The invention relates to a vaporization burner for a heating device operated by means of a liquid fuel, particularly for a motor vehicle heating device.
German Patent No. 32 33 321 and corresponding U.S. Pat. No. 4,530,658 disclose a vaporization burner, of the kind mentioned above, which has a combustion chamber within a combustion pipe. The combustion chamber contains an absorbent body disposed on a carrier to which a liquid fuel is supplied. At least part of the side of the carrier facing the combustion chamber is exposed. Furthermore, a combustion air inlet arrangement is provided to prepare a combustion mixture of fuel and air that is ignited by means of an ignition device and burned in the combustion chamber.
German Offenlegungsschrift No. 34 23 940 describes another variation of a vaporization burner for a heating device of the kind initially mentioned, in which the ignition device is an elongated glow plug which transverses the carrier and the absorbent body, projecting above it and extending into the combustion chamber. Still another vaporization burner is disclosed in German Patent No. 32 33 319 and corresponding U.S. Pat. No. 4,538,985, in which a glow ignition device is formed by an essentially flat glow heating body, made of heatable filaments, disposed parallel to the vaporizing surface, immediately in front of the vaporizing body or in the vaporizing body.
In all variations of the vaporization burners described above, the glow device extends into the combustion chamber, thereby exposing it to the high temperatures prevailing therein, causing a reduction in the service life of such a device. Moreover, the fact that the glow device extends into the combustion chamber makes it an impedance to the flow conditions within the combustion chamber itself.
It is, therefore, a primary objective of the invention to create a vaporization burner for a heating device operated with liquid fuel which overcomes the disadvantages described above, and which provides an extended service life for the ignition device, as well as an improvement with respect to the flow conditions in the combustion chamber.
In accordance with the preferred embodiments of the invention, a vaporization burner for a heating device operated with liquid fuel, especially a motor vehicle heating device having a combustion pipe, a combustion chamber in which an absorbent body is disposed on a carrier, to which liquid fuel is supplied and at least part of the side of the carrier facing the combustion chamber is exposed, a combustion air supply device, and an ignition device for the combustion mixture, is provided wherein the ignition device is arranged behind the carrier, i.e., at the side thereof facing away from the combustion chamber. Furthermore, the carrier has at least one opening extending through it that is covered by the absorbent body, in addition to at least one through-opening in the exposed part of the carrier.
Accordingly, in the vaporization burner of the invention, the ignition device is disposed outside of the actual combustion chamber, i.e., behind the carrier for the absorbent body which receives liquid fuel. As a result, the ignition device does not impede the flow conditions in the combustion chamber, thereby resulting in a more favorable combustion process. Moreover, such an arrangement prevents the ignition device from being directly exposed to the high temperatures in the combustion chamber and/or directly to the flame, resulting in a considerably longer service life for the ignition device than has been previously possible. In other words, a vaporization burner is obtained which operates with the utmost reliability, even over a long period of time.
The presence of at least one opening in the part of the carrier that is covered by the absorbent body permits fuel vaporized by the absorbent body to pass directly into the area of the ignition device so that, in combination with the combustion air supplied, an ignitable mixture can be prepared directly in the area surrounding the ignition device. When this mixture is ignited by means of the ignition device, a pilot flame is generated which extends through the through-opening in the exposed part of the carrier. This pilot flame then ignites the fuel-air mixture on the front side of the carrier and the absorbent body (i.e., at the side facing the combustion chamber), thereby initiating the combustion process in the combustion chamber. As is customary, the ignition device is turned off once the combustion is proceeding on its own in the combustion chamber.
Preferably, the ignition device is arranged in a chamber defined by an ignition housing at the rear of the carrier and such housing has at least one combustion air supply inlet which terminates in the ignition chamber formed thereby. It is also preferable that this combustion air supply inlet be opposite the opening in the carrier that is covered by the absorbent body so that the combustion air supplied to the ignition chamber is locally concentrated around the ignition device to promote mixing, in the ignition chamber, of the air with the fuel vaporized by the absorbent body, for the purpose of quickly obtaining a mixing ratio favorable to the ignition process.
Preferably, one housing wall of the ignition chamber is formed by the rear side of the carrier, resulting in a minimum space arrangement for the ignition device with the associated chamber. Further, such a construction facilitates placement of the ignition device in the closest possible proximity to the carrier supporting the absorbent body so that it can be rapidly heated when the ignition device is turned on, thereby promoting fuel vaporization.
In accordance with another aspect of the invention, the ignition device is surrounded by the housing from its free end up to its mounting thread. In this manner, cooling of the ignition device by the combustion air and passing of air into the chamber around the ignition device is prevented.
For reasons of functional efficiency, it has proven beneficial to divide the housing into an outer housing part, representing a separate component and containing the screw thread portion of the ignition device, and an inner housing part which is located in the vicinity of the carrier. Such a design aids in overcoming difficulties caused by variations in manufacturing tolerances, and, more particularly, facilitates direct contact of the outer housing with the ignition device, whereby the ignition device is threadingly engaged with this outer housing part. The inner housing part, on the other hand, has an enlarged interior space to accommodate the premixing of the fuel vapor and combustion air for generating the pilot flame. In order to ensure that the combustion air enters the ignition chamber only via the one combustion air inlet, and to further ensure that no so-called "false air" reaches the chamber, the upper and lower housing parts are sealed at their junction.
For the purpose of reducing sealing difficulties, the vaporization burner and the ignition device, in accordance with another advantageous variation of the invention, are enclosed by a cup-shaped housing part which is connected with the combustion pipe in the chamber by a single flange connection. Also, to avoid sealing problems, the flange is disposed in the plane of a ring of air openings for the supply of combustion air to the combustion pipe.
Appropriately, the flange of the combustion pipe defines a slot-shaped opening for the combustion air, which air is directed to the vaporization burner at a distance from the absorbent body on the carrier, in a direction into the combustion chamber.
In an advantageous manner, the ignition device forms an integrated unit with the cup-shaped housing part, which unit, appropriately, also includes the carrier with the vaporization element so that, if required, all of the elements essential to the functioning of the vaporization burner can be quickly and simply exchanged as a combined unit by removal and replacement of the cup-shaped housing part.
In a further aspect of the invention, the ignition device of the vaporization burner is arranged approximately parallel to the carrier surface. To this end, the ignition device, preferably, is formed by an elongated glow plug.
In accordance with an alternative variation of the invention, the housing surrounding the ignition device can form an integrated unit with the ignition device, and this unit can be removable in a radial direction without disassembly of the heating device. Such an arrangement has an advantage with respect to ease of maintenance.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.