WO2022229803A1

WO2022229803A1 - Magnetically boosted spark plug, ignition system and method

Info

Publication number: WO2022229803A1
Application number: PCT/IB2022/053743
Authority: WO
Inventors: Min Suk Cha
Original assignee: King Abdullah University Of Science And Technology
Priority date: 2021-04-28
Filing date: 2022-04-21
Publication date: 2022-11-03

Abstract

A magnetically boosted spark plug (100) for igniting a lean fuel mixture in an internal combustion engine includes a main electrode (104) configured to be electrically connected with a proximal end (104A) to a positive terminal of a voltage source (140) and to apply an electrical potential to a distal end (104B), which is opposite to the proximal end (104A); an insulator (106) configured to electrically insulate the main electrode (104) from an ambient, except for a distal region (105) extending from the distal end (104B); and a magnetic field generating element (120) configured to be connected to a ground terminal of the voltage source (140). The magnetic field generating element (120) is located around the (1) insulator (106) and (2) main electrode (104) so that the distal region (105) is exposed to the ambient.

Description

MAGNETICALLY BOOSTED SPARK PLUG, IGNITION SYSTEM

AND METHOD

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63/180,839, filed on April 28, 2021 , entitled “MAGNETICALLY BOOSTED SPARK PLUG,” the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

TECHNICAL FIELD

[0002] Embodiments of the subject matter disclosed herein generally relate to igniting a lean fuel mixture in an internal combustion engine, and more particularly, to an ignition system that generates a magnetically rotating arc string for igniting the lean fuel mixture in the internal combustion engine.

DISCUSSION OF THE BACKGROUND

[0003] The car industry (and other industries that use internal combustion engines) are facing increased regulations on the emission of CO2 and NOx from combustion to cope with the climate change issues. It is expected that governments worldwide will soon ask the car industry to use carbon free (or neutral) fuels only, such as hydrogen, ammonia, and e-fuels if the existing fossil fuel-based engines are not clean enough. However, the efficient use of fossil fuels can also reasonably mitigate the CO2 emission. In this light, the lean-burn combustion technology has been considered as one of the ways to allow a smooth transition towards a carbon neutral society.

[0004] Lean-burn combustion technology has been widely used to increase the thermal efficiency of spark ignition (SI) engines. A high thermal efficiency can be achieved mainly through the improvement of both pumping and heat losses. In addition, since the O2 contents in the exhaust neutralizes the 3-way catalytic converter, a significant reduction of NOx emission has to be obtained by lowering a flame temperature with the maximized amount of excessive air.

[0005] Therefore, the ignition has been a challenging issue for the lean-burn SI engines with an extremely lean mixture near the flammability limit. To facilitate the ignition process, various methods have been studied: i) stretched spark discharges using tumble flows, ii) enhanced ignition energy systems, iii) a pre-chamber ignition system, iv) a laser ignition system, v) nanosecond repetitive pulsed discharges, and vi) microwave boosted ignition systems.

[0006] On the other hand, the combustion duration becomes longer due to the substantially decreased laminar burning velocities in lean mixtures. Previous studies using the tumble flows have also shown improved combustion durations, since the highly wrinkled flame area due to the tumble flow results in increased overall burning rates. In fact, the combination of an inductive coil and a spark plug has been a common ignition method in SI engines. Thus, the concept of the stretched spark using a high-speed flow seems to be a practically feasible way of igniting lean mixtures in SI engines, solving issues with both the ignition of lean mixtures and a slow flame propagation.

[0007] A bigger ignition kernel can facilitate the ignition as the fuel mixture becomes leaner because the ignition process is related to the minimum quenching distance. The stretched spark channel can consequently promote the ignition by increasing the size of the spark, whereas the ignition probability deteriorates as the restrike phenomenon occurs (shortening of the spark channel as a result of bridging between any two points along the elongated spark). Therefore, the initial stage of a flame kernel, a spark discharge pattern, and the degree of the tumble flow can affect the cyclic variation of the ignition. Although the stretched spark concept has been applied successfully, there is a room for improvement if the underlying physicochemical mechanism is better understood.

[0008] Thus, there is a need for a better ignition system and associated method that is applicable to lean-burn combustion to improve the thermal efficiency of the internal combustion engines. The new system is required to extend a lean limit as much as possible to limit the NOx emission by reducing the flame temperature.

BRIEF SUMMARY OF THE INVENTION

[0009] According to an embodiment, there is a magnetically boosted spark plug for igniting a lean fuel mixture in an internal combustion engine. The magnetically boosted spark plug includes a main electrode configured to be electrically connected with a proximal end to a positive terminal of a voltage source and to apply an electrical potential to a distal end, which is opposite to the proximal end, an insulator configured to electrically insulate the main electrode from an ambient, except for a distal region extending from the distal end, and a magnetic field generating element configured to be connected to a ground terminal of the voltage source. The magnetic field generating element is located around the (1) insulator and (2) main electrode so that the distal region is exposed to the ambient. [0010] According to another embodiment, there is an internal combustion engine that burns a lean fuel mixture, and the internal combustion engine includes a cylinder, a piston located within the cylinder and configured to form a sealed chamber, and a magnetically boosted spark plug attached to the cylinder and partially entering into the chamber, the magnetically boosted spark plug configured to generate an arc string that ignites the lean fuel mixture. The magnetically boosted spark plug includes a magnetic field generating element that acts as a ground electrode. A magnetic field generated by the magnetic field generating element rotates the arc string with a given angular speed.

[0011 ] According to yet another embodiment, there is a method for igniting a lean fuel mixture within an internal combustion engine, and the method includes injecting the lean fuel mixture into a chamber of a cylinder of the engine, calculating a spark plug voltage Vd to be applied to a magnetically boosted spark plug so that a generated arc string rotates with a given angular velocity to generate an ignition kernel that covers a tip portion of the magnetically boosted spark plug, applying the spark plug voltage Vd between (1) a main electrode and (2) a magnetic field generating element of the magnetically boosted spark plug to generate the arc string, igniting the lean fuel mixture with the arc string, and forcing a piston of the engine to move within the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0013] Figures 1 A and 1 B are schematic diagrams of a magnetically boosted spark plug to be used in an internal combustion engine;

[0014] Figure 2 is a schematic diagram of a magnetic field generating element used with a spark plug to rotate an arc string;

[0015] Figures 3A and 3B illustrate the formation of a large ignition kernel at a bottom of the magnetically boosted spark plug due to the rotation of the arc string; [0016] Figure 4A schematically illustrates the formation of the arc string between a main electrode of the magnetically boosted spark plug and an annulus region of the magnetic field generating element;

[0017] Figure 4B illustrates the magnetic field generated by the magnetic field generating element, the current appearing in the arc string, and the Lorentz force appearing as a result of the magnetic field and the electrical current, which results in the rotation of the arc string;

[0018] Figure 5 shows the applied voltage to the magnetic field generating element and the generated current in the arc string;

[0019] Figure 6 shows an internal combustion engine having the magnetically boosted spark plug; and [0020] Figure 7 is a flow chart of a method for igniting a lean mixture inside the engine with the magnetically boosted spark plug.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to an internal combustion engine that has a single piston and uses a spark plug for igniting the injected fuel. However, the embodiments to be discussed next are not limited to a certain number of pistons or to a certain fuel.

[0022] Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0023] According to an embodiment, a novel ignition system has a magnetically boosted spark plug that initiates the ignition of a fuel-lean mixture in an internal combustion engine. The ignition system is capable of igniting an ultra-lean mixture. The magnetically boosted spark plug can be retrofitted to an existing internal combustion engine. Different from a traditional spark plug, the magnetically boosted spark plug has the ground electrode implemented as a magnetic field generating element. The spark is thus generated between a central high-voltage electrode and an annulus area of the magnetic field generating element, which is provided on the spark plug. For this novel configuration, various parameters of the central high-voltage electrode and the magnetic field generating element need to be specified. All these parameters are now discussed in more detail. Note that although each change is presented in a corresponding embodiment, these changes may be combined in any desired way by one skilled in the art, based on the present disclosure.

[0024] As illustrated in Figures 1 A and 1 B, a magnetically boosted spark plug 100 includes a high-voltage terminal 102 that is electrically connected to a high- voltage electrode 104 (also called “main electrode” or “central electrode”). The high- voltage electrode 104 may be centrally located within an insulation 106 that prevents an electrical discharge on a side of the electrode. The high-voltage electrode 104 may be made of any conductor material while the insulator 106 is preferably made of a ceramic material. It is noted that the ceramic insulator 106 extends from the high- voltage terminal 102, through a body 108 of the floating spark plug 100, up to a distal region 105 of the high-voltage electrode 104. The high-voltage electrode 104 has a proximal end 104A and a distal end 104B, when referenced to the terminal 102. The proximal end 104A is electrically connected to the terminal 102 while the distal end 104B is freely extending in the ambient, for a given length FI from the insulation 106. The electrode 104 extends from the terminal 102 through the body 108 up to the distal end 104A, leaving the distal region 105 completely free of the insulator. The length H of the distal region 105 is about 1 mm. The body 108 is made of a metal and has an upper part 110 that is shaped as a hex or square or rectangle, and a lower part 112 that has threads 114, which are configured to be attached to the body of an engine.

[0025] Different from the traditional spark plug, among other characteristics, the magnetically boosted spark plug 100 has a magnetic field generating element 120 as the ground electrode. The magnetic field generating element is called herein a magnetic ground electrode. The magnetic ground electrode 120 (this term is used interchangeable in this application with the term “magnetic field generating element”) may be made of any material that is used for a permanent magnet or may be implemented as an electromagnet, i.e., having a coil connected to an electrical source 140. The magnetic ground electrode 120 is shaped as a cylinder having a body 122 that defines an internal bore 124, as illustrated in Figure 2. An interior radius R1 (the radius of the bore) of the magnetic ground electrode 120 is selected to fit the external radius r of the ceramic insulator 106 so that the insulator fits snugly inside the bore 124. In one application, the magnetic ground electrode 120 is glued to the ceramic insulator 106 and is in direct contact with the body 108. In this or another application, the magnetic ground electrode 120 is concentric with the insulator 106. In another application, threads 129 may be formed on the inner surface of the magnetic ground electrode 120, as shown in Figure 2, and matching threads on the exterior of the insulator 106, and these threads are used to fix the magnetic ground electrode 120 to the insulator 106. Alternatively, the magnetic ground electrode may be fixed in place by its magnetic interaction with the main electrode 104 or other metallic parts of the system. A thickness R2 - R1 of the magnetic ground electrode 120 is selected to be less than 10 mm and a length L of the magnetic ground electrode 120, along the longitudinal axis X, is less than 10 mm.

[0026] As illustrated in Figures 1 A and 1 B, a length h of the insulator 106 that protrudes from the magnetic ground electrode 120 may have a value between zero and 2 mm and the radius r of the insulator 106 is selected to be at least 2 mm, more likely between 2 and 4 mm to ensure that a length of the spark gap of the spark plug 100 is about 2 to 4 mm. Note that in a traditional spark plug, a length of the spark gap between the central electrode and the ground electrode is about 1 to 2 mm. [0027] Such a configuration ensures that the magnetically boosted spark plug 100 achieves the ignition of fuel-lean mixtures, particularly in ultra-lean burn internal combustion engines, which is not possible with the traditional spark plugs. In one embodiment, all the dimensions not discussed herein of the magnetically boosted spark plug shares basic design criteria (e.g., overall shape) with a conventional spark plug to be compatible with existing engines. Unlike the conventional spark plug, the ring magnet ground electrode 120 is placed near the tip 104B of the electrode 104.

[0028] The purpose of having the magnet ground electrode 120 located closed to the tip of the main electrode 104 is to rotate the spark (arc string) 130 that forms between (1 ) the tip portion 105 of the electrode 104 and (2) an annulus region 128 of the magnetic ground electrode 120 or the edge 126 itself. The annulus 128, which is shown in Figure 2 (only a portion is shown for simplicity), may be located anywhere between R1 and R2. Note that the annular region 128 is the trajectory of the rotating root of the arc string 130 and not a physical or visible region of the ground electrode. If the arc string 130 rotates on the edge 126 or on the annulus region 128 next to the edge 126 of the magnetic ground electrode 120, as shown in Figures 3A and 3B, due to the magnetic field generated by the magnetic ground electrode 120, it generates a large ignition kernel 310 (larger than a corresponding kernel formed by a traditional non-magnetic spark plug) that facilitates the ignition of the fuel mixture (not shown), thus being able to ignite a fuel mixture leaner than what the traditional fuel mixture of the engine. In one application, as shown in Figures 3A and 3B, the ignition kernel 310 covers the entire bottom portion of the magnetically boosted spark plug 100. Note that the ignition kernel 310 in this embodiment looks like a dome and it is generated by the rotation of the arc string 130 with a desired angular speed. Although the generated arc string 130 is as shown in Figure 1 B, i.e., extends between one point of the tip portion 105 of the electrode 104 and one point of the annulus region 128 or rim 126, due to its fast rotation and latency of the device used to take its picture, the arc string 130 appears in Figures 3A and 3B to cover the entire ignition kernel 310.

[0029] To understand the rotation of the arc string 130 due to the magnetic field generated by the magnetic field generating element 120, Figure 4A shows the bottom of the magnetically boosted spark plug 100 and Figure 4B schematically illustrates the generated magnetic field B, current I, and Lorentz force F. Figure 4A shows the arc string 130 extending between the electrode 104 and the annular region 128 of the magnetic ground electrode 120. Note that the annular region 128 is circular and has a radius R3 larger or equal than R1 and smaller or equal than R2, which are shown in Figure 2. In one embodiment, it is possible that R3 = R2. The arc string 130 carries a current I as illustrated in Figure 4B as a voltage is applied by the voltage source 140 between the main electrode 104 and the magnetic field generating element 120. Due to the presence of the magnetic field B, within the region bordered by the magnetic ground electrode 120, insulator 106, and electrode 104, the Lorentz force F is exerted on the particles creating the current I, and thus, an end of the arc string 130 rotates on the magnetic ground electrode 120. As a first end 130A of the arc string 130 is fixed to the electrode 104 as shown in Figure 4B, only the second end 130B, which is connected to the annulus region 128, is free to move. Thus, this second end 130B moves along the circular region 128 to generate the kernel 310. The ring magnet electrode 120 establishes a uniform magnetic field B inside a hollow part, which is filled with the ceramic insulator having the metallic rod at the center. The current I is a positive direct current (DC), which is generated by an applied voltage in a range of 10 kV - 100 kV, which is applied to the central metallic rod 104. The location of the annulus region 128 on the side surface of the magnetic ground electrode 120 depends on the applied voltage, current, and magnetic force. The applied voltage can be varied depending on the ambient pressure and must be high enough to electrically breakdown the gaseous medium inside the cylinder where the magnetically boosted spark plug is placed. Once the arc string forms, the arc string is subjected to the Lorentz force of which direction is counterclockwise in Figures 4A and 4B due to the vector product of the current and magnetic field. The applied voltage may be generated by the power source 140, which is shown in Figure 1 A, and this power source may be connected with a positive terminal or lead to the terminal 102 and with a ground or negative terminal or lead to the magnetic ground electrode 120. In one embodiment, the power source 140 has its ground terminal electrically connected to the magnetic ground electrode 120.

[0030] In one embodiment, the magnetic component of the Lorentz force for a unit length of the arc string 130 can be expressed as Fm = IB, where I is the electrical current and B is the magnetic field intensity. Since the rotation of the arc is in a steady motion, this Lorentz force must be balanced with a drag force acting on the arc string 130. The drag force can be expressed as FD = 0.5CDdarcr_au², where CD is a drag coefficient, dare is the arc’s diameter, r_a is the ambient gas density, and u is the moving linear speed of the arc. As shown in Figure 4B, the arc shows an angular motion, and thus, the angular velocity (w) needs to be considered. One full turn of the arc string 130 can be considered as a minimum condition to make a large volume of the ignition kernel 310, and for a typical spark duration in ICE, which is around 0.5 ms, it follows that the arc string rotates with 1 rev./0.5ms = 2000 rev/s. Since the arc length is around few mm (~ 5mm), the tangential arc moving speed can be ranged up to 10 m/s (= u). Equating Fm = FD, and selecting reasonably estimated values of I = 180 mA, CD = 0.1 assuming streamlined body, darc= 1 mm, and p_a = 10 kg/m³ for a compression stroke, one can calculate that the required B is around 0.3 T, which can be achieved by using either a permanent magnet or an electromagnet. [0031] The magnetically boosted spark plug 100 advantageously facilitates the ignition of ultra-lean-burn engines. The spark plug 100 is configured to be compatible with conventional engine blocks, and thus, no significant modifications are required to be made. In one application, the magnetically boosted spark plug 100 needs a higher applied voltage than the conventional spark plug due to the increased gap between the high-voltage electrode 104 and the magnetic ground electrode 120 (in the 2 - 4 mm range), as compared to the conventional spark plug (in the 1 - 2 mm range).

[0032] The ultra-lean burn is known to be an effective way of combustion, which can reduce the fuel consumption, and thus, less CO2 emission can be achieved with such a system. While the conventional spark plug is not able to ignite the mixed fuel in the ultra-lean burn engine, the magnetically boosted spark plug 100 overcomes this problem by making the arc string longer and making it rotate with an angular speed of at least 2000 rev/s. For this angular speed, the magnetic ground electrode is selected to generate at least a magnetic field of about 0.3T.

[0033] As the fuel mixture becomes leaner, a flame quenching distance becomes larger indicating that a lean flame can be easily extinguished. The ignition process can be thought as an extremely opposite process, thus a larger ignition kernel should be required to ignite a leaner mixture. Previous studies also showed enhanced capability of igniting lean mixtures by using arc stretching blew by high tumble flow. Therefore, the conventional spark plug with the short arc string of 1-2 mm does not fit for an ultra-lean combustion. In this regard, the magnetically boosted spark plug 100 advantageously achieves a significantly large volume of the ignition kernel 310.

[0034] The inventor has tested the magnetically boosted spark plug 100 in an experimental chamber. A voltage V_a = 40 kV was applied by the source 140 to the spark plug 100 with a pulse duration, t_P, of 7 ms to roughly deliver an energy E_p as high as 200 mJ. Note that due to the highly fluctuating nature of the gap voltage ¼ and the current I, as illustrated in Figure 5, it was found that the effective E_p fluctuated from 232 mJ by about +/- 10%. For this embodiment, letter “d” indicates the length of the gap between the central electrode and the magnetic ground electrode.

[0035] As a result of these tests, the inventor found the lean propagation limit of f = 0.58 with t_P = 7 ms, while the limit was f =0.73 with a conventional spark plug at atmospheric pressure condition. The lean propagation limit is defined herein as the lowest f of the complete burning regime. Figure 5 shows a somewhat periodic oscillation in Vd, indicating organized oscillation of the length of the spark channel. In the initial phase, the voltage across the spark channel drops to ~ 1.1 kV at the minimum length of the spark. As the magnetic field exerts the Lorentz force to the conducting spark channel, the spark starts to rotate along the annulus surface 128 of the magnetic ground electrode 120, resulting in the elongated spark 130. Thus, ¼ increases due to the increased length as shown in Figure 5. In the oscillating regime of the voltage shown in Figure 5, the minimum ¼ is about 1 .4 kV, while the peak ¼ is about 1.7 kV, which corresponds to the length d in a range of 8-13 mm. It is noted that the mechanism of the magnetically rotating spark enlarges the length of the spark channel and thus, the design criterion for the spark plug 100 should be focused on how to maximize the spark length.

[0036] The magnetically boosted spark plug 100 discussed above may be integrated into an existing engine 600, as illustrated in Figure 6. The engine 600 includes at least one cylinder 602 to which the magnetically boosted spark plug 100 is attached to with threads 112. The cylinder 602 holds a piston 604 that is configured to move up and down relative to the cylinder. The piston 604 forms/define a sealed chamber 606 with the interior walls of the cylinder 602. Part of the magnetically boosted spark plug 100 enters inside the chamber 606. A spark 130 appears between the electrode 104 and the annulus region 128 of the magnetic ground electrode 120 as a voltage is applied by the power source 140, through corresponding leads 142 and 144. Note that one lead 142 is connected to the terminal 102 of the central electrode 104 while the other lead 144 is connected to a magnetic ground electrode lead 146. The lead 146 may be directly attached to the magnetic ground electrode 120 and may extend, along the longitudinal axis X of the spark plug 100, through the insulator 106, or between the insulator 106 and the body 108. Figure 6 further shows a fuel valve 610 that is configured to allow the fuel 612 (for example, a mixture of air and propane) to enter the chamber 606, through a fuel supply line 614. After the fuel mixture is burned, the exhaust gases are released from the chamber 606 through a valve 620, along an exhaust line 622.

[0037] The engine 600 further includes a controller 630 (e.g., a processor) that may be configured to coordinate the opening and closing of the valves 610 and 620, and also the activity of the voltage source 140. More specifically, the controller 630 determines, based on various parameters received from other components of the vehicle in which the engine is installed, e.g., load, speed, ambient conditions, etc., how often and how long to ignite the fuel mixture 612. Based on these requirements, the controller 630 may increase or decrease the applied voltage at the spark plug 100, to control the angular speed of the arc string 130. In addition or instead, the controller 630 may also control the magnetic field generating element 120, if implemented as an electromagnet, to increase or decrease the generated magnetic field, which affects the angular speed of the arc through the Lorentz force. Thus, the controller 630 can control the duration and the volume of the ignition kernel 310. If the magnetic field generating element 120 is implemented as an electromagnet, the voltage source 140 or another one may be used to supply the necessary voltage to the electromagnet.

[0038] A method for igniting a lean mixture in the internal combustion engine 600 with the magnetically boosted spark plug 100 is now discussed with regard to Figure 7. The method includes a step 700 of injecting the lean fuel mixture into a chamber of a cylinder of the engine, a step 702 of calculating a spark plug voltage Vd to be applied to a magnetically boosted spark plug so that a generated arc string rotates with a given angular velocity to generate an ignition kernel that covers a tip portion of the magnetically boosted spark plug (note that this step may be performed prior to firing the engine or in real time, as the conditions of the engine are changing), a step 704 of applying the spark plug voltage Vd between (1) a main electrode and (2) a magnetic field generating element of the magnetically boosted spark plug to generate the arc string, a step 706 of igniting the lean fuel mixture, and a step 708 of forcing a piston of the engine to move within the cylinder. The magnetic field generating element acts as a ground electrode, and a magnetic field generated by the magnetic field generating element rotates the arc string with the given angular speed.

[0039] The disclosed embodiments provide a magnetically boosted spark plug that can be retrofitted to an internal combustion engine to facilitate the ignition of a fuel lean mixture, particularly in ultra-lean burn internal combustion engines. It should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details. [0040] Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. [0041] This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.

Claims

WHAT IS CLAIMED IS:

1 . A magnetically boosted spark plug (100) for igniting a lean fuel mixture in an internal combustion engine, the magnetically boosted spark plug (100) comprising: a main electrode (104) configured to be electrically connected with a proximal end (104A) to a positive terminal of a voltage source (140) and to apply an electrical potential to a distal end (104B), which is opposite to the proximal end (104A); an insulator (106) configured to electrically insulate the main electrode (104) from an ambient, except for a distal region (105) extending from the distal end (104B); and a magnetic field generating element (120) configured to be connected to a ground terminal of the voltage source (140), wherein the magnetic field generating element (120) is located around the (1) insulator (106) and (2) main electrode (104) so that the distal region (105) is exposed to the ambient.

2. The spark plug of Claim 1 , wherein the magnetic field generating element is in concentric and in direct contact with the insulator.

3. The spark plug of Claim 1 , further comprising: a body (108) configured to receive a part of the main electrode (104) and the insulator (106), the body (108) being also configured to attach to the internal combustion engine, wherein the body is in direct contact with the magnetic field generating element (120).

4. The spark plug of Claim 1 , wherein the magnetic field generating element is a magnetic material.

5. The spark plug of Claim 1 , wherein the magnetic field generating element is an electromagnet.

6. The spark plug of Claim 1 , wherein the magnetic field generating element is configured to generate a magnetic field of at least 0.3T.

7. The spark plug of Claim 1 , wherein the magnetic field generating element is sized so that an arc string is generated between a tip region of the central electrode and an annulus region of the magnetic field generating element.

8. The spark plug of Claim 7, wherein a length of the arc string is between 2 and 4 mm.

9. The spark plug of Claim 1 , wherein a length of the tip region, along a longitudinal axis, of the central electrode is about 1 mm, and a length of the insulator along the longitudinal axis, between a tip of the central electrode and a side of the magnetic field generating element, is less than 2 mm.

10. The spark plug of Claim 1 , wherein the magnetic field generating element is a ring magnet.

11. An internal combustion engine (600) that burns a lean fuel mixture (612), the internal combustion engine (600) comprising: a cylinder (602); a piston (604) located within the cylinder (602) and configured to form a sealed chamber (606); and a magnetically boosted spark plug (100) attached to the cylinder (602) and partially entering into the chamber (606), the magnetically boosted spark plug (100) configured to generate an arc string (130) that ignites the lean fuel mixture (612), wherein the magnetically boosted spark plug (100) includes a magnetic field generating element (120) that acts as a ground electrode, and wherein a magnetic field generated by the magnetic field generating element (120) rotates the arc string (130) with a given angular speed.

12. The engine of Claim 11 , further comprising: a controller configured to determine a desired angular speed of the arc string and to control a voltage applied to the magnetically boosted spark plug to achieve the desired angular speed.

13. The engine of Claim 12, further comprising: a voltage source that applies the voltage to the magnetically boosted spark plug.

14. The engine of Claim 11 , wherein the magnetically boosted spark plug comprises: a main electrode (104) configured to be electrically connected with a proximal end (104A) to a positive terminal of a voltage source (140), and to apply an electrical potential to a distal end (104B), which is opposite to the proximal end (104A); an insulator (106) configured to electrically insulate the main electrode (104) from an ambient, except for a distal region (105) extending from the distal end (104B); and a magnetic field generating element (120) configured to be connected to a ground terminal of the voltage source (140), wherein the magnetic field generating element (120) is located around the (1) insulator (106) and (2) main electrode (104) so that the distal region (105) is exposed to the ambient.

15. The engine of Claim 14, wherein the magnetic field generating element is in direct contact with the insulator.

16. The engine of Claim 14, wherein the magnetic field generating element is a ring magnet.

17. The engine of Claim 14, wherein the magnetic field generating element is an electromagnet.

18. The engine of Claim 14, wherein the magnetic field generating element is configured to generate a magnetic field of at least 0.3T, a length of the arc string is between 2 and 4 mm, a length of the distal region, along a longitudinal axis of the central electrode, is about 1 mm, and a length of the insulator along the longitudinal axis, between a tip of the central electrode and a side of the magnetic field generating element, is less than 2 mm.

19. A method for igniting a lean fuel mixture (612) within an internal combustion engine (600), the method comprising: injecting (700) the lean fuel mixture (612) into a chamber (606) of a cylinder (602) of the engine (600); calculating (702) a spark plug voltage Vd to be applied to a magnetically boosted spark plug (100) so that a generated arc string (130) rotates with a given angular velocity to generate an ignition kernel (310) that covers a tip portion of the magnetically boosted spark plug (100); applying (704) the spark plug voltage V_d between (1) a main electrode (104) and (2) a magnetic field generating element (120) of the magnetically boosted spark plug (100) to generate the arc string (130); igniting (706) the lean fuel mixture (612) with the arc string (130); and forcing (708) a piston (604) of the engine (600) to move within the cylinder

(602).

20. The method of Claim 19, wherein the magnetic field generating element (120) acts as a ground electrode, and a magnetic field generated by the magnetic field generating element (120) rotates the arc string (130) with the given angular speed.