GENERAL TECHNICAL FIELD
The present invention relates to the aeronautical field, and
deals more specifically with an ignition unit for a turb5 ojet
engine for igniting a main combustion chamber and for igniting
afterburning.
BACKGROUND OF THE INVENTION
10 Turbojet engines for aircraft are currently equipped with an
afterburner device. An afterburner device comprises means for
injecting fuel in proximity to flame–holder members and at least
one afterburning ignition spark plug located in an afterburning
ignition area. Under afterburning conditions, additional fuel is
15 injected in order to obtain an increase in thrust.
Such a turbojet engine thus includes two ignition means: main
spark plugs for igniting the main combustion chamber, and
afterburning spark plugs for igniting afterburning.
For reasons of simplicity, bulkiness and costs, a single
20 ignition unit simultaneously controls the ignition of the main
combustion chamber as well as the afterburning ignition. In this
way, independently of whether activation of the ignition of the
main chamber or the afterburning is desired, the main spark plugs
and the afterburning spark plugs are simultaneously energized. The
25 main spark plugs fire even when only the firing of the
afterburning spark plugs is desired.
Now, during the operation of the turbojet engine, a main
spark plug is subject to very high pressure, of the order of 30
bars, in altitude. Under these conditions, the firing of a main
30 spark plug implies a rapid degradation of the latter. The lifetime
of a main spark plug may be considerably reduced by this, causing
additional maintenance costs and reducing the availability of the
aircraft as well as the reliability of their performances.
It is therefore desirable to only energize a main spark plug
35 when the latter should be sought, i.e. upon starting or restarting
the turbojet engine.
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Complete segregation between the routes for igniting a main
spark plug and the routes for igniting an afterburning spark plug
is capable of meeting this requirement, such that the energization
of a main spark plug is independent of the energization of an
afterburning spark plug5 .
However, the application of two ignition units, one dedicated
to the main plugs and the other to the afterburning spark plugs,
represents an overcost, increased bulkiness and a mass increase
which may not be acceptable. Further, the requirement of an
10 additional computer output for the independent controls may be
incompatible with the existing systems.
Further, replacement of an ignition unit may not be
concomitant with a possible adaptation of other elements of the
ignition system, and notably with the adaptation of the control
15 signal sent by the computer for controlling the ignition. Thus, it
is necessary that the modifications brought to the ignition system
may be applied independently of each other.
SUMMARY OF THE INVENTION
20 The object of the present invention is notably to provide a
solution allowing segregation of the energization of the main
spark plugs and of the afterburning spark plugs, which is
compatible with the existing elements of an ignition system
without any increase in mass and in the bulkiness of the ignition
25 system.
For this purpose, according to invention, an ignition unit is
proposed for a turbojet engine, said unit comprising:
- an electric power supply,
- a single control channel for receiving a control signal from
30 a computer,
- a channel for igniting a main spark plug in order to energize
at least one main spark plug of a main combustion chamber,
- a channel for igniting an afterburning spark plug in order to
energize at least one afterburning spark plug of an afterburning
35 chamber,
said unit being capable, in response to pulsed commands on
said single control channel, of selectively activating the main
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spark plug ignition channel or the afterburning spark plug
ignition channel.
The invention is advantageously but optionally completed by
the following features, taken alone or in any of their technically
possible combination5 :
- the unit further comprises a control module for decoding the
control signal in order to determine which ignition channel has to
be activated;
- selective activation of the main spark plug ignition channel
10 or of the afterburning spark plug ignition channel depends on the
pulse durations of the control signal;
- the duration of a pulse of the control signal for controlling
the activation of an ignition channel depends on the energy
required for energizing the spark plug corresponding to said
15 ignition channel;
- the signal has a time–out after each pulse of the control
signal, said time–out corresponding to a signal level different
from the signal level of the pulse and being followed by a
continuous command at a signal level corresponding to the signal
20 level of the pulse;
- the unit comprises an electric power supply channel common to
the main spark plug ignition channel and to the afterburning spark
plug ignition channel, said common electric power supply channel
comprising a single capacitive block intended to be brought to a
25 voltage depending on the ignition channel to be activated;
- each of the ignition channels includes a thyristor connected
to the single capacitive block, said thyristor being controlled
depending on the state of the common electric power supply channel
and of the pulse control;
30 - the unit is adapted for beginning the charging of the
capacitive block as soon as a pulse is detected and before
determining the ignition channel to be activated;
- the unit is capable, in response to a control voltage step on
said single control channel, of alternately activating the main
35 spark plug ignition channel and the afterburning spark plug
ignition channel.
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The invention also deals with an ignition system for a
turbojet engine, comprising:
- an ignition unit according to the invention,
- a main spark plug of a main combustion chamber which may be
energized through the main spark plug ignition channel of sai5 d
unit,
- an afterburning spark plug which may be energized through the
afterburning spark plug ignition channel of said unit,
- a computer connected to the control channel of said unit for
10 sending a control signal to said unit.
SHORT DESCRIPTION OF THE FIGURES
Other features, objects and advantages of the invention will
become apparent from the description which follows, which is
15 purely illustrative and non–limiting, and which should be read
with reference to the appended drawings wherein,
- Fig. 1 is a diagram illustrating an ignition unit from the
state of the art;
- Fig. 2 is a diagram illustrating an ignition unit according
20 to a possible embodiment of the invention;
- Fig. 3 is a time diagram illustrating the behavior of the
ignition unit of the state of the art in response to a control
signal of the state of the art;
- Fig. 4 is a time diagram illustrating the behavior of the
25 ignition unit according to a possible embodiment of the invention
in response to a control signal of the state of the art;
- Fig. 5 is a time diagram illustrating the behavior of the
ignition unit according to a possible embodiment of the invention
and of the ignition unit of the state of the art in response to a
30 control signal according to a possible embodiment of the invention
within the scope of the energization of a main spark plug;
- Fig. 6 is a time diagram illustrating the behavior of the
ignition unit according to a possible embodiment of the invention
and of the ignition unit of the state of the art in response to a
35 control signal according to a possible embodiment of the invention
within the scope of the energization of an afterburning spark
plug.
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DETAILED DESCRIPTION
Fig. 1 is a diagram illustrating an ignition unit 100 of the
state of the art and showing its most important components. Such
an ignition unit 100 has an electric power supply 101 and a single
control channel 102 for receiving a control signal from 5 a
computer. The control channel 102 is here materialized with two
physical lines for producing redundancy improving the reliability
of the control of the ignition unit 100.
An electric processing stage 103 applies electric filtering
10 of the power supply and of the control signal, and includes a
protective device against overvoltages, in order to protect the
unit against possible alterations of these inputs which may damage
the ignition unit 100 or deteriorate its operation.
The ignition unit 100 also includes a control module 104
15 which receives the control signal after that it has passed in
transit through the control channel 102 and has been processed by
the electric processing stage 103. This control module 104
determines the activation of the channels for igniting spark plugs
from the control signal, and controls the electric conversion
20 stage 105 so that the latter converts the received power supply of
28 volts into 2,800 volts.
The electric conversion stage 105 for this purpose includes a
switching power supply 106 of the flyback converter type and a
transformer 107 for raising the voltage to the intended level. A
25 rectifier 108 then rectifies the current for charging the
capacitors 111, 121 of each of the channels 110,120 for igniting
spark plugs.
A spark–gap 109 allows discharging of the capacitors 111, 121
when the desired voltage threshold is attained, both at a channel
30 for igniting the main spark plugs 110 and at a channel for
igniting the afterburning spark plugs 120. The discharge current
of the capacitors 111, 121 is then transmitted to the induction
coils of the output stages 112, 122 and causes firing of the
ignition spark plugs to which energy is transmitted through means
35 113, 123 for connections with the latter. The output stage 112,
122 notably allows control of the duration of the spark of the
plugs with which it is associated.
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Fig. 3 illustrates the charging of the capacitors 111, 121 of
the ignition unit 100 of the state of the art in response to a
control signal of the state of the art. The upper curve 30
illustrates the time–dependent change in the control signals. The
middle curve 31 illustrates the charging energy of the capacit5 or
111 of the main spark plug ignition channel 110, and the lower
curve 32 illustrates the charging energy of the capacitors 121 of
the afterburning spark plug ignition channel 120. The scale is
arbitrary.
10 A voltage step or front of the control signal causes
activation of the channels for igniting the main spark plugs 110
and of the channels for igniting the afterburning spark plugs 120.
As explained earlier, there is no segregation between the ignition
spark plugs. The main spark plugs therefore fire at the same time
15 as the afterburning spark plugs, as shown by the simultaneity of
the drops in the energy stored by the capacitors 111,121 on the
charging energy curves 31, 32 of the latter.
In order to overcome the drawbacks discussed earlier,
according to the invention, an ignition unit for a turbojet engine
20 is proposed, which is capable, in response to pulse commands on a
single control channel, of selectively activating the main spark
plug ignition channel or the afterburning spark plug ignition
channel. Fig. 2 illustrates a possible embodiment of such an
ignition unit and the description which follows will be made in
25 reference to this embodiment illustrated by Fig. 2.
The ignition unit 200 has an electric power supply 201 and a
single control channel 202 for receiving a control signal from a
computer. The control channel 202 is here materialized by two
physical lines for producing redundancy improving the reliability
30 of the control of the unit 200.
An electric processing stage 203 applies electric filtering
to the power supply and to the control signal, and includes a
protective device against overvoltages, in order to protect the
unit against possible alteration of these inputs which may damage
35 the ignition unit 200 or deteriorate its operation.
The ignition unit 200 includes a main spark plug ignition
channel 210 for energizing at least one main spark plug of a main
combustion chamber and a channel for igniting an afterburning
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spark plug 220 in order to energize at least one afterburning
spark plug of an afterburning chamber.
The ignition unit 200 also includes a control module 204
which receives the control signal after it has passed in transit
through the control channel 202 and has been processed by 5 the
electric processing stage 203. This control module 204 decodes the
control signal in order to determine the ignition channel which
has to be activated.
The ignition unit 200 also comprises an electric power supply
10 channel 205 common to the main spark plug ignition channel 210 and
to the afterburning spark plug ignition channel 220, said common
electric power supply channel 205 comprising a single capacitive
block 209 intended to be brought to a given voltage depending on
the ignition channel to be activated.
15 Thus, unlike the control unit 100 of the state of the art
illustrated by Fig. 1, the control unit 200 according to the
possible embodiment of the invention has optimized volume in that
it has a single capacitive block 209 for both ignition channels
210, 220, whereas the control unit 100 of the state of the art
20 illustrated by Fig. 1 provides a capacitor for each ignition
channel 110, 120.
In order to charge the single capacitive block 209 to a
desired voltage, the common electric power supply channel 205
includes a switching power supply module 206 of the flyback
25 converter type and a transformer 207 for raising the voltage. A
rectifier 208 then rectifies the current for charging the
capacitive block 209.
Each of the ignition channels 210, 220 includes a thyristor
211, 221 connected to the single capacitive block 209, said
30 thyristor 211, 221 being controlled depending on the state of the
common electric power supply channel 205 and on the pulse command
decoded with the control module 204. The switching power supply
module 206 manages the charging of the transformer 207 for
switching control to the thyristor 211, 221.
35 The thyristor 211, 221 of the ignition channel 210, 220 to be
activated is made to be conducting when the desired charging
energy of the capacitive block 209 is attained. The discharge
current of the capacitive block is then transmitted to the
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induction coils of the output stages 212, 222 and causes firing of
the ignition spark plug to which the energy is transmitted through
means 213, 223 for connections with the latter.
The ignition unit 200 according to invention thus gives the
possibility of having two distinct ignition channels 210, 220 5 in
spite of a single common electric power supply channel 205. It
therefore allows an appreciable gain in weight and in volume, as
well as in components, having a favorable impact on the unit costs
of an ignition unit.
10 In a preferred embodiment, the selective activation of the
main spark plug ignition channel 210 or of the afterburning spark
plug ignition channel 220 depends on the durations of the pulses
of the control signal.
Fig. 5 is a time diagram on which is illustrated the time–
15 dependent change 50 of the control signal according to a possible
embodiment of the invention within the scope of the energization
of a main spark plug.
A main spark plug ignition pulse 51 with a determined
duration, for example 40 ms, during which the signal assumes a
20 high level, followed by a time–out 52 of 40 ms during which the
signal assumes a low level, tells the control module 204 that it
is the main spark plug ignition channel 213 which should be
activated in order to energize the main spark plug so that the
latter fires.
25 The middle curve 55 illustrates the charging energy of the
capacitive block 209 in response to the control signal illustrated
by curve 50. The pulse 51 and the time–out 52 are followed by a
continuous control 53 at a signal level corresponding to the pulse
signal level 51. The charging of the capacitive block 209 begins
30 with the continuous control 53, after the control module 204 has
decoded the control signal.
The response time to the first firing is formed by the
duration of the pulse 51 i.e. 40 ms, the duration of the time–out
52, i.e. 40 ms, and the charging time during the application of
35 the continuous control 53. The characteristics of the common
electric power supply channel 205 are selected so that the
charging time of the capacitive block 209 is reduced relatively to
the charging time of the state of the art, so that the response
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time to the first firing remain substantially the same as in the
state of the art, i.e. 180 ms. The response times of the following
firings are preferably substantially the same, i.e. 180 ms. The
firing sequence of said at least one main spark plug is maintained
as long as lasts the continuous control 5 l 53.
The lower curve 56 illustrates the charging energy of the
capacitor 111 of the main spark plug ignition channel 110 in an
ignition unit 100 of the state of the art, in response to the
control signal illustrated by curve 50. The charging of the
10 capacitor 111 begins as soon as the pulse 51 occurs since the
ignition unit of the state of the art interprets said pulse as the
voltage step of the control signal in the state of the art. First
charging 57 then begins right from the beginning of the pulse 51,
and the charging is then interrupted at a stable level 58 during
15 the time–out 52 before resuming in a second phase 59 when the
continuous control 53 is applied. The following firings are
similar to those of the state of the art since the then applied
continuous control 53 is similar to the voltage step of the
control signal of the state of the art.
20 Thus, the pulse control gives the possibility of controlling
the ignition unit 100 of the state of the art within the scope of
the energization of the main spark plugs, with simply introduction
of the delay, here 40 ms, due to the time–out 52 in the control
signal. Consequently, the response time to the first firing is 220
25 ms while the period of the following firings remains 180 ms during
the continuous control 53 since there is then no time–out.
Fig. 6 is a time diagram on which is illustrated the time–
dependent change 60 of the control signal according to a possible
embodiment of the invention within the scope of the energization
30 of an afterburning spark plug.
An afterburning spark plug ignition pulse 61 of a determined
duration, in this case 80 ms, during which the signal assumes a
high level, followed by a time–out 62 of 40 ms during which the
signal assumes a lower level, tells the control module 204 that
35 the afterburning spark plug ignition channel 223 is the one which
has to be activated in order to energize the afterburning spark
plug so that its firing causes afterburning ignition.
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The middle curve 65 illustrates the charging energy of the
capacitive block 209 in response to the control signal illustrated
by the curve 60. The pulse 61 and time–out 62 are followed by a
continuous control 63 at a signal level corresponding to the pulse
signal level 61. The charging of the capacitive block 209 5 begins
with the continuous control 63, after the control module 204 has
decoded the control signal.
The response time to the first firing of the afterburning
spark plug is formed by the duration of the pulse 61, i.e. 80 ms,
10 the duration of the time–out 62, i.e. 40 ms, and the charging time
during the application of the continuous control 63. The
characteristics of the common electric power supply channel 205
are selected so that the time for charging the capacitive block
209 is reduced relatively to the charging time of the state of the
15 art, so that the response time to the first firing remains
substantially the same as in the state of the art i.e. 180 ms. The
response time to the following firings are preferably
substantially the same, i.e. 180 ms. The firing sequence of said
at least one main spark plug is maintained as long as lasts the
20 continuous control 63.
The lower curve 66 illustrates the charging energy of the
capacitors 121 of the ignition channel 120 of the afterburning
spark plug in an ignition unit 100 of the state of the art, in
response to the control signal illustrated by curve 60. The
25 charging of the capacitors 121 begins as soon as the pulse 61
since the ignition unit of the state of the art interprets said
pulse as an applied voltage step of the controlled signal in the
state of the art. First charging 67 therefore begins from the
beginning of the pulse 61, since the charging is interrupted at a
30 stable level 68 during time–out 62 before resuming in a second
phase 69 when the continuous control 63 is applied until the
firing. The following firings are similar to those of the state of
the art since the continuous control 63 which is then applied, is
similar to the voltage step of the control signal of the state of
35 the art.
Thus, the pulse control gives the possibility of controlling
the ignition unit 100 of the state of the art within the scope of
energization of afterburning spark plugs, with simply introduction
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of a delay of 40 ms due to the time–out 62 of the control signal.
Consequently, the response time to the first firing is 220 ms
while the period of the following firings remains 180 ms.
The compatibility of the pulsed controls is complete with the
existing systems. The result of this is that the control 5 signal
may be adapted for having pulsed controls before setting into
place an ignition unit 200 according to invention. Further, the
pulsed controls do not require any additional control channel and
are compatible with the existing computers, as well as with the
10 connections of these computers with the control units.
The pulsed commands have the advantage of being easily
identifiable with the ignition unit according to the invention.
Also, selecting the ignition by the pulse duration is also easy to
process with the ignition unit according to the invention. Indeed,
15 the logic of such a control is simple and does not require any
complex detection circuit.
Further, the pulse command may easily be developed for
integrating other functionalities. Notably, preheating of the
spark plugs may be set into place by means of a dedicated pulse
20 width, with a pulse width corresponding to the preheating of a
main spark plug and another width corresponding to the preheating
of the afterburning spark plug.
The wear of the spark plugs may also be monitored by
injecting different energy levels into the spark plugs. In this
25 case, a specific pulse command is sent to the unit 200 by the
control signal in order to inject a corresponding energy level.
The determination of the energy level below which said spark plug
does not fire, allows determination of the wear of the spark plug,
in order to be able to possibly proceed with preventive
30 replacement.
Preferably, the duration of a pulse of the control signal for
controlling the activation of an ignition channel depends on the
energy required for energization of the correspondent spark plug
at said ignition channel. The duration of the pulse of the control
35 signal may thus be selective, all the shorter since the charging
energy of the capacitive block 209 required for energization of a
spark plug is significant. For example, in the case when the
energization of an afterburning spark plug requires 0.5 J and the
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energization of the main spark plug requires 2.2 J, the duration
of a pulse of the control signal for activating the afterburning
spark plug ignition channel is greater than the duration of a
pulse of the control signal for activating the main spark plug
ignition channel. Thus, the charging of the capacitive block 205 9
starts all the faster since the required energy is high.
The ignition unit 200 according to the invention is
compatible with the control signal in the form of a voltage step,
of the system of the state of the art. Fig. 4 is a time diagram
10 illustrating the behavior of the ignition unit 200 according to a
possible embodiment of the invention in response to a control
signal of the state of the art. The control signal has a voltage
step 40 for controlling the firing of the main spark plugs and of
the afterburning spark plugs. The lower curve 41 illustrates the
15 charging of the capacitive block 209 of the ignition unit 200.
In the presence of a voltage step in the controlled signal,
not preceded with a pulse, the ignition channel of the
afterburning spark plugs 220 and the ignition channel 210 of the
main spark plugs are activated alternately, causing in alternation
20 firing of the afterburning spark plugs and of the main spark
plugs, respectively.
However, the presence of a voltage step is only determined
after the longest duration of the two pulse durations respectively
corresponding to the pulse controlling the activation of the
25 ignition channel of the main spark plugs and of the afterburning
spark plugs, by the absence of a falling front and of a time–out
which would determine the presence of a pulse. With the
exemplified durations, a duration of 120 ms is reached
corresponding to the 80 ms pulse followed by the 40 ms time–out
30 controlling the ignition of the afterburning spark plugs.
When the control module 204 is in presence of a voltage step
and has determined the absence of pulses at the end of a
predetermined duration, the control module determines that the
main spark plugs and the afterburning spark plugs should fire
35 alternately.
For this purpose, the charging of the capacitive block 209
has in this case a first charging phase 42 at the end of which
firing of the afterburning spark plugs occur, followed by a second
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charging phase 43 at the end of which firing of the main spark
plugs occurs, followed by a third charging phase 44 at the end of
which firing of the afterburning spark plugs occurs followed by a
fourth charging phase 45 at the end of which firing of the main
plugs occurs, etc. The firing alternation of the main spark p5 lugs
and of the afterburning spark plugs continues as long as lasts the
voltage step of the control signal.
Preferably, the duration between two consecutive firings of a
spark plug is the same during the firing sequence, and preferably
10 the same durations separate two consecutive firings of the
ignition spark plugs and two consecutive firings of the
afterburning spark plugs.
In the example shown, the consecutive firings of the main
spark plugs are spaced apart by 180 ms and the consecutive firings
15 of the afterburning spark plugs are also spaced apart by 180 ms.
Thus, the ignition unit according to invention may be
controlled by means of a control signal of the state of the art.
Therefore, the ignition unit according to the invention may be set
into place before adapting the control signal.
20 The response times of the ignition unit according to the
invention may be improved, both in the case of a control signal
with pulses and with the control signal of the state of the art
only having one voltage step, by beginning the charging of the
capacitive block 209 as soon as the control signal passes to a
25 signal level corresponding to a pulse or a voltage step. Indeed,
since the capacitive block 209 is unique, the indication by the
control signal that ignition is desired necessarily causes the
requirement of charging the capacitive block 209, both in the case
when the control signal indicates that only one of the ignition
30 channels should be activated and in the case when both ignition
channels have to be activated alternately.
Typically, an ignition system for a turbojet engine according
to invention will comprise:
- an ignition unit 200 as described above,
35 - a main spark plug of a main combustion chamber which may be
energized through the main spark plug ignition channel 210 of said
unit,
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- an afterburning spark plug which may be energized through the
afterburning spark plug ignition channel 220 of said unit,
- a computer connected to the control channel 202 of said unit
for sending a control signal to said unit.
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15
I/We Claim:
1. An ignition unit (200) for a turbojet engine, said unit
composing :
- an electric power supply (2015 ),
- a single control channel for receiving (202) a control
signal from a computer,
- a main spark plug ignition channel (210) for energizing at
least one main spark plug of a main combustion chamber,
10 - an afterburning spark plug additional channel (220) for
energizing at least one afterburning spark plug of a post
combustion chamber,
said unit being characterized in that, in response to pulsed
controls on said single control channel (202), it is able to
15 selectively activate the main spark plug channel (210), or the
afterburning spark plug channel (220), depending on the pulse
durations (51, 61) of the control signal.
2. The ignition unit (200) for a turbojet engine according
20 to the claim 1, further comprising a control module (204), for
decoding the control signal in order to determine which ignition
channel (210, 220) should be activated.
3. The ignition unit (200) for a turbojet engine according
25 to one of preceding claims, wherein the duration of a pulse (51,
61) of the control signal for controlling the activation of an
ignition channel (210, 220) depends on the required energy for
energizing the spark plug corresponding to said ignition channel
(210, 220).
30
4. The ignition unit (200) according to one of preceding
claims, wherein the signal has a time–out (52, 62) after each
pulse (51, 61) of the control signal, said time–out (52, 62)
corresponding to a signal level different from the signal level of
35 the pulse (51, 61) and being followed by a continuous control (53,
63) at a signal level corresponding to the signal level of the
pulse (51, 61).
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5. The ignition unit (200) for a turbojet engine according
to any of the preceding claims, comprising an electric power
supply channel (205) common to the ignition channel of the main
spark plug (210) and to the afterburning spark plug ignition
channel (220), said common electric power supply channel (205)5 ,
comprising a single capacitive bloc (209) intended to be brought
to a voltage depending on the ignition channel (210, 220) to be
activated.
10 6. The ignition unit (200) for a turbojet engine according
to claim 5, wherein each of the ignition channels (210, 220)
includes a thyristor (211, 221) connected to the single capacitive
bloc (209), said thyristor (211, 221) being controlled depending
on the state of the common electric power supply channel (205) and
15 on the pulsed control.
7. The ignition unit (200) according to one of claims 5 or
6, said unit (200) being adapted so as to begin charging the
capacitive bloc (209) as soon as a pulse (51, 61) has being
20 detected and before determining the ignition channel (210, 220) to
be activated.
8. The ignition unit (200) according to one of the
preceding claims, said unit (200) being able, in response to a
25 control step on said single control channel, to alternately
activate the main spark plug ignition channel (210) and the
afterburning spark plug ignition channel (220).
9. The ignition system for a turbojet engine, comprising:
30 - an ignition unit (200) according to any of the preceding
claims,
- a main spark plug of a main combustion chamber which may be
energized through the main spark plug ignition channel (210) of
said unit,
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- an afterburning spark plug which may be energized through
the afterburning spark plug ignition channel (220) of said unit,
- a computer connected to the control channel (202) of said
unit for sending a control signal to said unit.