoustic resonator
5
is placed across the second main face of the precombustion chamber
1
facing the injection nozzle
3
. The acoustic resonator
5
includes a frustoconical first portion that converges from the inlet opening thereof, and a cylindrical second portion that defines a cavity which terminates in an end wall of the cylindrical portion. Outlet orifices
2
of the precombustion chamber
1
enable the burning mixture after ignition to pass towards a downstream chamber
11
which communicates via at least one outlet orifice
21
with a main combustion chamber of a rocket engine.
The acoustic igniter as shown in
FIG. 2
operates as follows: a gaseous component, e.g. an oxidizer, is injected under pressure into the injection nozzle
3
where it is subjected to acceleration. Simultaneously, another component, fuel,is injected into the injector
4
. Together, the injection nozzle
3
and the injector
4
thus serve to form a propellent mixture in the precombustion chamber
1
. A portion of the mixture penetrates into the cavity of the acoustic resonator
5
and remains therein. The resulting shock waves heat up the portion of the mixture situated in the acoustic resonator
5
. The mixture catches fire on reaching its ignition temperature. The flame leaves the cavity of the acoustic resonator and ignites all of the mixture in the precombustion chamber
1
, after which it escapes via the outlet orifices
2
towards the downstream chamber
11
which itself communicates via an outlet orifice
21
with the main combustion chamber of the rocket engine (not shown).
Prior art acoustic igniters are not optimized with respect to operation or with respect to geometry. In particular, in an acoustic igniter as shown in
FIG. 2
, a flow of cold gas circulates through the orifices
2
and through the downstream chamber
11
prior to ignition, which cold gas is in contact with the outer wall of the acoustic resonator
5
. This contributes to reducing the development of heat inside the acoustic resonator
5
and thus lengthens the time required for ignition. Combustion stability is not very good, and given the low initial temperature of the gaseous component, ignition does not take place with the desirable degree of reliability.
Also known, from patent document SU-A-1 657 883, is an acoustic igniter or a dynamic gas igniter as shown in
FIG. 3
, in which the fuel gas and the oxidizing agent are injected into a precombustion chamber
10
via an injector
4
and via a concentric injection nozzle
3
thereabout, both facing an acoustic resonator
5
mounted on the opposite wall of the precombustion chamber
1
, with the gaseous mixture escaping from the precombustion chamber via at least one orifice
20
that is situated laterally relative to the gas injection assembly
3
,
4
and to the acoustic resonator
5
. The operation of that acoustic igniter is improved by the fact that the fuel gas injector
4
opens out into the converging portion of the injection nozzle
3
, upstream from the outlet of said injection nozzle
3
, thus obtaining a mixture that is more uniform and increasing the stability of the ignition process. Nevertheless, the acoustic igniter of
FIG. 3
is still not sufficiently reliable, and in particular it does not enable the maximum length of time required for ignition to be reduced.
OBJECT AND BRIEF DESCRIPTION OF THE INVENTION
The present invention seeks to remedy the above-mentioned drawbacks, and in particular to provide an acoustic igniter presenting oscillations of greater intensity due to shock waves, smaller thermal losses that are from the acoustic resonator, and in general, operation that is optimized so as to be more stable and more reliable than existing devices, thus contributing in particular to reducing the time required for ignition.
These objects are achieved by an acoustic igniter (
FIG. 1
) for igniting a mixture of propellents in the combustion chamber of a liquid propellent rocket engine, the igniter comprising a cylindrical precombustion chamber having a cylindrical wall and first and second end walls, a propellent injector nozzle opening out into the precombustion chamber through the first end wall via an orifice of minimum diameter d
n
, a fuel injector disposed inside said nozzle on the axis thereof, at least one outlet orifice of minimum diameter d
f
, formed through the cylindrical wall, and an acoustic resonator defining a cavity opening out into the precombustion chamber opposite the nozzle through the second end wall via an opening of diameter d
r
, the igniter being characterized in that the acoustic resonator is surrounded by a housing which defines an auxiliary chamber around the acoustic resonator, the auxiliary chamber being closed with the inside thereof being in communication only with the precombustion chamber via at least one duct.
According to a preferred characteristic, the acoustic resonator presents, running from its opening: an essentially frustoconical converging portion extended by a cylindrical portion of inside diameter d
c
and closed by an end wall that is essentially parallel to the second end wall of the precombustion chamber, and the wall of the cylindrical portion of the acoustic resonator is made of a metal material having thermal conductivity &lgr; which is less than 25 W/m.° C., with the thickness &dgr; of said cylindrical wall being less than 0.1 d
c
.
Advantageously, the converging portion of the acoustic resonator has a convergence angle &ggr; lying in the range 10° to 24° and the cylindrical portion of the acoustic resonator has an inside diameter d
c
lying in the range 0.15 to 0.35 times the diameter d
r
of the opening of the acoustic resonator, and a length l
c
lying in the range one to three times the diameter d
r
of said opening.
In an optimized embodiment, the precombustion chamber has a diameter d
ch
greater than 2.2 d
n
, the distance &Dgr; between the orifice of the nozzle and the opening of the acoustic resonator lies in the range 1.5 d
n
to 3.2 d
n
, the diameter d
r
of the opening of the acoustic resonator lies in the range 1.1 d
n
to 1.6 d
n
, and the minimum diameter d
f
of the outlet orifice lies in the range 2.0 d
n
to 2.8 d
n
, where
n
represents the number of outlet orifices and d
n
represents the diameter of the orifice of the nozzle.
Preferably, the downstream end of the fuel injector is situated in the converging portion of the nozzle.
The invention also provides an ignition method using an acoustic igniter of the invention, the method being characterized in that it consists in a first step of injecting an inert gas under pressure via the nozzle so that at least a portion of the jet of expanded inert gas at the outlet from the nozzle penetrates into the acoustic resonator via its opening to be heated by oscillations due to shock waves until it reaches a temperature suitable for igniting a propellent mixture that is injected during a second step, and in said second step, once said temperature has been reached, the method consists in injecting oxidizer through the nozzle and fuel through the injector to co-operate with the inert gas to form a propellent mixture which penetrates into the acoustic resonator to catch fire on contact with the hot gases and create a flame that then ignites the propellent mixture throughout the precombustion chambe
Demtchenko Vladimir
Kessaev Khoze
Zinoviev Vassili
Freay Charles G.
Gartenberg Ehud
Societe Nationale d'Etude et de Construction de Moteurs d&a
Weingarten, Schurgin Gagnebin & Hayes LLP
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