Method for operating an exhaust gas heater and exhaust gas heater

Abstract

A method is proposed for operating an exhaust gas heater (1) having a combustion chamber (2) into which an air stream is introduced by an air pump (6) and fuel by a fuel injector (16), and the air-fuel mixture is ignited by a glow plug (4). The hot exhaust gases thus formed are passed through the exhaust system (8) of an internal combustion engine (2). A quantity of condensate in the exhaust gas heater (1) is determined, and the output of the glow plug (4) is adjusted to the determined quantity of condensate. Furthermore, an exhaust gas heater is proposed with means for determining the quantity of condensate in the region of the glow plug (4).

Description

Prior ArtThe invention is based on a method for operating an exhaust gas heater and an exhaust gas heater according to the preamble of the independent claims. DE 195 08 013 C1 already discloses a method for operating an exhaust gas heater or an exhaust gas heater, by means of which a heating of an exhaust system of an internal combustion engine takes place. This ensures rapid heating of the exhaust system.Advantages of the InventionThe method according to the invention for operating an exhaust gas heater according to the species of the independent method claim has the advantage over the related art that an improved operation of the exhaust gas heater is ensured by adapting the operation of the exhaust gas heater to the determined quantity of condensate. Damage to the exhaust gas heater is thus prevented, more rapid heating of the internal combustion engine is ensured and the generated emissions of the internal combustion engine are reduced. The operation of the internal combustion engine is thus improved. The exhaust gas heater according to the invention according to the species of the independent device claim has the advantage over the related art that a diagnosis of the quantity of condensate in the exhaust gas heater is made possible. The method according to the invention is thus made possible.Further advantages and improvements are obtained by the features of the dependent claims. An amount of condensate is determined particularly easily by evaluating the heating power of the glow plug. It is thus possible to determine the presence of condensate and also the quantity of condensate in the exhaust gas heater by means of a direct measurement. Alternatively or additionally, a model can be used for determining the amount of condensate. An additional plausibility check or checking of the measured quantity of condensate can thus take place. Matching a start of the internal combustion engine to an amount of condensate in the exhaust heater enables an improved start of the internal combustion engine in which the amount of exhaust gases discharged is reduced. By adapting to the quantity of condensate, an unnecessary delay of the city is avoided. Furthermore, the quantity of condensate in the exhaust gas heater can be determined already during ongoing operation of the internal combustion engine and can be reduced by correspondingly adapted methods. During ongoing operation, it is thus ensured that a safe start with a small amount of emitted emissions can take place at any time. Likewise, suitable method steps can be used when the internal combustion engine is shut down to take measures which make possible a safe start with a small amount of emitted emissions.DRAWINGSExemplary embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. The following are shown: FIG. 1 shows an exhaust gas heater 1 and an internal combustion engine 2, FIG. 2 shows details of the configuration of the combustion chamber 3, FIGS. 3 and 4 show details of the actuation of the glow plug 4, FIG. 5 shows the air flow of the air pump 6, FIG. 6 shows method steps at a start of the internal combustion engine 2, FIG. 7 shows method steps during operation of internal combustion engine 2, and FIG. 8 shows method steps when internal combustion engine 2 is shut down.DESCRIPTION OF THE INVENTIONFIG. 1 schematically illustrates the exhaust gas heater 1 and an internal combustion engine 2. The exhaust gases of the internal combustion engine 2 are conducted through an exhaust pipe 7 to an exhaust system 8. A lambda probe 11 is arranged in the exhaust pipe 7, by means of which the oxygen content of the exhaust gas of the internal combustion engine 2 is measured. The exhaust system 8 serves for cleaning the exhaust gases and usually has one or two 3-way catalytic converters and / or a system for NOx reduction and optionally also a particle filter. The exact details of the construction of the exhaust system 8 are not important for understanding the invention. Such an exhaust system 8 only purifies the exhaust gases from a certain operating temperature, which is ensured during operation by the heating by the hot exhaust gases. When the internal combustion engine 2 is started, in particular when the ambient temperature is cold, the exhaust system 8 is not yet ready for operation and high emissions of exhaust gases thus arise.In order to achieve rapid heating of the exhaust system 8, an exhaust gas heater 1 is shown in FIG. 1. The exhaust heater 1 includes an air pump 6, a shut-off valve 5 arranged downstream, a combustion chamber 3 and then a connection pipe 9. The combustion chamber 3 is provided with a fuel injector 16 and a glow plug 4. Ambient air is drawn in by the air pump 6 through an air filter 13 and an air flow is thus generated, which flows through the opened exhaust gas valve 5 into the combustion chamber 3. Between the air filter 13 of the air pump 6 there is also arranged an air mass sensor 12 by means of which the amount of air pumped by the air pump 6 into the combustion chamber 3 is measured. Fuel is injected into the combustion chamber 3 by the fuel injector 16, and the air-fuel mixture in the combustion chamber 3 is ignited by the glow plug 4. For this purpose, the glow plug 4 is typically heated to a temperature of approximately 1300° C. The exhaust gases of the combustion chamber 3 are conducted through the connecting pipe 9 to the exhaust system 8 and ensure a rapid temperature increase of the exhaust system 8. In the connecting pipe 9, a lambda probe 10 is arranged, which measures the oxygen content of the exhaust gas of the combustion chamber 3. This ensures rapid attainment of the operating temperature of the exhaust system 8, in particular in a cold starting situation of the internal combustion engine 2. Furthermore, a control device 100 is shown, which is used for regulating the temperature of the glow plug 4, for controlling the shut-off valve 5, the air pump 6 and the fuel injection 16. For this purpose, the control device 100 reads in the values of all the sensors shown and exchanges data with an engine control device, not shown here.In Figure 1, the shut-off valve 5 is shown in an open state to ensure unobstructed flow of air from the air pump 6 through the combustion chamber 3 into the exhaust system 8. This is illustrated in FIG. 1 by the closure element 17 arranged parallel to the flow direction. If the heating device is not operated, this closure element 17 is arranged transversely to the flow, whereby a flow of exhaust gases from the exhaust system 8 or the exhaust pipe 7 back into the air pump 6 is prevented. Contamination of the air pump 6 by the exhaust gases of the internal combustion engine 2 is thus prevented. In addition, exhaust gas is prevented from reaching the environment via the intake air system in an uncleaned / unfiltered manner. Exhaust gases of the internal combustion engine 2 can, however, pass into the combustion chamber 3 and constituents of the exhaust gases of the internal combustion engine 2 can be deposited there. In particular, under corresponding operating conditions, liquid constituents of the exhaust gas, in particular water, can condense in the combustion chamber 3 or in the connecting pipe 9. This occurs in particular when the heater is not operated for a longer time and has a low temperature, in particular of the combustion chamber walls, which are cooled from the outside. The condensation is explained in more detail below with reference to FIG. 2.In FIG. 2, combustion chamber 3 with glow plug 4 and fuel injection nozzle 16 is shown in greater detail in an exemplary manner than in FIG. 1. It should be taken into account here that the specific configuration of the combustion chamber 3 must meet a multiplicity of design requirements and therefore cannot always be configured in an optimized manner for avoiding condensate.In FIG. 2, an exhaust pipe 7 and an exhaust system 8 are shown, which are oriented vertically. The combustion chamber 3 is arranged obliquely with respect to this vertical axis and is connected to the exhaust pipe 7 by a bent connecting pipe 9.The fuel injection 16 is arranged centrally at one end of the combustion chamber 3 and is surrounded by an air gap 25. The air of the air pump 6 is blown into the combustion chamber 3 through the annular air gap 25. This arrangement ensures optimum mixing of fuel and air. The glow plug 4 is arranged in the lower region of the combustion chamber 3 in a trough-shaped wall region of the combustion chamber 3. In this way, several areas are formed in which condensate can collect in the combustion chamber 3 or in the connecting pipe 9. In a first collecting region 21, condensate can collect in the region in front of the diaphragm which forms the air gap 25. In a second collecting region 22, in the region of the trough-shaped wall region, condensate can collect in the region of the glow plug 4. In a lower region of the combustion chamber 3, a third collecting region 23 is shown. A further fourth collecting region 24 is formed at the lowest point of the connecting pipe 9. the collecting regions 21, 22, 23, 24 shown here are only exemplary and other collecting regions can also form or individual collecting regions shown can also be omitted. Whenever a point at which the condensate cannot flow off forms as a result of a specific structural configuration of the exhaust gas heater 1, a collecting region for condensate forms.The retention of condensate or at very low temperatures of ice in the combustion chamber 3 and in the connecting pipe 9 influences the operation of the heating device in a variety of ways. During operation of the heater, the enthalpy of vaporization of the condensate extracts energy from the combustion and the combustion thus takes place less hot and, as a result, the exhaust system is also heated less strongly. Furthermore, individual droplets of condensate can be agitated by the air flow or the combustion, which then lead to a thermal load of the glow plug or of a lambda probe 10. There is thus the risk of mechanical damage to a ceramic sheathed-element glow plug or to a lambda probe. Furthermore, the startability of the heater or the smoothness or uniformity of combustion in the heater is also impaired by agitated water. This may result in higher emission levels of both the exhaust heater 1 and the downstream exhaust system 8. Furthermore, the condensate is predominantly water, which can freeze at very low temperatures. This results in a change in the volume of the condensate, which generates high forces under unfavourable conditions, which is transmitted to the mechanical structure of the heater 1. This can lead to deformation of the combustion chamber 3, as a result of which the properties of the exhaust gas heater 1 are influenced. The quality of the combustion is thus impaired. The collecting region 22, in which condensate accumulates in the region of the glow plug 4, has a particular importance. The condensate in the collecting region 22 directly influences the thermal properties of the glow plug 4. This influence on the thermal properties of the glow plug 4 can be used for a diagnosis by which the presence and quantity of condensate in the collecting region 22 is directly determined by measuring the current and voltage of the glow plug 4. The characteristic curve for heating the glow plug 4 is shifted by the necessary energy for evaporating the condensate in the collecting region 22, and it can thus be directly established that condensate is present in the collecting region 22 in the region of the glow plug 4. By the variation over time of the heating properties of the glow plug 4, a time can be determined from which the condensate in the collecting region 22 has evaporated, and thus a determination of the quantity of condensate can also be made. Alternatively, the amount of shift of the characteristic curve of the glow plug 4 can also provide an indication of the amount of condensate. The presence of condensate in the collecting region 22 or the determined quantity of condensate in the collecting region 22 then allows a conclusion to be drawn about the total quantity of condensate in the combustion chamber 3 or the connecting pipe 9.Alternatively, the amount of condensate in the combustion chamber 3 can also be determined by a model. For such a model, the condensation of condensate or water in the exhaust gas heater 3 and the aging of water from the exhaust gas heater 3 must be taken into account. An essential parameter in this case is the temperature of the combustion chamber 3 and of the connecting pipe 9, which are determined, for example, from an ambient temperature, or a calculated temperature or a measured temperature in the combustion chamber 3. Further, the temperature and water content of the exhaust gases of the internal combustion engine 2, the amount of the exhaust gases of the internal combustion engine 2 and the proportion of the exhaust gases entering the combustion chamber 3 and the connection pipe 9 must be taken into account. The composition of the exhaust gases of the internal combustion engine 2 depends on, for example, environmental conditions such as the moisture content of the supplied air and internal operating conditions of the internal combustion engine such as the fuel composition and the operating conditions of the internal combustion engine 2. Furthermore, the development over time of the relevant parameters must be taken into account. Typically, at least 2 parameters should be taken into account for the model, for example external temperature of the exhaust gas heater 3, temperature of the exhaust gases of the exhaust gas heater 1, temperature of components of the exhaust gas heater, composition of the exhaust gas of the internal combustion engine 2, moisture content of the exhaust gas of the internal combustion engine 2, an exhaust gas back pressure of the exhaust system 8 of the internal combustion engine 2, composition of the fuel of the internal combustion engine 2 and the exhaust gas mass flow of the internal combustion engine 2.A determination of the quantity of condensate by evaluating the glow behavior of glow plug 4 and the calculation of a quantity of condensate on the basis of a model can also be correlated with one another in suitable operating phases. For example, after a very long period of operation of the exhaust heater 1, it may be assumed that no condensate is present in the exhaust heater 1, and thus a model for the amount of condensate may be set to an initial value of 0. Furthermore, on the basis of the measurement at the glow plug 4, an amount of condensate in the combustion chamber 3 can be determined. If a large deviation from the modeled quantity of condensate results, the corresponding parameters of the model can be adapted or a malfunction of the glow plug 4 can be diagnosed.FIGS. 3 and 4 show the behavior of the glow plug 4 during heating over time. FIG. 3 shows a glow plug with a push phase. In order to ensure particularly rapid heating of the glow plug 4 starting from a starting state, a push phase is provided in which the glow plug is actuated with a maximum permissible power P 1. This increased power P 1 is applied only for a very short period of time from 0 to T 1 and leads to a very rapid heating of the glow plug 4. The temperature is controlled to 1300° C. for example. Owing to the steep rise in the temperature, an influence of the condensate on the operation of the glow plug 4 is difficult to detect in the push phase between the points in time zero and T 1. At the time T1, the system switches over to the lower power P2 and it takes a short period of time between T1 and T2 until the power requirement of the glow plug has adjusted to a constant temperature. In the phase after the time T 2, the condensate in the region of the glow plug 4 is clearly noticeable by an increased power requirement of a glow plug with condensate (curve 31) and a glow plug 4 without condensate (curve 32). The increased power requirement of the curve 31 is a clear feature for the existence of condensate in the region of the glow plug 4. The length of time until the time T3 is reached is a measure of the amount of condensate that has accumulated in the collecting region 22 of the glow plug 4. After the time T3, the glow plug 4 is still operated with the heating power P2 until the time T4, the exhaust system 8 has reached its operating temperature and no further operation of the glow plug 4 is necessary and the glow plug 4 is switched off.To determine the quantity of condensate in the combustion chamber 3, the magnitude of the deviation between the curves 31 and 32 after the time T 2 can also be used. Furthermore, it can be judged on the basis of this deviation whether the condensate is present in liquid form or as ice. If the condensate is initially present as ice, the heating behavior can also change in that the condensate in the aggregate state changes from frozen to liquid.FIG. 4 shows the same subject matter as in FIG. 3, wherein here the glow plug 4 is operated without a push phase. At time 0, a power P2 for continuous operation is applied to the glow plug 4. The glow plug is then heated and, starting from the time T2, an approximately static operating state is reached. Curve 41 shows an increased power requirement during the regulation of sheathed-element glow plug 4 on the basis of condensate in collection region 22 of glow plug 4. As can be seen, a higher power must also be used for the regulation in order to achieve a sufficient temperature of the glow plug 4. Curve 42 shows the profile for a glow plug 4 without condensate in the region of glow plug 4. Here, too, it can be seen that in the phase between the times T 2 and T 3 a distinct difference in the regulation of the glow plug 4 can be seen. This difference in power is a measure of condensate in the region of the glow plug 4 and the time interval of the time T 3 can be used again for determining the quantity of condensate. Likewise, the difference between curves 41 and 42 can be used to determine the amount of condensate.FIGS. 3 and 4 each proceed from otherwise constant conditions in the heater 1 and in the internal combustion engine 2, respectively. In the case of real operation of the internal combustion engine 2 and of the exhaust gas heater 1, it is of course possible for deviations from this idealised profile to take place, which makes measurement more difficult.Regular operation of the exhaust heater 1, i.e., injection of fuel by the fuel injector 16, should be performed only after the time T3 when ignition of the injected fuel is ensured by normal operation of the glow plug 4. Even if the amount of condensate in the collecting region 22 has been evaporated at the time T 3, condensate may still be present in the other collecting regions 21, 23 and 24, since these are only evaporated by operation of the exhaust gas heater 1. Depending on the modeled amount of condensate or the amount of condensate determined by glow plug 4 as a sensor for the amount of condensate, different methods for operating exhaust gas heater 1 should be used. In particular, provisions should be made in this case for the glow plug 4 not to be wetted again by fluidized condensate, since this causes sudden and very local cooling, which can lead to stress cracks in the material of the glow plug 4.In FIG. 5, the delivery amount of the air pump 6 is shown with respect to time. Curve 51 corresponds to that during operation of the exhaust gas heater 1 when no condensate has been detected. Curve 52 corresponds to operation of the exhaust heater 1 when a critical amount of condensate has been detected. As can be seen, for curve 51, there is a sharp increase in the delivery rate of the air pump 6, which saturates at a time T 5. Curve 52 also shows an increase in the delivery rate of the air pump 6, which saturates at a time T6. The time T6 is significantly later than the time T5; furthermore, the delivery rate of the curve 51 after the time 5 is significantly higher than the delivery rate of the curve 52 after the time 6. It is thus ensured that the vaporization of the condensate in the exhaust gas heater 1 does not take place abruptly. The condensate is thus prevented from being stirred up or sprayed and leads to sudden cooling of individual mechanical components with possible stress loads. In particular, the glow plug 4 or the lambda probes 10, 11 or components of the catalytic converter in the exhaust system 8 should not be wetted with liquid condensate. These components have a temperature of a few 100° C. during normal operation and sudden and very local cooling due to direct contact with condensate could lead to thermal stress cracks.This results in various strategies for operating the exhaust gas heaters 1 in cooperation with the internal combustion engine 2, and in FIG. 6, the operation of the exhaust gas heater 1 for starting the internal combustion engine will be described. In FIG. 7, the operation of the exhaust heater 1 in a running operation of the internal combustion engine will be described. In FIG. 8, the operation of the exhaust heater 1 when the internal combustion engine 2 is stopped will be described.In FIG. 6, in a first step 61, the start of an internal combustion engine 2 as shown in FIG. 1 is decided. In the following step 62, a diagnosis is made as to whether condensate is present in the exhaust gas heater 1, that is to say in the combustion chamber 3 or in the connecting pipe 9. This can be done either by evaluating the behavior of the glow plug 4, as was described with reference to FIGS. 3 and 4, or else by evaluating a model of the formation of condensate. Step 62 is followed by step 63 in which it is determined whether condensate is present in the exhaust gas heater 1. Step 63 was followed by step 64 when it was determined that no condensate is present. In step 64, the exhaust gas heater 1 is then started and the internal combustion engine 2 is started, as was provided for a normal start. Step 64 is then followed by step 69, in which the internal combustion engine is operated regularly.Step 63 was followed by step 65 when condensate was detected. After step 65, step 67 occurs if the amount of condensate has been judged to be non-critical. In step 67, the glow plug is operated until the time T3 of FIG. 3 or 4 has been detected. From this point in time, the desired temperature is present at the glow plug 4 and a start of the exhaust gas heater 1 can take place safely. In the following step 68, the internal combustion engine 2 is then started with the exhaust gas heater 1 switched on.After step 65, step 66 occurs if the amount of condensate is judged to be critical. In step 66, the exhaust gas heater 1 is started with reduced power in order to remove the amount of condensate evaluated as critical from the exhaust gas heater 1. Here, a start of the internal combustion engine is also additionally delayed until the exhaust gas heater 1 has reached a predefined power or temperature. Then, when the start of the engine 2 has been made, the step 66 is followed by the step 69, i.e., the regular operation of the engine 2.In FIG. 7, the first step 70 corresponds to a regular operation of the internal combustion engine. During this regular operation of the internal combustion engine, a diagnosis for condensate formation is regularly carried out, which is illustrated in process step 71. The frequency of the diagnosis depends on operating parameters of the internal combustion engine, such as the external temperature of the internal combustion engine 2, the exhaust gas temperature, the moisture content of the exhaust gas or the driving profile (long-range operation, short-range operation, stop-and-go). The diagnosis can be carried out by operating the sheathed-element glow plug on a test basis in order to ascertain condensate in the collecting region 22, or by modelling. In the following step 73, it is checked whether condensate is present. If no condensate is present, step 70 follows, i.e. the internal combustion engine continues to be operated regularly. If condensate is detected, step 72 follows in which a check is made as to whether or not the amount of condensate is critical. If it is determined in step 72 that the amount of condensate is not critical, step 70 follows again, i.e. the regular operation of the internal combustion engine is continued. If it is determined in step 72 that the amount of condensate is critical, step 74 follows in which the exhaust heater 1 is operated with reduced power and dynamics until the condensate is removed (i.e., vaporized) from the exhaust heater 1. If the condensate is removed, step 74 is followed again 70, i.e. the regular operation of the internal combustion engine. Step 74 is carried out only under suitable operating conditions of the internal combustion engine 2. In particular, it must be ensured that the operation of the exhaust gas heater 1 does not result in too great a thermal load on the exhaust system 8. Alternatively, it can also be provided that the condensate is removed in step 74 only by an air flow, i.e. switching on the air pump 6 and opening the shut-off valve 5. However, this may only take place in suitable operating phases in order not to have a negative influence on the composition of the mixture of air and exhaust gas in the catalytic converter. Typically, overrun phases of the internal combustion engine 2 are suitable for such operation.In FIG. 8, a stop of the internal combustion engine 2 is determined in the first step 81. If this has been done, a diagnosis is then made in step 82, in which it is determined whether condensate has accumulated in the exhaust gas heater 1. If it is determined in the subsequent step 84 that no condensate has accumulated in the exhaust gas heater 1, step 84 is followed by step 85, in which it is established that no further measures have to be taken until the next starting process. Step 85 is followed by step 88, in which it is determined that the internal combustion engine is ready for starting.If condensate is detected in step 84, step 83 follows, in which the amount of condensate is judged to be critical or non-critical. If the amount of condensate is not critical, step 86 follows, in which the glow plug 4 is operated until the operating temperature is achieved with the normal power. By this procedure, the condensate in the collecting region 22 is removed and a safe start of the exhaust gas heater 1 is ensured. Condensate still remaining in the combustion chamber is still present to an non-critical small extent and is vaporized by the operation of the exhaust gas heater 1 when the internal combustion engine is started. The transition then takes place to step 88, in which it is established that the internal combustion engine is ready for starting. If a critical amount of condensate is detected in step 83, step 87 follows in which the exhaust heater is operated with reduced power and dynamics until the condensate is removed (i.e., vaporized) from the exhaust heater 1. Step 87 was followed by step 88 in which it is established that the internal combustion engine 2 is ready to start.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 195 08 013 C1

[0001]

Claims

Method for operating an exhaust gas heater (1) having a combustion chamber (2) into which an air stream is introduced by an air pump (6) and fuel is introduced by a fuel injection (16), and the air-fuel mixture is ignited by a glow plug (4), and the hot exhaust gases thus formed are conducted through the exhaust system (8) of an internal combustion engine (2), characterized in that an amount of condensate is determined in the exhaust gas heater (1) and the power of the glow plug (4) is adapted to the determined amount of condensate.Method according to Claim 1, characterized in that the quantity of condensate is determined by evaluating the heating power of the glow plug (4).Method according to Claim 1, characterized in that the quantity of condensate is determined by a model, wherein at least two of the following parameters are taken into account for the model: external temperature of the exhaust gas heater (1), temperature of the exhaust gas of the exhaust gas heater (1), temperature of components of the exhaust gas heater (1), composition of the exhaust gas of the internal combustion engine (2), moisture content of the exhaust gas of the internal combustion engine, exhaust gas back pressure of the exhaust system of the internal combustion engine (1), composition of the fuel of the internal combustion engine and exhaust gas mass flow of the internal combustion engine (1).Method according to one of the preceding claims, characterized in that before a start of the internal combustion engine (2) the amount of condensate in the exhaust gas heater (1) is determined, in that if the amount of condensate is below a first threshold value the internal combustion engine (2) is started with a first method for operating the exhaust gas heater (1), and in that if the amount of condensate is above a second threshold value the exhaust gas heater (1) is operated with a second method in which at least temporarily the exhaust gas heater is operated with a lower power than in the first method, and in that the start of the internal combustion engine (1) is delayed until the exhaust gas heater (1) has reached a predetermined temperature with a predetermined power.Method according to Claim 4, characterized in that, if the amount of condensate is above the first threshold value and below a second threshold value, the exhaust gas heater (1) is operated using the first method and the start of the internal combustion engine (2) is delayed until the exhaust gas heater (1) has reached a predefined temperature with a predefined power.Method according to one of the preceding claims, characterized in that during a running operation of the internal combustion engine the quantity of condensate in the exhaust gas heater (1) is determined, that if the quantity of condensate is above a third threshold value, the exhaust gas heater (1) is operated using a third method.Method according to Claim 6, characterized in that, in the third method, the exhaust gas heater (1) is operated at least temporarily with a lower power than in the first method, or in that, in the third method, only the air pump (6) is switched on and generates an air stream through the exhaust gas heater (1) without fuel being injected.Method according to one of the preceding claims, characterized in that, when the internal combustion engine (1) is shut down, the amount of condensate in the exhaust gas heater is determined, in that, if the amount of condensate is below a fourth threshold value, the restart of the internal combustion engine (2) is stored as possible, in that, if the amount of condensate is above the fourth threshold value and below a fifth threshold value, the exhaust gas heater (1) is operated with the first method and the restart of the internal combustion engine (2) is stored as possible, if the exhaust gas heater has reached a predefined temperature with a predefined power, and in that, if the amount of condensate is above the fifth threshold value, the exhaust gas heater (1) is operated with a fourth method in which, at least temporarily, the exhaust gas heater is operated with a lower power than in the first method, and the restart of the internal combustion engine (2) is stored as possible, when the exhaust heater (1) has reached a predetermined temperature with a predetermined performance.Method according to one of the preceding claims, characterized in that a heating power of the glow plug (4) is measured, in that a modeled heating power of the glow plug (4) is determined from a model, wherein the model takes into account at least two of the following parameters: ambient temperature of the exhaust gas heater (1), temperature of components of the exhaust gas heater (1), composition of the exhaust gas of the internal combustion engine (2), exhaust gas back pressure of the exhaust system of the internal combustion engine (2), exhaust gas mass flow of the internal combustion engine (2), in that a comparison of the measured heating power and the modeled heating power takes place and, as a function of the comparison, a diagnosis of the operation of the exhaust gas heater takes place.Exhaust gas heater (1) having a combustion chamber (3) into which an air stream is introduced by an air pump (6) and fuel is introduced by a fuel injection (16), and the air-fuel mixture is ignited by a glow plug (4), and the hot exhaust gases formed in this way are conducted through the exhaust system of an internal combustion engine (2), characterized in that the glow plug (4) is arranged in the combustion chamber (3) in such a way that a condensate in the combustion chamber collects in the region of the glow plug (4), such that heating of the glow plug (4) is influenced by the condensate in the region of the glow plug (4).Exhaust gas heater according to Claim 10, characterized in that means are provided which, by measuring the power consumption of the glow plug (4) in order to achieve a predetermined temperature, determine the quantity of condensate in the region of the glow plug (4).

Images