EP1079179A1 - Process for adapting the operating condition of a gas-turbine staged combustion chamber - Google Patents

Abstract

An overall fuel mass flow rate (WF) metered through a control valve (6) and adapted to a defined operating point for a power mechanism is fed into a combustion chamber. A stepped valve (7) adjusts what proportion of the overall fuel mass flow rate is fed to pilot and main burners. An electronic power mechanism regulator (8) has first (8a) and second (8b) regulating blocks. The first block adjusts the control valve. The second block controls the stepped valve.

Description

The invention relates to a fuel injection system for a tiered combustion chamber, for example of an aircraft gas turbine engine or a static gas turbine, whose pilot burner is always supplied with a certain amount of fuel, during their main burner (s) only with higher engine power Fuel is metered, with the whole downstream Control valve unit determining the fuel quantity this total fuel mass flow to the pilot burner (s) as well as the grading valve unit, which divisible the main burner is provided, both by an engine controller can be controlled, for the control of the step valve unit the desired engine performance sets. Such a fuel injection system is from the WO 95/17632 known.

With a so-called stepped combustion chamber on a gas turbine, especially on an aircraft gas turbine engine Pollutant emissions achievable when fuel injection suitably designed in the combustion chamber for this becomes. In particular, the step valve unit mentioned must be used for this appropriately controlled, that is, the division that of the combustion chamber at a certain operating point measured total amount of fuel on their so-called Pilot zone, which is or mostly the duplicate Pilot burner is / are assigned, as well as on their main zone, which of the or mostly the multiple existing main burner is / should be assigned using maps take place, which is preferred with regard to low pollutant emissions the combustion chamber or the one taking place in it Are designed for combustion. Of course can also use other criteria when designing these maps are taken into account, for example the largest possible stability reserve against flame extinction. In this Context it should be expressly pointed out that under the aforementioned division of the total fuel mass flow on the pilot zone as well as on the main zone of the combustion chamber the state to be understood in which the total amount of fuel is only supplied to the pilot burner (s).

In the above-mentioned WO 95/17632 a so-called thrust indicative parameters, based on which the mentioned division of the total fuel mass flow made is, that is, this thrust-indicative parameter serves as an input variable for the control of a so-called step valve unit, the said division of a Control valve unit metered total amount of fuel the pilot burner and the main burner. This there so-called thrust-indicative parameters, which in general also can be referred to as a grading parameter and as such is also used as a parameter for the desired one Engine power with the metered total fuel mass flow can be generated. For this grading parameter, which of course is easy to grasp respectively should be measurable, are mentioned in this document either the gas temperature at the compressor outlet or the quotient from the total fuel mass flow and the pressure in the Combustion chamber suggested.

As already mentioned, the step valve unit should be preferred Controlled using emission-optimized maps or operated, that is, the so-called Grading parameters, based on which the grading valve unit (because of the recourse to the maps mentioned) a switching line should be controlled, should not only one Related to engine performance, but more directly Are also related to the operation of the combustion chamber, about the advantages that a stepped combustion chamber has in terms of generally has reduced pollutant emissions, to actually be able to use.

When regulating a gas turbine aircraft engine with a Low-pollution, stepped combustion chamber is a constant back and forth Switch between pilot and two-stage operation with small ones Avoid speed or load oscillations. This has not only affects engine stability but affects the service life of the hot parts is negative. A so-called Switching hysteresis prevented by a correspondingly broadly defined Hysteresis band unwanted cyclic switching of the Fuel rating.

Such hysteresis methods are generally used in the control often used. By defining an upper and a lower grading point, for example, a downgrading to pilot operation only carried out when the lower grading point was undershot and therefore a corresponding major engine load change has occurred. Such one The method is described in WO 95/17632.

The use of a switching hysteresis has the following disadvantages itself: The constant calculation of two grading points (lower and upper) requires a higher software effort than that Use of a single grading point. Still requires the use of a hysteresis band in the grading diagram further compromise with regard to optimization Low levels of pollutants as the use of a individual grading point. Also the quality of the grading parameter becomes a concession in practice due to signal noise lead in the width of the hysteresis band. Suffer from also pollutant optimization or it has to be expensive Measurement technology are used. When using a The switching hysteresis is flexible and depends on the to maintain the transient state of the engine. This also poses high demands on the measurement signal.

The object of the present invention is therefore on a Fuel injection system according to the preamble of claim 1 To show measures with the help of which the operation of the combustion chamber of the aircraft gas turbine engine in particular with regard lower pollutant emissions can be further improved.

According to the invention, the object is characterized by the features of Main claim solved, the sub-claims show further advantageous Embodiments of the invention.

The invention is characterized by a number of significant advantages out.

According to the invention, a control concept for safe and loss-minimizing Operation of a staged combustion chamber for aircraft engines found. The stepped combustion chamber can with the help of the control system according to the invention in two different operating states operate. In the lower load range all the fuel is sprayed into the pilot zone of the combustion chamber. In this mode, the mode of operation corresponds to the tiered one Combustion chamber of an unclassified combustion chamber. In addition become the main burner with fuel in non-staged operation cooled from the pilot branch to reduce the risk of coking reduce. From a certain operating point, the defined one takes place Connection of the main stage, so that both ring lines (Pilot stage and main stage) are supplied with fuel. The The fuel is distributed via an additional metering valve, that the total fuel on the pilot and the Main branch distributed. This operating state of the combustion chamber is called tiered mode.

An essential element of the new process is the time element "TIMER". The upstream logic for calculating a nominal Grading point thus enables that via a summation point various influences such as transient Operation and altitude can be taken into account. Is the Difference between the new adjusted switching point and the current measured value is less than a limit value, the graded Mode selected (command for grading point, SPK = 1). To the exceeding or falling below the nominal grading point the switching process is delayed if the length of time since the last step was carried out is as a predefined time constant in a map is filed.

As soon as SPK assumes the value 1, the "TIMER" time element is activated. The "TIMER" function has the current, current value of SPK as the input variable. The parameter t _{MIN, gradation} is used to control the "TIMER" element and describes the length of time that must be adhered to at least between two grading events if it is to be switched between the two operating states. If the command for a further grading is within the time window, the output variable of the time element (time-delayed command for grading point, SPK *) is kept at the value of the input variable (= SPK) until the current period of time since the last grading is greater than the minimum Step interval, that is t _TIMER > t _{MIN, step} .

The map for the minimum grading cycle t _{MIN, grading} takes into account the influence of rapid load changes of the aircraft engine. In the case of rapid load changes, in which an immediate system response of the engine is required, for example when taking off, the requirement for compliance with a minimum grading cycle is of minor importance, so that the value of t _{MIN, gradation} is 0. The slower the load change, the greater t _{MIN, gradation} and, in the case of quasi-stationary load changes, reaches the maximum value that is infinitely large (t _{MIN, gradation} >> 1 sec). In this case, if there is no load change or the thrust lever position remains unchanged, the operating state of the combustion chamber is "frozen", that is to say does not change and the combustion chamber remains in its previous operating mode (either un-stepped or stepped). Only when a load change occurs due to a change in speed (IdNH / dtl> 0) can the operating state of the combustion chamber change and a finite minimum step cycle (t _{MIN, step} <1 sec) is selected again.

The output variable SPK * of the "TIMER" function serves as a control variable for a subsequent selection element. If SPK * has the value 0, "F" (= wrong) is selected on the selection element. In this state, the calculated operating state (BZ) of the stepped combustion chamber is equal to SPK, which means that the current value of the staging point calculation is used to select the operating mode. In contrast, as soon as SPK * = 1, that is to say a gradation within t _{MIN, gradation is to} take place (selection element "T" (= true, correct)), the historical value of BZ, ie the value from the last time step Z ^-1 used. This ensures that there is no cyclical switching of the step valve between the two operating modes. If the time criterion for the minimum grading cycle is exceeded, the operating state (0 = not graded, 1 = graded) is checked again according to the calculation rule according to the invention.

The present invention thus enables a high degree of Flexibility in regulating the operating state of a tiered Combustion chamber because by introducing a variable Time function a stable operation of the combustion chamber in the non-graded and tiered operation is ensured. An elevated one Signal noise from the control parameters, for example from P30, has an effect does not rely on the selection of the operating state in the stationary Operation of the aircraft engine, since in this case a switchover not possible. Only when there is a load change that is in shape a change in the high-pressure speed is detected (IdNH / dtl > 0), another switching process is enabled.

According to the invention it is further provided that the engine power due to the load on the gas turbine combustion chamber Characterized form of a so-called grading parameter (SP) on the basis of which the step valve unit is corresponding a switching line is controlled and the grading parameter (SP) from one of the following functional relationships is derived:

After the first functional relationship, the total fuel mass flow (WF) is divided by the gas pressure at the combustion chamber inlet (P30) and this quotient is multiplied by the gas temperature at the combustion chamber inlet (T30), i.e. the step parameter SP is a function of [ WF / P30 · T30 ].

After the second functional relationship, the total fuel mass flow (WF) is divided by the gas pressure at the combustion chamber inlet (P30) and this quotient is multiplied by the square root of the gas temperature at the combustion chamber inlet (T30), i.e. the step parameter SP is a function of [ WF / P30 · (T30) 1/2 ].

After the third functional relationship, the total fuel mass flow (WF) is divided by the gas pressure at the combustion chamber inlet (P30) and this quotient with the square root of the quotient of the gas temperature at the combustion chamber inlet (T30) and the gas temperature at the engine inlet ( T20) multiplied, i.e. the grading parameter SP is a function of [ WF / P30 · (T30 / T20) 1/2 ].

After the fourth functional relationship, the total fuel mass flow (WF) is divided by the gas pressure at the combustion chamber inlet (P30) and this quotient is multiplied by the value of the size of the total temperature downstream of the high-pressure turbine (= T44) or by the square root thereof, that is, the grading parameter SP is a function of [ WF / P30 · T44 ] or SP is a function of [ WF / P30 (T44) 1/2 ].

In other words, the regulation of the fuel injection system a tiered gas turbine combustor by characterizing the load on this combustion chamber Grading parameters take place, said step valve unit is controlled according to a switching line and the grading parameter from one of the relationships listed above is derived.

According to the invention, the grading parameter (SP) less about a thrust-indicative parameter but rather about a parameter reflecting the combustion chamber load, so that the maps, on which of these grading parameters is accessed and from which the step valve unit is controlled according to a switching line, under much stronger reference to the combustion chamber and thus to the combustion taking place in it can be designed. This means improved combustion in almost all combustion chamber operating states, in which a staged combustion takes place, that is, in which both the pilot burner and the main burners are supplied with fuel, achievable.

In this context it should be noted that the total fuel mass flow (WF) via a special calibration table depending on the valve position of those already mentioned Control valve unit, this in the form of a primary Metering valves determined, can be calculated. It can this signal representing the total fuel mass flow, the can be particularly susceptible to signal noise with Be filtered using suitable low-pass elements. Further can meet the requirements for the desired fuel-air ratio in the individual operating points (in particular also with regard to the respective flame extinguishing limits) functional correlations in corresponding maps be mapped.

As already explained, a stepped combustion chamber can be used With the help of a control system according to the invention in two different operating modes are operated. At the bottom The load range of the engine is all the fuel in the Pilot zone of the combustion chamber sprayed, so in this mode the operation of the stepped combustion chamber of that one unrated combustion chamber corresponds. From a certain Operating point is the defined connection of the Main stage, after which both the pilot burner and Main burner can be supplied with fuel. Switching between the non-tiered and tiered operating modes takes place with the inclusion of the time element according to the invention (TIMER), whereby if the engine power increases over the grading point switched on the main burner and when it drops the main burner in terms of engine performance below the staging point be switched off.

In a quasi-stationary operating state of the engine the grading point is preferably dependent on a map determined by the grading parameter according to the invention. But with that Desirably always at the same value for the fuel-air ratio is toggled after an advantageous Further development of the invention different influences be taken into account. The grading point results from Addition or subtraction of correction elements (ΔSP) to or from the nominal, from one of the derived functional relationships mentioned above Grading parameters (SP). It should be noted that for each influencing parameter has its own additive correction element can be provided, which can then all be added up, so that practically all essential influencing parameters in the Calculation of the grading point by simple summation can be taken into account. The single contribution of Influence parameter is used as a relative change to nominal grading point recorded.

A first such influencing parameter is the absolute value of the Gas pressure (P30) and / or the gas temperature (T30) at the combustion chamber inlet. In this regard, it is proposed that Grading process from the non-graded to the graded operation delay as soon as the combustion chamber inlet pressure (P30) and / or the combustion chamber inlet temperature (T30) below certain limit values determined by combustion chamber tests for the stable operation of the combustion chamber decreases / decreases. this function is particularly active in tiered mode and leads Falling below the specified limit values for (P30) and / or (T30) to switch to pilot mode, in which only the Pilot burners are supplied with fuel.

A second influencing parameter is the corrected speed of the High pressure compressor (N2RT20) and the gas pressure at the engine inlet (P20). With the help of this additional redundant function can switch from non-tiered to tiered mode below the idle operating state of the engine be prevented. Specifically, it is proposed in Dependence on defined limit values for the corrected Speed of the high pressure compressor (N2RT20) and for the fan inlet pressure (P20) the grading point artificially too high To shift values for the grading parameter (SP) and thus to prevent switching until these limits are exceeded.

A third influencing parameter is the flight altitude of the aircraft gas turbine engine as well as changes in environmental conditions.

Finally, a fourth influencing parameter is the load change speed of the engine, with the following background: In the stepped mode, the combustion stability is in the pilot zone to ensure safe operation of the Combustion chamber vital. So in everyone Operating state no flame extinction of the pilot burner an unfavorable fuel distribution between the two Fuel circuits, that is, on the pilot burner and on the Main burner can occur, the switching process from pure pilot operation in staged operation at fast unsteady load change processes delayed. For this, the already mentioned basic value of the grading point a from Operating state of the combustion chamber dependent offset added. As a result, the grading point in the case of rapid load changes becomes too higher values of the grading parameter (SP) according to the invention postponed.

A fifth influencing parameter takes into account the influence of the Compressor pumping on the stability of the combustion in the staged Combustion chamber.

In this context, it will be described how a fast, safe and loss-free transition between the two operating modes of the stepped combustion chamber can be guaranteed. A grading process that is Switching the operating mode should not be significant Effects on the behavior of the entire engine, such as e.g. Compressor pumps due to unstable combustion or reduced Surge limit distance, thrust loss, flame extinction, Cause damage to the turbine due to overheating, etc. The following methods are for quick and safe Transition between the modes of operation suggested:

During rapid load changes, stability and Ignitability of combustion by a short-term Enrichment (greasing) of the fuel-air mixture Pilot zone ensured by the main stage and emaciated the excess fuel is fed to the pilot burners becomes. The pilot zone then always works within its Stability range and serves for the fuel-air mixture the main stage as an ignition source. To achieve this, in Dependence on the current acceleration respectively Delay an extended fuel splitting table in the depending on the grading parameter (SP) the division of the Total fuel mass flow to the pilot burner and the Main burner is used firmly. As an indicative Parameters for this fuel splitting table respectively for this map, both the time derivative of the Speed of the high pressure compressor (N2) as well as the time Derivation of the combustion chamber inlet pressure (P30) used. In addition, one is closed using defined closing rate limiters strong change in the fuel mass flow for the Pilot burner and thus an excessive change in the fuel-air ratio prevented in the pilot zone.

A so-called Split value, which is the fuel distribution to the pilot burner and main burner describes (and thus from the above Fuel splitting table can be found) and based on this the step valve unit is controlled, also in transient conditions can be adjusted. As already several times was mentioned, is in quasi-stationary operating states of the Engine a pollutant-optimized map for control the step valve unit used, the or one of the grading parameters according to the invention as indicative Input variable for this map is used. Complementary is now proposed during transient engine maneuvers adjust the calculated split value by a correction factor, this correction factor depending on the temporal change in the speed, in particular the high-pressure wave of the engine is calculated. This adjustment can be done take place in such a way that the commanded pilot fuel mass flow and thus the fuel-air ratio of the pilot zone is briefly increased to extinguish the flames in the pilot zone of the combustion chamber. Recommends it is the split value calculated in this way, for example, for electronic Control circuits known high-win and low-win elements within defined limits.

In order in a further advantageous development of the invention Fuel injection system upon detection of a pump the compressor of the aircraft gas turbine engine a stable Operation of the stepped combustion chamber is to be ensured Provided the following: The already known or Existing engine control laws can be an emerging one Compressor pumps are preferred due to the detection of strongly fluctuating Values of the gas pressure (P30) at the combustion chamber inlet and by a subsequent comparison with a set limit detect. Now it is suggested that the output size this logic in a digital electronic control unit to implement the fuel injection system according to the invention a flag for the period of the detected pumping process to the value "1". This flag is then used to move in that also implemented in the electronic control unit Rules for staged combustion for the period to change the switching line of the compressor pumping (for what already at this point to the figure explained in more detail later 5). To do this, the grading point is in the area high load points shifted so that the stepped combustion chamber in the operating mode before the compressor pumping occurred lingers. This means that if there is a major change in the grading parameter a cyclical switching between the two Operating modes of the combustion chamber (i.e. between pilot operation, in which only the pilot burners are supplied with fuel, and the staged operation, in which the main burner Received fuel) prevented. After pumping - that is as soon as the flag returns to "0" - the value for the grading point again according to those described here (Regular) rules for staged combustion chamber operation calculated. The advantage of this method lies in the prevention Cyclical switching also means that the current fuel split during the brief pumping of the compressor without changing the operating mode still from a map is calculated. This ensures that the Pilot fuel mass fraction according to the air-fuel ratio is determined and a sufficiently high stability reserve against flame extinction is retained.

In a preferred development of the invention, a Limit substitute value for the split value is used if the calculated and then time-differentiated split value one Limit difference value exceeds. This can possibly occurring disturbances in the controlled variable e.g. during fastest load change or unexpected malfunctions by limiting the opening respectively Closing rate of the grading valve unit can be intercepted. In this regard, the attached, Figure 4 briefly explained later. For this, the Time derivative of the calculated split value over a Time step formed and limited with the help of a limiter. This limiter is only active if the commanded or determined split value below a defined limit falls, the maximum permissible in tiered mode Fuel distribution between the pilot burners and the main burners considered. The current rate of change of the position the step valve unit is with the maximum allowed Rate of change is applied as long as the predefined limit is reached.

It is also proposed during a grading process or a transition from pilot operation (that is only the pilot burners are supplied with fuel) in the tiered Operation (i.e. the pilot burner and the main burner are fueled) a change in terms suppress bleed air extraction from the engine. This allows an additional variation of the fuel-air mixture be avoided. Afterwards in the tiered Operation mode fell below a maximum value for the split value then the desired delay is minimal Bleed air extraction in staged operation.

Finally, it is advantageous if a so-called step anticipation logic, the looming connection of the Main burner a brief filling of the main burner with Causes fuel. This is done with the aim of Occurrence of thrust losses and combustion chamber instabilities in the Course of a grading process (that is, if in addition to the pilot burners previously operated exclusively, now also the Main burner to be supplied with fuel) prevent. In the case of such a transient Engine maneuvers can occur because of the filling process. of the small dead volume of the main burner nozzles briefly to a decrease in the fed to the combustion chamber Total fuel mass flow come. This can now be done through a so-called staging anticipation logic can be prevented during the grading process in the fuel system provided pressure control valve (metering valve of the total fuel mass flow) briefly continues to open on the one hand the fuel pressure in the pilot burners and thus the fuel throughput through the pilot burner maintain as well as the dead volumes in the Refill main burners faster. Both the period of Change in position of the valve as well as the amount of Position changes are dependent on parameters which determines the steady state and the change take this operating state into account. At the same time thereby also a certain enrichment of the total fuel-air ratio in the combustion chamber, the is necessary due to a certain ignition delay in the Main stage of the combustion chamber is delayed implementation to compensate for the fuel in heat. Beside exist however, there are other options in an emerging Grading process briefly an enlarged To provide fuel mass flow to hereby the Main burner to fill completely and thus one otherwise it may occur for a short time To prevent thrust loss.

As a query condition for this proposed function claimed every possible parameter related to the implemented basic formula or the basic rules regarding the grading process stands as well any combination of the parameters with each other, as also the possibility of expanding the query condition through additional tables based on this parameter. Basically, this requires the specified query condition based only on appropriate tables that correspond to the expected loss or excess of the total fuel mass flow consider.

As shown in Fig. 5, the split value (S) gives the current one Value of the distribution of the mass flows of the fuel the pilot stage or the main stage of the combustion chamber in front. The grading point (SPK) gives a statement in which mode the fuel injection system is located, he thus gives a status display. With ABS is in Fig. 5 Absolute value of the grading point, which is always positive is. The downstream comparator, in which also the Limit value is received, then generates an SPK rating point value from 0 or 1.

5 also shows that the derivative of the high-pressure shaft speed is included in the map for controlling the TIMER according to time. As already explained in the description above, the selection element comprises two states, namely "T" for "true" and "F" for "false". In the state "T", since the value SPK * = 1, the historical value of BZ (operating state), that is to say the value from the last time step Z ^{-1, is} used. In the legend of FIG. 5, SPK denotes the command for the classification point, while SPK * means the time-delayed command for the classification point. State 0 denotes an unstaged operating state of the combustion chamber in which the pilot stage is switched on but the main stage is switched off. 1 denotes an operating state in which both the pilot stage and the main stage are switched on.

In this context, there is still a method of pre-filling the fuel lines leading to the main burners, preferred when starting the engine can be. Usually a so-called Fuel ring line leading to the main burners each time the engine is switched off passively, i.e. with air, flushed and the fuel in it in a flushing tank emptied. However, when the engine is operating it is required that the fuel ring line to the Main burner nozzle is completely filled when from unscheduled pilot operation for staged operation respectively Operation mode should be switched. this is a Prerequisite for the safe and stable operation of the Engine across its entire performance range. thats why a special measure is required to ensure that when starting the engine, connect the fuel ring line to the Main burners in parallel with the replenishment of the Pilot burner leading fuel ring line is filled. The following method is proposed for this:

The main burner ring line is always before starting the engine flushed out of fuel. If the engine is started (this can be ground starts and Trade starts in flight), first takes place via a replenishment of the whole taking place as short as possible Fuel line volume between the fuel metering unit or control valve unit and the injectors of the Pilot burner as well as the main burner. The fast one Filling process keeps the injection delay in the combustion chamber and thus the ignition delay taking place there as low as possible. For this there is an additional logic in the electronic Engine controller implemented. Accordingly, first of all an increased fuel mass flow that is several times above the Ignition fuel mass flow is, all fuel ring lines replenished. So that this fuel also in the to the lines leading to the main burners the mentioned step valve unit temporarily from the only the pilot burner in a semi-open position Position driven in which the main burner with fuel be supplied. This will be parallel to the pilot lines also the fuel lines leading to the main burners replenished. The corresponding opening time and the The opening position of the step valve unit is suitable predetermined. The advantage of this method is that on the Monitoring the filling level of the line in / to the Main burners can be dispensed with.

To ensure that the main burner fuel lines to be completely filled is the fuel pressure in these lines by appropriate positioning of the Of course, to keep the staged valve unit so large that the check valves in the main burner injectors be pressed briefly and both the forming Air cushion as well as a small amount of fuel in the Combustion chamber to be pressed. This minor The amount of fuel then burns together in the combustion chamber with the one injected simultaneously by the pilot burner Ignition fuel mass flow. The main burner injectors are then re-activated by the passive flushing system Fuel flushed out, causing the main burner to coke is prevented. Then the step valve unit closed (i.e. only the pilot burners are switched on) and at the same time the fuel mass flow from the Fuel metering unit or control valve unit to the level of the ignition fuel mass flow required for the ignition reduced. The further regulation of Fuel supply until ignition and acceleration will be like for an engine with a conventional system handled.

Fig. 1

eine schematische Darstellung einer gestuften Brennkammer eines Fluggasturbinen-Triebwerks,

Fig. 2

eine schematische Teilansicht eines erfindungsgemäßen Triebwerkreglers,

Fig. 3

ein Teil-Prinzipschaltbild des erfindungsgemäßen Triebwerkreglers,

Fig. 4

ein weiteres Teil-Prinzipschaltbild des erfindungsgemäßen Triebwerkreglers, und

Fig. 5

ein Prinzipschaltbild zur Umsetzung in einer digitalen elektronischen Steuereinheit bei einem bevorzugten Ausführungsbeispiel des erfindungsgemäßen Brennstoffeinspritzsystems.

The invention is described below using an exemplary embodiment in conjunction with the drawing. It shows:

Fig. 1

1 shows a schematic representation of a stepped combustion chamber of an aircraft gas turbine engine,

Fig. 2

2 shows a schematic partial view of an engine regulator according to the invention,

Fig. 3

a partial schematic diagram of the engine controller according to the invention,

Fig. 4

another partial block diagram of the engine controller according to the invention, and

Fig. 5

a schematic diagram for implementation in a digital electronic control unit in a preferred embodiment of the fuel injection system according to the invention.

In Figure 1, in which a usual partial section through a stepped Ring combustion chamber of an aircraft gas turbine engine shown is with the reference number 1 the combustion chamber and with the reference number 2 denotes the exit from this combustion chamber 1. The combustion chamber 1 reaches according to the illustrated Arrows a pumped by an upstream compressor and thereby compressed gas flow or air flow into it, which carries the required oxygen to the over the (or the multiple rings) Pilot burner 3 and possibly over the (or the multiple existing ring-shaped) main burner 4 in the combustion chamber 1 introduced fuel (this is punctured shown) to burn in the combustion chamber 1. The combustion exhaust gases then pass through the combustion chamber outlet 2 according to the arrow first into the turbine of the engine.

The combustion chamber 1 is spatially divided into a pilot zone 1a, which is located directly downstream of the pilot burner 3, and in one adjoining it in the direction of flow of the gases Main zone 1b, into which the main burners 4 discharge the fuel. The latter, that is, a fuel supply to the main zone 1b the combustion chamber 1 via the main burner 4, however, only happens in those operating points of the engine in which a higher Performance development or performance submission required becomes. On the other hand, 3 fuel is constantly passed through the pilot burner into the combustion chamber 1. Depending on the respective operating point of the aircraft gas turbine engine thus pass between 10% and 100% of the total fuel mass flow supplied via the pilot burner 3 into the combustion chamber 1 while consequently via the main burner 4 at high engine output 90% and with low engine power 0% of the total fuel mass flow be introduced into the combustion chamber 1.

FIG. 2 shows a fuel injection system according to the invention, with which the pilot burner 3 and the main burner 4 with Fuel are supplied, schematically and greatly simplified shown. The arrow WF illustrates the total fuel mass flow, dosed via a control valve unit 6 and thus to a certain operating point of the engine adapted is introduced into the combustion chamber 1. Such a thing called step valve unit 7 sets what proportion this total fuel mass flow WF according to arrow 3 ' the pilot burners 3 and which ones (which are complementarily related) Share of this total fuel mass flow WF according to Arrow 4 'is fed to the main burners 4.

With the reference number 8 is the (electronic) engine controller referred to, which usually contains several rule blocks. Here a first control block 8a is now shown, which is the control valve unit 6 operated or positioned appropriately or sets, and the appropriate (usual) engine control laws contains or takes into account. Further is a second control block 8b is shown, the staging valve unit 7 controls and therefore rules for the tiered Combustion contains or takes into account. This Control block 8b thus determines the so-called split value S, the distribution of the total fuel mass flow WF identifies the pilot burner 3 and the main burner 4 and adjusts the step valve unit 7 accordingly.

WF =

Gesamt-Brennstoffmassenstrom,

P30 =

Gasdruck am Brennkammer-Eintritt,

T30 =

Gastemperatur am Brennkammer-Eintritt, oder

T44 =

Total-Temperatur stromab der Triebwerks-Hochdruck-turbine
gegebenenfalls auch auf

T20 =

Gastemperatur am Triebwerks-Eintritt

zurückgegriffen. Hieraus ergibt sich nach obigen Erläuterungen der so genannte Stufungsparameter SP.FIG. 3 shows schematically and in a highly simplified manner the calculation of the distribution of the total fuel mass flow WF between the pilot burners 3 (fuel flow 3 'in FIG. 2) and the main burners 4 (fuel flow 4' in FIG. 2), this division being carried out by a so-called Split value S is described. As has been explained in detail above, this refers to the known sizes

WF =

Total fuel mass flow,

P30 =

Gas pressure at the combustion chamber inlet,

T30 =

Gas temperature at the combustion chamber inlet, or

T44 =

Total temperature downstream of the high pressure engine turbine
if necessary also on

T20 =

Gas temperature at the engine inlet

resorted to. According to the above explanations, this results in the so-called grading parameter SP.

Furthermore, the temporal change in the speed of the high-pressure shaft of the engine, that is to say the quotient (dNH / dt) _Ref , can also be taken into account, as will be explained below in connection with claim 3.

This results in a split value S ′ via maps 5, which initially still a conventional low-win link 9a and a high-win link 9b is performed, resulting in a nominal Split value S * results. The low-win link 9a takes into account here a maximum split value MAX (this corresponds to 100% fuel content for the pilot burner 3) while the high-win link 9b takes into account a minimum split value MIN which is between 10% and 40% fuel share for the pilot burner 3 are can. In this regard too, the explanations of the patent claim 3 referenced.

FIG. 4 shows a preferred way of limiting the fuel distribution on the pilot burner 3 and on the main burner 4 shown. In this regard, refer to the explanations Claim 5 referenced. A (temporal) differentiator for the nominal split value S *, reference numerals 10 and the limiter referred to in claim 5 above the reference number 11. The limit value for this query if necessary, is taken as the input variable with the reference number Denoted 12 and can be, for example, 50%. At a Grading from pilot operation to so-called dual operation - (in the pilot burners and the main burners are operated) - the commanded split value runs through the range between 100% and 40%. Only from a pilot fuel content below The fuel distribution is limited to 50% Pilot burner. This means that the share 4 'of the total fuel mass flow WF, which over the main burner 4 in the Combustion chamber 1 can reach between 0% and 50% can lie.

Finally, FIG. 5 shows a diagram for the preferred calculation the operating mode of the combustion chamber 1, that is, whether this is operated in pilot operation or in staged operation. The The output variable of this scheme is a digital yes / no variable, which indicates whether the main burners 4 are supplied with fuel or not.

In addition to the calculated split value S * (nominal grading point), as well as the current split value "Actual" go into this Determination or calculation of the grading point such as can be seen additively several correction elements ΔSP, such as this has also already been explained in detail. This individual Consider correction terms that are added up to ΔSP thereby - as already explained - via suitable Maps 5 several influencing parameters. The consideration the load change speed is also with "transient" and that of the flight altitude also referred to as "altitude". The one switch from the unrated pilot operation to the tiered operation mode below the idle mode the engine preventing function is also with "Idle" denotes, and the function that has an absolute value for gas pressure (P30) and / or gas temperature (T30) considered at the combustion chamber inlet to ensure a stable Ensure operation of the combustion chamber is also included Denoted "Stability".

With the features described so far, a fuel injection system results for a stepped combustion chamber in particular of an aircraft gas turbine engine, with which an essentially optimal operation of this combustion chamber 1 is made possible. Possible is in particular a map-based, optimized for pollutants Regulation of staged combustion in quasi-stationary Business. The control block 8b of the engine controller 8 implementable and previously described rules for staged combustion allow operation of one or the tiered combustion chamber 1 in the tiered Pilot operation and in tiered mode without significant influence on the safety, stability and thrust of the entire engine during a staging process, including a switching process between the two operating modes is understood. In particular, it becomes almost shear loss-free transition from the operating state with sole Actuation of the pilot burner 3 in the staged operation, in in addition to the pilot burners 3 and also the main burners 4 Fuel is guaranteed. The so-called The grading process advantageously does not claim that existing stability reserve of the compressor.

The continuously adjustable staging valve unit 7 ensures that both the emission level of the combustion chamber, in particular with regard to NO _x, and the temperature profile at the turbine inlet downstream of the combustion chamber 1 are optimized over the entire operating range of the engine. The selected method of setting the fuel split, that is to say the split value S, between the pilot burners 3 and the main burners 4 thus enables flexible distribution of the fuel in accordance with the current requirements for the control system in the respective operating state. In addition to an optimal setting of the fuel distribution to minimize pollutant emissions, this method also enables the combustion chamber's operating behavior to be optimized with regard to combustion stability, burnout behavior and the temperature exit profile over the entire load range of the engine.

As described, a separate detection of the significant influencing factors, e.g. Flight altitude, transient Operating maneuvers on the grade point as well as the correct one Setting the fuel distribution on both fuel circuits in tiered mode. All major influences on the Grading characteristics are recorded using simple maps and their influence additively both on the grade point and also on the fuel split, i.e. on the split value S, considered. This will optimize both Combustion in the two combustion chamber zones, namely the Pilot zone 1a and the main zone 1b, as well as compliance with the Guaranteed combustion stability.

Generally there is an improved control quality due to the use of easily measurable engine parameters, such as WF, P30, T30 and others A synthesis of engine parameters is avoided. Also when implementing the so called step anticipation logic during a Staging process a significant reduction in engine thrust be prevented. Also the consideration described a starting process is in an inventive Fuel injection system extremely beneficial. Finally is the software for regulating the grading process simply in an existing engine controller can be integrated, although still it should be noted that of course a variety be deviated from details deviating from the above explanations can without leaving the content of the claims.

In summary, the following can be stated:

The invention relates to a fuel injection system for a tiered combustion chamber 1 of an aircraft gas turbine engine, the Pilot burner 3 always supplied with a certain amount of fuel will / will, during their main burner (s) 4 only at higher Engine power is metered to fuel, where downstream of a control valve unit determining the total amount of fuel 6 a this total fuel mass flow (WF) changeable on the pilot burner 3 and on the main burner 4 dividing stage valve unit 7 is provided, both be controlled by an engine controller 8, which for the Control of the staging valve unit 7 the desired engine power based, characterized in that the Engine performance due to the load on the gas turbine combustion chamber 1 in the form of a so-called grading parameter (SP) is characterized, on the basis of which the step valve unit 7 is controlled according to a switching line that the Grading parameters (SP) derived from a functional relationship is that a downstream summation point for Calculation of the difference between a current value of the grading point and a value of the nominal grading point and that the summation point is a time element (TIMER) is subordinate, which is designed so that after the exceeding or falling below the adjusted grading point the switching process is delayed if the length of time since the last step was carried out is as a predefined time constant in a map is filed.

Claims (15)

Fuel injection system for a stepped combustion chamber (1) an aircraft gas turbine engine, its pilot burner (3) always supplied with a certain amount of fuel will be, during their main burner (s) (4) only at higher Engine power is metered to fuel, where downstream of one that determines the total amount of fuel Control valve unit (6) this total fuel mass flow (WF) on the pilot burner (3) and on the Main burner (4) variable division valve unit (7) is provided, both by an engine controller (8) can be controlled for the control the staged valve unit (7) the desired engine power on the basis, characterized in that the engine performance due to the load on the gas turbine combustion chamber (1) in the form of a so-called grading parameter (SP) is characterized, on the basis of which the step valve unit (7) corresponding to a switching line is controlled that the grading parameter (SP) from a functional relationship is derived that a downstream summation point for calculating the difference between a current grade point value and a value of the nominal grading point is provided, and that the summation point has a time element (TIMER) is subordinate, which is designed so that after the exceeding or falling below the adjusted Grading point of the switching process delayed if the amount of time since the last Gradation is smaller than a predefined time constant, which is stored in a map. Fuel injection system according to claim 1, characterized in that that the time element (TIMER) can be activated, as soon as the current value of the grading point is 1 assumes. Fuel injection system according to claim 1 or 2, characterized characterized in that the time element (TIMER) by means of a Map control is controllable. Fuel injection system according to claim 3, characterized in that the map control is designed to deliver a control parameter t _{MIN, gradation} to the time element (TIMER). Fuel injection system according to claim 4, characterized in that that the control parameter with fast load path is small and large for slow load travel. Fuel injection system according to one of claims 3 to 5, characterized in that the map control for the time element (TIMER) as the input variable the derivative the high pressure turbine shaft speed over time (dNH / dt) is feedable. Fuel injection system according to one of claims 1 to 6, characterized in that the initial value SPK * des Time element (TIMER) can be fed to a selection element. Fuel injection system according to claim 7, characterized in that the selection element is designed such that the current value of the grading point calculation is used for SPK * = 0 and that the value of the last time step (Z ^-1 ) is used for SPK * = 1. Fuel injection system according to one of claims 1 to 8, characterized in that the grading parameter (SP) is derived from a functional relationship: {Total fuel mass flow (WF)} divided by {gas pressure at combustion chamber inlet (P30)} multiplied by {gas temperature at combustion chamber inlet (T30)}, this means SP = function of [WF / P30 · T30] or {Total fuel mass flow (WF)} divided by {gas pressure at the combustion chamber inlet (P30)} multiplied by {square root of the gas temperature at the combustion chamber inlet (T30)}, this means SP = function of [WF / P30 · (T30) 1/2 ] or {Total fuel mass flow (WF)} divided by {gas pressure at the combustion chamber inlet (P30)} multiplied by {square root of the quotient of the gas temperature at the combustion chamber inlet (T30) and the gas temperature at the engine inlet (T20)}, this means SP = function of [WF / P30 · (T30 / T20) 1/2 ] or {Total fuel mass flow (WF)} divided by {gas pressure at combustion chamber inlet (P30)} multiplied by {total temperature (T44) downstream of the high-pressure turbine or the square root thereof}, this means SP = function of [WF / P30 · T44] , or SP = function of [WF / P30 · (T44) 1/2 ] Fuel injection system according to one of Claims 1 to 9, characterized in that it is provided with regard to the switching on and switching off of the main burner (4) that when the engine power rises above the staging point the main burner is switched on and when the engine power drops below the staging point the main burner is switched off , and that at least one correction element (ΔSP) in the form of an offset is added to a basic value of the grading point, which is determined in particular from a characteristic map, by which one of the following influencing parameters is taken into account: Absolute value of the gas pressure (P30) and / or the gas temperature (T30) at the combustion chamber inlet corrected speed of the high pressure compressor (N2RT20) and gas pressure at the engine inlet (P20) Flight altitude and / or selected environmental conditions Load change speed Compressor pumps Fuel injection system according to one of claims 1 to 10, from the grading parameter (SP) via a map a so-called split value (S) is determined, which is the Fuel distribution between the pilot burners (3) and Main burner (4) describes and on the basis of this the step valve unit (7) is controlled, characterized in that that in transient states of the engine the Split value (S) is adjusted by a correction factor, depending on the change in speed over time especially the high pressure shaft of the engine becomes. Fuel injection system according to one of claims 1 to 11, characterized in that on a limit replacement value is used for the split value if the time-differentiated calculated split value a limit difference value exceeds. Fuel injection system according to one of claims 1 to 12, characterized in that during a grading process, in which the main burner (4) switched on or be switched off, initiated by the engine controller (8) a change in bleed air extraction rate from the Engine is prevented. Fuel injection system according to one of claims 1 to 13, characterized by a step anticipation logic, the looming connection of the main burner (4) causes a short filling of the main burner. Fuel injection system according to one of claims 1 to 14, characterized in that during a starting process the fuel lines to the engine Main burners at the same time as the lines to the pilot burners be filled without the filling state in the Main burner lines to measure.

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