Ignition method and device

Abstract

A method for igniting a continuous combustion engine including an electronic engine control member, a high energy box, a spark plug ignition circuit and a fuel solenoid valve, cooperating with a starter motor, the method being implemented by the electronic engine control member and including precharging the high energy box before an engine starting procedure, activated on an engine starting command, the precharging being controlled by switching on the electronic engine control member, or by putting the engine in idle mode.

Claims

1. A method for igniting a continuous combustion engine comprising an electronic engine control member, a high energy box, a spark plug ignition circuit and a fuel solenoid valve, cooperating with a starter motor, said method being implemented by the electronic engine control member and comprising a step of precharging the high energy box before an engine starting step, the engine starting step being activated on an engine starting command, said step of precharging being controlled: by switching on the electronic engine control member, or by putting the continuous combustion engine in idle mode.

2. The method according to claim 1, wherein the step of precharging comprises a measurement of an output voltage of the high energy box and a command to open or close a first switch controlling a power supply to the high energy box as a function of the output voltage of the high energy box.

3. The method according to claim 2, wherein the first switch opens when the output voltage becomes greater than or equal to a voltage set-point U.sub.precharging strictly lower than a breakdown voltage U.sub.breakdown, the latter being a voltage required to produce a spark.

4. The method according to claim 2, wherein the first switch opens when the output voltage becomes greater than or equal to a breakdown voltage U.sub.breakdown, U.sub.breakdown being a voltage necessary to produce a spark, and wherein a second switch disposed before the spark plug ignition circuit remains open until the engine starting command.

5. A device for igniting the continuous combustion engine comprising the high energy box, the spark plug ignition circuit, and the fuel solenoid valve, cooperating with the starter motor, the device comprising the electronic engine control member adapted to implement the method according to claim 2, connected to a voltage output of the high energy box and to the first switch allowing the high energy box to be supplied.

6. The device according to claim 5, wherein the high energy box is connected to the spark plug ignition circuit via a second switch.

7. The device according to claim 6, wherein the electronic engine control member controls the second switch.

8. The device according to claim 6, wherein the second switch is in an open state during the step of precharging and in a closed state at start-up.

9. A turboshaft engine comprising the device according to claim 5.

10. An aircraft comprising a turboshaft engine according to claim 9.

11. The device according to claim 5, wherein the electronic engine control member comprises an electronic circuit for the high energy box.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The figures are set forth by way of indicating and in no way limiting purposes of the invention.

(2) FIG. 1 is an operating flow chart of the ignition of the state of the art;

(3) FIG. 2 is an operating time chart of the ignition of an engine in idle mode of the state of the art;

(4) FIG. 3 is an operating flow chart of the ignition according to the invention;

(5) FIG. 4 is an operating time chart of the ignition of an engine in idle mode according to a first alternative of the invention with partial precharging;

(6) FIG. 5 is an operating time chart of the ignition of an engine in idle mode according to a second alternative of the invention with total precharging;

(7) FIG. 6 is an electrical diagram of a device for controlling the HEB according to the first alternative of the invention;

(8) FIG. 7 is an electrical diagram of a device for controlling the HEB according to the second alternative of the invention.

DETAILED DESCRIPTION

(9) Unless otherwise specified, a same element appearing in different figures has a single reference.

(10) A method for igniting a continuous combustion engine according to the state of the art is illustrated in FIG. 1. When the vehicle is switched on O1, the electronic engine control member is switched on, a possible self-test and preparing the engine are carried out E1, the vehicle is ready to start. When the start command O2 is given by the pilot or the electronic engine control member, the HEB, all the starting accessories, that is the starter motor and the fuel solenoid valve, are supplied with electricity E2, the HEB is supplied via a switch directly driven by the start command O2. From this moment on, the high voltage converter of the HEB is supplied by the DC low voltage of the on-board electrical network, the high voltage storage element of the HEB, typically one or more capacitors, is (are) charging. The output voltage across the storage element rises to the required breakdown voltage level creating a first spark 1. Further sparks 1, 1 occur at approximately the same frequency until the engine E3 actually starts.

(11) In FIG. 2, the charging time T0 of the HEB, which corresponds substantially to the time elapsed between the starting command O2 and the creation of the first spark, can thus be seen. This charging time T0 is a characteristic parameter of the electronics of the HEB considered. In practice, it is a function of the topology and performance and technological differences of the high-voltage converter components. The subsequent sparks 1, 1 occur at a frequency corresponding to this charging time T0 of the HEB.

(12) The charging time sequence of the HEB for breaking down sparks is found in the event of restarting the engine when the latter has been put into a so-called idle state, by an idle command during a flight phase of the aircraft. The possibility of putting one of an aircraft engines into an idle state is especially used to reduce the aircraft fuel consumption and carbon footprint. In this idle state, the fuel solenoid valve is cut off, other starting conditions (air flow rate and pressure in the combustion chamber) being maintained, the starter motor being especially always switched on and driven so as to maintain the speed of the gas generator of the turboshaft engine within the optimum ignition window of the combustion chamber. In this state, it is possible, on an O2 start command from the pilot or the electronic engine control member, to reignite combustion and rapidly increase power. In other words, restarting the engine from idle requires refuelling and reactivating sparking. The time sequence described in connection with FIGS. 1 and 2, of supplying the HEB through the switch directly controlled by the start command to obtain the spark plug breakdown voltage is thus repeated. The time required to restart the engine then depends mainly on the charging time of the HEB that cannot be shortened.

(13) In the different figures illustrating the invention, a HEB has been represented for 2 spark plugs, but it could be for 1, 2, . . . , n spark plugs.

(14) The method according to the invention illustrated in FIG. 3 provides that switching on the electronic engine control member or switching the engine to idle mode on an idle command OV triggers switching on of the HEB allowing at least partial precharging O3 of the HEB and maintenance of this precharging throughout the engine idle time or combustion chamber pressurisation time. When a start command O2 is received, the remaining charging time of the HEB is significantly reduced, making it possible to accelerate occurrence of the first spark and therefore starting of the engine.

(15) Thus, for a first start, the method is applied as follows: switching on the HEB is controlled by switching on the engine control electronics (engine calculator or by an electronic circuit specific to the HEB), allowing at least partial precharging O3 of the HEB before the engine start command O2. In particular, in this case, the HEB is supplied before the starter motor and the fuel solenoid valve.

(16) The time charts of FIGS. 4 and 5 illustrate the time saving made possible by the method of the invention in the time sequence for starting an engine switched to idle mode, with a precharge phase triggered by the engine idle command OV: the first spark 1 occurs very shortly after the start command O2. After this 1st spark, the following sparks 1, 1 break down at the same frequency as in the state of the art, corresponding to the charging time T0 of the HEB after each spark.

(17) FIG. 4 corresponds to a first alternative implementation of the invention corresponding to partial precharging of the HEB during a precharging phase prior to the start command O2.

(18) A corresponding control device of the HEB is illustrated in FIG. 6.

(19) The HEB 2 conventionally comprises a voltage booster stage charging a capacitive storage element represented by a capacitor C, a gas discharge tube 20 and a power output stage which supplies the high voltage applied to the spark plug electrodes. The supply input of the HEB 2 is connected to an electric power supply 3 (typically the low-voltage DC electrical network of the aircraft or vehicle) by a first, low-voltage switch 4, which is naturally in the open state; the voltage output U of the HEB 2 is measured across the capacitor C, at the input of the gas discharge tube 20. If voltage losses F occur, the device monitors the voltage U so as to set it to the value k?U.

(20) In the case of continuous combustion engine systems or continuous combustion systems (water heater, boiler, etc.) for which atmospheric conditions are not critical and which would use a HEB without a gas discharge tube, the high voltage applied to the spark plugs is that supplied across the HEB storage element. The operation is quite similar: the supply input of the HEB 2 is connected to an electric power supply 3 (typically the low-voltage DC electrical network of the system) by the first, low-voltage switch 4, which is naturally in the open state; the voltage output U of the HEB 2 is measured across the capacitive storage element, corresponding in this case to the output of the HEB (before the spark plugs 6 of the ignition circuit).

(21) According to the invention, the level of the output voltage U of the HEB 2 is measured by a sensor 8 and is controlled by an electronic engine control member 7 which drives and controls charging of the HEB by appropriately controlling opening and closing of the first switch 4.

(22) As soon as the engine electronics is switched on, the electronic engine control member 7 is able to place the HEB in precharging mode at a voltage set-point. The electronic engine control member 7 is configured to measure the output voltage U of the HEB, typically by means of the sensor 8, and compare it with a voltage set-point U.sub.precharging, which is set to a level close to but lower than the required breakdown threshold voltage level, U.sub.breakdown. The required breakdown threshold voltage level is the minimum voltage level that enables the spark plugs to cause a spark in the combustion chamber, other fuel and compressed air conditions being otherwise met.

(23) As long as the voltage U is below the voltage set-point, the electronic engine control member 7 drives the first switch in the closed state; as soon as the voltage set-point level is reached, it drives the first switch 4 in the open state.

(24) If, for the duration of the precharging mode, the output voltage were to drop (for example due to losses in the high voltage capacitive storage stage) F, the electronic engine control member 7 is able to reactivate partial charging of the HEB by switching the first switch 4 back to the closed state. In practice, this situation relates to the case of an engine in idle mode instead, which can last for one hour or more.

(25) In this first alternative, precharging the output voltage of the HEB 2 driven by the electronic engine control member 7 is partial.

(26) When it receives the start command O2, the electronic engine control member 7 leaves the precharge control mode O3 of the HEB to switch to the operational control mode of the HEB allowing spark breakdown. In this mode, the first switch 4 is controlled or maintained in the closed state to supply power to the HEB 2.

(27) As illustrated in FIG. 4, the voltage gap (U.sub.breakdown?U.sub.precharging) to be bridged to reach the breakdown voltage enabling breakdown of the first spark being small, the additional charging time t0 of the HEB from reception of the start command O2, to switch from the U.sub.precharging level to the U.sub.breakdown level is short compared with the charging time T0 corresponding to the complete excursion, from zero volts to U.sub.breakdown. As soon as this breakdown voltage is reached, the first spark occurs. The subsequent sparks occur successively at the same frequency, corresponding to the charging time T0.

(28) In practice, it is shown that 0.4 to 0.45 s can be saved in charging time from the reception of the start command, that is a saving of 80 to 90% on the time taken to produce the first spark compared with the conventional ignition method. This gain is invaluable in some critical operational situations, in the context of aircraft with several engines and designed to allow at least one of the engines to switch to idle mode during some flight phases, to save fuel and reduce their carbon footprint. As already explained, in the event of an emergency (climatic conditions, engine failure, etc.) it must be possible to switch the engine(s) back on and restore power very quickly.

(29) Synchronisation of the different ignition conditions in the combustion chamber: fuel, compressed air, spark (spark plugs) is also facilitated. This makes engine starting (first start) more reliable.

(30) A second alternative implementation of the invention is illustrated in FIG. 5, corresponding to a voltage set-point equal to the breakdown voltage. The electronic engine control member 7 is then configured to control total precharging O3 of the HEB. Namely the electronic engine control member 7 compares the output voltage U of the HEB with a voltage level which is the required breakdown threshold voltage level U.sub.breakdown.

(31) A second switch 5, of the high voltage type, is then provided at the output of the HEB 2, so as to isolate the circuit for generating and storing the high voltage of the HEB 2 from the spark plug ignition circuit 6 during the precharging mode, before a start command O2 from the pilot. This second switch 5 is naturally in the open state and remains open in HEB precharging mode. It is controlled by the electronic engine control member 7 in the closed state as soon as a start command signal O2 from the pilot is received, until the engine is ignited.

(32) In the case where the precharging mode of the HEB according to the invention is used for a first engine start, synchronisation of the ignition conditions is facilitated by the presence of this second switch 5, while the HEB is precharged to the necessary breakdown voltage: the second switch 5 makes it possible to control the moment when the breakdown voltage is provided to the spark plugs 6, the switching time of the second switch being negligible.