DE102010027811A1 - Method for operating fuel operated heater, particularly vehicle heater, involves comparing temperature parameter in warm-start phase with temperature threshold assigned to temperature parameter - Google Patents

Abstract

The method involves comparing a temperature parameter in the warm-start phase with a temperature threshold assigned to the temperature parameter. The temperature parameter is associated with the temperature of a medium (M) heated by the heater (10). The combustion air-supply arrangement is set into operation when the temperature parameter falls below the temperature threshold and during a cold blowing phase is operated for supply of air (L).

Description

The present invention relates to a method by which a fuel-operated heater, in particular a vehicle heater, preferably with an evaporator burner, can be operated or put back into operation in a warm start phase.

Fuel-powered vehicle heaters are operable to adjust the amount of heat energy provided in the combustion operation to the actual heat energy demand at various heat output levels. Depending on the required heat requirement, a combustion air quantity adapted thereto and a correspondingly adapted quantity of fuel are fed into a combustion chamber of the vehicle heater. In the embodiment of the vehicle heater with an evaporator burner, a porous evaporator medium is generally provided, into which the liquid fuel supplied via a supply line is introduced, which is distributed by capillary action and possibly also by gravity and then evaporated in the direction of the combustion chamber. The heat provided during the combustion is transferred in a heat exchanger arrangement to a medium to be heated. When integrating the vehicle heater in a coolant circuit of an internal combustion engine, this medium to be heated is a liquid, generally water. When building the Faharzeugheizgeräts as an air heater, the medium to be heated is the example to be introduced in a vehicle interior air.

If the medium heated by the vehicle heater, for example the liquid circulating in a coolant circuit or the air in a vehicle interior, has a comparatively high temperature which does not necessitate the additional heating in the heat exchanger arrangement, then if the vehicle heater is already equipped with the operated lowest heater power level, the vehicle heater are brought into a Ausregelzustand, so be stopped by stopping the fuel supply and the combustion air supply combustion operation at least temporarily. Since in this Ausregelzustand in the heat exchanger assembly then substantially no heat is transmitted, the temperature of the heated medium, so for example, the temperature of the coolant or, the temperature of the already introduced into a vehicle interior air, gradually decrease. By monitoring this temperature, it can be determined when it is again necessary to provide heat in the area of the vehicle heater, in order to avoid an excessive lowering of the temperature. Here, a criterion for the resumption of the combustion operation in the vehicle heater is generally specified by comparing this temperature with an associated temperature threshold.

In this resumption of combustion operation, the various system areas of the vehicle heater that were previously heated by the ongoing combustion are generally still relatively warm. This also applies, above all, to that region in which the liquid fuel is fed in, that is to say, for example, the porous evaporator medium or the end region of a fuel feed line. Too high a temperature in this range, however, can result in a comparatively spontaneous fuel evaporation, which in turn leads to the pulse-like release of fuel vapor in the direction of the combustion chamber and thus jeopardizes the start of the combustion or can lead to unfavorable combustion conditions. In order to avoid this, it is possible to proceed in such a way that, when the temperature of the heated medium drops below the associated threshold, air is first conveyed through a combustion air delivery device into the vehicle heater in a cold-blowing phase. This air cools the system areas flowing around it and thus contributes to the fact that favorable conditions for a restart of the combustion can be generated more quickly.

It is the object of the present invention to provide a vehicle for operating a fuel-operated vehicle heating device in a warm start phase, with which, when a resumption of the combustion operation is required, delays in the combustion start can be reduced.

According to the invention, this object is achieved by a method for operating a fuel-operated vehicle heater, preferably with an evaporator burner, in a warm start phase, in which method a temperature variable associated with the temperature of a medium heated by the heater is compared with a first temperature threshold associated therewith and then when the temperature magnitude is less than the first temperature threshold, a combustion air delivery assembly is operated and operated during a cold blowing phase to convey air, wherein during the cold blowing phase, a fuel delivery assembly is not operated to deliver fuel, wherein the temperature magnitude and / or the first temperature threshold is determined as a function of the rate of change of the temperature of the medium.

In the procedure according to the invention not only the temperature of the heated medium, so for example the Coolant temperature or the temperature in a vehicle interior, compared with an associated threshold and then, when the temperature is below the threshold, begun with the cold-blowing phase. Rather, by taking into account the rate of change of the temperature of this medium, a temperature development is anticipated. This makes it possible to start the cold-blowing phase earlier, for example, because a relatively large change in temperature, ie a sharp drop in temperature will quickly lead to thermal conditions that make the resumption of combustion operation required and therefore also the beginning of the cold-blowing already to one earlier date.

For example, it can be provided that the temperature variable is determined on the basis of the temperature of the medium and a correction term representing the rate of change of the temperature of the medium.

T_G

= Temperaturgröße,

T_M(x)

= Temperatur des Mediums bei einem letzten Ermittlungszeitpunkt x,

T_M(x – 1)

= Temperatur des Mediums bei einem vorletzten Ermittlungszeitpunkt x – 1,

B

= Temperaturänderungsbewertungsfaktor.

The temperature can be determined, for example, as T _G = T _M (x) + [T _M (x) - T _M (x - 1)] × B where:

T _G

= Temperature size,

T _M (x)

= Temperature of the medium at a last determination time x,

T _M (x - 1)

= Temperature of the medium at a penultimate determination time x - 1,

B

= Temperature change evaluation factor.

Since, for the purposes of the present invention, the rate of change of the temperature of the medium is to be taken into account so that the cold-blowing phase can be started earlier if the temperature trend is expected to be normal, that is to say when the temperature drops, the correction bath generally has a negative sign, which already results therefrom shows that the temperature measured at an earlier point in time was greater than the temperature measured at a later time and thus the difference calculated from these values will have a negative sign. In this case, the temperature change evaluation factor has a positive sign. Of course, a temperature change evaluation factor with a negative sign could be used even if this temperature difference is set up differently.

To ensure that the conditions favorable for a restart of the combustion can be achieved by conveying air in the region of a combustion chamber, it is proposed that the cold-blowing phase last at least until the temperature of the medium falls below the first temperature threshold.

Should, for example due to the fact that the air conveyed in the cold-blowing phase has a comparatively high temperature, a state occur, in which then, when the temperature of the medium falls below the first temperature threshold, the temperature of the air leaving the heater over a second associated therewith Temperature threshold is, the cold-blowing phase can be continued until the temperature of the air leaving the heater falls below the associated second temperature threshold. In this way it can be ensured that the cold-blowing phase is continued for a sufficient time to ensure favorable conditions for the combustion resistance.

It is further proposed that if the temperature of the medium does not fall below the first temperature threshold within a predetermined period of time after the start of the cold-blowing phase, the cold-blowing phase is ended. If the temperature of the medium does not drop sufficiently quickly, this is an indication that comparatively little heat energy requirement exists. In this case, it is possible to wait with the restart of the combustion and thus also the cold blow phase can be terminated, which contributes to the saving of electrical energy. For example, then the cold-blowing phase can be restarted when the temperature of the medium falls below the first temperature threshold.

In a procedure according to the invention which also allows the temperature development of the heated medium to be taken into account, it is proposed that the first temperature threshold be determined on the basis of a basic temperature threshold and a correction term representing the rate of change of the temperature of the medium.

T_S'

= erste Temperaturschwelle,

T_S

= Grund-Temperaturschwelle,

T_M(x)

= Temperatur des Mediums bei einem letzten Ermittlungszeitpunkt x,

T_M(x – 1)

= Temperatur des Mediums bei einem vorletzten Ermittlungszeitpunkt x – 1,

B

= Temperaturänderungsbewertungsfaktor.

For example, the first temperature threshold can be determined as: T _S '= T _S - [T _M (x) - T _M (x - 1)] × B where:

T _S '

= first temperature threshold,

T _S

= Basic temperature threshold,

T _M (x)

= Temperature of the medium at a last determination time x,

T _M (x - 1)

= Temperature of the medium at a penultimate determination time x - 1,

B

= Temperature change evaluation factor.

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

1 In a schematic representation of a vehicle heater, in which the procedure according to the invention can be implemented;

2 a time-temperature diagram illustrating the procedure of the invention.

In 1 is a vehicle heater generally with 10 designated. The vehicle heater 10 comprises a burner region designed as an evaporator burner 12 with a combustion chamber 14 , In the combustion chamber 14 is by means of a combustion air conveyor assembly 16 , For example, side channel blower, combustion air L promoted. By means of a fuel conveying arrangement 18 For example, metering pump, liquid fuel B is first in a porous evaporator medium 20 initiated. The fuel B is distributed by Kapillarförderwirkung in the inner volume region of the porous evaporator medium and is then in the direction of the combustion chamber 14 evaporated. The exhaust gas flow S produced during combustion leaves the vehicle heater 10 via a corresponding exhaust duct area.

In a heat exchanger arrangement 22 Heat generated during combustion is transferred to a medium M to be heated. This medium may be, for example, the circulating in a coolant circuit of an internal combustion engine coolant, so generally water. When building the vehicle heater 10 as an air heater, the medium may also be the air to be introduced into a vehicle interior.

To start the combustion operation is an ignition device 24 , For example, a Glühzündstift provided. By energizing the same locally high temperatures are generated that the mixture of combustion air and fuel is ignited and the combustion of the combustion chamber 14 spreads.

The combustion air conveyor assembly 16 , the fuel delivery system 18 and for example, the ignition device 24 are under the control of a drive arrangement 26 , This controls or regulates the operation of the various system areas on the basis of various specifications. For example, temperature information can also be used for this purpose. A temperature sensor 28 For example, the temperature of the medium M in the heat exchanger assembly 22 capture, in which case a positioning at the inlet region and / or at the outlet region of the heat exchanger assembly 22 is possible. A temperature sensor 30 For example, the temperature of the heater 10 leaving stream S The through the temperature sensor 28 detected temperature is generally used as a controlled variable for by the heater 10 used to be provided heat energy amount. At comparatively low temperature of the medium becomes the heater 10 operated at a higher heating power level, at a comparatively high temperature of the medium M is the heater 10 operated in a lower heating power level. The through the temperature sensor 30 detected temperature can be used as an indicator of whether in the combustion chamber 14 a combustion takes place or was started. The temperature sensor 30 So it can be used as a flame sensor, since at starting or expiring combustion of the heater 10 leaving stream S, in this state then the exhaust stream, will have a relatively high temperature.

As stated above, the heating power of the vehicle heater 10 adjusted so that it is adapted to the actual heat energy requirement. If the temperature of the medium M is comparatively high, the vehicle heater can 10 be brought into a Ausregelzustand, ie in a state in which neither fuel B nor combustion air L are supplied and thus by adjusting the combustion, no further heat energy is provided. The vehicle heater 10 can still remain in a standby state, then, when the temperature of the medium M, so for example, the temperature of the coolant circulating in the coolant circulation or the temperature in a vehicle interior, too much decreases to prevent by the resumption of combustion operation too high a temperature drop to allow a renewed warming.

When resuming combustion, various system areas of the vehicle heater will generally still have a comparatively high temperature. For example, the porous evaporator medium 20 or a combustion chamber 14 be enclosing housing at a relatively high temperature level, as well as the area of the fuel supply line, which adjoins this housing or runs therein. Especially when using low-boiling fuels there is a risk that when resuming the supply of fuel B spontaneous, pulse-like Brennstoffabdampfung takes place, which can lead to delays in the ignition and unfavorable combustion conditions. In order then when the vehicle heater 10 can be put back into operation after a rest period, to avoid pulsatile fuel evaporations without excessive time delays occur in one below with reference to the 2 explained procedure initially for a cooling of the vehicle heater 10 be taken care of.

The 2 shows, plotted over the time t, the evolution of the temperature T or different temperature variables. It is first assumed that at a time t ₀ a previously operated vehicle heater was brought into the Ausregelzustand, so the combustion was stopped by stopping the fuel supply and the combustion air supply. The curve T _M illustrates the time evolution of the temperature of the vehicle heater 10 heated medium M. This, that in the region of the heat exchanger assembly 22 heat is no longer transferred to this medium M, its temperature T _M gradually decreases. In the case of an air heater takes the detected, for example, in a vehicle interior air temperature due to the fact that no heated air is fed, from.

With T _S is a temperature threshold referred to, the falling below a relatively strong cooling of the medium M indexed and therefore makes the resumption of combustion and provision of combustion heat required. It is assumed for this purpose that at a time t _S, the temperature T _{M of} the medium falls below the temperature threshold T _S. In order to avoid the preceding effect of a spontaneous fuel evaporation, the combustion air delivery arrangement can take place in a cold-flash phase I _KB following the time point t _S 16 be operated to air L in the vehicle heater 10 to dine. In this cold blow I _KB , the fuel delivery system 18 not operated, leaving alone the vehicle heater 10 flowing air absorbs heat and from the area of the vehicle heater 10 erodes. The duration of the cold blowing phase I _KB may be fixed, but may also be dependent on, for example, the temperature sensor 30 detected temperature of the air flow S are set.

The temperature of the air flow S in the cold-blowing phase I _KB depends to a great extent on the temperature at which the various system areas of the vehicle heating device flow around this air 10 to have. If its temperature has dropped sufficiently, this is reflected in a corresponding lower temperature of the current S at the output of the vehicle heater 10 again, so that's when passing through the temperature sensor 30 detected temperature falls below an associated temperature threshold, the cold-blow phase I _{KB is} terminated. In a subsequent Vorglühphase I _VG can then first by energizing the ignition 24 ensure that sufficient high temperatures are generated in its environment to start combustion. After this Vorglühphase can then at a time t _DP, the fuel delivery system 18 be put into operation to actually restart the combustion.

Although it can be ensured with the procedure described above that the fuel feed starts again only when the occurrence of spontaneous fuel evaporation is no longer to be expected. However, there is a comparatively long delay until after completion of the combustion operation at time t ₀ , ie the transition to the Ausregelzustand, at time t _S, the cold blow phase is started and then at time t _{DP of} the fuel supply is started again and therefore the Combustion is started.

T_G

= Temperaturgröße,

T_M(x)

= Temperatur des Mediums bei einem letzten Ermittlungszeitpunkt x,

T_M(x – 1)

= Temperatur des Mediums bei einem vorletzten Ermittlungszeitpunkt x – 1,

B

= Temperaturänderungsbewertungsfaktor.

In order to avoid this comparatively long delay until initiation of the cold-blowing phase, according to the invention a temperature variable represented by the curve T _{G is} determined. When determining this temperature variable, a trend value of the actually occurring temperature of the medium T _M is taken into account in that, in addition to the actually detected temperature T _M , its rate of change is also used. In particular, the temperature variable T _G can be determined from the following relationship: T _G = T _M (x) + [T _M (x) - T _M (x - 1)] × B where:

T _G

= Temperature size,

T _M (x)

= Temperature of the medium at a last determination time x,

T _M (x - 1)

= Temperature of the medium at a penultimate determination time x - 1,

B

= Temperature change evaluation factor.

Thus, at a respective calculation or determination cycle, the temperature T _M (x) present or detected at this cycle or a change compared to the temperature T _M (present at the last or a preceding detection or calculation cycle) x - 1), the temperature change evaluation factor ultimately defining to what extent this temperature change is actually taken into account.

If the temperature of the medium changes comparatively slowly, the curve T _{G will be} very close to the actual temperature profile T _M. However, if the temperature changes faster, which speaks for a relatively high removal of heat energy from the medium, the curve T _G will fall much steeper and thus the temperature threshold T _S below earlier, namely at time t _{S '} . This in turn means that the cold blow phase I _KB 'can begin earlier and therefore ends earlier. After the subsequent preglow phase I _VG ', the metering pump can then be put into operation at time t _DP ' and the combustion started.

It should be noted here that in the pre-glow phase I _VG 'of course, the combustion air conveyor assembly 16 can be throttled in their capacity or can be disabled because on the one hand, a sufficient cooling has already been achieved, on the other hand by the reduced or terminated air flow excessive heat removal from the then to be brought to operating temperature ignition device 24 is avoided. With the onset of fuel delivery is then of course again adapted to the volume of fuel delivered amount of combustion air into the combustion chamber 14 initiated.

The cold blow phase I _KB 'can extend over a basically predetermined time interval. In order to ensure sufficient cooling, it should be continued, for example, at least until not only the temperature variable T _G , but also the actual temperature T _{M of} the medium falls below the temperature threshold T _S. Should at this time, so in the presentation of the 2 at the time T _s , it can be determined that by the second temperature sensor 30 detected temperature of the current S is still above an associated temperature threshold, which is an indication that the promoted in the cold-blowing phase still absorbs comparatively much heat, so the cold-blowing phase can be continued until the temperature of the current S falls below the associated temperature threshold.

Should also be determined that after the beginning of the cold-blowing phase at the time the temperature T _{M of} the medium is not within a predetermined. maximum period of time under the temperature threshold T _S is also fallen, so the Kaltblasphase may be terminated or interrupted and then, when the temperature T _M is actually dropped below the threshold T _S, continued or re-started.

T_S'

= Temperaturschwelle,

T_S

= Grund-Temperaturschwelle,

T_M(x)

= Temperatur des Mediums bei einem letzten Ermittlungszeitpunkt x,

T_M(x – 1)

= Temperatur des Mediums bei einem vorletzten Ermittlungszeitpunkt x – 1,

B

= Temperaturänderungsbewertungsfaktor.

In an alternative approach, with which the temperature development in the determination of the beginning of the cold-blowing phase can be considered, the temperature threshold, the falling below the start of the cold-blowing phase, depending on the temporal evolution of the temperature T _{M is} set. For example, the relationship can be chosen: T _S '= T _S - [T _M (x) - T _M (x - 1)] × B where:

T _S '

= Temperature threshold,

T _S

= Basic temperature threshold,

T _M (x)

= Temperature of the medium at a last determination time x,

T _M (x - 1)

= Temperature of the medium at a penultimate determination time x - 1,

B

= Temperature change evaluation factor.

By taking into account the correction term for the determination of the temperature threshold T _S ', it can be shifted further upwards at a comparatively fast rate, so that in fact the same state can be achieved as stated above, namely the temperature variable to be taken into account, in this case, for example the temperature T _{M of} the medium, the then associated threshold T _S 'at an earlier time, in the example shown at time t _S ', below and thus the start of the cold-blowing phase is triggered.

With the procedure according to the invention, it is possible, in particular also by the specification of the weighting of the correction term or the specification of the temperature change evaluation factor, ie the extent to which the temporal change of the temperature of the observed medium is to be taken into account, the delay until the restart of the vehicle heater or to make sure earlier that conditions are suitable for the restart. An excessive drop in the temperature of the medium below a predetermined temperature level, which may be, for example, in the case of a liquid heater at 70 to 90 ° C, is thus avoided. However, unevenness in fuel evaporation can be precluded at the start of the fuel feed for the restart.

Claims (9)

Method for operating a fuel-operated heater ( 10 ), preferably vehicle heater, preferably with an evaporator burner, in a warm start phase, in which method one with the temperature of one through the heater ( 10 ) Heated medium (M)-related temperature variable (T _G T _M) having one of the associated first temperature threshold (T _S T _S ') is compared, and then when the temperature variable (T _G T _M), the first threshold temperature ( T _S ; T _S '), a combustion air conveying arrangement ( 16 ) is operated and operated during a cold blowing phase (I _KB ') for conveying air (L) wherein during the cold blowing phase (I _KB ') a fuel delivery assembly ( 18 ) is not operated to convey fuel (B), wherein the temperature variable or / and the first temperature threshold (T _G ') in dependence on the rate of change of the temperature (T _M ) of the medium (M) is determined. Method according to claim 1, characterized in that the temperature variable (T _G ) is determined on the basis of the temperature (T _M ) of the medium and a correction term representing the rate of change of the temperature (T _M ) of the medium (M). A method according to claim 1 or 2, characterized in that the temperature variable is determined as: T _G = T _M (x) + [T _M (x) - T _M (x - 1)] × B where: T _G = temperature size, T _M (x) = temperature of the medium (M) at a last determination time x, T _M (x - 1) = temperature of the medium (M) at a penultimate determination time x - 1, B = temperature change factor A method according to claim 2 or 3, characterized in that the cold blow phase (I _KB ') at least until the temperature (T _M ) of the medium (M) falls below the first temperature threshold (T _S ). A method according to claim 4, characterized in that when the temperature (T _M ) of the medium (M) falls below the first temperature threshold (T _S ) and thereby the temperature of the heater ( 10 ) leaving the air above one of these associated second temperature threshold, the cold-blowing phase (I _KB ') is continued until the temperature (T _M ) of the heater ( 10 ) leaving the air below the assigned second temperature threshold. Method according to one of claims 1 to 5, characterized in that when the temperature (T _M ) of the medium (M) after the beginning of the cold blow phase (I _KB ') does not fall below the first temperature threshold (T _S ) within a predetermined period of time, the cold blow phase (I _KB ') is terminated. A method according to claim 6, characterized in that the cold blow phase (I _KB ') is then restarted when the temperature (T _M ) of the medium (M), the first temperature threshold (T _S ) falls below. Method according to one of Claims 1 to 7, characterized in that the first temperature threshold (T _S ') is determined on the basis of a basic temperature threshold (T _S ) and a correction term representing the rate of change of the temperature (T _M ) of the medium (M). Method according to one of claims 1 to 8, characterized in that the first temperature threshold (T _S ') is determined as: T _S '= T _S - [T _M (x) - T _M (x - 1)] × B where: T _S '= first temperature threshold, T _S = basic temperature threshold, T _M (x) = temperature of the medium (M) at a last determination time x, T _M (x - 1) = temperature of the medium (M) at a penultimate determination time x - 1, B = temperature change evaluation factor.

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