Hot-gas Engine

Abstract

A hot-gas engine having a heater which is composed of pipes and which supports an assembly of a burner device, and a fuel atomizing device which is displaceable axially with respect to the enveloping housing corresponding to thermal expansion of the heater pipes.

Description

BACKGROUND OF THE INVENTION

The invention relates to a hot-gas engine provided with a heater which comprises at least one row of pipes arranged in the form of a cylinder about a space for combustion gases and which extend mainly parallel to the cylinder axis. The heater has a free end supporting a burner device provided with a chamber for air and fuel. This chamber is bounded on its side which is remote from the heater by a fuel atomizing device comprising an atomizer which debouches into said chamber, the fuel atomizing device being passed to the outside through a wall of a housing enveloping the heater and the burner device.

Hot-gas engines of the relevant prior art are known as appears from FIG. 1 of British Patent Specification No. 892,962 and from FIG. 13 of the article "Der Philips Stirlingmotor" (MTZ-Motortechnische Zeitschrift 29, No. 7, July 1968); however these known hot-gas engines have some drawbacks.

During operation of the engine, the heater pipes reach a high operating temperature of 700.degree. C or higher. Consequently, the heater pipes exhibit a substantial thermal expansion, with the result that the pipe length is substantially increased. The length increase of the heater pipes, i.e., in the axial direction of the cylinder formed by the pipes is much greater than that of the housing enveloping the heater and that of the pre-heater which is usually arranged around the heater inside the housing. In the preheater combustion air is pre-heated by the combustion gases discharged from the engine, these combustion gases having previously transferred most of their heat to the heater pipes.

It is obvious that this difference in expansion is mainly caused by the fact that the mean temperatures reached by the housing and the pre-heater are substantially lower than that of the heater. The large difference in expansion between the heater and the enveloping housing or the pre-heater, respectively, is the cause of a variety of problems.

In the hot-has engine known from British Patent Specification No. 892,962, in which the burner device which bears on the heater is mounted inside the enveloping housing so as to be rigid with respect to this housing, the difference in expansion gives rise to deformation of the heater pipes and of the walls of the burner device. Consequently, leakage of the heater pipes is likely to occur, so that the working medium present in the working space of the engine escapes and the engine becomes inoperative. Due to the deformation of the walls of this burner device, the orientation of the burners is altered and the flames are liable to be directed onto the heater pipes, which is undesirable. Moreover, the adjustment of the burner and hence the fuel dosing is liable to be changed.

In the hot-gas engine known from "MTZ-Motortechnische Zeitschrift" the burner device which bears on the heater can follow the expansion of the heater. However, a problem is that, when the burner device moves upwards, the atomizer of the fuel atomizing device which is rigidly connected to the housing will be situated deeper into the chamber where the combustion of the air fuel mixture takes place. The atomizer nozzle is then exposed to undesirably high temperatures, which results in deformation and a reduced service life of the atomizer.

A further drawback of the known hot-gas engines is that the mounting and removal of the burner device and the atomizer device can be effected only after removal of the pre-heater. This makes mounting and disassembly time-consuming, and hence expensive.

The invention has for its object to provide a hot-gas engine of the kind set forth in which the said drawbacks are simply eliminated.

SUMMARY OF THE NEW INVENTION

The hot-gas engine according to the invention is characterized in that the fuel atomizing device forms one rigid assembly with the burner device, the assembly being displaceable with respect to the housing in the axial direction of the heater and being capable of following length variations of the heater which are caused by temperature variations, at least one flexible seal being provided between the housing and the assembly.

In the case of expansion or shrinking of the heater pipes, the assembly of the burner device and the fuel atomizer device bearing thereon will move freely along with the heater with respect to the enveloping housing and the pre-heater which have a smaller absolute thermal expansion. Consequently, no material stresses occur between the heater with the assembly of the burner device and the fuel atomizing device on the one side, and the housing, with or without pre-heater, on the other side. The atomizer always remains in the same position with respect to the burner device.

The assembly of the burner device and the fuel atomizing device can be readily slid into and out of the housing, without removal of the pre-heater being necessary.

Owing to its properties, the flexible seal can readily follow the relative movement of the assembly and the housing, the sealing action also ensuring that the overpressure under which the combustion air is applied to the engine is not lost. As a result of the overpressure, the combustion gases can overcome the flow resistance encountered on their way to the outlets. The combustion gases will thus flow to the atmosphere without further aids being required.

The invention will now be described in detail with reference to the drawing .

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 and 2 are partial elevation views in section which show diagrammatically and not to scale, two embodiments of the heating system of a hot-gas engine.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The reference 1 in FIG. 1 denotes a cylinder in which a piston 2 and a displacer 3 can move at a phase difference with respect to each other. The piston 2 and the displacer 3 are connected, by means of piston rod 4 and a displacer rod 5, respectively, to a drive system not shown. Present between the piston 2 and the displacer 3 is a compression space 6 which communicates, via a cooler 7, a regenerator 8 and a heater 9, with an expansion space 10 above the displacer. The heater 9 is formed by a row of pipes which are arranged in a circle about a space 11 for combustion gases.

The heater 9 consists of a number of first pipes 12 which open into the regenerator 8 on the one side, and into a ring duct 13 on the other side, and a number of second pipes 14 which are alternately arranged between the first pipes 12 and which connect the ring duct 13 to the expansion space 10. Only two sets of first and second pipes are shown for the sake of clarity.

Via a centrally apertured plate 16 which bears on ring duct 13, the heater 9 supports a burner device 17 having a combustion chamber 18 which is bounded on its upper side by a fuel atomizing device 19. The fuel atomizing device 19 comprises an atomizer 20 which opens into combustion chamber 18. A fuel inlet 21 and an inlet 22 for atomizing air open into atomizer 20. Combustion chamber 18 is provided with inlet openings 23 for air. Burner device 17 and fuel atomizing device 19 together form one rigid assembly 24.

The hot-gas engine is furthermore provided with a housing 25 which envelops the heater 9 and also the greater part of the assembly 24. Housing 25 comprises an inlet 26 for combustion air and an an outlet 27 for combustion gases.

Situated inside the housing 25 is a heat-exchanger 28, the pre-heater, which is arranged about the heater 9, and in which combustion gases can transfer heat, on their way to outlet 27, to combustion air which enters via inlet 26.

From inlet 26 the combustion air first flows upwards via an annular duct 29, subsequently downwards through ducts 30, and then upwards again via an annular duct 31, after which the combustion air enters the burner device 17 via openings 23.

In the ducts 30 the combustion air takes up heat from combustion gases as a result of a heat-exchange in counter flow with these combustion gases which rise in exhaust ducts 32. The combustion gases, formed in combustion chamber 18, reach the inlet 33 of the exhaust ducts 32 via space 11 and after having passed the heater pipes 12 and 14 while transferring heat thereto. The exhaust ducts 32 open on their upper side into a common annular collecting chamber 34 which communicates with outlet 27.

Assembly 24 can be moved to and fro in the vertical direction with respect to housing 25. Bellows 35 are provided as a flexible seal between housing 25 and assembly 24, the bellows being connected to the housing at the area 36 and to the assembly 24 at the area 37.

In this case the bellows 35 are situated within housing 25. When the engine is started and the heater pipes 12 and 14 reach a high temperature, the length of the pipes increases considerably due to the thermal expansion. The thermal expansion of housing 25 and preheater 28 is much less due to the lower temperature level. Consequently, in the vertical direction a relative upward displacement takes place of the heater 9 with respect to housing 25 and pre-heater 28. Assembly 24 is then forced upwards by heater 9. As this assembly can move freely with respect to the housing 25, the entire heating system remains free of material stresses which might give rise to a variety of material deformations and leakage of the heater pipes. Because the fuel atomizing device 19 moves together with burner device 17, the position of atomizer 20 is not changed with respect to combustion chamber 18. Consequently, overheating of the atomizer is not liable to occur, and the atomizer need not be prematurely replaced.

Assembly 24 can be readily lifted from plate 16 and be removed from housing 25 after detachment of bellows 35 at the area 36, without previous removal of pre-heater 28. The mounting of assembly 24 is, of course, also very simple.

Bellows 35 not only follow the relative movement of assembly 24 and housing 25, but also ensure that the combustion air which is supplied via annular duct 31 cannot escape to the surroundings.

FIG. 2 shows only the upper part of a hot-gas engine. Parts which correspond to the engine shown in FIG. 1 are denoted by the same reference numerals but with a suffix "a". Annular duct 31a is now separated from pre-heater 28a by a jacket 40a of a thermally insulating material. In this case bellows 35a are not situated inside but outside the housing 25a. The remainder of the operation is as described for the hot-gas engine according to FIG. 1, so the description need not be replaced. Even though bellows are shown as flexible seals in the FIGS. 1 and 2, other seals are feasible such as, for example, diaphragm seals.

Claims

What is claimed is:

1. In a hot-gas engine including an upper part defining therein an expansion space, a heater having a plurality of pipes disposed generally in parallel and in the form of a cylinder about a space for combustion gases, the heater having a near end secured to said upper part and a remote free end, the engine further including a burner device including therein a chamber for air and fuel, a housing wall enveloping said heater, burner and upper part of the engine, the chamber having a near side communicating with said space for combustion gases and a remote side, a fuel atomizing device on said remote side and extending through said wall, the improvement in combination therewith wherein said fuel atomizing device and burner device form a single rigid assembly engaged to said remote ends of said heater pipes, the assembly being displaceable relative to said housing axially of said heater and movable a distance corresponding to axial expansion of said pipes when heated, said engine further comprising a flexible seal interconnecting said housing and said movable assembly.

2. Apparatus according to claim 1 wherein said seal is a metal bellows having one end secured to said housing wall and the other end secured to said fuel atomizing device.