GB2432630A

GB2432630A - Near-adiabatic internal combustion rotary engine

Info

Publication number: GB2432630A
Application number: GB0523865A
Authority: GB
Inventors: Paul John Worley
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-11-23
Filing date: 2005-11-23
Publication date: 2007-05-30
Also published as: GB0523865D0

Abstract

A Wankel rotary engine has a rotor 30 and stator housing 11 comprising low thermal conductivity ceramic material to ensure that combustion heat is retained within the engine during expansion, thereby approaching adiabatic ideal expansion and increasing the work extracted from fuel. The rotor may be made entirely from ceramic, may be a composite with another material forming a gear and bearing race or the rotor may be clad with ceramic tiles 12. The housing may have ceramic tiles 13 covering the surface heated during combustion and may be grouted and plasma sprayed with a further ceramic material. The rotor does not have contacting tip seals and leakage is controlled by close tolerance. The tips may be roughened, ribbed or knurled to minimise leakage with tip radius of 0.5 times the engine eccentricity radius. The rotor sides may have grooves to form a labyrinth with housing scavenging channels.

Description

Near-Adiabatic Internal Combustion Engine This invention relates to a

design of internal combustion engine that minimises the heat transmitted through the engine casing and, thereby, retains more heat in the working fluid during the combustion and expansion phase of the working cycle.

Internal combustion engines often need to maintain an internal surface temperature below the maximum working temperature of lubricating oil in order to retain an oil film on sliding metal surfaces or below the maximum working temperature of the engine's metal surface components. This can mean that the engine casing is forcibly cooled by a liquid coolant or air stream with the effect gas temperatures and, consequently, gas pressures in the working fluid during the expansion part of the engine cycle are also reduced. This results in a considerable proportion of the energy contained in the fuel being discarded through the cooling system when it might otherwise be utilised as useful work.

To overcome the need to discard excessive energy through the engine casing during the engine's working cycle, the present invention proposes using engine components made from ceramic with a low thermal conductivity coupled with a seal-tess design of rotary engine that does not require sliding contact between engine components in the hot' region of the engine i.e. in the area of combustion and expansion.

The ceramic components inside the engine will retain a high proportion of the heat of combustion of the fuel within the working gas during the expansion part of the engine cycle and, thereby, increase the proportion of useful energy extracted from the fuel. The expansion cycle of this engine, therefore, approaches the adiabatic ideal expansion and will result in improved combustion efficiency, reduced fuel consumption, and higher power density.

This invention will now be described by referring to the following drawings: Figure 1 shows the radial cross section through an engine that uses a ceramic rotor housing and a ceramic rotor.

Figure 2 shows the axial cross section through an engine that uses a ceramic rotor housing and a ceramic rotor.

Figure 3 shows a view of the inner face of a side plate.

Figure 4 shows the radial cross section through an engine that uses a ceramic lined rotor housing and a ceramic lined rotor.

Figure 5 shows an isometric view of a rotor that has a roughened surface on its tip radii.

Figure 6 shows an isometric view of a rotor that has a knurled surface on its tip radii.

Figure 7 shows an isometric view of a rotor that has transverse ridges on the surfaces of its tip radii Figure 8 shows an isometric view of a rotor that has profiled tip radii.

Figure 9 shows a radial cross section through an engine that has a labyrinth seal on the side of the rotor and a scavenge channel in the rotor housing side plates.

The engine is a Wankel rotary internal combustion engine of either a single rotor or multiple rotor design. The engine differs significantly in two respects from a conventional Wankel engine: firstly, rotor tip seals also known as rotor apex seals are absent and, secondly, engine surfaces that are subjected to heat during the working fluids combustion or expansion are either made from or lined with a ceramic material that has a low co-efficient of thermal conductivity. The ceramic material allows the engine's internal surface temperatures to rise until they match those of the hot gases that they contain and, thereby, inhibit the transfer of heat from the hot gases to the engine casing.

Such internal surface temperatures may be too hot to support a film of lubricating oil. It is, therefore, essential that the engine operates without rotor tip seals that contact the rotor housing because they would otherwise require lubrication.

Figure 1 shows the radial cross section through an engine that uses a ceramic rotor housing 1 and a ceramic rotor 2. The rotor housing 1 is shown manufactured entirely from ceramic, but may also be reinforced with an external structure of some other material. Similarly, the rotor 2 is manufactured from ceramic either in its entirety, or as a composite component with the gear and/or bearing race or housing manufactured from some other material. In this example, figure 1 shows a ceramic rotor 2 bonded to a metallic bearing housing and rotor gear 3.

Figure 2 shows the axial cross section through an engine that uses a ceramic rotor housing 1 and a ceramic rotor 2. Heat which does permeate through the ceramic of the rotor is conducted away through the rotor bearings 4 and eccentric shaft 5. This heat may be subsequently lost from the ends of the eccentric shaft to the balance weights 6 whereon radial vanes 7 may assist in the cooling of these weights in a stream of air. The air used to cool the balance weights and forced across the surface of the weights by the action of radial vanes 7 may be further utilised as charge air for the engine and may be at a pressure above the local atmospheric pressure as a result of the action of the cooling vanes.

Heat which permeates through the rotor housing wall is lost to the engine's surroundings.

Figure 2 also shows the rotor housing side plates 8.

Figure 3 shows an arrangement of side plate construction which consists of a metallic inner surface 9 over the area subjected to contact with the rotor side seal and a ceramic outer surface 10 over the area which forms the chamber walls when the engine is rotating. This arrangement of side plate construction will retain the insulating characteristics of the ceramic in the chamber walls whilst providing a degree of thermal conduction and consequent cooling over the area covered by the side seal, and thereby permit lubrication of the side seal. Item 29 is the stator gear.

Figure 4 shows the radial cross section through an engine that uses a ceramic lined rotor housing 11 and a rotor 30 clad with a number of ceramic tiles 12. The rotor housing may be lined by any number of ceramic tiles 13 which cover at least the area of the rotor housing surface which is subjected to heating during combustion or expansion of the working fluid. Such tiles may be mechanically fixed to the housing, or bonded, or both.

The edges of the tiles may be sealed with a grout material 14. The exposed epitrochoidal surface of the tiles and rotor housing may be further seated by a thin coating of ceramic material 15 which may be plasma sprayed onto the surface.

To ameliorate the absence of rotor tip seals, certain design features may be incorporated into the engine in order to minimise the gas leakage past the rotor tips. These features may include; i) Control of the manufacturing tolerances associated with the profiles of the rotor and rotor housing, and the positioning of the rotor such as the indexing and backlash of the rotor/stator gearing and the stiffness of the eccentric shaft such that a minimal clearance between the rotor and rotor housing may be maintained.

ii) The introduction of tip radii to the rotor and consequential offset to the epitrochoid profile of the rotor housing in order to increase the physical length of the leak path between the rotor flanks. Such tip radii may be at least 0.5 times the engine's radius of eccentricity.

iii) A surface texture at the rotor tip radii 16 as shown in figures 5 to 8 such as a surface roughness or controlled dimpling 17, knurling 18, transverse grooves 19 or a rotor tip profile 20. Such rotor tip surface features are all designed to disrupt the flow past the rotor tip and thereby improve rotor seating performance under dynamic conditions.

Figure 9 shows details of the grooves 21 that may be included in the side of a rotor 12 in order to create a labyrinth seal array that inhibits the passage of gas from the rotor flanks 22 to the rotor side seal 23, or between rotor flanks 22. Scavenging of the rotor labyrinth grooves 21 may be effected via channels 24 included in the engine housing side plates 8. These channels connect the labyrinth grooves in the sides of the rotor with the low pressure volume within the rotor housing when the engine rotates.

Fuel is injected directly into the combustion area of the rotor housing and may be ignited by the latent heat present in the rotor or rotor housing surfaces, or by the heat in the charge air caused by its compression (diesel ignition), or by spark ignition, or by a glow plug.

Referring to figure 5, fuel may be injected into the combustion recess 25 of the rotor at a rate which is proportional to the flow rate of the charge air passing through the combustion recess. In this manner, a satisfactory initial air/fuel mix may be obtained for the fuel charge irrespective of the size of the fuel charge.

Claims

Claims 1 A Wankel rotary engine able to operate with elevated internal

surface temperatures in the areas of combustion and expansion by virtue of the absence of rotor tip seals and the presence of ceramic heat barriers between the rotor flanks and rotor bearing, and around the epitrochoidal surface of the rotor housing in the areas of combustion and expansion within the engine.

2 A Wankel rotary engine according to claim 1, in which the ceramic used in rotors and rotor housings as heat barriers has a low thermal conductivity such as may be found with various forms of zirconia.

3 A Wankel rotary engine according to claim 1, in which the rotors are characterized by having no rotor tip seals, but create and maintain compression within the engine by virtue of their rotational motion together with a minimal clearance between the rotor peripheral surface and the epitrochoidal internal surface of the rotor housing.

4 A Wankel rotary engine according to claim 1, in which the heat barrier between the rotor flanks and the rotor bearing is effected by manufacturing the rotor entirely out of ceramic, or manufacturing the rotor outer profile out of ceramic and the bearing race or bearing housing or rotor gear out of an alternative material, or by cladding a rotor with ceramic tiles on the rotor flanks or rotor flanks and rotor tips A Wankel rotary engine according to claim 1, in which the heat barrier between the rotor housing epitrochoid wall in the area of combustion and expansion and the exterior surface of the engine casing is effected by manufacturing the rotor housing using monolithic ceramic, or by tiling the relevant internal surface of the rotor housing with ceramic tiles.

6 A Wankel rotary engine according to claim 1, in which the peripheral surface of the rotor and/or the epitrochoidal surface of the rotor housing, when these surfaces are clad or part clad with ceramic tiles, are sealed by a thin coating of ceramic material such as may be applied using a plasma coating process.

7 A Wankel rotary engine according to claim 1 in which the rotor tips have a radius of at least 0.5 times the engines eccentricity.

8 A Wankel rotary engine according to claim 1, in which the rotor tip radii have been textured using a surface roughness, or controlled dimpling, or knurling, or transverse grooves in such a manner as to discourage gas flow past the tips.

9 A Wankel rotary engine according to claim 1, in which the rotor tip radii have been profiled in such a manner as to discourage gas flow past the tips.

A Warikel rotary engine according to claim 1, in which the side plates are manufactured entirely from ceramic or clad or part clad in ceramic to inhibit heat flow through the sides of the rotor housing.

11 A Wankel rotary engine according to claim 1, in which rotor side seals are augmented by an array of labyrinth grooves in the sides of the rotor arranged to create a labyrinth seal between the rotor flanks and the rotor side seals and/or between adjacent rotor flanks.

12 A Wankel rotary engine according to claim 1, in which rotor labyrinth grooves in the sides of the rotor are scavenged via channels in the side plates that connect the labyrinth grooves to the low pressure section of the rotor housing.

13 A Wankel rotary engine according to claim 1, in which the ignition of the fuel charge may be initiated by the heat retained in the rotor or rotor housing wall once the engine has reached operating temperature.

14 A Wankel rotary engine according to claim 1, in which air flowing over radial vanes affixed to the eccentric shaft may be contained within the engine's outer casing and used as charge air for the engine.

A Wankel rotary engine according to claim 1, in which the rate of injection of fuel into the combustion recess of the engine's rotor is proportional to the flow rate of the charge air passing through the combustion recess.