IMPROVEMENTS IN ENGINES INCLUDING GAS EXPANSION ACTUATED PISTON AND CYLINDER DEVICES

Abstract: A "Brayton" type engine has its operating efficiency improved, by obviating cooling apparatus, lining the expansion chamber and piston head with insulating material (56-47) and positioning the piston/cylinder gas seal (46) at that end remote from the gas inlet. The piston is maintained concentric with the cylinder, by, in one mode, supporting it from fixed structure (38) externally of the cylinder. Any lubrication is applied to parts which are in areas which are cool relative to known devices.

Description: IMPROVEMENTS IN ENGINES INCLUDING GAS EXPANSION ACTUATED PISTON AND CYLINDER DEVICES The present invention relates to an engine including a device comprising a piston within a cylinder, which piston is caused to move axially within the cylinder by the expansion of hot pressurised gases against an end face thereof. The resulting movement enables work to be done by the piston. The present invention has particular efficacy in that system known as the "Brayton Cycle" engine, wherein air is compressed in one piston and cylinder combination, passed to an external combustor source where it is mixed with fuel and burned and the resulting hot gases passed to a further piston and cylinder combination and expanded against the further piston to achieve the desired result. A drawback common to such engine cycles as those described hereinbefore lies in their need for cooling and lubrication. Such needs generate complex structures including cooling medium channels and supplies and lubrication conduits and supplies in the region of maximum heat, and means for pumping those fluids in a recirculatory manner. A more serious drawback is generated however, by the satisfying of the needs as described above, in that cooling of the cylinder walls removes heat from the gases from within the cylinder, which heat should have been usefully employed by providing the gases with more energy. The present invention seeks to provide an improved engine which includes a gas expansion actuated piston and cylinder device. According to the present invention an engine including a gas expansion actuated piston and cylinder device comprises a cylinder having hot pressurised gas inlet means at one end, exhaust porting spaced from said one end, a piston which for operation rests coaxially within said cylinder in radially spaced relationship therewith, an annular seal fixed to the cylinder downstream of the exhaust porting and engaging the piston in gas sealing, sliding relationship, and means engaging the piston skirt for maintaining the piston and cylinder in said coaxial, radially spaced relationship. The invention will now be described, by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic example of a "Brayton Cycle" engine incorporating an embodiment of the present invention. Figure 2 is a view in the direction of arrow 2 in Figure 1. Figure 3 is an enlarged, cross-sectional part view of the engine of Figure 1. Figure 4 is a cross-sectional part view of an alternative embodiment of the present invention. Figure 5 is a cross-sectional part view of a further embodiment of the present invention. Figure 6 is a diagrammatic example of a "Brayton Cycle" engine incorporating a further embodiment of the present invention. Figures 7 and 8 are enlarged, cross-sectional views of optional constructional features of the valve stem and expansion cylinder respectively. Referring to Figure 1. A "Brayton Cycle" engine 10 has a compressor 12 in the form of a piston 14 sliding within a cylinder 16. Reciprocatory motion of the piston 14 is brought about by, for example, a flywheel and crosshead slide arrangement (not shown) connected to a piston rod 18, and a compression spring 20 positioned between the pressure surface of the piston 14 and the end wall of the cylinder 16. Air compressed in the cylinder 16 is passed to an external combustor device 22, mixed therein with fuel from a supply 24, and burned. The gaseous products of combustion are passed to a further cylinder 26 which contains a further piston 28 in radially spaced relationship, wherein the gases expand and in so doing, push the piston 28 to the right as viewed in the drawing. The piston 28 in the present example, is connected via rod 32, to a linear generator 34, whilst the expanded gases are exhausted via a port 36. If it is so desired, the exhausted gases can be passed to a heat exchanger (not shown). The piston 28, as shown, would need the provision of a compression spring or other return means, to effect each return stroke. However, it could be directly connected to the piston 14 for self perpetuating reciprocation, assisted by the flywheel (not shown), after initiation by the linear generator 34 acting in reverse as a starter motor. These features are known, and do not form part of the present invention. In a first embodiment of the present invention, both cylinders 16 and 26 are fixed to three rods 38, which are spaced by spiders 40 and 42. The spider 40 is suitably earthed. The expansion piston 28 is affixed to the spider 42 which in turn, is slidably mounted on the three rods 38. Referring now to Figure 3. The cylinder 26 has external annular grooves 44 formed in its walls, so as to provide thin portions 46, which act to reduce the conduction of heat along the cylinder. Further heat containment is achieved by surrounding the cylinder 26 with a blanket of suitable heat insulation material 47. An annular seal 46 is provided, also at that end of the cylinder remote from its gas inlet end. Thus, although the seal 46 is exposed to the expanding gases by virtue of the radial gap between the piston 28 and the cylinder 26, its exposure is minimised because the exhaust port 36 is positioned between the inlet 52 and the seal 46, and an axial temperature gradient is established in the cylinder wall. The piston 28 supports the stem 49 of a valve 50, the head of which opens and closes a gas inlet port 52 at the upstream end of the cylinder 26. Movement of the valve coaxially of the piston 26 is brought about by a cam (not shown) which is connected for rotation by or with the flywheel (not shown) so as to act on the end of the stem 49 remote from the head 52, in known manner. The exhaust valve 37 is operated in a similar manner thereto. A seal 54 similar to seal 46, is affixed to the stem support structure and engages the stem 49 in sliding relationshi . The upstream face of the piston 28 is covered in a layer of refractory material 56, so as to reduce heat transfer along the piston 28 to the seal 46, to a minimum. Referring now to Figure 4. In this embodiment, the valve stem 49 is provided with a heat insulating portion 60 within its length, which serves to reduce heat conduction from the expansion chamber. The embodiment depicted in Figure 5 has a lengthened cylinder 26 and piston 28, so as to enable the fitting of a standard type of piston ring seal 62 to the bore of the cylinder 26, in a cool area adjacent the end extremity of the piston 28. Referring to Figure 6. In this arrangement, wherein parts corresponding to those shown in Figure 1 have like numbers, the spiders 40 and 42 are fixed to the rods 38, which are slidable in the fixed bushes. The compression piston 14 is fixed to the spider 40, so that it is mechanically connected to the expansion piston 28 for simultaneous reciprocation. The need for return springs is thus obviated. Referring now to Figure 7. By way of example, the stem 49 of the valve 50 is constructed from two parts 49a and 49b, which are spaced by heat insulating material 60. The whole is bolted together. Similarly, in Figure 8, the cylinder 26 is depicted as comprising two parts 26a and 26b, spaced by heat insulating material 70, the whole being clamped by an annular 'U' clamp 72 of known kind. The invention described herein relates to a single expansion cylinder 28. In practice however, a number of such, cylinders arranged for phased operation would be utilised, which would result in force and energy balancing, and provide a more uniform flow of gas through the combustor 22. Further a "Brayton Cycle" engine, when constructed in accordance with the present invention, operates more efficiently then hiterto and thus takes advantage of the inherently cleaner exhaust emissions that are possible with continuous combustion, relative to intermittent spark ignition or compression ignition engines. The invention also provides advantages over and above known cooled systems. Thus, the radial clearance between the piston and cylinder is of sufficient magnitude as to not create problems when the cylinder distorts through rise in temperature. The seal 46 is not affected by the heat, firstly because it is positioned at the relatively cold end of the cylinder, downstream of the exhaust port and secondly, the bulk of the hot gas exits the cylinder without reaching the seal. Further, the lack of a cooling system simplifies the construction and reduces its cost, and any lubrication which may prove to be necessary, would be applied in relatively cold areas. Finally, the provision of thermal barriers and layers of insulation reduces heat losses through conduction, and thus improves operating efficiency.

Claims: Claims:- 1. An engine including gas expansion means comprising a cylinder having hot gas inlet means at one end, exhaust porting spaced from said one end, a piston (28) which for operation rests coaxially within .said cylinder in radially spaced relationship therewith, characterised by an annular seal (46) fixed to the cylinder (26) downstream of the exhaust porting (36) and engaging the piston (28) in gas sealing, sliding relationship, and means engaging the piston skirt for maintaining the piston (28) and cylinder (26) in said coaxial, radially spaced relationship. 2. An engine as claimed in claim 1 wherein the means for maintaining the piston and cylinder in their coaxial relationship is characterised by earthed guide means (38) positioned externally of the cylinder (26) and to which the cylinder (26) is fixed, said guide means (38) being in parallel with the cylinder axis, and piston connection means (42) fixed to the skirt of the piston (28) which projects from the cylinder (26), said piston connection means (42) being engaged with said guide means (38). 3. An engine as claimed in claim 2 characterised in that the guide means (38) comprises a plurality of rods supported in egui-angularly spaced relationship about the exterior of the cylinder (26) by spiders (42). 4. An engine as claimed in claim 3 wherein said piston connection means comprises one of said spiders (42). 5. An engine as claimed in claim 1 characterised in that the means for maintaining the piston (28) and cylinder (26) in their coaxial relationship comprises portions of the cylinder and skirt which are extended beyond said annular seal ( 6), and a piston ring seal (62) is provided and retained in the wall of the bore of the cylinder (26) adjacent its end extremity and in sliding engagement with the extended skirt portion of the piston (28). 6.* An engine as claimed in any previous claim characterised in that the cylinder (26) has a plurality of axially spaced annular grooves (44) in its external surface, so as to form thin wall portions which reduce heat transfer in a direction towards the annular seal (46) . 7. An engine as claimed in claim 6 characterised in that the pressure surface (56) of the piston (28) comprises a refractory layer. 8. An engine as claimed in any of claims 1 to 7 characterised in that the piston (28) has the stem of an inlet valve (50) coaxially passing through it and said inlet valve stem (50) comprises metal portions spaced by a heat insulating spacer (60) . 9. An engine as claimed in any previous claim and characterised by a heat insulating cover (47) surrounding the cylinder (26).

Inventors: HUFTON PETER FREDERICK, HUFTON, PETER, FREDERICK
Applicants: NORTHERN ENG IND, NORTHERN ENGINEERING INDUSTRIES PLC
Application year: 1992
Main classification: F02G1
IPC codes: F02G1, F02G3