Microwave spark plug for injecting microwave energy

Abstract

A microwave spark plug for injecting microwave energy into a combustion chamber of an engine including an elongated housing, including an elongated chamber forming a hollow conductor in an interior of the housing, and including a microwave window arranged at a first end of the chamber in the housing, wherein the microwave window closes the hollow conductor relative to the combustion chamber, wherein the hollow conductor includes a connection element for a high frequency feed conductor at a second end arranged opposite to the microwave window, wherein the connection element includes a high frequency inlet cross section geometry which differs from a high frequency outlet cross section geometry at the microwave window. The microwave sparkplug is configured to be threaded into typical boreholes for sparkplugs and facilitates safe injection of microwave energy into a combustion chamber of an internal combustion engine.

Claims

1. A microwave spark plug for injecting microwave energy into a combustion chamber of an engine, the microwave sparkplug comprising: an elongated housing, including an elongated chamber forming a hollow conductor in an interior of the housing, and a microwave window arranged at a first end of the hollow conductor in the housing, wherein the microwave window closes the hollow conductor relative to a combustion chamber of an engine, wherein the hollow conductor includes a connection element for a high frequency feed conductor at a second end of the hollow conductor arranged distal from the microwave window, wherein the connection element includes a high frequency inlet cross section geometry which differs from a high frequency outlet cross section geometry at the microwave window, wherein a transition from the high frequency entry cross section geometry at the first end of the hollow conductor to the high frequency outlet cross section geometry at the second end of the hollow conductor is provided continuously expanding from the second end to the first end of the hollow conductor, and wherein a thread for threading into an engine housing defining the combustion chamber is arranged at an outer circumference of the elongated housing.

2. The microwave spark plug according to claim 1, wherein a ratio of an outer diameter of the thread to a diameter of the hollow conductor is in a range of 1.15-1.45 over a length of the thread.

3. The microwave spark plug according to claim 1, wherein an inner wall surface of the hollow conductor is made from a material with good electrical conductivity.

4. The microwave spark plug according to claim 1, wherein the microwave window is made from a highly pure ceramic material with a purity greater than 99%.

5. The microwave spark plug according to claim 4, wherein the microwave window is configured disc shaped, and wherein a side of the microwave window oriented towards the hollow conductor is flat and another side of the microwave window oriented towards the combustion chamber is configured flat or non-flat.

6. The microwave spark plug according to claim 5, wherein the microwave window is glued, pressed or shrunk into the housing at the first end of the hollow conductor.

7. The microwave spark plug according to claim 1, wherein a thickness of the microwave window is half a wave length or an integer multiple of half the wave length of an electromagnetic wave transmitted by the hollow conductor.

8. An internal combustion engine, comprising at least one bore hole configured for threading in at least one spark plug; at least one combustion chamber including at least one inlet valve and at least one outlet valve, wherein a microwave spark plug according to claim 1 is arranged in the at least one bore hole.

9. The microwave spark plug according to claim 4, wherein the highly pure ceramic material is sapphire glass or quartz glass.

10. The microwave spark plug according to claim 3, wherein the material with good electrical conductivity is copper or a noble metal.

11. A microwave spark plug for injecting microwave energy into a combustion chamber of an engine, the microwave sparkplug comprising: an elongated housing, including an elongated chamber forming a hollow conductor in an interior of the housing, and a microwave window arranged at a first end of the hollow conductor in the housing, wherein the microwave window closes the hollow conductor relative to a combustion chamber of an engine, wherein the hollow conductor includes a connection element for a high frequency feed conductor at a second end of the hollow conductor arranged distal from the microwave window, wherein the connection element includes a high frequency inlet cross section geometry which differs from a high frequency outlet cross section geometry at the microwave window, wherein a transition from the high frequency entry cross section geometry at the first end of the hollow conductor to the high frequency outlet cross section geometry at the second end of the hollow conductor is provided continuously expanding from the second end to the first end of the hollow conductor, and wherein a transition from the high frequency inlet cross section geometry to the high frequency outlet cross section geometry is provided linear.

12. A microwave spark plug for injecting microwave energy into a combustion chamber of an engine, the microwave sparkplug comprising: an elongated housing, including an elongated chamber forming a hollow conductor in an interior of the housing, and a microwave window arranged at a first end of the hollow conductor in the housing, wherein the microwave window closes the hollow conductor relative to a combustion chamber of an engine, wherein the hollow conductor includes a connection element for a high frequency feed conductor at a second end of the hollow conductor arranged distal from the microwave window, wherein the connection element includes a high frequency inlet cross section geometry which differs from a high frequency outlet cross section geometry at the microwave window, wherein a transition from the high frequency entry cross section geometry at the first end of the hollow conductor to the high frequency outlet cross section geometry at the second end of the hollow conductor is provided continuously expanding from the second end to the first end of the hollow conductor, wherein a transition from the high frequency inlet cross section geometry to the high frequency outlet cross section geometry is provided linear, and wherein the high frequency inlet cross section geometry is rectangular and the high frequency outlet cross section geometry is circular or oval.

13. The microwave spark plug according to claim 1, wherein the hollow conductor expands from the first end to the second end.

14. The microwave spark plug according to claim 1, wherein the high frequency inlet cross section is substantially rectangular and the high frequency outlet cross section is substantially circular.

15. The internal combustion engine according to claim 8, wherein the high frequency inlet cross section is substantially rectangular and the high frequency outlet cross section is substantially circular.

16. The microwave spark plug according to claim 11, wherein the high frequency inlet cross section is substantially rectangular and the high frequency outlet cross section is substantially circular.

17. The microwave spark plug according to claim 12, wherein the high frequency inlet cross section is substantially rectangular and the high frequency outlet cross section is substantially circular.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Additional features of the invention can be derived from the following description in combination with the drawing figures and the patent claims. Individual features can be implemented by themselves or in combination in embodiments of the invention, wherein:

(2) FIG. 1A illustrates a perspective view of a flange of a microwave sparkplug;

(3) FIG. 1B illustrates a perspective view of a microwave window of a microwave sparkplug;

(4) FIG. 2A illustrates a face view of the microwave sparkplug;

(5) FIG. 2B illustrates a longitudinal sectional view of the microwave spark plug along the line A-A;

(6) FIG. 3A illustrates a face view of the microwave spark plug that is rotated by 90 relative to the view in FIG. 2A;

(7) FIG. 3B illustrates a longitudinal sectional view along the line B-B through the microwave spark plug wherein the view is rotated by 90 relative to the view in FIG. 2B;

(8) FIG. 4 illustrates a cylinder head of a reciprocating piston engine with a microwave spark plug.

DETAILED DESCRIPTION OF THE INVENTION

(9) The perspective views of FIG. 1A and FIG. 1B illustrate the microwave spark plug 1 with an elongated housing 2 on which a thread 3 is arranged for threading into a respective bore hole in an engine. The diameter of the microwave spark plug 1 with the thread 2 corresponds to typical diameters for conventional spark plugs. At one end of the housing 2 there is a flange 4 with bore holes 6 and a groove 5 for receiving a seal ring 9 that is not illustrated in this figure, wherein a connecting conductor of a hollow conductor for transmitting the microwaves is attachable at the seal ring 9. The attachment requires a precise match of the mechanically connected/flanged on hollow conductor interior geometry and the interior geometry of the MW spark plug. Thus, all types of attachments like form coded plug connectors or suitable quick connectors are useable. In the flange there is a rectangular opening for injecting in the microwave energy. At the other end of the longitudinal housing as evident from FIG. 1B a ceramic disk 8 configured as a microwave window is arranged which can be pressed in, glued in or shrunk in.

(10) FIG. 2 illustrates a face view of the flange 4 in FIG. 2A and the sectional line through the microwave spark plug 1 along the line A-A. FIG. 2B illustrates the sectional view through the microwave spark plug 1 along the sectional line A-A with a seal ring 9 inserted into the groove 5 at the flange 4 and the inserted ceramic disc 8 at the other end of the housing 2. FIGS. 2A and 2B show the thread 3 and in an interior of the housing a chamber 10 is shown which is used as a hollow conductor for the microwave energy and whose height expands in a linear manner from the height of the opening 7 up to a height that is approximated to the diameter of the ceramic disc 8. The diameter of the ceramic disc 8 is slightly larger so that it provides a stop 11 in the housing 2 for the ceramic disc 8.

(11) FIG. 3 similar to FIG. 2 illustrates a face view of the flange with the sectional line B-B in FIG. 3A, this time without the seal ring 9 illustrated in FIG. 2. FIG. 3B illustrates a longitudinal sectional view through the microwave spark plug 1 wherein the ceramic disc 8 is also removed in this illustration so that a face opening 12 with a stop 11 is visible in the housing 2 for receiving the ceramic disc 8. The chamber 10 also expands in this embodiment from a width of the opening 7 in a linear manner up to the stop 11 so that in combination of FIGS. 2 and 3 the hollow conductor 10 has a circular configuration at the stop 11 at the microwave window.

(12) Since the ceramic disc 8 is arranged in a recess with a stop 11 it is larger than the effective cross section of an outlet geometry in the hollow conductor 10 shortly before the stop 11. Theoretically the ceramic disc 8 can also have a totally different shape than the outlet cross section of the hollow conductor 10 which is circular in the embodiments.

(13) FIG. 4 illustrates a schematic detail of a cylinder 13 of a piston engine with a cylinder head 14, a piston 19 and an inlet portion 15 made from a plurality of openings. An outlet from the piston 19 is not illustrated and can be provided in any known typical manner. Two bore holes 17 are provided in the cylinder head wherein a respective microwave spark plug 1 is screwed into each bore hole in order to inject the microwave energy through the microwave window 8 into a combustion chamber 18. It is helpful to inject in microwave energy with identical frequency and identical phase in particular engine operating ranges. By the same token a frequency deviation and a phase shift is required in other engine operating ranges. Therefore it can be necessary to use different inner geometries of the microwave spark plugs. In the embodiment a reciprocating piston engine is illustrated in an exemplary manner wherein the spark plug can certainly also be used for a rotating piston engine. Thus, the microwave spark plug for injecting in the microwave energy can be used for all engine types in which ignition is desirable in the combustion chamber that is caused by microwave energy.