DE102007031264B4 - Method for operating a fuel-operated heater, in particular vehicle heater - Google Patents

Abstract

A method of operating a fuel-fired heater in a start-up phase of combustion, the heater including a combustor portion (12) having a combustor (14), a combustion air supply assembly (16) for supplying combustion air to the combustor (14), a fuel supply assembly (18) for supplying Fuel to the combustion chamber (14) and an electrically excitable ignition member (28) for igniting a combustion air / fuel mixture in the combustion chamber (14), the method comprising the measures: a) determining a deviation of a with the applied to the ignition Voltage-related actual voltage magnitude (U) from a target voltage magnitude (Uz), characterized in thatb) when the actual voltage magnitude (U) is below the desired voltage magnitude (Uz) based on the desired voltage magnitude (Uz) and the actual voltage magnitude (U), reducing at least the combustion air supply amount and continuing the operation on the Basis of the reduced combustion air supply.

Description

The present invention relates to a method for operating a fuel-operated heater, in particular vehicle heater, in a starting phase of the combustion, which heater a burner area with a combustion chamber, a combustion air supply arrangement for supplying combustion air to the combustion chamber, a fuel supply arrangement for supplying fuel to the combustion chamber and a electrically energizable ignition device for igniting a combustion air / fuel mixture in the combustion chamber comprises, according to the preamble of claim 1.

A method for operating a fuel-operated heater, in particular vehicle heater, is known from EP 1 674 794 A1 known. In this known approach takes place in a start phase, a power control of an electrically excitable ignition device. The electrical power is integrated over time to obtain a value representing the energy introduced into the heater. If this energy is entered before reaching a predetermined reference time, it is assumed that sufficiently high temperatures are present for ignition, so that the starting procedure is continued. If the value of the energy entered is too low, it is concluded that a sufficiently high temperature for igniting a fuel / combustion air mixture could not be generated, so that the starting procedure is terminated.

The DE 103 11 898 A1 discloses a starting procedure in a fuel-powered vehicle heater, in which a resistance control of the electrically excitable ignition device takes place. By adjusting the resistance value of the same to a predetermined desired value, it is possible to conclude on the presence of combustion when observing the heating power applied by the electrically excitable ignition device, namely with a significant drop in the same.

From the EP 0 384 280 A2 it is known to operate in the startup phase of a fuel-fired heater, the combustion air blower initially with relatively high speed, then turn off the fan motor and during the then occurring drop in fan speed and thus waste the amount of combustion air supplied to energize an ignition device and also start the fuel supply, so that at any time an ignitable mixture of air and fuel is generated.

In such fuel-operated heaters, which are used in vehicles, for example, as auxiliary heaters or heaters, combustion air and fuel is promoted in the starting phase simultaneously with the excitation of the electrically energizable ignition and thus heating combustion air and fuel in the combustion chamber, on the one hand to provide an ignitable mixture of combustion air and fuel On the other hand, by exciting the ignition device to generate locally high enough temperatures to trigger the ignition. In order to start up the combustion after ignition as quickly as possible in the direction of maximum heating power, comparatively large Verbrennungsluftzuführmengen or Brennstoffzuführmengen are already used in the start phase, of course, make sure that the Verbrennungsluftzuführmenge and the Brenntsofftzuführmenge in the lowest possible pollutant emissions lying relationship.

In the course of this starting phase, the temperature of the electrically excitable ignition element and thus the temperature in its environment is essentially determined by the electrical heating power of this ignition element, ie the heat energy provided in the ignition, and the heat dissipation by the circulation of this ignition device with combustion air. Care must be taken that, under these conditions, the heat dissipation does not become so great that, despite excitation of the ignition device, the temperatures required to ignite the combustion air / fuel mixture can not be achieved or maintained. Especially if, during the starting phase of the combustion, the power supply for the electrically excitable ignition device can not be ensured, for example, because more consumers load an on-board system heavily, this critical case may occur that the operating voltage available for energizing the ignition device drops so much in that even with permanent excitation, ie a duty cycle of 100%, the heat dissipation through the flow around the ignition with the generally comparatively cold combustion air exceeds the heat input and thus drops the temperature of the ignition or not reach the required values for ignition.

It is the object of the present invention to provide a method for operating a fuel-operated heater, in particular a vehicle heater, in a starting phase of the combustion, with which a reliable starting can be ensured even when the supply voltage drops.

1. a) Ermitteln einer Abweichung einer mit der an das Zündorgan angelegten Spannung in Zusammenhang stehenden Ist-Spannungsgröße von einer Soll-Spannungsgröße,
2. b) dann, wenn die Ist-Spannungsgröße unter der Soll-Spannungsgröße liegt, beruhend auf der Soll-Spannungsgröße und der Ist-Spannungsgröße, Reduzieren zumindest der Vebrennungsluftzuführmenge und Fortführen des Betriebs auf der Grundlage der reduzierten Verbrennnungsluftzuführmenge.

According to the invention, this object is achieved by a method for operating a fuel-operated heater, in particular a vehicle heater, in a starting phase of the combustion, which heater comprises a burner section having a combustion chamber, a combustion air supply arrangement for supplying combustion air to the combustion chamber, a fuel supply arrangement for supplying fuel to the combustion chamber, and an electrically energizable ignition device for igniting a combustion air / fuel mixture in the combustion chamber, the method comprising includes:

1. a) determining a deviation of an actual voltage magnitude associated with the voltage applied to the ignition device from a desired voltage magnitude,
2. b) when the actual voltage magnitude is below the target voltage magnitude based on the target voltage magnitude and the actual voltage magnitude, reducing at least the combustion air supply amount and continuing the operation based on the reduced combustion air supply amount.

If, therefore, in the procedure according to the invention, it is recognized that a critical state can arise as a result of a voltage undersupply of the electrically excitable ignition element, since the energy input may become too low, it is ensured that by reducing at least the amount of combustion air supplied, then the flow around and therefore the heat removal also be reduced to the ignition. In other words, ignitable conditions can nevertheless be ensured with a lower amount of heat energy provided in the ignition device and correspondingly less heat dissipation. In this case, preferably, the Brennstoffzuführmenge be reduced in order to provide in this phase for a suitable ratio of the fuel supply and the combustion air supply.

For example, it can be provided in the method according to the invention that a combustion air supply quantity setpoint associated with the combustion air supply quantity supplied by the combustion air supply arrangement is specified in association with the desired voltage value and that the combustion air supply quantity desired variable is determined based on the setpoint value when the measure b) is carried out. Voltage size and the actual voltage size is reduced.

wobei:

• VLSGR = reduzierte Verbrennungsluftzuführmengen-Sollgröße
• VLSG = Verbrennungsluftzuführmengen-Sollgröße
• SSG = Soll-Spannungsgröße
• ISG = Ist-Spannungsgröße

For example, the determination of the reduced combustion air supply amount target quantity may be based on the following relationship: $$\text{VLSGR = VLSG}\times \left[\text{ISG / SSG}\right]$$

in which:

• VLSGR = reduced combustion air supply quantity target value
• VLSG = combustion air supply quantity target value
• SSG = target voltage size
• ISG = actual voltage size

In order to avoid an excessive pollutant emissions in this phase of reduced fuel supply at then occurring ignition, it is further proposed that in relation to the desired voltage magnitude in the context of the supplied fuel feed through the Brennstoffzuführmenge fuel supply set target size is specified and that when performing the Measure b) the target fuel supply amount is reduced based on the target voltage magnitude and the actual voltage magnitude. For example, a reduced target fuel supply amount may be determined based on the reduced amount of combustion air supply amount.

In order to avoid abrupt changes in the transition to reduced supply quantities, since these can always lead to noticeable reactions, for example in a vehicle interior, it is proposed that the combustion air supply quantity and / or the fuel supply amount are reduced in a ramp-like manner.

In the method according to the invention, the measures a) and b) are preferably carried out repeatedly, for example periodically.

By repeatedly performing, it becomes possible to adjust the reduced combustion air supply amount and, if necessary, the reduced fuel supply amount when a change in the actual voltage magnitude occurs.

In this case, for example, it is possible to proceed in such a way that an adjusted reduced amount of combustion air supply quantity is determined based on a desired amount of combustion air supply and a desired voltage value which were used at the time of the first decrease of the actual voltage magnitude below the desired voltage value.

In an alternative approach, the adjusted reduced combustion air supply amount setpoint may be determined based on a desired amount of combustion air supply and a desired voltage magnitude to be used at the time of adjustment.

Even with such adaptation of the combustion air supply quantity desired variable triggered by a variation of the actual voltage magnitude, an adapted reduced fuel supply quantity desired variable can be determined based on this adapted reduced amount of combustion air supply quantity.

In order to avoid impulsive changes in the operating states of a heater even when adapting the reduced supply quantities, it is proposed to perform the transition to respective adapted supply quantities in a ramp-like manner.

If, in the procedure according to the invention, it is recognized that ignition has occurred while the actual voltage magnitude is still below the desired voltage magnitude, then the combustion air supply quantity and, if it has even been reduced, the fuel supply quantity can also be increased again.

In the starting phase of combustion, in the method according to the invention, the excitation of the ignition device is continued at least until a predetermined amount of fuel has been delivered into the combustion chamber or the occurrence of the ignition is detected. In this way it can be ensured that even with a particularly reduced amount of fuel supplied a sufficient amount of fuel has been provided in order to produce an ignitable mixture in the combustion chamber can.

The voltage magnitude may be the voltage applied to the ignition device, but may also be the electrical ignition performance of the ignition device.

The combustion air supply amount set value may be a voltage applied to an electric drive motor of the combustion air supply arrangement, and when the variable duty cycle clocked excitation is used, the average voltage based on each duty ratio may be considered, for example.

Alternatively, it is possible that the combustion air supply amount target quantity is a rotational speed of a drive motor and / or a delivery wheel of the combustion air supply arrangement.

The target fuel supply amount may be a delivery frequency of a metering pump of the fuel delivery assembly.

• 1 eine prinzipartige Darstellung eines Fahrzeugheizgeräts;
• 2 über der Zeit aufgetragen die an einem elektrisch erregbaren Zündorgan anliegende Spannung;
• 3 über der Zeit aufgetragen die an einem Elektroantriebsmotor einer Verbrennungsluftzuführanordnung anliegende Spannung;
• 4 über der Zeit aufgetragen die Förderfrequenz einer Dosierpumpe;
• 5 über der Zeit aufgetragen die in einem Fahrzeug verfügbare Versorgungsspannung;
• 6 den Zusammenhang zwischen der an einen Elektroantriebsmotor einer Verbrennungsluftzuführanordnung angelegten Spannung und der Förderfrequenz einer Dosierpumpe.

The present invention will be described below in detail with reference to the accompanying drawings. It shows:

• 1 a schematic representation of a vehicle heater;
• 2 Over time, the voltage applied to an electrically energizable ignition device is applied;
• 3 over time, the voltage applied to an electric drive motor of a combustion air supply assembly is applied;
• 4 plotted over time the delivery frequency of a metering pump;
• 5 over time, the supply voltage available in a vehicle plots;
• 6 the relationship between the applied to an electric drive motor of a Verbrennungsluftzuführanordnung voltage and the delivery frequency of a metering pump.

In 1 For example, a vehicle heater is generally designated 10. The vehicle heater 10 includes a burner area 12 with a combustion chamber formed in a housing 14 , In this combustion chamber 14 is through a combustion air supply arrangement 16 Combustion air L fed. Through a fuel supply arrangement 18 In general, liquid fuel is fed. In the combustion chamber 14 a mixture of fuel and combustion air is formed and burned. The heat generated during combustion can be in a heat exchanger area 19 be transferred to a medium flowing through this M. This medium may for example be the air to be introduced into a vehicle interior, but may also be the coolant of the coolant circuit of an internal combustion engine. The combustion exhaust gases A leave the burner area in the direction of an exhaust gas routing system.

The combustion air supply arrangement 16 , which may be formed for example as a side channel blower, comprises an electric drive motor 20 and a driven by this conveyor wheel 22 , The fuel supply arrangement comprises, for example, a metering pump (not shown) which supplies the liquid fuel from a reservoir 24 removes and him by intermittent reciprocation of a pump piston in a pumping chamber in the direction of the combustion chamber 14 promotes. The in the combustion chamber 14 fed fuel can be passed, for example, in a porous evaporator medium, in the inner volume region of the fuel is distributed by Kapillarförderwirkung and then in the direction of the combustion chamber 14 is evaporated. To assist this evaporation, an electrically energizable heater 26 be provided, for example in the bottom region of the combustion chamber 14 which heats the porous evaporator medium and thus the liquid fuel contained therein.

To the ignition of the in the combustion chamber 14 To promote existing mixture of combustion air and fuel or to start the combustion, is an example designed as Glühzündstift ignition device 28 intended. In a starting phase, ie in a phase in which the combustion operation is to be started, this ignition device 28 energized by applying an electrical voltage to generate due to the existing electrical resistance and the heat generated during excitation locally high temperatures so that in this area the ignition is triggered, thus starting the combustion.

The different ones to activate the vehicle heater 10 system areas to be operated, ie in particular the Verbrennungsluftzuführanordnung 16 , the fuel supply assembly 18 , the heater 26 and the ignition device 28 are under the control of a drive device 30 , This generates, for example, depending on various parameters, such as the ambient temperature or the temperature in a vehicle interior, control commands or signals and thus activates the various addressed system areas 16 . 18 . 26 and 28 , In the case of the electric drive motor 20 the combustion air supply arrangement 16 can at this by the drive device 30 a clocked voltage signal, so a voltage signal with a predetermined duty cycle, are applied, so that according to a by the duty cycle also defined average voltage associated therewith a speed of the electric drive motor 20 and thus also the conveyor wheel 22 will adjust. In the case of the fuel conveying arrangement 18 can also be applied a clocked signal whose clock frequency is designed for the desired movement frequency of the metering pump. As with each stroke of a pump piston, a predetermined volume of the liquid fuel is conveyed, determines this frequency, similar to the speed in the case of the feed wheel 22 , the quantity subsidized per time unit. In the case of the heater 26 can the drive device 30 create a substantially constant or pulsed voltage, especially during the start phase, in order to support the evaporation by electrical excitation and the resulting heating. Also to the ignition device 28 can be applied with a predetermined duty cycle, an electrical voltage so that also determined by the resulting average voltage, a corresponding average heating power is obtained, which has a significant influence on the temperature of the ignition device 28 or the surroundings of the ignition device 28 will have.

The drive device 30 uses to be able to activate or control the various described system area, a in the 1 schematically indicated on-board voltage system 32 or its supply voltage.

With reference to the 2 to 6 hereinafter, the operation of the vehicle heater 10 especially described in the starting phase of the combustion.

The 2 shows over time applied to the ignition device 28 applied ignition voltage Uz, which is thus defined in particular when applying a pulsed voltage by the supply voltage and the duty cycle. By varying the duty cycle, it becomes possible to influence the level of the average voltage applied to the ignition element. This can, as on the course K1 in 2 recognizable to be varied in the starting phase, for example, first a higher voltage is applied, this is then lowered, and then gradually, as shown by the dashed line K2, continue to increase.

The 3 shows with the course K3 the course of the electric drive motor 20 applied voltage U _GS , so for example, mean voltage. It can be seen here that, at the beginning of operation, a constant voltage is initially applied for a short time, in particular in order to perform an operational check, the voltage is then reduced again to zero and then ramped up. A dashed curve K4 shows that this specified for the electric drive motor target voltage gradually increases up to a Maximlawert and then held at this maximum value. It should be noted here that the to the electric drive motor 20 applied voltage generally corresponds to that through the combustion air conveying arrangement 16 promoted Verbrennungsluftzuführmenge, so that by varying this voltage U _GS on the electric drive motor 20 an influence on the combustion air supply amount can be taken. In correspondence to the supply of combustion air, so the application of a voltage to the electric drive motor 20 , Also, a corresponding drive signal to the fuel supply system 18 sent, so they are operated at a certain conveyor frequency Fs, like the 4 this shows. Here, for example, as shown by the course of the curve K5, the supply of fuel with some delay for supplying the combustion air done. On the basis of the course K6 it can be seen that the fuel supply amount also increases until it reaches a maximum value.

When supplying the combustion air and the fuel, it must be ensured that the feed quantities defined on the basis of the respective setpoint voltages or setpoint delivery frequencies are coordinated with one another in such a way that the pollutant emissions from the vehicle heater 10 is minimal. For the combustion air conveying arrangement 16 is the course of this setpoint voltage U _GS represented by the curve represented by the two curves K3 and K4. For the fuel supply assembly 18 Thus, for example, a metering pump, the course of the associated desired conveyor frequency is defined by the curve, which results from the two contiguous courses K5 and K6.

A comparison of 2 to 4 shows that when about when the ignition device 28 applied voltage Uz reaches its maximum value, also the combustion air supply amount and the fuel supply amount, each represented by the to the electric drive motor 20 applied voltage U _GS and the delivery frequency Fs of the metering pump, reach their maximum value. That is, at the time when the ignition device 28 is operated with maximum heating power, a maximum amount of the combustion air / fuel mixture is provided to generate the most favorable conditions for starting the combustion.

As already stated above, the temperature is in the region of the ignition device 28 essentially determined by its heating power, which in turn is proportional to the square of the voltage applied thereto. Another influence parameter, however, is the flow around the ignition device 28 especially in his in the combustion chamber 14 lying area through the combustion air L. In a phase in which a combustion has not been started, wearing the ignition device 28 Surrounding combustion air L Heat from the area of the ignition device 28 so contributes to its cooling. The heating power of the ignition device 28 must therefore be adjusted so that even taking into account that comparatively cold combustion air L into the combustion chamber 14 is encouraged, at least in the vicinity of this ignition device 28 the temperature can become so high that the combustion actually starts.

The 5 shows that of the drive device 30 used and by the on-board voltage system 32 Provided supply voltage Uv. This is normally at an operating voltage value U _B of, for example, 12 V or 24 V. The various system components or the way in which they are activated and thus operated are also coordinated with one another taking account of this normally available operating voltage U _B in that the start of the combustion can be reliably achieved.

However, they occur in the area of the on-board voltage system 32 Problems on, for example, by an overload of a plurality in the startup phase put into operation consumer electrical energy, so it is to ensure that the combustion operation of the vehicle heater 10 nevertheless can be started reliably. For this purpose, the measures according to the invention described below are taken.

In 5 It can be seen that at time t _1, a drop in the supply voltage Uv from the operating voltage value U _B to the reduced operating voltage value U _BR occurs. For example, a drop from 12V to 9V may occur. During such a voltage drop with respect to the operation of the electric drive motor 20 and the metering pump of the fuel supply assembly 18 in general uncritical, since they are operated with such clocked voltages that nevertheless the predetermined voltages or nominal conveyor frequencies given by the curves K3, K4 or K5, K6 are achievable, such a voltage drop results in the triggering of the ignition device 28 In addition, the voltage to be applied and the heating power to be set can no longer be achieved. This is in the 2 made recognizable by the fact that from the time t _{1 is} not the predetermined course K2, which in conjunction with the existing before the time t ₁ course K1 the course of the target voltage for the ignition 28 defined, only a limited ignition voltage U _ZI can be reached, which is represented by the curve K7. This means that from the time t _1, even at a duty cycle of 100%, a substantially constant actual voltage U _ZI at the ignition device 28 is applied and this can therefore only be operated with reduced heating power. Since the to the ignition 28 applied voltage is monitored, it is recognized that there is a significant deviation from the target voltage, ie the course K2. Here, a threshold can be specified, so that it can be concluded that the presence of a critical deviation, if this threshold is exceeded, so in the case of 2 the course K7 is a predetermined extent below the course K1 or K2. If this is detected, according to the invention, first of all, a corresponding adaptation is also made to the amount of combustion air supplied, that is to say to the electric drive motor 20 applied voltage U _GS . Here, starting from the value U _GS 'existing at time t ₁ , the setpoint voltage defined by the curves K3 and K4 is determined to be a reduced value of the setpoint voltage U _GSR , which subsequently also remains unchanged in accordance with the electric drive motor 20 is created. The consequence of this is that it will operate at a speed defined by the voltage or average voltage which will be at the reduced value U _GSR . The extent of reducing the target voltage can be determined from the extent of reduction in the ignition device 28 applied ignition voltage. These reduced setpoint voltage U _GSR can thus be determined according to the following formula: $${\text{U}}_{\text{GSR}}={\text{U}}_{\text{GS}}\text{'}\times \left[{\text{U}}_{\text{ZI}}/{\text{U}}_{\text{ZS}}\right],$$

It can thus be seen that in the same ratio, in which at the time t ₁ , at which the critical reduction of the supply voltage Uv has occurred for the first time, that to the electric drive motor 20 voltage to be applied and therefore the amount of combustion air to be reduced. A reduced combustion air flow rate has the consequence that also a lower heat removal from the ignition device 28 occurs, so that despite reduced heating power this can produce a sufficiently high temperature to trigger the ignition.

In adaptation to the reduced Verbrennungsluftzuführmenge, so the reduced setpoint of the electric motor 20 To be applied voltage U _GSR also the fuel supply _amount is reduced. One recognizes in the 6 a linear relationship, for example, between the through the target voltage U _GS for the electric drive motor 20 defined combustion air flow rate and by the delivery frequency Fs a metering pump of the fuel supply 20 defined fuel supply. The voltage U _GS 'is assigned a delivery frequency or nominal delivery frequency Fs'. Accordingly, the reduced setpoint voltage U _{GSR is assigned} a reduced setpoint frequency F _SR .

One recognizes thus in the 3 and 4 Based on the courses K8 and K9 that after the time t ₁ not only on the ignition 28 applied voltage is forcibly reduced, but in adaptation to this forcibly reduced actual voltage U _ZI also a reduction of the target voltage U _GS for the electric drive motor and the target delivery Fs a metering pump to the values U _GSR and F _SR done. The transition from the respectively existing value U _GS 'or FS' at the time T1 to the respective reduced values U _GSR and F _SR can take place in a ramp-like manner in order to avoid spontaneous changes in operation.

Subsequently, then the vehicle heater 10 operated on the basis of these variables, of course, the monitoring, in particular the ignition voltage applied to the ignition element Uz is preferably repeated periodically. If there is a change, for example in the direction of a higher supply voltage, it is of course possible to obtain a corresponding adaptation of the setpoint voltage U _GS or the nominal delivery frequency F _SR by determining respective adjusted values. These adjusted values can be calculated in the same manner or determined by functional correlation, as described above. The starting basis, however, is always the value of the setpoint voltage U _GS for the electric drive motor present at the time of the first critical drop in the supply voltage Uv 20 to be applied voltage and at this time in each case also existing setpoint Uzs for the ignition voltage of the ignition device 28 , The adaptation then takes place taking into account the actual value U _{ZI of} this ignition voltage detected at the respective time. Of course, the same also applies if a further drop in the supply voltage occurs. Such adjustments of the reduced setpoint voltage or the reduced supply frequency can of course also be ramped, in order to avoid spontaneous operating state changes here as well.

In the in the 2 to 5 shown system or operation then occurs at time t _2, the ignition. This can be done, for example, by a flame detector, a spontaneous change in the resistance of the ignition device 28 or in different ways. If it has been detected that the ignition has occurred and thus the combustion has been started, then, for example, as represented by the curve K10, the excitation of the ignition device 28 be set, for example, step-like, ramp-like, or otherwise. Accordingly, then the excitation of the heater 26 be terminated because then only from the running combustion sufficient heat for evaporation support is available. Furthermore, according to the invention, the setpoint voltage U _GS and thus also the setpoint conveying frequency Fs are then raised again in the direction of the values actually provided for the normal starting sequence, represented by the courses K4 and K6. This can, as represented by the courses K11 and K12, again take place in a ramp-like manner, for example also with a plurality of ramps whose pitch decreases, if the currently existing still reduced value of the setpoint voltage U _GS or setpoint conveyor frequency Fs does not reduce to that predetermined for the normal operating case Value approaches. From the time t ₃ are both for the target voltage U _GS for the electric drive motor 20 as well as for the delivery frequency Fs for the metering pump again reaches the intended values for the normal course, so that then the combustion can be continued even with continued reduced supply voltage in a manner unaffected therefrom.

If the supply voltage Uv returns to its initial value U _B before the ignition occurs, the reduced setpoint values U _GSR or F _SR are naturally adjusted again in the direction of the non-reduced setpoint values specified in advance, for example in one Way, as in the 3 and 4 is represented by the courses K11 and K12.

Furthermore, in the case of the invention, it is possible to proceed in such a way that the conditions required for the ignition, that is the excitation of the ignition device 28 and maintaining the supply of fuel and combustion air either until the occurrence of the ignition is detected, or until a predetermined amount of fuel enters the combustion chamber 14 has been promoted. This predetermined amount of fuel may be defined, for example, by a total number of strokes of a metering pump, which ensure that sufficient fuel has been provided to start the combustion. Thus, regardless of the fact that, by reducing the various setpoints, this amount of fuel will actually be reached later than in the case of a start procedure not affected by a reduction in the supply voltage.

With the procedure according to the invention, it is thus possible to take into account by simple measures, namely the adjustment of the Verbrennungsluftzuführmenge and in connection with the adjustment of Brennstoffzuführmenge an otherwise critical in terms of ignition reduction of the supply voltage and nevertheless provide for the conditions allow the ignition. In particular, if it is not only the Verbrennungsluftzuführmenge, but also the Brennstoffzuführmenge is reduced, it can be ensured that the ratio of combustion air and fuel in the combustion chamber is always at a value that leads to a minimum pollutant emissions in this phase. In this case, as stated above, the fuel supply quantity to be selected in adaptation to a reduced amount of combustion air supply can be effected by a functional relationship based on, for example, the reduced setpoint voltage U _GSR . Of course, it is also possible to calculate the reduced fuel supply quantity, that is, for example, the reduced nominal delivery frequency F _SR , with the same relationship as is done for the target voltage U _GS on the basis of the formula given above.

It should also be noted that, especially in the area of the combustion air supply arrangement, it is not necessarily the case of the electric drive motor 20 to be applied target voltage U _GS is to be used as the size that is to be adjusted by their direct relationship with the supported amount of combustion air. For example, the speed of the electric drive motor 20 or the conveyor wheel 22 be monitored and carried out in accordance with a reduction or adaptation of the target speed to a possibly reduced ignition voltage. In principle, therefore, it is possible here to act on any operating parameter which is directly related to the amount of combustion air or fuel quantity delivered in each case. In particular, it should be noted that in the context of the invention with the monitoring or, if necessary, required reduction or adaptation of the setpoint voltage for the electric drive motor 20 Of course, the reduction or adaptation of the duty cycle of the clocked applied voltage when applying a pulsed voltage for changing an applied voltage or average voltage can be made. This is in fact equal to the variation of the applied voltage or the average applied voltage resulting from the variation of the duty cycle.

In the inventive approach may be alternatively provided that when a reduction of the combustion air supply and the fuel supply is to be made, this target values does not exist with the time t ₁ for the starting voltage, that is CW, and for example, to the electric drive motor 20 voltage to be applied, ie U _GS 'is worked, but that at any time after the time t ₁ when, due to a change in the Istzündspannung U _ZI an adjustment can be made, which are taken into account by the predetermined default values for the normal case , ie those setpoints that are defined by the curves K2, K4 and K6 by the time t ₁ . This may result in the determination of, for example, the reduced setpoint voltage U _{GSR being based} on a value which is increased in comparison to the value U _GS ', which, however, is to be multiplied by a smaller scaling factor, as is the case in FIG 2 shows that the deviation between the actual voltage U _ZI and the nominal voltage actually set at a later time for the normal case will also be larger and thus this quotient will be smaller.

Claims (19)

A method of operating a fuel-fired heater in a start-up phase of combustion, the heater including a combustor portion (12) having a combustor (14), a combustion air supply assembly (16) for supplying combustion air to the combustor (14), a fuel supply assembly (18) for supplying Fuel to the combustion chamber (14) and an electrically excitable ignition member (28) for igniting a combustion air / fuel mixture in the combustion chamber (14), the method comprising the measures: a) determining a deviation of a with the applied to the ignition Tension in connection standing actual voltage magnitude (U _ZI ) of a desired voltage magnitude (Uz), characterized in that b) when the actual voltage magnitude (U _ZI ) is below the desired voltage magnitude (Uz), based on the desired voltage magnitude (Uz) and the actual voltage magnitude (U _ZI ), reducing at least the combustion air supply _amount and continuing the operation based on the reduced combustion air supply _amount . Method according to Claim 1 , characterized in that in association with the target voltage magnitude (Uz) in connection with the combustion air supplied by the Verbrennungsluftzuführanordnung (16) supplied Verbrennungsluftzuführmenge stationary Verbrennungsluftzuführmengen target size (U _GS ) is specified and that when performing the measure b) the Verbrennungsluftzuführmengen target size (U _GS ) based on the target voltage magnitude (Uz) and the actual voltage magnitude (U _ZI ) is reduced. Method according to Claim 2 characterized in that a reduced amount of combustion air supply amount (U _GSR ) is determined based on the relationship: $$\text{VLSGR = VLSG}\times \left[\text{ISG / SSG}\right]$$

where: VLSGR = reduced combustion air supply amount setpoint (U _GSR ) VLSG = combustion air supply amount setpoint (U _GS ) SSG = target voltage magnitude (Uz) ISG = actual voltage magnitude (U _ZI ). Method according to one of Claims 1 to 3 , characterized in that in association with the desired voltage value (Uz) a fuel supply quantity setpoint (Fs) associated with the fuel supply arrangement fed through the fuel supply arrangement (18) is specified and in that the fuel supply setpoint parameter (B) is executed when the measure b) is carried out ( F _S ) is reduced based on the desired voltage magnitude (Uz) and the actual voltage magnitude (U _ZI ). Method according to Claim 4 and Claim 2 or 3 characterized in that a reduced amount of fuel supply target (F _SR ) is determined based on the reduced amount of combustion air supply amount (U _GSR ). Method according to one of Claims 1 to 5 , characterized in that the Verbrennungsluftzuführmenge and / or the Brennstoffzuführmenge be reduced in a ramp. Method according to one of Claims 1 to 6 , characterized in that the measures a) and b) are carried out repeatedly. Method according to Claim 7 , characterized in that when a change of the actual voltage magnitude (U _ZI ) occurs, at least the reduced combustion air supply _amount (U _GSR ) is adjusted. Method according to Claim 3 and Claim 8 characterized in that an adjusted reduced amount of combustion air supply amount (U _GSR ) based on a combustion air supply amount target (U _GSR ) and a target voltage amount (Uz) determined at the time (t ₁ ) of the first drop of the actual voltage magnitude (U _ZI ) below the target voltage magnitude (Uz) were used. Method according to Claim 3 and Claim 8 characterized in that an adjusted reduced amount of combustion air supply amount (U _GSR ) is determined based on a combustion air supply amount target (U _GS ) and a target voltage amount (Uz) to be used at the time of adjustment. Method according to Claim 9 or 10 characterized in that an adjusted reduced amount of fuel supply target (F _SR ) is determined based on the adjusted reduced amount of combustion air supply amount (U _GSR ). Method according to one of Claims 8 to 11 , characterized in that the transition to a customized reduced Verbrennungsluftzuführmengen target size (U _GSR ) or / and a matched reduced Brennstoffzuführmenge (F _SR ) is ramped. Method according to one of Claims 1 to 12 Characterized in that when lying at less than the target voltage value (Uz) actual voltage value (U _ZI) the occurrence of ignition is detected, at least the combustion air is increased again. Method according to one of Claims 1 to 13 characterized in that the energization of the ignition member (28) continues at least until a predetermined amount of fuel delivery into the combustion chamber (14) has been promoted or the occurrence of the ignition is detected. Method according to one of Claims 1 to 14 , characterized in that the voltage magnitude (Uz) is the voltage applied to the ignition device (28) voltage (Uz). Method according to one of Claims 1 to 14 , characterized in that the voltage magnitude is the electrical power of the ignition device (28). Method according to Claim 2 or one of the Claims 3 to 16 if on Claim 2 rear-biased, characterized in that the combustion air supply target quantity (U _GS ) is a voltage applied to a drive electric motor (20) of the combustion air supply arrangement (16). Method according to Claim 2 or one of the Claims 3 to 16 if on Claim 2 referred back, characterized in that the Verbrennungsluftzuführmengen target size is a rotational speed of a drive electric motor (20) and / or a delivery wheel (22) of the combustion air supply assembly (16). Method according to Claim 4 or one of the Claims 5 to 18 if on Claim 4 rear-biased, characterized in that the fuel supply amount setpoint (Fs) is a delivery frequency (F _S ) of a metering pump of the fuel supply assembly (18).

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