WO2013189470A1

WO2013189470A1 - Combustion engine

Info

Publication number: WO2013189470A1
Application number: PCT/CZ2013/000074
Authority: WO
Inventors: Zdenek Janda
Original assignee: FESA s.r.o.
Priority date: 2012-06-20
Filing date: 2013-06-10
Publication date: 2013-12-27
Also published as: CZ2012415A3

Abstract

A combustion engine contains a mechanical rotor (4, 7) comprising at least one working tube (6) that is branched or unbranched, for supplying fuel into the mechanical rotor (4, 7), passing fuel through the working tube (6) and exhausting combustion products from the mechanical rotor (4, 7). The working tube (6) is spatially arranged in the mechanical rotor (4, 7) in such a way that each of its branches comprises a compressor section for compression of fuel until its ignition by the effect of the centrifugal force acting upon the fuel during rotation of the mechanical rotor (4, 7) around the rotation axis, an adjacent combustion section for burning of fuel and an expansion section, adjacent to combustion section, for expansion of fuel combustion products to reduce their pressure and temperature, where the mechanical work obtained by the expansion drives the mechanical rotor (4, 7).The combustion section is more distant from the rotation axis than the compressor section and the expansion section and each branch of the working tube (6) is, in the direction from the entrance of the working tube (6) to the mechanical rotor (4, 7), in its compression section routed in the mechanical rotor (4, 7) in such a way that besides getting farther away from the rotation axis it is also angled in or against the rotation direction of the mechanical rotor (4, 7) so that in the axial direction the part of the housing of the mechanical rotor (4, 7) that covers the combustion section can be as narrow as possible while the expansion section then returns to the rotation axis as well as to the direction of this axis.

Description

Combustion engine Field of the Invention

The invention deals with a combustion engine and especially such a combustion engine that is, based on the way of utilization of its work, called a gas or combustion turbine, respectively.

State of the Art

Combustion turbines with high outputs, i.e. on the order of hundreds of kilowatts to hundreds of megawatts have been successfully used for several decades to drive means of transport and to generate electricity. They are one of the types of combustion engines, i.e. heat machines where the chemical energy of fuel is converted to heat by its burning and the produced heat is further transformed to mechanical energy by the action exerted on rotating parts of the engine. Their main disadvantage is their high complexity, demands for precise production and expensive materials resulting in their high price.

Smaller versions of combustion turbines are commercially available as small combined electricity and heat production units. Their outputs amount to tens to hundreds of kilowatts, their total dimensions being in the range of a few metres. As these are much smaller parameters than usual in the power industry, they are commonly commercially referred to as micro-turbines . In some cases - also relevant for this invention - the "micro-" prefix is used to identify very small parts that are used in micro-fluidics and in the MEMS ("Micro-Electro- Mechanical Systems") technology, where the dimensions of the smallest parts as e.g. the width of channels distributing the fluid are on the order of micrometres. In this context the term "micro-turbine" is used for a miniature combustion turbine with the total dimensions on the order of centimetres and the smallest details in micrometres or hundreds of micrometres (Chou et al . , Development of micro power generators - A review. Applied Energy 88 (2011) 1-16) . Some variants of these micro-turbines are patented as e.g. the U.S. patent 7,521,815 and U.S. patent 5,932,940.

In the last two decades the demand for portable devices providing electricity for outputs on the order of tens of watts to tens of kilowatts has been steadily rising due to the development of the electronic industry.

Although the performance of electric accumulators is getting better from year to year thanks to the technological progress, their characteristics cannot provide, at present, or in the near future) the desired combination of power density and endurance that are necessary for such applications as e.g. autonomous robots, pilotless aircrafts, electromechanical devices supporting physical capabilities of humans, etc.

Chemical fuels have up to a hundred times higher power density than accumulators, which makes them very suitable to generate electricity in portable devices. However, they require existence of efficient miniature engines - generators that make it possible to convert the chemical energy of fuel to electricity.

Such devices may be based on many principles; they are especially fuel cells, piston combustion engines, steam turbines and combustion turbines.

It is true that fuel cells have high efficiency, but in the proportion to the provided output they have large dimensions and weight, which does not make them suitable for portable systems. Low-output piston combustion engines . have very low efficiency and short service life. Their heat losses are high and the pistons and piston rings of miniature engines get worn due to friction much more quickly than those of large piston engines .

Thus, a combustion engine designed for low outputs should have as small friction areas as possible, which is only fulfilled by engines with continuous combustion, i.e. combustion turbines and steam turbines.

A steam turbine is very complex equipment that is difficult to produce in small dimensions and therefore the combustion turbine appears to be the most promising type of small combustion engines, especially for use in small electricity generators.

Specialized literature describes two different types of developed miniature combustion turbines (Chou et al., 2011). One of them are combustion turbines that have purely radial, two-dimensional rotors of the compressor and turbine. Such combustion turbines are designed for outputs on the order of single watts to tens of watts and for their production silicon technology is used that is similar to the production of computer chips. The main disadvantage of this type of combustion turbines is very low (a few percent) efficiency due to high heat losses caused by the two-dimensional structure of all parts of the engine (and thus a relatively large area where heat losses occur) and the necessity to use silicon as a material, which is not ideal from the heat conductivity point of view.

The other type of developed miniature combustion turbines are such turbines that have fully three-dimensional rotors of the compressor and turbine (similarly to high-output combustion turbines) and that are designed for outputs on the order of tens of watts to tens of kilowatts. The rotors of these combustion turbines are produced by casting and machining, which gives them the advantage of the possibility to use materials with high strength at high temperatures and low heat conductivity as e.g. special alloys and ceramic materials, which means that the efficiency of these three- dimensional types of combustion turbines is much higher than that of the above mentioned type of two-dimensional combustion turbines. Designers of miniature combustion engines had problems with extremely high speeds of the compressor and turbine rotors amounting to several hundreds of thousands up to one million revolutions per minute for many years, but they gradually manage to solve these problems by the development of new bearing types.

A continuing common disadvantage of the existing types of miniature combustion turbines is a high relative distance between the compressor and turbine rotor blades and the surrounding wall. While in large combustion turbines with the outputs of hundreds of kilowatts and more the gap between the rotor blades and the adjacent wall is up to one percent of the rotor blade height, in miniature combustion turbines this distance amounts to 5-10% of the rotor blade height for technological reasons, which significantly reduces the aerodynamic efficiency of the compressor and turbine and consequently the entire combustion turbine.

Another continuing disadvantage of the above mentioned miniature combustion turbines is that their bladed rotors have, due to the relatively large area of the rotor disk and its blades (in relation to the volume flow), intensive heat exchange with the adjacent wall, several times higher when expressed in percent, than at large combustion turbines, which also reduces the efficiency of the compressor and turbine and thus the entire combustion turbine.

The compressor and turbine of all the used types of combustion turbines require blades for the transformation of energy (to increase pressure or obtain mechanical work) .

A well-known bladeless turbine is a patent of N. Tesla dating back to 1913 (US patent 1,061, 206) . It is a turbine that transforms the energy of the flowing fluid to the rotor energy by means of friction between the fluid and rotor disks, which means that it does not use a rotating channel for the fluid flow unlike this invention. However, this turbine is not used in combustion turbines due to much lower efficiency as compared to standard bladed turbines. Also, a bladeless turbine of the Czech inventor Senk (AO 262 707, 1990), converts the energy of a fluid stream to mechanical work by means of friction force and therefore it features substantially lower efficiency as compared to bladed turbines and it is not suitable for use in combustion turbines.

An interesting concept of a bladeless turbine is described in the German patent document DE3306971A1 (1984), which uses a rotating U-shaped tube for the combustion turbine function. The operation principle of this bladeless combustion turbine is that the mechanical rotor contains at least one U-shaped working tube while each working tube is spatially arranged in the mechanical rotor in such a way that it contains a compressor section to compress the fuel and air mixture supplied to the mechanical rotor until its ignition by the effect of the centrifugal force acting upon the fuel during rotation of the mechanical rotor, an adjacent combustion section of the working tube for fuel burning and an expansion section as a continuation of the combustion section that enables expansion of the fuel combustion products to a lower pressure and reduction of their temperature while the combustion section is more distant from the rotation axis than the compressor section and expansion section . A similar concept of a bladeless combustion turbine is described in a PCT application published under number WO2008088225A1, where the working tube is branched and each branch of the working tube is U-shaped again. Unlike the above mentioned German document DE3306971A1 according to this PCT application fuel is only injected into each branch of the working tube in the place where air is most compressed by means of the corresponding branched fuel pipe that is installed separately in the rotor.

A principal disadvantage of the above mentioned bladeless combustion turbines is that their authors use a U-shaped working . tube . Although this shape of the working tube appears to be obvious, it requires a rotor that has a large area on its outer perimeter. To achieve sufficient compression, the peripheral speed of the rotor must be on the order of several hundreds of metres per second (approx. 300 - 700 m/s), which results in high power losses due to friction between the perimeter part of the rotor and the surrounding environment, i.e. air .

The authors of both the above mentioned patents realize this obvious disadvantage of their inventions; however, as the only solution to reduce the influence of friction power losses they mention that the rotor is placed in a container in which artificial vacuum is produced through permanent exhaustion of air with a vacuum pump. However, this design leads to a high demanded output of the vacuum pump as for the required high speed of the rotor permanent penetration of air into the space where vacuum is required cannot be prevented with sealing between the rotating and fixed part of the combustion turbine. Another drawback of this design is short service life of the sealing as it is stressed by high friction forces at simultaneously high peripheral speeds in the friction contact place. Moreover, the friction power losses of the sealing consume, similarly to the necessary vacuum pump, another part of the output generated by the rotor and both these power losses considerably reduce the efficiency of the entire combustion turbine.

For these reasons the efficiency of the bladeless combustion turbines designed in the German patent document DE3306971A1 and the PCT application published under number WO2008088225A1 is very problematic.

The above mentioned disadvantages of the known types of miniature gas turbines are the main obstacles preventing practical use of miniature combustion turbines.

Summary of the Invention

The above mentioned disadvantages of the state of the art are eliminated by a combustion engine based on this invention that can also be called a bladeless combustion mini-turbine containing a mechanical rotor comprising a working tube, either unbranched (simple) or branched, for fuel supply into the mechanical rotor, pass fuel through the working tube and exhaust of the fuel combustion products from the mechanical rotor while the working tube is spatially arranged in the mechanical rotor in such a way that each of its branches comprises a compressor section for compression of fuel supplied to the mechanical rotor until its ignition by the effect of centrifugal forces acting upon the fuel during rotation of the mechanical rotor around the rotation axis, an adjacent combustion section of the working tube for fuel burning and an adjacent expansion section of the working tube for expansion of the fuel combustion products to a lower pressure and reduction of their temperature, where the mechanical work obtained by expansion drives the mechanical rotor while the principle of the combustion engine is that the combustion section is more distant from the rotation axis than the compressor section and the expansion section and that each branch of the working tube is routed in its compression section in the mechanical rotor in the direction from the entrance of the working tube into the mechanical rotor in such a way that besides getting farther away from the rotation axis it is also angled in or against the rotation direction of the mechanical rotor so that in the axial direction the width of the part of the mechanical rotor housing that covers the combustion section can be as narrow as possible while the expansion section of the working tube branch then returns to the rotation axis of the mechanical rotor and also to the direction of this axis. As mentioned above, the working tube in accordance with the invention may be branched and in such a case the working tube contains two and more branches, or unbranched, i.e. simple while in this case for the purpose of the invention we say that the working tube consists of one branch, i.e. does not contain more branches.

The above mentioned new spatial arrangement of the working tube achieves, as compared to the combustion turbines described in the patent documents DE3306971A1 and the PCT application WO2008088225A1, very low friction of the rotor against the external environment (air) without the rotor having to be enclosed in a vacuum container.

The described new design of the shape of the working tube in accordance with the invention also features another advantage compared to the previously designed combustion turbines with a working tube, namely that if the fuel mixture flows in the working tube of the new combustion engine in the rotation direction, the perimeter speed of the rotor adds up to the speed of the flowing mixture, which leads to an increase of compression and thus enhancing of efficiency of the new combustion engine as compared to combustion turbines with the same diameter and the same speed that however have a U-shaped working tube. The thermodynamic cycle of the bladeless combustion micro-turbine can be approximately described as an idealized open Brayton cycle, similarly to a standard combustion turbine, which consists of isenthropic compression, isobaric combustion and isenthropic expansion.

The fuel/air mixture flows through the working tube into its compressor part. Rotation of the rotor and the resulting centrifugal force causes an increase of pressure and temperature there, which results in ignition of the fuel/air mixture. The ignited mixture continues to the adjacent combustion part where it burns, which means that heat is supplied to the flowing mixture. The combustion products flow through the adjacent expansion part of the working tube towards the rotation axis where they expand, which results in a reduction of their pressure and temperature. The mechanical work obtained through the expansion drives the rotor, and thus the electromagnetic generator as -well.- After expansion the combustion products leave the working tube, exhausting residual heat. This residual heat can be further used, e.g. to heat water, etc.

The main difference from standard combustion turbines with blades consists in the fact that the fuel/air mixture continuously flows through the working tube and the thermodynamic cycle of the combustion engine consisting of the compression, combustion, expansion and exhaust goes on during this flow. The fuel/air mixture is driven by an external device, e.g. an external low-pressure fan, into the inlet part of the working tube located in the mechanical rotor. Fuel is added to the supplied air before entering the working tube e.g. by an atomizing pressure nozzle.

An electromagnetic rotor is conveniently connected to the mechanical rotor and during burning of fuel it rotates together with the mechanical rotor driven by the mechanical work obtained by expansion while the rotation of the electromagnetic rotor induces electromagnetic voltage in the electromagnetic stator, which acts as an electric generator.

In one of convenient embodiments the mechanical rotor, connected to the electromagnetic rotor, is set in motion to achieve the speed required for ignition of fuel by the torque produced by the electromagnetic stator acting in this stage as an electromagnetic motor. The fuel is ignited by self-ignition. The entrance of the compressor section of the working tube and the exit from the expansion section of the working tube conveniently lie on the common axis of rotation of the mechanical rotor and electromagnetic rotor. The working tube can be conveniently arranged in such a way that the mechanical rotor is statically balanced.

In a convenient embodiment fuel is fed into the working tube by an external device, e.g. a fan.

The fuel may be a fuel mixture containing air.

In a convenient embodiment the transversal dimensions of the working tube are on the order of 10° mm to 10¹ mm and the total diameter of the mechanical rotor is on the order of 10¹ mm to 10² mm while the speed of the mechanical rotor is, depending on the size of the combustion engine, on the order of 10³ to 10⁶ rpm. The equipment contains a fixed and a rotary part. The fixed part contains a frame, electric motor/generator stator and two bearings. The rotary part, which is mounted on bearings in a rotating way, contains an electromagnetic rotor and a mechanical rotor containing a spatially shaped working tube. The electromagnetic rotor is attached to the mechanical rotor, both of them forming one single rotor. The shaping of the working tube is determined by its three sections or parts, which are the compressor, combustion and expansion parts. These parts are connected to each other in this order while the entrance of the compressor part and the exit of the expansion part lie on the rotation axis defined by the pair of bearings. Out of the above mentioned parts the combustion part of the tube is the most distant part from the rotation axis. The working tube can be conveniently shaped in such a way as the rotor can be statically balanced. The working tube may also have more branches . The material of the rotor must have high heat resistance and mechanical strength so that it should not get disrupted due to heat and mechanical stress. The most frequently used materials for these purposes are refractory alloys, e.g. Inconel, or non-metallic refractory materials as special types of technical ceramic materials. If refractory alloys are used, the rotor can be produced e.g. by machining, forming, welding or casting while in the case of non-metallic refractory materials it can be produced e.g. by casting or the Rapid Prototyping technology.

The main advantage of the invention compared to bladed combustion turbines is integration of all the basic parts of the combustion turbine that are necessary for the functionality of the thermodynamic cycle of a combustion turbine in one working tube.

As the working tube does not have any blades and its individual parts (compression, combustion and expansion) gradually pass into each other, it exhibits considerably lower aerodynamic losses related to turbulences and friction of flowing air as compared to standard bladed combustion turbines. Therefore, the external device feeding the fuel/air mixture to the working tube only consumes a few percent of energy generated by the bladeless combustion turbine. However, if a sufficiently large portion of (or even all) the electric energy produced by the electromagnetic generator is applied to drive the external device pushing the fuel/air mixture into the working tube (to achieve the maximum possible flow rate of the fuel/air mixture), the kinetic energy of the exhausted combustion products is so high that it creates sufficient thrust force to drive e.g. a pilotless or piloted aircraft.

With suitable shaping of the rotor enabled by the new shape of the working tube in accordance with the invention the power loss caused by friction of the rotor of the bladeless combustion turbine in accordance with the invention against the surrounding air is relatively low in proportion to the maximum turbine power. As mentioned above, this is the main advantage of the new combustion engine in accordance with the invention over the bladeless combustion turbines based on the present state of the art.

The wall of the working tube has a significantly lower area than the working parts of a standard bladed combustion turbine (compressor rotor, diffuser, combustion chamber, guiding nozzles, turbine) with the same output, and therefore the bladeless combustion turbine manifests, compared to standard bladed miniature combustion turbines, very low power losses caused by heat transmission between the compressor part, turbine part and the environment.

A substantial reduction of aerodynamic losses and heat losses, together with a significant simplification of the design eliminates the disadvantages of the present state of the art.

Brief Description of the Drawings

The invention will be clarified in a detailed way with the use of embodiment examples and drawings in which:

- Fig. 1 shows a general diagram of an embodiment example of a combustion engine based on the invention;

Fig. 2 shows a diagram of the rotor of an embodiment example of a combustion engine based on the invention with a single working tube;

- Fig. 3 shows a diagram of the rotor of another embodiment example of a combustion engine based on the invention with a branched working tube; and

- Fig. 4 schematically illustrates the mechanical rotor shown in fig. 2 in a side view perpendicular to the section made through the plane on which the rotor axis lies.

Examples of Embodiments of the Invention An embodiment example of a combustion engine - bladeless combustion mini-turbine in accordance with the invention is shown in fig. 1. Bearings 2 and an electromagnetic stator _3 are attached to the frame 1. In the bearings 2 a mechanical rotor 4 is mechanically mounted that contains a working tube 6 and is connected to the electromechanical rotor _5.

On the start of the bladeless combustion mini-turbine in accordance with the invention the connected mechanical and electromagnetic rotors _ and _5 are set in rotary motion so as to achieve the working speed (i.e. so that the peripheral speed of the rotor can be several hundreds of metres per second) by the torque provided by the electromagnetic stator 3, which, together with the electromagnetic rotor 5_, acts as an electromagnetic motor at the start.

Then, a mixture of air and fuel starts to flow into the working tube 6, the mixture being forced in by an external device (e.g. a fan) .

In the compressor section or part of the working tube 6, which is the part from the entrance of the working tube 6 up to the place where the working tube 6 is farthest away from the rotation axis, the air/fuel mixture is compressed by the centrifugal force, which increases its pressure and temperature until the mixture gets ignited.

In the adjacent, combustion section or part of the working tube 6 the mixture burns, i.e. heat is supplied to the flowing mixture.

Combustion products flow through the adjacent expansion section or part of the working tube 6 towards the rotation axis, thereby the combustion products expand to achieve a lower pressure and temperature. The mechanical work obtained through the expansion drives the mechanical rotor _4 and the electromagnetic rotor _5, which is connected to it, to induce electromagnetic voltage in the electromagnetic stator _3, which acts as an electric generator. After the expansion the combustion products leave the working tube _6 and the entire mechanical rotor _4.

Fig. 2 shows a mechanical rotor 4 of a bladeless combustion mini-turbine in accordance with the invention having a single working tube 6 while fig. 3 shows a mechanical rotor 1_ of a bladeless combustion mini-turbine in accordance with the invention with a branched working tube 6. In this mechanical rotor 7_ with a branched working tube 6 the thermodynamical cycle runs simultaneously in both the branches of the working tube 6.

As you can see in figs. 2, 3 and 4, the working tube 6 is routed in the direction from the entrance of the working tube 6 into the mechanical rotor _4, 1_ in its compression section in the mechanical rotor 4, 1_ in such a way that besides getting farther away from the rotation axis it is also angled in or against the rotation direction of the mechanical rotor _4, T_. This is important to make the part of the housing of the mechanical rotor 4_, 1_ that covers the combustion section as narrow as possible. Thanks to such a routing of the combustion tube 6, as you can clearly see in fig. 4, the axis of the major part of the combustion section lies on the plane that is perpendicular to the axis of the mechanical rotor 4_, 1_, so the width of the part of the housing of the mechanical rotor _4, Ί_ that covers the combustion section is minimal, i.e. only a little bigger than the thickness (diameter) of the working tube 6 in the combustion section. Such a design minimizes friction, thus maximizing the efficiency of the combustion engine.

The presented invention has been described with the use of the above mentioned embodiment examples; however, the invention is not limited to them. The scope of the invention also comprises modifications that fall within the scope of patent claim 1.

Claims

CLAIMS 1. A combustion engine containing a mechanical rotor (4, 7) comprising at least one working tube (6) that is branched or unbranched - i.e. consisting of one branch, for supplying fuel into the mechanical rotor (4, 7), passing fuel through the working tube (6) and exhausting combustion products of burning fuel from the mechanical rotor (4, 7) while the working tube (6) is spatially arranged in the mechanical rotor (4, 7) in such a way that each of its branches comprises a compressor section for compression of fuel fed into the mechanical rotor (4, 7) until its ignition by the effect of the centrifugal force acting upon the fuel during rotation of the mechanical rotor (4, 7) around the rotation axis, an adjacent combustion section of the working tube (6) for burning of fuel and an expansion section of the working tube (6), adjacent to combustion section, for expansion of fuel combustion products to reduce their pressure and temperature, where the mechanical work obtained by the expansion drives the mechanical rotor (4, 7), characterized in that the combustion section is more distant from the rotation axis than the compressor section and the expansion section and each branch of the working tube (6) is, in the direction from the entrance of the working tube (6) to the mechanical rotor (4, 7), in its compression section routed in the mechanical rotor (4, 7) in such a way that besides getting farther away from the rotation axis it is also angled in or against the rotation direction of the mechanical rotor (4, 7) so that in the axial direction the part of the housing of the mechanical rotor (4, 7) that covers the combustion section can be as narrow as possible while the expansion section of the branch of the working tube (6) then returns to the rotation axis of the mechanical rotor (4, 7) as well as to the direction of this axis.

2. The combustion engine according to claim 1, wherein an electromagnetic rotor (5) is connected to the mechanical rotor (4, 7) and during the burning of fuel it rotates together with the mechanical rotor (4, 7) driven by mechanical work obtained by expansion while the rotation of the electromagnetic rotor (5) induces electromagnetic voltage in the electromagnetic stator (3), which then acts as an electric generator.

3. The combustion engine according to any of the previous claims, wherein the mechanical rotor (4, 7) connected with the electromagnetic rotor (5) is set in motion to achieve the speed necessary to ignite fuel by torque produced by the electromagnetic stator (3) acting as an electromagnetic motor in this stage.

4. The combustion engine according to any of the previous claims, wherein the fuel is ignited by self-ignition.

5. The combustion engine according to any of the previous claims, wherein entrance of the compressor section of the working tube (6) and the exit of the expansion section of the working tube (6) lie on the common rotation axis of the mechanical rotor (4, 7) and electromagnetic rotor (5). β. The combustion engine according to any of the previous claims, wherein the working tube

(6) is arranged in such a way that the mechanical rotor (4, 7) is statically balanced.

7. The combustion engine according to any of the previous claims, wherein the fuel is fed into the working tube (6) by an external device, conveniently a fan.

8. The combustion engine according to any of the previous claims, wherein the fuel is a fuel mixture containing air.

9. The combustion engine according to any of the previous claims, wherein the transversal dimensions of the working tube (6) are on the order of 10° mm to 10¹ mm and the total diameter of the mechanical rotor (4, 7) is on the order of 10¹ mm to 10² mm while the speed of the mechanical rotor (4, 7) is, depending on the size of the combustion engine, on the order of 10³ to 10⁶ rpm.