Evaporative burner

Details Evaporative burner Evaporative burner

2002-06-21

2004-04-27

Boles, Derek (Department: 1714)

Heating systems

Automatic control

Heat source is a reverse cycle refrigerating system or heat...

C126S390100, C431S168000

Reexamination Certificate

active

06726114

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to an evaporative burner, for example, such as used for heating devices in motor vehicles.
TECHNICAL FIELD
Patent document WO 98/49494 discloses an evaporative burner, in which a porous evaporative medium, for example nonwoven material, is arranged in the floor region of a combustion chamber. Liquid fuel is conducted into this porous evaporative medium to be distributed in the evaporative medium by capillary action. The fuel evaporates on the side toward the combustion chamber, so that an ignitable or combustible mixture is formed on the side toward the combustion chamber by the accumulation of fuel vapor and combustion air in the region of the combustion chamber. A heating device is furthermore provided that includes a glow ignition pin projecting into the region of the combustion chamber. By heating the glow ignition pin, a high temperature is produced in its surroundings, such that the ignitable mixture in this region ignites and thereupon propagates into the region of the combustion chamber.
An evaporative burner is also known from German patent document DE 32 33 319 A1 in which a porous material is again provided in the floor region of a combustion chamber for the distribution and evaporation of fuel. A heating device constituted in the manner of a heating coil is provided on the side of the porous medium lying open toward the combustion chamber, and when current is applied can produce in the region of the porous medium the temperatures of about 1,100° C. required for combustion.
Such evaporative burners known from the prior art have the disadvantage that they require a comparatively long time to reach a high heating power, and the time is distinctly longer than that required, for example, by pressure pulverizers, air atomizer burners, or ultrasonic atomizer burners. A substantial reason for this is that energy for the evaporation of further fuel is also withdrawn from the flame arising from ignition, and prevents rapid flame propagation into the combustion chamber, particularly at low external temperatures and with large component masses with comparatively good thermal conduction. This disadvantage of evaporative burners that are basically of interest due to their cost-effective construction is of little effect when they are used as auxiliary (stationary) heaters, for example. Here, the spontaneous production of comparatively high temperatures is not a matter of prime importance. However, it is another matter when such a burner is used as a supplementary heater, which is effective particularly for the cold start of an engine at low environmental temperatures. In this case, it is required that a very high heating power of the supplementary heater can be provided in a very short time, in order above all to reduce the pollutant emission in the starting phase of a drive assembly heated in this manner.
SUMMARY OF THE INVENTION
The present invention has as its object to provide an evaporative burner in which the operating phase of high heating power can be attained more rapidly.
According to the present invention, in order to attain this object an evaporative burner is provided, having an evaporative medium for feeding fuel vapor into a combustion chamber, a first heating device having at least one ignition heating element projecting at least with its heating region into the combustion chamber, for igniting the fuel vapor present in the combustion chamber, and also a second heating device, comprising at least one evaporative heating element associated with the evaporative medium in order to affect on its evaporation characteristics.
The present invention eliminates the prior art disadvantage by providing respective separate heating devices, one for ignition and the other for evaporating the fuel supplied in liquid form. These can be respectively optimally matched to what is required as regards the temperatures that they produce and the heating power required therefor. The rate of evaporation is increased by preheating the fuel to be evaporated, the withdrawal of heat energy from the propagating flame nevertheless being prevented. Flame propagation in the starting phase of such an evaporative burner clearly takes place more quickly, so that full load operation is finally also clearly attained more rapidly than with the evaporative burners known from the prior art.
In order to not expose the evaporative heating element, used solely to preheat the fuel to be evaporated, to the comparatively high temperatures prevailing in the combustion chamber, the at least one evaporative heating element is arranged on a side of the evaporative medium remote from the combustion chamber. This can be achieved, for example, by providing the evaporative medium on an evaporative medium support, and by arranging at least one evaporative heating element between the evaporative medium and the evaporative medium support. A still further protection of the evaporative heating element from excessively high temperatures can be achieved in that the evaporative medium is provided on a evaporative medium support and that the at least one evaporative heating element is provided on a side of the evaporative medium support remote from the evaporative medium.
In the evaporative burner according to the invention, there is furthermore provided a fuel feed channel arrangement for introducing the liquid fuel into the evaporative medium. In order to achieve an approximately uniform combustion characteristic over the whole combustion chamber, the fuel feed channel arrangement is constructed so as to distribute the liquid fuel over the evaporative medium. This can be attained, for example, in that the fuel feed channel arrangement has at least one annular channel region and/or at least one radial channel region going out from a fuel feed duct substantially radially in the evaporative medium and/or in an evaporative medium support.
The evaporative burner according to the invention has, for providing the ignitable mixture in the combustion chamber, an air supply channel arrangement for supplying air to the combustion chamber for combustion with the fuel vapor. For this purpose it can for example be provided that the air supply channel arrangement has at least one air inlet opening in the wall bounding the combustion chamber and open toward the combustion chamber.
In order to also deliver the combustion air required for ignition, simultaneously with the fuel vapor coming from the evaporative medium, into that spatial region in which the ignition occurs, the air supply channel arrangement has at least one air inlet opening which is open to the evaporative medium. For this purpose it can further be provided that the air inlet opening has at least one air supply channel region passing through the evaporative medium.
Since the heat removal occurring in the region of an evaporative burner is an important parameter affecting rapid flame propagation, according to a further aspect of the invention a better thermal insulation, and thus a further acceleration of flame propagation, can be provided for in that the at least one evaporative heating element and the evaporative medium are provided on an evaporative medium support made of ceramic material.
The evaporative medium can comprise porous material that can be of multilayer construction in order to achieve as rapid as possible a dispersion of the liquid fuel in the evaporative medium itself and then for the evaporation of the distributed liquid fuel. A nonwoven material can be used here, for example.
A general problem that arises in the operation of evaporative burners is in the first place the required high variability of the burner power. For example, a ratio of maximum to minimum burner power of at least 4:1 is required. In the second place, evaporative burners of this kind are to be operated with many different fuels, or with fuels of different quality. For example, besides being able t

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