Method for operating a vehicle heating system

Abstract

Method for operating a vehicle heating system (38), the vehicle heating system (38) comprising a fuel-operated heater (10) with a burner section (12) supplied with combustion air (L) by a combustion air supply arrangement (28) and with fuel (B) by a fuel supply arrangement (24) and a heat exchanger section (48) for transferring heat generated in the burner section (12) to a heat transfer medium to be heated, wherein the combustion air supply arrangement (28) and the fuel supply arrangement (24) are controlled by a control arrangement (30) and the control arrangement (30) is configured to control the combustion air supply arrangement (28) and the fuel supply arrangement (24) depending on a heating output of the heater (10) to be provided for heating operation, in order to carry out a delivery operation associated with the heating output,wherein, during combustion operation, combustion air (L) and fuel (B) are supplied to the burner section (12) of the heating appliance (10) in such quantities to provide a mixture of combustion air (L) and fuel (B) that, during heating operation, the maximum heating output of the heating appliance (10) is less than the nominal heating output of the heating appliance (10) throughout the entire combustion operation and the mixture is provided with a lambda value of at least 1.8.

Description

[0001] The present invention relates to a vehicle heating system which can be used, for example, as a parking heater or as an auxiliary heater to heat a heat transfer medium, for example the air to be introduced into a vehicle interior or the coolant circulating in a coolant circuit of an internal combustion engine.

[0002] The operation of fuel-powered vehicle heaters is subject to legal regulations regarding pollutant emissions. These regulations, depending on the heating output required during combustion, necessitate the precise adjustment of the combustion air and fuel quantities supplied to each burner within narrow limits. Providing a mixture that results in a very low soot number, for example according to the Bacharach standard, leads to high CO emissions, while a mixture optimized for CO2 content in the exhaust gases results in a soot number that is within or even above the legally prescribed limit.

[0003] The object of the present invention is to provide a vehicle heating system or a method for operating a vehicle heating system with which an operation of a fuel-operated vehicle heater optimized with regard to pollutant emissions can be achieved.

[0004] According to a first aspect of the present invention, this problem is solved by a vehicle heating system comprising a fuel-operated heater with a burner section supplied with combustion air by a combustion air supply arrangement and with fuel by a fuel supply arrangement, and a heat exchanger section for transferring heat generated in the burner section to a heat transfer medium to be heated, wherein the combustion air supply arrangement and the fuel supply arrangement are controlled by a control arrangement, and the control arrangement is configured to control the combustion air supply arrangement and the fuel supply arrangement as a function of a heating output to be provided by the heater for heating operation, in order to carry out a delivery operation associated with the heating output, wherein a maximum heating output to be provided by the heater in heating operation is smaller,as the nominal heating output of the heating appliance.

[0005] According to the principles of the present invention, the nominal heating output of such a fuel-operated heater is the maximum possible heating output that could be provided by the heater with a corresponding supply of combustion air and fuel. A heating output even higher than the nominal output, i.e., the supply of an even larger quantity of combustion air and fuel, could, for example, lead to damage to system areas of the vehicle heater or to components interacting with it, due to the correspondingly greater amount of heat released.It should be noted at this point that in order to provide a given heating output, for example the nominal heating output or the maximum heating output to be provided in a heating operation, a correspondingly larger combustion output must be provided, taking into account the efficiency of the respective heating appliance, which can generally be around 75%–90%.

[0006] In the vehicle heating system constructed according to the invention, the heating unit is dimensioned such that the maximum heating output required during heating operation, taking into account the system areas to be heated in a vehicle and the amount of heat required, is less than the nominal heating output, i.e., the maximum possible heating output that this heating unit could at least theoretically provide with a corresponding supply of combustion air and fuel. During heating operation, the heating unit is operated essentially throughout the entire combustion process in such a way that the nominal heating output is not reached.This allows the heating appliance to be operated even at a comparatively high heating output in a state where, with a comparatively low CO2 content in the combustion gases, the soot number is below the legally prescribed limit and the CO content is also within a permissible range, or can be reduced to a permissible value by using a CO catalyst system.

[0007] In an advantageous embodiment of the vehicle heating system according to the invention, it is proposed that the maximum heating power is less than or equal to 90%, preferably less than or equal to 85%, of the nominal heating power.

[0008] In order to achieve a comparatively low CO2 content and a correspondingly low smoke number during combustion operation, it is proposed that the control arrangement be designed to control the combustion air supply arrangement and the fuel supply arrangement in such a way as to provide a superstoichiometric mixture of combustion air and fuel during heating operation.

[0009] By oversizing the heating device according to the invention for the maximum heating output required in heating operation, it becomes possible to design the control arrangement in such a way that the combustion air supply arrangement and the fuel supply arrangement are controlled for all heating outputs to be provided in the heating operation of the heating device to provide the superstoichiometric mixture of combustion air and fuel.

[0010] For optimized pollutant emissions, it is proposed according to the principles of the present invention that the control arrangement is configured to control the combustion air supply arrangement and the fuel supply arrangement to provide a mixture of combustion air and fuel to provide a lambda value of at least 1.8, i.e. a lambda value that is at or above 1.8.

[0011] In this context, it should be noted that, according to the present invention, heating operation is present when the heating device, after generating a command to commence operation, has completed a start-up phase and the combustion has stabilized, so that the heating device can be operated to provide the required amount of heat. For example, during such a start-up phase, a richer mixture of combustion air and fuel could be used than in stabilized combustion or heating operation to stabilize the combustion as quickly as possible; for example, a mixture set for a lambda value of no more than 1.8, preferably in the range of 1.2 to 1.8.

[0012] To ensure that, even with low heat demand, the heating appliance can be operated in a state that guarantees stable combustion while simultaneously avoiding excessive pollutant emissions, it is further proposed that the minimum heating output to be provided by the heating appliance during operation be less than or equal to 25% of the rated heating output of the heating appliance, and / or that the minimum heating output to be provided by the heating appliance during operation be greater than or equal to 10% of the rated heating output of the heating appliance. Such a minimum heating output also ensures that the combustion gases leaving the burner section of a heating appliance constructed and operated in this manner have a sufficiently high temperature to be converted into CO by a catalyst assembly positioned in the exhaust system.The oxidation catalyst arrangement is designed to trigger the catalytic oxidation reaction to be carried out there. In particular, this ensures that the temperature of the combustion gases leaving the burner area is above the activation temperature of such a catalyst arrangement, which is generally in the range of approximately 150°C.

[0013] To provide a lower heating output, for example, the minimum heating output, a correspondingly reduced quantity of fuel is generally fed into a combustion chamber for combustion, compared to a higher heating output, for example, the maximum heating output. Although a correspondingly reduced quantity of combustion air would also suffice for complete combustion of this fuel quantity, a particularly advantageous aspect of the present invention proposes that the control arrangement be configured to control the combustion air supply arrangement and the fuel supply arrangement to provide a mixture of combustion air and fuel, thus providing a lambda value that increases with decreasing heating output.An increasing lambda value means that the engine operates with a corresponding excess of air, which promotes a homogeneous mixing of the combustion air with the fuel fed into the combustion chamber.

[0014] For example, the control arrangement may be designed to control the combustion air supply arrangement and the fuel supply arrangement during heating operation with minimum heating power to provide a mixture of combustion air and fuel to provide a lambda value of at least 2.1, preferably a maximum of 4.0.

[0015] When a mixture of combustion air and fuel is used to minimize the CO2 content, the CO content in the combustion exhaust gases can be comparatively high, possibly exceeding a legally prescribed limit. To nevertheless be able to operate with such a low CO2 content and correspondingly low soot number, it is proposed that a CO catalyst assembly be provided through which the combustion exhaust gases leaving the burner area flow.

[0016] To ensure the flow of the heat transfer medium to be heated through the heat exchanger area, it is proposed that a conveying arrangement be provided to convey the heat transfer medium to be heated in the heat exchanger area through the heat exchanger area.

[0017] The heat transported in the heat transfer medium can be utilized, for example, by providing a heat exchanger arrangement to release the heat transported in the heat transfer medium. In particular, heat can be transferred in this heat exchanger arrangement to the air introduced into a vehicle interior. In such a design, it can be provided that the heat exchanger section is integrated into a coolant circuit of an internal combustion engine, through which coolant circulating in the coolant circuit acts as the heat transfer medium.

[0018] In order to be able to directly heat the air to be introduced into a vehicle interior by the heating device or its heat exchanger area, it is proposed that the heat exchanger area be permeable to air flowing into a vehicle interior.

[0019] According to a further aspect, the aforementioned problem is solved by a method for operating a vehicle heating system constructed according to the invention, wherein, during combustion operation, combustion air and fuel are supplied to the burner area of ​​the heater in such quantities to provide a mixture of combustion air and fuel that a maximum heating output of the heater is less than a nominal heating output of the heater and / or that the mixture is provided with a lambda value of at least 1.8.

[0020] The present invention is described in detail below with reference to the accompanying figures. These show:

[0021] Fig. 1. In principle, a fuel-operated heating device for a vehicle heating system;

[0022] Fig. 2 plotted against the CO2 content in the combustion exhaust gas of a fuel-operated heating appliance, the CO content and the soot number;

[0023] Fig. 3 plotted against the CO2 content in the combustion exhaust gas of a fuel-operated heating appliance, the nitrogen oxide content;

[0024] Fig. 4 in a schematic representation of the heating device of the Fig. 1 vehicle heating system included.

[0025] The Fig. Figure 1 shows in a schematic representation the essential system areas of a heating device that can be used as a parking heater or as an auxiliary heater in a motor vehicle. 10 This includes a burner area. 12 with a combustion chamber housing 14 A perimeter wall 16 and a floor area 18 of the combustion chamber housing 14 limit a combustion chamber 20 . On the ground 18 is a porous evaporation medium 22provided for, into which by means of a fuel supply arrangement 24 For example, a metering pump delivers liquid fuel B from a reservoir (not shown). This is particularly important during the start-up phase of the heating unit's operation. 10 the evaporation of fuel B into the combustion chamber 20 To support this, an electrically excitable heating device is used. 26 on the ground area 18 intended. To supply the combustion air L required for combustion into the combustion chamber. 20 is a combustion air supply arrangement 28 , for example, side channel blowers are provided.

[0026] The combustion air supply arrangement 28 and the fuel supply arrangement 24 are under the control of a generally with 30 designated control arrangement. This also controls the heating device. 26 of the floor area 18 on. Also one in the combustion chamber20 extending ignition organ 32 is under the control of the control arrangement 30 , in order to ensure that the combustion chamber is used during the start-up phase 20 The mixture of combustion air L and fuel B is ignited, thus initiating combustion. The resulting combustion gases A leave the combustion chamber. 20 via a flame damper 34 and flow through, for example, the circumferential wall 16 provided flame tube 36 and one in Fig. The heat exchanger area (not shown) transfers some or all of the heat generated during combustion to a heat transfer medium. The combustion exhaust gases A leave the heat exchanger area via an exhaust gas routing system and are expelled to the environment.

[0027] The integration of such a heating device 10 in a general with 38The designated vehicle heating system is in Fig. 4 illustrates the vehicle heating system. 38 includes a coolant circuit 40 , which is formed by a water jacket of an internal combustion engine 42 and a heat exchanger arrangement 44 leads to. During the operation of the internal combustion engine 42 The generated heat is thus transferred via a coolant pump. 46 Promoted, generally liquid coolants for the heat exchanger arrangement 44 transported to where it can transfer heat to the air H, i.e., the heated air, which is to be introduced into a vehicle interior.

[0028] For example, parallel to the heat exchanger arrangement 44 is in the coolant circuit 40 the heat exchanger area 48 of the heating unit 10 Integrated. Promoted by a heat exchanger area 48 associated coolant pump 50 Could this happen in the coolant circuit? 40The intended coolant, for example, can be routed in such a way that it only affects the heat exchanger arrangement. 44 can flow through and thus is located in the area of ​​the heat exchanger. 48 absorbed heat in the heat exchanger arrangement 44 can transfer H to the air. In this case, a valve 52 the flow through the water jacket of the internal combustion engine 42 prevent this. For example, should the internal combustion engine also or only the internal combustion engine be used during a preheating phase? 42 The coolant can flow through it, for example, if it is pumped by the coolant pump. 46 , through the water jacket of the internal combustion engine 42 and the heat exchanger area 48 to be guided through it. In order to maintain the flow through the heat exchanger assembly in this state. 44 To prevent this, another valve can be used. 54 be planned.

[0029] In the case of such a vehicle heating system provided for in a vehicle or to be integrated into a vehicle 38 The heat demand occurring in various operating states, or the maximum required heat demand, is known per se. Taking this heat demand into account, the vehicle heating system is designed according to the principles of the present invention. 38 the heating device 10 It is designed or dimensioned so that its nominal heating output is greater than the maximum heating output required to meet the maximum demand. For example, it could be provided that when the maximum required heating output of the heating appliance is exceeded, the heating output must be increased accordingly. 10 at 5 kW, the heating unit 10 with its burner area 12 and its heat exchanger area 48with a nominal heating output of approximately 6 kW. To ensure stable and low-emission combustion even in operating conditions where only a comparatively small amount of heat is required, a minimum heating output of the heating unit may also be provided. 10 , i.e., the minimum heating output of the heating device obtained by feeding in a corresponding amount of fuel during heating operation. 10 , not greater than 25% of the nominal heating output, but not less than approximately 10% of the nominal heating output. In the example given above, this means, for instance, that the minimum heating output of the heater is 10 It should be in a range between 0.6 kW and 1.5 kW.

[0030] The heating device can be constructed in such a way or controlled by the control arrangement. 30The system is operated in such a way that different, discrete heating output levels can be set during heating operation, and one of these heating output levels is selected depending on the available heat demand. The fuel supply arrangement is assigned to each heating output level that can be set during heating operation, i.e., to each heating output level. 24 and the combustion air supply arrangement 28 Operating conditions are specified which ensure that the required amount of fuel and, in relation to this, the required amount of combustion air are supplied to the combustion chamber for a given heating output. 20 can be promoted. For example, in relation to the combustion air supply arrangement. 28For each heating output level, a specific speed of a blower motor or blower wheel is specified, ensuring that a defined quantity of combustion air L is supplied. This is related to the fuel supply arrangement. 24 For example, if this is designed as a metering pump, a clock frequency, i.e. an output frequency for the intermittently supplied fuel B, can be specified for a respective heating power level.

[0031] The heating appliance is oversized with its nominal heating output in relation to the maximum heating output to be provided during heating operation. 10 can be operated according to the principles of the present invention in such a way that, preferably for all adjustable heating outputs or heating output levels, the combustion chamber 20The mixture of combustion air L and fuel B supplied is significantly overstoichiometric, i.e., a very lean mixture. The mixture in the combustion chamber 20 The combustion process therefore takes place with an excess of air or oxygen, resulting in a comparatively low CO2 content in the combustion exhaust gases A and reduced NOx levels.

[0032] This can be seen from the Fig. Figure 2 illustrates this. There, curve K1, plotted against the CO2 content, shows the CO content in the combustion gases A for operation at a heating output near the minimum heating output. Curve K2 shows the smoke number, here the Bacharach smoke number RZ, also as a function of the CO2 content. According to the principles of the present invention, the mixture of combustion air L and fuel B is supplied, for example, with a lambda value, i.e., a combustion air ratio, of at least 1.8. This results in a CO2 content in the range of 5 to 6.5%. At this CO2 content, the smoke number RZ is significantly below the specified limit, which is, for example, a value of 4. It can be provided, for instance, that the lambda value is set to approximately 1.8 in relation to the maximum heating output.As the required heating output decreases, the lambda value can be increased, so that, for example, at the minimum heating output, i.e., the minimum output of the heating device during heating operation, it is . 10 The heating output drawn is at least 2.1, preferably in a range between 2.1 and 4.0.

[0033] The Fig. 3 illustrated in relation to Fig. 2. Based on a curve K3 representing the NOx content as a function of the CO2 content, it can be shown that a CO2 content in the range of 5 to 6.5% also results in a comparatively low value, significantly below a legally prescribed limit of 200 ppm, for example.

[0034] By operating the heating device 10With a superstoichiometric mixture of combustion air L and fuel B, it is ensured for all required heating outputs, including those set during heating operation, that combustion can proceed with a comparatively low CO2 content and thus a correspondingly low smoke number. This may result in a slightly reduced efficiency in heat transfer within the heat exchanger. 48 have consequences. Since the heating unit 10 However, the heat exchanger area is fundamentally oversized for the required heating operation according to the principles of the present invention. 48 , which of course also applies to the higher nominal heating output of the heating appliance 10 It is designed to be oversized for the actual heating operation and can therefore compensate for a loss in efficiency.

[0035] The heating operation of the heating unit 10This can, for example, proceed in such a way that, in relation to a heating output to be provided or a heating output level to be set, corresponding operating states or operating modes for the combustion air supply arrangement are selected. 28 and the fuel supply arrangement 24 The parameters are specified and then controlled accordingly by the control arrangement. Alternatively, it is possible, for example, for the combustion air supply arrangement. 28 A control system should be provided such that the ratio of combustion air quantity to fuel quantity results in the provision of the specified lambda value. For this purpose, the exhaust gas temperature and / or the exhaust gas composition can be monitored by means of a dedicated sensor, and the combustion air supply arrangement adjusted accordingly. 28can be controlled. In this way, environmental influences, such as different altitude positions of a vehicle, can be compensated for, as it is ensured that the combustion always takes place in such a way that the composition of the mixture on the one hand and the combustion exhaust gases A on the other hand correspond to the specified requirements.

[0036] Increasing the lambda value from a value corresponding to maximum heating output, for example approximately 1.8, to a value corresponding to minimum heating output, for example in the range between 2.1 and 4.0, leads to the following when operating the heating device: 10 with the minimum heating output to a CO2 content in the range between 7% and 4%.

[0037] By increasing the amount of combustion air in relation to the amount of fuel, it is ensured that the heating appliance is optimized with regard to the flow conditions, in particular the flow momentum of the combustion air. 10 The system operates approximately as if it were operating in a state with a higher required heating output, for example, the maximum heating output. Since such heating appliances are generally optimized for high or maximum heating outputs with regard to the inflow conditions and thus also the mixing conditions of combustion air and fuel, this ensures that very good mixing of combustion air and fuel is achieved even at lower required heating outputs, especially at the minimum heating output.

[0038] If the CO2 content and thus the NOx content in the combustion exhaust gases A is further reduced or kept at a low value, for example when the heating appliance 10 Operating with the previously described high lambda value under operating conditions with low required heating output, or to achieve an even lower smoke number, results in a significant increase in the CO content, which the Fig. 2 clearly shows this based on curve K1. However, in order to comply with a legal requirement for the upper limit of the CO content, the heating appliance can be... 10 associated exhaust system 56 a CO catalyst arrangement 58 These are assigned to components through which the combustion exhaust gases A are passed to reduce the CO content. This CO catalyst arrangement 58 This could, for example, be a passive catalyst arrangement. The use of this CO catalyst arrangement 48This results in the CO content in the combustion exhaust gases A emitted into the environment being reduced to a value close to 0.

[0039] In particular, such a CO catalyst arrangement can be 58An oxidation catalyst is used in which platinum and / or palladium are employed as catalyst material to carry out the catalytically induced oxidation reactions. When the combustion exhaust gas containing hydrocarbons, CO, and NO flows through such a CO catalyst arrangement, the catalytically induced oxidation with oxygen as the oxidizing agent converts hydrocarbons into CO2 and water, CO into CO2, and NO into NO2. Since a low soot particle fraction, i.e., a low soot number, is essential for the function of such catalysts, it is particularly advantageous, according to the principles of the present invention, to operate a vehicle heating system or vehicle heater with a high lambda value, especially with lower heating outputs, while still increasing the lambda value, in order to achieve a low soot number.

Claims

[1] Vehicle heating system comprising a fuel-operated heater ( 10 ) with a combustion air supply arrangement ( 28 ) with combustion air (L) and by means of a fuel supply arrangement ( 24 ) burner area to be supplied with fuel (B) 12 ) and a heat exchanger area ( 48 ) for the transmission of in the burner area ( 12 ) generated heat onto a heat transfer medium to be heated, wherein the combustion air supply arrangement ( 28 ) and the fuel supply arrangement ( 24 ) under the control of a control arrangement ( 30 ) stand and the control arrangement ( 30 ) is designed to control the combustion air supply arrangement ( 28 ) and the fuel supply arrangement ( 24 ) depending on the heating output to be provided by the heating appliance for heating operation ( 10) to control the execution of a conveying operation assigned to the heating output, whereby a heating operation is carried out by the heating device ( 10 ) the maximum heating output to be provided is less than the nominal heating output of the heating device ( 10 ). [2] Vehicle heating system according to claim 1, characterized by that the maximum heating output is less than or equal to 90%, preferably less than or equal to 80%, of the nominal heating output. [3] Vehicle heating system according to claim 1 or 2, characterized by that the control order ( 30 ) is designed to control the combustion air supply arrangement during heating operation ( 28 ) and the fuel supply arrangement ( 24 ) such that a superstoichiometric mixture of combustion air (L) and fuel (B) is provided. [4] Vehicle heating system according to claim 3 characterized by that the control arrangement is designed to be effective for all functions in the heating operation of the heating appliance ( 10) heating outputs to be provided the combustion air supply arrangement ( 28 ) and the fuel supply arrangement ( 24 ) to provide the superstoichiometric mixture of combustion air (L) and fuel (B). [5] Vehicle heating system according to claim 3 or 4, characterized by that the control order ( 30 ) is designed to control the combustion air supply arrangement ( 28 ) and the fuel supply arrangement ( 30 ) to provide a mixture of combustion air (L) and fuel (B) to provide a lambda value of at least 1.

8. [6] Vehicle heating system according to one of the preceding claims, characterized by that a heating device in heating mode ( 10 ) minimum heating output to be provided less than or equal to 25% of the nominal heating output of the heating appliance ( 10 ) is, or / and that a heating operation is carried out by the heating device ( 10) minimum heating output to be provided greater than or equal to 10% of the nominal heating output of the heating appliance ( 10 ) is. [7] Vehicle heating system according to one of the preceding claims, characterized by that the control order ( 30 ) is designed to control the combustion air supply arrangement ( 28 ) and the fuel supply arrangement ( 30 ) to provide a mixture of combustion air (L) and fuel (B) to provide a lambda value that increases with decreasing heating power. [8] Vehicle heating system according to claim 6 and claim 7, characterized by that the control order ( 30 ) is designed to control the combustion air supply arrangement ( 28 ) and the fuel supply arrangement ( 30) during heating operation with minimum heating power to provide a mixture of combustion air (L) and fuel (B) to provide a lambda value of at least 2.1, preferably a maximum of 4.

0. [9] Vehicle heating system according to any of the preceding claims, characterized by that one of the burner area ( 12 ) CO catalyst arrangement through which exhaust gases flow ( 58 ) is planned. [10] Vehicle heating system according to one of the preceding claims, characterized by that a funding order ( 46 , 50 ) to promote the in the heat exchanger area ( 48 ) the heat transfer medium to be heated through the heat exchanger area ( 48 ) through which it is provided. [11] Vehicle heating system according to one of the preceding claims, characterized by that a heat exchanger arrangement ( 44 ) is intended for the release of heat transported in the heat transfer medium. [12] Vehicle heating system according to one of the preceding claims, characterized by that the heat exchanger area ( 48 ) into a coolant circuit ( 40 ) an internal combustion engine ( 42 ) for flow through in the coolant circuit ( 40 ) circulating coolant is integrated as a heat transfer medium. [13] Vehicle heating system according to one of claims 1–10, characterized by that the heat exchanger area ( 48 ) is permeable to air (H) being introduced into a vehicle interior. [14] Method for operating a vehicle heating system according to one of the preceding claims, wherein in combustion operation combustion air (L) and fuel (B) are supplied to the burner area in such quantities as to provide a mixture of combustion air (L) and fuel (B) ( 12 ) of the heating appliance ( 10 ) are supplied so that in heating mode the heating device has a maximum heating output ( 10) is smaller than the nominal heating output of the heating appliance ( 10 ) or / and that in heating mode the mixture is provided with a lambda value of at least 1.8.