Focused microwave or radio frequency ignition and plasma generation

A method of providing spark ignition for an engine or other equipment having a combustion chamber. A radio frequency wave or a microwave (RF/microwave) generator delivers radio frequency waves or microwaves to a transmit antenna inside the combustion chamber. At least one RF/microwave receive antenna is attached to an internal surface of the combustion chamber and comprises two or more RF/microwave focusing features with a spark gap between them. The transmit antenna wirelessly energizes the receive antenna, which generates a spark between the two focusing features.

TECHNICAL FIELD OF THE INVENTION

This patent application relates to internal combustion engines and other devices that use spark ignition, and more particularly to ignition systems for such engines and devices.

BACKGROUND OF THE INVENTION

Internal combustion engines require ignition of an air-fuel mixture, either by spark ignition (SI) or compression ignition (CI). Ignition subsystems for internal combustion engine vehicles are highly refined computer-controlled systems incorporating many significant technical advances.

Today's conventional spark-ignited engines use a spark plug to initiate a spark in the engine's combustion chamber, which ignites an air-fuel mixture in the chamber. Spark plugs are cylindrical devices that are installed into the combustion chamber via mounting holes on the cylinder head. The cylinder head also has other moving parts and internal cooling and lubrication circuits, and so only one spark plug can be installed per cylinder with perhaps two for very large engines. Only the center area of the cylinder head is suitable for spark plug installation, which means that the flame kernel must be at the top of the cylinder. Spark plug ignition systems suffer from problems with spark duration and energy, which limits dilution tolerance and combustion stability.

Alternative ignition methods have been explored, seeking improvements in thermal efficiency and emissions.

DETAILED DESCRIPTION OF THE INVENTION

The following description is directed to a radio frequency or microwave (abbreviated as RF/microwave herein) ignition system that eliminates spark plugs in conventional internal combustion engines. By “RF/microwave” is meant either radio frequency waves or microwaves at a predetermined frequency or frequency range.

The system may also be used for other equipment having a combustion chamber, for jet engines, chemical reactors, and for any equipment or device that requires a wireless spark for ignition. The RF/microwave ignition system is suitable as an alternative to spark plug ignition systems as well as to provide a wireless spark in environments where a spark plug system is not suitable.

The RF/microwave ignition system not only generates a wireless spark but may also generate plasma during and/or after the spark event. Both are both beneficial to chemical reactions such as combustion.

As explained below, the RF/microwave ignition system uses focused radio frequency or microwave energy. Radio frequency waves or microwaves are delivered into the combustion chamber via a wired transmit antenna. A receive antenna is implemented as a pair of small features inside the combustion chamber that wirelessly receive radio frequency or microwave energy and focus the energy to a spark gap, thereby producing a spark and igniting the combustion fuel.

For ignition purposes, the RF/microwave generated spark ignition and combustion are simultaneous. This is in contrast to microwave enhanced combustion, which is used to enhance a flame ignited by a spark plug.

FIG.1is a cut away view of the inside of a typical cylinder100of an internal combustion engine. The engine may be any internal combustion engine for which a combustion product is ignited by a spark. This may include various engine platforms, such as gasoline, natural gas, and dual fuel.

The combustion chamber101is the volume between the piston102and the cylinder head. The example engine ofFIG.1is an overhead cam engine, with an intake valve and exhaust valve having ports at the top of the cylinder. Of particular significance to this description is the compression of an air-fuel mixture, followed by ignition and combustion.

In accordance with the invention, combustion chamber101does not use a spark plug. Instead, ignition occurs as a result of an RF/microwave ignition system, which eliminates the need for a spark plug. RF/microwave energy produces a spark, which ignites a flame and is delivered directly to the flame front.

An RF/microwave generator109, external to the combustion chamber101, delivers radio frequency waves or microwaves at a predetermined power and frequency via a cable, waveguide, or other wired transmission line109ato a transmit antenna110within the combustion chamber101. Transmit antenna110may be implemented as any one of various antenna suitable for radio frequency or microwave transmission. One example is a dipole antenna.

A second antenna within the combustion chamber101is a receive antenna111. A wireless RF/microwave energy transfer occurs between antennas110and111within the combustion chamber101. As explained below, receiving antenna111is a spark ignitor and may also be a plasma generator after ignition.

An advantage of the invention is that transmitting antenna110and receiving antenna111may be located anywhere inside the combustion chamber101; they need not be under the cylinder head. The antennas110and111may be located on the combustion chamber walls or they may be located anywhere that has fluid communication with the combustion chamber, including in the intake port, cylinder head, cylinder wall, piston head, or exhaust port. For purposes of this description, these various openings in fluid communication with the combustion chamber are deemed to be “in the combustion chamber”.

FIG.2schematically illustrates the generation of focused RF/microwaves within the combustion chamber101to create a spark. The transmit antenna110wirelessly delivers RF/microwave energy to the receive antenna111. As explained below, the receiving antenna111is implemented as a pair of “focusing features”, which receive and focus RF/microwaves across a gap to produce a spark.

FIG.3illustrates how the receiving antenna111is implemented as a pair of “focusing features” with a gap between them. Each focusing feature extends from the combustion chamber wall into the combustion chamber. These features may take various geometries, such as described in the examples below. Examples are features in the shape of sharp edges, ditches, bumps, wires, two-halves, pyramids, cones, tappers, balls, or any combination.

FIG.4illustrates one embodiment of receiving antenna111, comprising a pair of focusing features22aand22b. Each feature is attached to or integrated onto the inner surface of the combustion chamber101.

In the embodiment ofFIG.4, one focusing feature22ahas the shape of a curved arm, raised above the inner surface of the combustion chamber101, with a point of attachment to the inner surface. Feature22ahas a distal end (relative to the point of attachment), which is the focus point for spark generation. Although not shown inFIG.4, feature22amay have a defined focusing point on its distal end. Feature22bis a raised feature formed on the inner surface of the combustion chamber101. It is arranged so that there is a small gap between its distal end (relative to the chamber wall) and the distal end of feature22a. This gap is where the RF/microwave energy is focused to create a spark for ignition.

FIGS.5and6illustrate alternative embodiments of the receiving antenna111. In bothFIGS.5and6, instead of a pair of focusing features, there are multiple perimeter focusing features arranged in a circular pattern around a center focusing feature. There is a spark gap between each perimeter focusing feature and the center focusing feature.

In general, receiving antenna111is at least one pair of focusing features, raised from the inner surface of the combustion chamber. Each feature has a focusing point, spaced from a focusing point of the other feature.

In operation, RF/microwaves generated by RF/microwave generator109are delivered to transmit antenna110using cable109aor other “wired” transmission. Standing waves of high-strength electrical fields are created within the combustion chamber. An example of a suitable microwave energy is energy produced at 2.45 GHz. The gap between the features of receive antenna111focusses energy to create a strong electric field to create a spark for ignition.

FIG.7illustrates an example in which the focusing features of receiving antenna111are implemented as raised hemispheres on the inner wall of the combustion chamber101.

FIG.8illustrates a receiving antenna111having one feature implemented as an “arm”82having a triangular point83at its end. The other feature of receive antenna111is a pointed triangular feature84.

In general, receive antenna111may comprise two or more features that function to receive radio frequency or microwave energy and to focus that energy to create a spark. The features extend from the inner surface of the combustion chamber to create a gap between at least two focusing points. This gap creates a radio frequency or microwave spark gap.

Antennas110and111are easily implemented by manufacturing them as integral parts of the combustion chamber. However, if desired, either or both of the antennas can be configured as a replaceable metal and dielectric part. In either case, an advantage of using antennas110and111for ignition that it saves design and component cost compared to the traditional spark plug. It provides ease of maintenance and fabrication. It simplifies cylinder head design and does not block in-cylinder flow compared to the traditional spark plug.

In other embodiments, combustion chamber101could be equipped with multiple receive antennas111. A distributed spark would no longer need the Stark Effect to hurry along the burn front.

FIG.9illustrates multiple receive antennas306, such as might be installed on a combustion chamber wall. In the example ofFIG.9, the antennas have the same configuration as inFIG.8, but any of the various configurations described herein could be used to provide a spark gap between RF/microwave focusing points.

In the example ofFIG.9, the receive antennas306are arranged in a circular pattern. This type of array could be located at the top of a combustion chamber101or other suitable locations.

RF/microwave spark ignition with multiple ignitors can be individually controlled by phasing using a single antenna pair, or by an RF/microwave phase array using multiple antenna pairs.

The above-described RF/microwave ignition system enhances combustion by enhancing flame kernel development, chemical kinetics, and flame speed. The ignitor thereby enables higher dilution, faster burn, and cooler combustion. Thermal efficiency is improved and knock is mitigated.

If desired, RF/microwave spark ignition can be followed by RF/microwave enhanced combustion to generate radicals or heating to enhance combustion or emission reactions from chemical kinetics.