Patent Application
20230083067
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.
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.
A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:
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.
The combustion chamber 101 is the volume between the piston 102 and the cylinder head. The example engine of
In accordance with the invention, combustion chamber 101 does 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 generator 109, external to the combustion chamber 101, delivers radio frequency waves or microwaves at a predetermined power and frequency via a cable, waveguide, or other wired transmission line 109a to a transmit antenna 110 within the combustion chamber 101. Transmit antenna 110 may 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 chamber 101 is a receive antenna 111. A wireless RF/microwave energy transfer occurs between antennas 110 and 111 within the combustion chamber 101. As explained below, receiving antenna 111 is a spark ignitor and may also be a plasma generator after ignition.
An advantage of the invention is that transmitting antenna 110 and receiving antenna 111 may be located anywhere inside the combustion chamber 101; they need not be under the cylinder head. The antennas 110 and 111 may 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”.
In the embodiment of
In general, receiving antenna 111 is 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 generator 109 are delivered to transmit antenna 110 using cable 109a or 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 antenna 111 focusses energy to create a strong electric field to create a spark for ignition.
In general, receive antenna 111 may 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.
Antennas 110 and 111 are 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 antennas 110 and 111 for 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 chamber 101 could be equipped with multiple receive antennas 111. A distributed spark would no longer need the Stark Effect to hurry along the burn front.
In the example of
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.
