Process for operating a heater that can be operated with hydrocarbon fuel

Abstract

A process for operating a heater that can be operated with hydrocarbon fuel, especially for a vehicle includes providing a substoichiometric air/fuel mixture in a precombustion chamber (18) for a combustion operation and performing a cold flame combustion in the precombustion chamber (18). The precombustion products forming in the precombustion chamber (18) during the cold flame combustion are supplied to a catalyst arrangement (32) and a partial catalytic oxidation is performed for producing a gas containing hydrogen and carbon monoxide. The gas produced during the partial catalytic oxidation is supplied to a main combustion chamber (34) for producing a hydrogen/carbon monoxide/air mixture. The hydrogen/carbon monoxide/air mixture is burned in the main combustion chamber (34).

Claims

1. A heater for a vehicle, the heater comprising: a precombustion chamber; a fuel supply which supplies hydrocarbon fuel to the precombustion chamber; a primary combustion air supply which supplies combustion air to the precombustion chamber; a catalyst arrangement disposed downstream of the precombustion chamber for receiving precombustion products from the precombustion chamber and for producing a gas containing hydrogen and carbon monoxide by means of partial catalytic oxidation; a main combustion chamber downstream of the catalyst arrangement for receiving the gas containing hydrogen and carbon monoxide from the catalyst arrangement; and a secondary combustion air supply which supplies combustion air to the main combustion chamber, wherein said main combustion chamber is free of an ignition element.

2. A heater in accordance with claim 1, wherein the fuel supply comprises a fuel feed arrangement for feeding liquid fuel and a porous evaporator medium receiving the liquid fuel and releasing fuel vapor from the porous evaporator medium into the precombustion chamber.

3. A heater in accordance with claim 1, wherein the primary combustion air supply and the secondary combustion air supply comprise a common combustion air blower.

4. A heater in accordance with claim 1, further comprising an ignition device associated with the precombustion chamber.

5. A heater in accordance with claim 1, further comprising a water vapor supply which supplies water vapor to the precombustion chamber.

6. A heater in accordance with claim 5, wherein the water vapor supply routs some main combustion products leaving the main combustion chamber into precombustion chamber.

7. A vehicle heater comprising: a precombustion chamber; a fuel supply which supplies hydrocarbon fuel to the precombustion chamber; a primary combustion air supply which supplies combustion air to the precombustion chamber; a catalyst arrangement disposed downstream of the precombustion chamber for receiving the precombustion products from the precombustion chamber and performing a partial catalytic oxidation, of the supplied precombustion products, to produce a gas containing hydrogen and carbon monoxide; a main combustion chamber downstream of the catalyst arrangement for receiving the gas containing hydrogen and carbon monoxide from the catalyst arrangement; a secondary combustion air supply which supplies combustion air to the main combustion chamber for burning a mixture of the hydrogen and the carbon monoxide and the supplied air in the main combustion chamber; and an ignition device associated with the precombustion chamber, wherein the mixture of the hydrogen and the carbon monoxide and the supplied air in the main combustion chamber ignite exclusively based on a temperature of one or more of the hydrogen, the carbon monoxide and the supplied air.

8. A heater in accordance with claim 7, wherein the fuel supply comprises a fuel feed arrangement for feeding liquid fuel and a porous evaporator medium receiving the liquid fuel and releasing fuel vapor from the porous evaporator medium into the precombustion chamber.

9. A heater in accordance with claim 7, further comprising a return line routing some combustion products leaving the main combustion chamber into the precombustion chamber, wherein combustion products include water or water vapor and carbon dioxide and the return line supplies water vapor to the precombustion chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a basic longitudinal sectional view showing a heater, especially for a vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(2) Referring to the drawings in particular, the heater 10 shown in FIG. 1 in a basic view and in longitudinal section comprises a housing 12, which is, for example, tubular and extended in the direction of a longitudinal central axis A, which is closed by means of a bottom area 14 in the end area lying on the left in FIG. 1. For example, a porous evaporator medium 16 is provided adjacent to the bottom area 14. This can be provided as foam ceramic, metal foam, mesh, knitted fabric or material designed as porous in another way. An electrically excitable heater 20, for example, in the form of a heating coil, can be provided on the back side of the bottom area 14 or of the porous evaporator medium 16 lying facing away from a precombustion chamber 18 to heat the porous evaporator medium. Liquid hydrocarbon fuel, called only fuel below, can be introduced into the porous evaporator medium 16 by means of a fuel supply arrangement 22 designed, for example, as a metering pump, and a fuel line 24. Supported by the excitation of the heater 20, the fuel pre-fed by capillary feed action in the inner volume area of the porous evaporator medium 16 can be released in vapor form in the direction of the precombustion chamber 18.

(3) A combustion air supply arrangement generally designated by 26, for example, a side channel blower or the like, feeds air, for example, into a channel area 28 surrounding the housing 12. Air inlet openings, through which a part L.sub.1 of the air L fed into the channel arrangement 28 is able to enter the precombustion chamber 18, may be provided in the housing 12 in the axial area of the precombustion chamber 18.

(4) Further, an ignition means 30, for example, a glow-type ignition pin or the like, is associated with the precombustion chamber 18 in order to ignite the air/fuel mixture to be provided therein and thus to start the combustion.

(5) A catalyst arrangement, generally designated by 32, is provided in the direction of the longitudinal central axis A following the precombustion chamber 18 and thus arranged downstream in relation to this. This catalyst arrangement 32 may comprise a body coated or constructed with catalyst material. To increase the catalytically effective surface, this body may be designed with a large number of openings passing through same, for example, in the direction of the longitudinal central axis A. The catalyst arrangement 32 or the catalyst material provided at same forms a CPOX (Catalytic Partial Oxidation) catalyst.

(6) In the direction of the longitudinal central axis A, a main combustion chamber 34 is provided following the catalyst arrangement 32 and thus downstream in relation to same. In the body 12 are provided passage openings, through which the remaining part L.sub.2 of the air L fed into the channel arrangement 28 may enter the main combustion chamber 34. Thus, a mixture of this air L.sub.2 with the gas leaving the catalyst arrangement 32 can be produced in the main combustion chamber 34.

(7) At a, for example, axially open end area of the housing 12, the gases flowing through the body 12 exit from the body 12 and enter a backflow chamber 38. The gases flow into this backflow chamber 38 in a flow direction to an outlet 40 essentially opposite the flow direction in the interior of the housing 12. The backflow chamber 38 may be surrounded by a heat exchanger arrangement 42, which is only indicated in the form of a wall, to transfer heat transported in the gases leaving the housing 12 to a heat carrier medium.

(8) In the design described in FIG. 1, fuel feed arrangement 22 together with fuel line 24 essentially provides a fuel supply means 43, via which the fuel B is fed into the area of the precombustion chamber 18. The combustion air feed arrangement, together with the channel arrangement 28 and the openings letting the air portion L.sub.1 into the precombustion chamber 18, provides essentially a primary combustion air supply means 44, while the combustion air feed arrangement 26, together with the channel arrangement 28 and the openings letting the air portion L.sub.2 into the main combustion chamber 34, provides essentially a secondary combustion air supply means 46. The ratio of air portion L.sub.1 to air portion L.sub.2 may be adjusted, for example, by the flow cross sections of the openings letting each of these air portions through or even by the cross-sectional shape of the channel arrangement 28. As an alternative or in addition, valve arrangements may be provided, by means of which this ratio of air portions L.sub.1 and L.sub.2 to one another can be affected even during the operation.

(9) In order to provide heat in a vehicle, for example, a vehicle operated by electric motor, fuel B and combustion air L are fed in a start phase upstream of the normal combustion operation in such amounts and thus also in the precombustion chamber 18 that a superstoichiometric mixture of air or oxygen and fuel is present in the precombustion chamber 18. This mixture is ignited by exciting the ignition means 30 and fed through the catalyst arrangement 32 and the main combustion chamber 34 in the direction of outlet 40. By operating the heater 10 with superstoichiometric air/fuel mixture, the heater 10 and especially its catalyst arrangement 32 can be heated in the start phase in order to guarantee a sufficiently high operating temperature to achieve a catalytic reaction in the subsequent combustion operation. If a sufficient heating is guaranteed, a transition is made from the state, in which a superstoichiometric air/fuel mixture is provided, into a state, in which a substoichiometric ratio is produced in the precombustion chamber 18. In this case, a lambda value can preferably be set in the range of 0.3 to 0.5. By operating in a substoichiometric range, the combustion in the precombustion chamber 18 changes over into a so-called cold flame combustion. The fuel contained in the air/fuel mixture is not completely oxidized here. Rather, only a partial or preliminary oxidation takes place, in which even the long-chain hydrocarbon molecules are broken up and split up into shorter chains. In this cold flame combustion, a highly intensive, thorough mixing of the fuel, provided beforehand by evaporation with the combustion air, takes place at the same time, as a result of which it is guaranteed that a very efficient reaction of the reactants involved may take place in subsequent reactions.

(10) The precombustion products forming in the cold flame combustion in the precombustion chamber 18, which contain short-chain hydrocarbon molecules and unreacted atmospheric oxygen, arrive at the catalyst arrangement 32 positioned downstream. In the catalyst arrangement 32, a partial catalytic oxidation takes place, in which the hydrocarbon and the oxygen transported with same are converted essentially into carbon monoxide (CO) and hydrogen (H.sub.2). Because of very good thorough mixing of the fuel with the atmospheric oxygen and the short-chain hydrocarbons, an almost complete conversion can be achieved in this case, such that the gas leaving the catalyst arrangement 32 in the direction of the main combustion chamber 34 contains essentially only carbon monoxide and hydrogen, i.e., molecular hydrogen (H.sub.2).

(11) In the main combustion chamber 34, the gas exiting from the catalyst arrangement 32 is thoroughly mixed with the air portion L.sub.2 introduced into the main combustion chamber 34, the thus produced mixture of hydrogen (H.sub.2), carbon monoxide and oxygen (O.sub.2) automatically ignites because of the comparatively high temperatures and can thus be essentially completely burned into water or water vapor and carbon dioxide. Thus, the main combustion products leaving the main combustion chamber 34 in the direction of the backflow chamber 38 contain essentially water or water vapor and carbon dioxide.

(12) To be able to increase the lambda value range that can be used in the substoichiometric combustion in the precombustion chamber 18, provisions may be advantageously made for some of the main combustion products leaving the main combustion chamber 34, i.e., a partial flow of the gas flowing from the outlet 40, for example, in the direction of an exhaust system or the like, to be introduced into the precombustion chamber 18 via a return line 48 indicated by dotted line in FIG. 1. This gas contains water or water vapor. Thus, the danger that a strong soot formation occurs because of a lambda value that is too low or the catalyst material of the catalyst arrangement 32 is damaged by heat because of a lambda value that is too high can be avoided. Provisions could be made here, for example, for the line 48 to lead in the direction of the combustion air feed arrangement 26, i.e., the portion of the waste gases to be fed into the precombustion chamber 18 is drawn from combustion air feed arrangement 26 and is fed in the direction of the precombustion chamber 18 together with the air L. To be able to adjust the feed amount of this back-fed waste gas portion, a variable or fixed inductor may be provided in the line 48.

(13) In the design of a heater according to the present invention or the process according to the present invention, the hydrocarbon fuel used for providing heat energy can be used in a very efficient way, since a very good thorough mixing of the combustion air with the fuel is achieved, on the one hand, in the precombustion chamber 18 by the cold flame combustion running therein, and, on the other hand, the reaction efficiency in the catalyst arrangement 32 is increased by the splitting up of the long-chain hydrocarbon molecules. Since water or water vapor is additionally produced in the main combustion chamber as a substantial waste gas component in the primary combustion then running for producing heat, a very low-pollutant conversion of the hydrocarbon fuel during the production of heat is guaranteed at the same time. Since the waste gas values can be affected especially by the adjustment of the lambda values in the precombustion chamber 18 and even the main combustion chamber 34, the heater 10 designed or operating according to the present invention can be used in conjunction with the heat carrier media, i.e., for example, water or the like, which are currently usually used in vehicles.

(14) While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.