EP0638776A1 - Method and device for reducing the emission of odour and pollutants of heating apparatus for vehicles - Google Patents

Abstract

A method for reducing the emission of odour and pollutants arising during the operation of a heating apparatus for vehicles is described, by which method the exhaust gases produced in the combustion chamber (1) of the heating apparatus during the combustion of the liquid fuel are guided over catalytically active layers arranged within the heating apparatus. Also disclosed is an arrangement having the two possibilities, which can be employed individually but also in combination, whereby a) the layers forming the flow path for the exhaust gas within the heating apparatus, namely the outer surface of the flame tube (7) and the inner surface of the heat exchanger (12), are coated to be catalytically active and/or b) a catalytically active knitted fabric (21.3) is arranged in the space formed between flame tube and heat exchanger. <IMAGE>

Description

The invention relates to a method for reducing odor and pollutant emissions in the operation of a heater for vehicles, in which heat is generated by burning liquid fuel, which is fed to a heating heat exchanger via a heat transfer medium and serves to heat a vehicle compartment, and an arrangement for carrying it out this method in a heater independent of the vehicle engine, in which the heat exchanger is arranged concentrically with the combustion chamber and the flame tube and the exhaust gas is deflected after it leaves the flame tube and is guided through the heat exchanger to the exhaust gas outlet.

Heaters are known for heating the vehicle interior and for defrosting windows, in order to improve driving safety and driving comfort, especially in the period until the engine of the vehicle emits sufficient heat for heating the vehicle interior and during the time in which the engine of the vehicle does not have sufficient heat generated, for example at extremely low outside temperatures. In addition, such heaters are also used to preheat the vehicle engine so that it starts more easily. In this context, a vehicle is understood not only as a passenger car but also as a commercial vehicle, construction machinery and ships which have a drive motor and a cabin intended for the operator's stay or a cargo hold to be heated. These heaters are classified into "gasoline" and "diesel" based on the type of liquid fuel used for heating, and each of the two types after the heat transfer medium in "air" and "water devices".

DE 38 08 061 C2 shows a heater working with air as a heat transfer medium, DE 39 43 335 A1 shows a heater working with a liquid heat transfer medium. Both in gasoline and diesel fueled heaters, after appropriate treatment, they are burned in a combustion chamber and a subsequent flame tube, and the hot exhaust gases are passed along a heat exchanger (heating heat exchanger) for heat transfer to the heat transfer medium. Then the exhaust gas leaves the heater via an exhaust outlet and a generally short exhaust pipe. This means that the distance the exhaust gas travels to the outside is very short compared to the exhaust pipes of a vehicle engine with several silencers. While the exhaust gases from the vehicle engine are passed and cleaned by exhaust gas purification devices, e.g. in a 3-way catalytic converter or a particulate filter in engines operated with diesel fuel, this is not the case with heaters and so far did not seem possible or necessary either, since the combustion can be optimally adjusted in one heater and with the combustion in one Vehicle engine is not comparable in terms of the operating loads that occur (standstill to full throttle and push operation).

According to DE 37 13 476 C2, a heater is known in which effective sound damping is to be effected by means of sound damping inserts or pads in the interior of the heater. For this purpose, sound-absorbing pads and / or inserts are arranged in a flameless area within the combustion chamber. These layers or inserts can be porous or provided with holes and consist of a catalytically active material, layers of sound-absorbing material and those of catalytic material should also be arranged distributed within the combustion tubes of the flame tube. However, this arrangement has the disadvantage that the cleaning effect is only very slight and the sound damping effect deteriorates with increasing clogging of the pores by, for example, soot particles and that the flow conditions in the combustion chamber, for example through passage openings in the combustion chamber inner lining, deteriorate.

It has been shown that the exhaust gas from heating devices, despite the optimal setting, contains pollutants in an amount which make cleaning appear desirable, in particular that odorous substances are emitted which can be a nuisance because they occur as aromatic hydrocarbons or hydrogen sulfides.

The present invention is therefore based on the object of demonstrating a method according to which exhaust gas purification takes place in the area of the heater in heater devices for vehicles, that is to say not in an exhaust gas line arranged outside the heater, and an arrangement with which the method can be carried out.

This object is achieved in that the hot exhaust gas which arises in the combustion chamber with the subsequent flame tube of the heater during the combustion of the liquid fuel is passed over a catalytically effectively coated section arranged within the heater, downstream of the combustion chamber and the flame tube. It has surprisingly been shown that for most of the applications there is a sufficient surface area exposed to the exhaust gas when it is guided through the heat exchanger. which can be used in a catalytically effective coating to reduce odor emissions. It is advantageous if the surface of the heat exchanger has a certain roughness so that the coated surface is enlarged. In cases where these areas are insufficient or for retrofitting existing devices, such sections can be introduced in the form of catalytically active coated elements. It was particularly surprising that no deterioration in the efficiency of the heater was found, at most a certain flattening of the heating curve, which can, however, be accepted.

The arrangement for carrying out the method is accordingly characterized in that catalytically effectively coated sections are arranged in the flow path of the exhaust gas between the combustion chamber with the subsequent flame tube and the exhaust outlet connection. It has been found that it is sufficient if the surfaces of the heat exchanger acted upon by the exhaust gas from the heater and the outer surfaces of the flame tube are at least partially catalytically coated. It is particularly advantageous here that the heat exchanger on its inner surface, i.e. on the side facing the combustion chamber and the flame tube, is provided with ribs, so that there is a relatively large area suitable for the catalytically active coating. The coating is in the micro range, so that in this case there is no impairment of the area provided for the flow.

According to a further development, a catalytically coated metallic knitted fabric is arranged in a section of the exhaust gas flow path between the outer wall of the combustion chamber / flame tube and the inner wall of the heat exchanger. Such knitted fabrics are known from exhaust gas purification technology and can easily be adapted to the contour specified by the ribs of the heat exchanger. It has proven to be advantageous if the knitted fabrics are made of metal and this version is adapted to the contour of the heat exchanger. This gives an annular element which is smooth on the inside, so that it can be placed on the flame tube, while the outer contour corresponds to that of the heat exchanger and its ribs. According to a further development, this element can be surrounded by an elastic layer, so that an elastic intermediate layer is formed between the metallic frame of the knitted fabric and the heat exchanger. According to a further development of the invention, this can consist of swelling material, so that as the temperature increases, the element is fitted more and more firmly in the space offered to it. There are various options for the axial bearing of this element. In the simplest case, a corresponding shoulder is provided on the flame tube against which the element rests. The axial loading of this ring is only from one side, and the ribbing provides a radial fixation, so that a simple securing against axial displacement is sufficient. This arrangement of the element also has the great advantage that existing heaters can be retrofitted with no special effort and that this component can be replaced at any time in a very simple manner. Such a metallic knitted fabric is also suitable for retaining soot particles which occur in heaters operated with diesel fuel. Burning free of the element can be achieved at the specified temperatures in the heater without additional effort.

The catalytically active element can either be a ceramic monolith, as is usually used in exhaust gas purification, or a metallic corrugated body, as is used in automotive engineering, e.g. is used in pre-catalysts. In any case, such an element must have a sufficient longitudinal extent, since otherwise the exhaust gas dwell time in the element when it flows through is too short. This applies in particular if the element is also intended to act as a soot filter. A configuration can also be selected for the ceramic body that is particularly suitable for retaining soot particles that occur. Such ceramic bodies have a multiplicity of continuous channels which are closed on the input or output side in the manner of a chessboard, so that the exhaust gas in each case enters the open channels, then passes through the ceramic body to the adjacent channels and from there leaves the exhaust gas treatment body. The soot particles accumulated during the passage through this exhaust gas treatment body can then be easily removed by burning out at the given temperature conditions in the flame tube.

It has been shown that mostly one of the options shown is sufficient to bring about an effective reduction in pollutant and odor emissions. However, these three possibilities, namely the coating of the existing surfaces or the use of a knitted body or the use of a coated element, can be combined with one another as desired, so that the present invention relates to each of the individual variants, but also to any combination of the disclosed variants .

Fig. 1

einen Längsschnitt durch ein Heizgerät mit Luft als Wärmeübertragungsmedium;

Fig. 2

einen Querschnitt durch den brennerseitigen Teil eines Heizgerätes mit einem flüssigen Wärmeübertragungsmittel bei sonst gleichem Aufbau wie das Heizgerät nach Fig. 1.

1 and 2, in which an arrangement for carrying out the method according to the invention is simplified and shown schematically, the invention and further developments are explained and described. It shows:

Fig. 1

a longitudinal section through a heater with air as the heat transfer medium;

Fig. 2

2 shows a cross section through the part of a heater on the burner side with a liquid heat transfer medium with otherwise the same structure as the heater according to FIG. 1.

The heater shown in longitudinal section in FIG. 1 differs from the heater shown in cross section in FIG. 2 only by the different guidance of the heat transfer medium, which is air in the example of FIG. 1 and a liquid in the example of FIG. 2. Therefore, the heat exchanger according to FIG. 1 is provided on both sides with ribs, inner and outer ribs, and the heat transfer medium is supplied and removed differently. The differently chosen exemplary embodiments show that the structure of the heater is of no importance for the arrangement of the catalysts. The decisive factor is the presence of a heat exchanger which is arranged around the combustion chamber.

1 has a combustion chamber 1, in which fuel supplied via the spark plug connector 2, which receives air sucked in via the combustion air supply connector 3 via a combustion air blower 4 and thus forms an ignitable mixture which is ignited by means of the ignition device 4, is burned . A flame shield 6, which acts as a flame holder, and a flame tube 7 are connected to the combustion chamber 1. On the opposite side, a blower motor 8 is arranged with the hot air blower 9, over the air is sucked in as heat transfer medium from the air intake connector 10 and is guided inside the housing 11 via the heat exchanger 12 before it leaves the heater via the outlet connector 13 in order to heat the vehicle cabin directly or via a heating heat exchanger and to effect deicing of the windscreen. In the exemplary embodiment, the ignitable fuel / air mixture takes place in a prechamber 14. The combustion takes place in the combustion chamber 1. The flame extends into the flame tube 7, and the hot exhaust gases leave the flame tube 7 and strike the curved wall of the heat exchanger 12 and are deflected there and flow into the annular space 19 to the exhaust outlet connection 16 and leave the heater there. The temperature in the combustion chamber 1 is approximately 800 ° C. and that at the outlet 16 is approximately 200 to 300 ° C.

In the exemplary embodiment according to FIG. 1, a baffle 17 is arranged in the path of the hot exhaust gases directly in front of the exhaust gas outlet connection 16 in order to achieve a longer residence time of the hot exhaust gas in the heat exchanger 12. The heat exchanger 12 has external ribbing 12.1 in the annular space 19 between the housing 11 and the heat exchanger wall 12 for guiding the air as heat transfer medium and in order to improve the heat transfer from the hot exhaust gas to the heat transfer medium. Furthermore, the heat exchanger 12 has inner fins 12.2, which likewise serve to improve the heat transfer in a known manner. These inner ribs 12.2 protrude into the annular space 15 between the flame tube 7 and the wall of the heat exchanger 12. In the heater according to FIG. 2, the heat exchanger 12 has no outer ribs, and the position of the connecting pieces 10, 12, 16 is different from that of the heater Fig. 1, since in the case of the heater according to Fig. 2, a liquid heat transfer medium is used. Both heaters are known and have proven themselves even under extreme operating conditions.

In such a heater, the combustion can be optimally set, but pollutant is still contained in the exhaust gas, even if in very small amounts. Disturbing are odorous substances contained in the exhaust gas, some of which occur as aromatic hydrocarbons, some as hydrogen sulfides. In order to remove these substances from the exhaust gas, the arrangement of catalysts, as is known for exhaust gas purification in engines operated with liquid fuel, is appropriate. The arrangement of such catalysts in the exhaust pipe of heaters requires a relatively large installation space, which is not available under normal installation conditions.

In the illustrated embodiment, three variants for the arrangement of a catalyst are shown. Firstly, a knitted wire mesh with a catalytic effect is shown, secondly a monolith arrangement and in the third case a catalytic coating. It is expressly pointed out that these arrangements can each be arranged individually or in combination, the arrangement of a monolith in the flame tube not falling within the scope of protection.

It is possible, as shown in Fig. 2 in the upper half, the surfaces acted upon by the exhaust gas from the flame tube 7, i.e. the outer surface of the flame tube 7 and the surface of the fins 12.2 of the heat exchanger 12, with a for carrying out a catalytic treatment of the To provide suitable exhaust gas layer 20. The application of such a layer is known from the coating of metal wound catalysts. It has been shown that the arrangement of catalytically active layers 20 already gives good, in many cases also sufficient results. This applies in particular to heaters operated with petrol engine fuel (petrol). Since there are generally no regulations for the quality of the fuel for such heaters operated with gasoline as fuel, that is to say fuels can also be used in which a hydrogen sulfide compound can be released, a catalytically active element 21 in can additionally or if sufficiently alone the annular space 15 between the flame tube 7 and the heat exchanger 12 may be arranged. This element 21 is designed as a ring, the outer contour 21.1 corresponding to that of the ribbed part of the heat exchanger 12, while the inner contour 21.2 is correspondingly smooth to the flame tube 7. The outer contour 21.1 and the inner contour 21.2 form a covering for a catalytically coated wire mesh 21.3. The inlet and the outlet in this element 21 is covered by a corresponding perforated plate 21.4 or 21.5 in Fig. 1, so that the hot exhaust gas can flow through the element 21 without discharging wire particles. The element 21 can additionally be surrounded with a thin swelling mat so that it fits more firmly into the contour of the annular space 15 with increasing temperature and load and is also secured against axial displacement. As a rule, however, this is not necessary since a stop can easily be arranged behind the element 21 in the direction of loading. 1, the baffle 17 arranged in the flow of the hot exhaust gas already satisfies the requirements for holding the element 21 in the flow direction. Instead of the element 21 with the knitted fabric 21.3, it is also possible to use a ceramic, catalytically coated monolith with a multiplicity of passages for the exhaust gas or one with a multiplicity of Passages provided catalytically coated SiC block can be used.

Another variant which can be derived from the prior art and which can be used alone or in combination with one or the other variants described above or both together is the arrangement of a catalytically active coated element 23 in the end of the flame tube 7. This can be a be a catalytically active monolith or an SiC body with a corresponding coating. The holder is made in a known manner via a wire mesh or / and a swelling mat. The axial change in position can take place by means of a stop, a constriction or an inserted ring in the flame tube 7, the axial position being fixed in the flow direction behind the element 23.

In particular in the case of heaters which use diesel fuel as the heating medium, the element 21 can be designed as a soot filter in a known manner. Such soot filters consist of a catalytically effective coated body with parallel, continuous channels, which are closed on the inlet and outlet side in a chessboard-like manner, so that the exhaust gas enters one channel closed on the outlet side and then enters through the monolith in the other outlet side open channel, the soot particles deposit as they pass through the body. This element 21 is arranged in the flow direction behind the combustion chamber 1 and the flame tube 7 in the area after the flow deflection of the exhaust gas. Temperatures there still allow the element 21 to burn free from the soot particles that have accumulated. The element 21 can also be formed from SiC.

Claims (7)

Process for reducing odor and pollutant emissions when operating a heater for vehicles, in which heat is generated by burning liquid fuel, which is fed to a heating heat exchanger via a heat transfer medium and is used to heat a vehicle compartment,
characterized,
that the resulting in the combustion chamber (1) with the following flame tube (7) of the heater during the combustion of the liquid fuel exhaust gas is guided via a catalytically effectively coated section arranged downstream of the combustion chamber (1) and the flame tube (7) within the heater . Arrangement for carrying out the method according to claim 1 in a heater independent of the vehicle engine, in which the heat exchanger (12) is arranged concentrically with the combustion chamber (1) and the flame tube (7) and the exhaust gas is deflected after exiting the flame tube (7) and through the heat exchanger (12) is led to the exhaust outlet connection (16), characterized in that catalytically effective coated sections are arranged in the flow path of the exhaust gas between the combustion chamber (1) together with the flame tube (7) and the exhaust outlet connection (16). Arrangement according to claim 2, characterized in that the surfaces of the heat exchanger (12) acted upon by the exhaust gas of the heating device and the outer surfaces of the flame tube (7) are at least partially catalytically coated. Arrangement according to claim 2, characterized in that a catalytically coated, metallic knitted fabric (21.3) is arranged in a section of the exhaust gas flow path between the outer wall of the combustion chamber / flame tube and the inner wall of the heat exchanger. Arrangement according to claim 4, characterized in that the knitted fabric (21.3) is made of metal and the contour (21.2) of the heat exchanger (12) is adapted. Arrangement according to claim 5, characterized in that an elastic intermediate layer is arranged between the metallic frame of the knitted fabric (21.3) and the heat exchanger (12). Arrangement according to claim 6, characterized in that the intermediate layer consists of swelling mat material.

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