A spark plug and engine

Abstract

This invention addresses the technical problem of spark plugs easily overheating and burning in existing technologies by providing a spark plug comprising a main shell disposed on the outer periphery of an insulator and an outer shell connected to a metal tail cover. The outer shell is disposed on the outer periphery of the main shell. The plane orthogonal to the axis at the front end of the main shell is plane A, and the plane orthogonal to the axis at the lower support point of the outer shell is plane B. The distance between plane A and plane B is L, which satisfies the following formula: 50*[H+(D-d) / 2] / λ+T≤L≤324*S / (80+λ)H+2T. This spark plug, with its pre-combustion chamber, ensures good ignition performance while its excellent heat dissipation structure and material selection effectively solve the spark plug overheating problem.

Description

Technical Field

[0001] This invention belongs to the field of engine component technology, and more specifically, relates to a spark plug. Background Technology

[0002] A spark plug is an ignition device assembled in an internal combustion engine to ignite the air-fuel mixture. A traditional spark plug includes a center electrode, an insulator, a housing, and a ground electrode. The insulator is a ceramic insulator with an axial bore. The center electrode is inserted through this bore. The housing is fitted onto the surface of the insulator. The ground electrode is connected to the end of the housing and extends opposite the center electrode, forming a gap for spark discharge. An electric arc is generated between the center electrode and the ground electrode by a pulse of electricity, which in turn produces an electric spark to ignite the air-fuel mixture around the electrodes, achieving automatic ignition.

[0003] In the field of spark-ignition internal combustion engines, a pre-combustion chamber spark plug has been used. It has a metal tail cover at the ignition end of the spark plug, with an opening on the metal tail cover. A pre-combustion chamber is formed inside the metal tail cover. An ignition gap is set inside the pre-combustion chamber. The air-fuel mixture is ignited by the spark plug through the gap and is injected out from the opening of the metal tail cover, thereby rapidly igniting the air-fuel mixture in the combustion chamber.

[0004] Existing technologies do not address issues such as ensuring that pre-combustion chamber spark plugs do not overheat and burn out. This is especially true when pre-combustion chamber spark plugs are used in vehicles, where engine miniaturization and increased power result in more severe thermal conditions, making them more susceptible to electrode burnout due to overheating. Patent CN110867729A discloses a spark plug with a pre-combustion chamber and specifies the proportional relationship between two hypothetical surfaces to improve ignition performance, but it still does not solve the overheating problem. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a spark plug that, while ensuring good ignition performance of the pre-combustion chamber spark plug, provides a structural design and material selection scheme with good heat dissipation to solve the spark plug overheating problem.

[0006] The present invention adopts the following technical solution:

[0007] A spark plug includes a main housing disposed on the periphery of an insulator and an outer housing connected to a metal tail cover. The outer housing is disposed on the outer periphery of the main housing. The plane orthogonal to the axis of the projection of the front end point of the main housing is plane A, and the plane orthogonal to the axis of the projection of the lower sealing surface of the outer housing is plane B. The distance between plane A and plane B is L, and L satisfies the following formula: 50*[H+(Dd) / 2] / λ+T≤L≤324*S / (80+λ)H+2T.

[0008] In the formula, D is the outer diameter of the outer shell thread, d is the outer diameter of the main shell thread, H is the axial projection height of the spark plug side electrode extending out of the main shell end face, T is the height from the sealing surface of the outer shell to its thread start point, λ is the thermal conductivity of the outer shell, and S is the distance from the front end point of the outer shell thread to plane B, where 1.8mm≤H≤8mm, 0mm≤T≤4mm, and 1mm≤(Dd) / 2≤3mm.

[0009] Furthermore, the spark plug includes a center electrode and a side electrode. The insulator has an axial hole extending along the axis. The center electrode is disposed in the axial hole. The side electrode is disposed at the front end of the main housing and extends in an arc shape to a position opposite to the discharge surface of the center electrode and forms a gap. The main housing with the side electrode end extends into the interior of the outer housing and is fixed by threads.

[0010] Furthermore, the outer housing is provided with a metal tail cover at the threaded front end, and the metal tail cover is provided with at least one through hole.

[0011] Furthermore, the distance S from the threaded front end point of the outer housing to plane B is greater than 17.5 mm.

[0012] Furthermore, the thermal conductivity λ of the outer shell is higher than that of the main shell, and the range of λ is 45 to 400 W / (mk).

[0013] Furthermore, the thermal conductivity λ of the outer shell is in the range of 80 to 330 W / (mk).

[0014] Furthermore, the main shell material is low-carbon steel, and the outer shell material is a copper / nickel alloy.

[0015] Furthermore, the outer housing mounting thread is M14, and the length of L satisfies any of the following values:

[0016] ①When λ is 45W / (mk), the length L is 7.61~15.96mm;

[0017] ②When λ is 80W / (mk), the length L is 4.94~13.13mm;

[0018] ③When λ is 330W / (mk), the length L is 2.33~6.95mm;

[0019] ④ When λ is 400W / (mk), the length of L is 2.19~6.38mm.

[0020] The outer housing has an M12 mounting thread, and the length of L satisfies any of the following values:

[0021] ①When λ is 45W / (mk), the length L is 7.06~24.6mm;

[0022] ②When λ is 80W / (mk), L is set between 4.63 and 19.88 mm;

[0023] ③ When λ is 330W / (mk), L is set between 2.26 and 9.59 mm;

[0024] ④ When λ is 400W / (mk), L is set between 2.13 and 8.63mm.

[0025] Furthermore, spark plugs with an L size of 3–20 mm have better overall performance. Too small an L size will affect the installation size of the center electrode; too large an L size will increase engine fuel consumption.

[0026] The present invention also provides an engine that uses any of the above-described spark plugs.

[0027] The front end and the back end described in this invention refer to the end closer to the central electrode as the front end and the opposite end as the back end.

[0028] The spark plug with a pre-combustion chamber of the present invention has a reasonable distance between the front end point of the main shell and the lower support point of the outer shell and two planes orthogonal to the axis. The main shell, the outer shell and the outer sealing gasket are made of materials with progressively higher thermal conductivity. The main shell and the outer shell are selected with appropriate thread specifications and lengths, which makes the spark plug dissipate heat faster, prevents overheating damage, and improves the life of the spark plug. Moreover, the spark plug also has the advantage of fuel economy. Attached Figure Description

[0029] Figure 1 This is a partial cross-sectional view of the spark plug with a pre-combustion chamber according to the present invention;

[0030] Figure 2 for Figure 1 The diagram shows an enlarged view of the spark plug's discharge and ignition section.

[0031] 1. Center electrode; 2. Insulator; 3. Main housing; 4. Side electrode; 5. Sealing gasket one; 6. Outer housing; 7. Metal tail cover; 8. Sealing gasket two. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments. Unless otherwise specified, the raw materials and methods used in the embodiments of the present invention are commercially available materials and conventionally used methods in the art. The thermal conductivity refers to the thermal conductivity at 20°C. The front end and rear end of the present invention refer to the end closer to the central electrode as the front end and the opposite end as the rear end.

[0033] like Figure 1 , Figure 2 As shown, a spark plug has a pre-combustion chamber and includes a main housing located on the periphery of an insulator, an outer housing connected to a metal tail cover, a center electrode, and a side electrode. The insulator has a shaft hole extending along its axis. The center electrode is disposed within the shaft hole. The side electrode is disposed at the front end of the main housing and extends to form a gap with the discharge surface of the center electrode. The main housing, with its side electrode end extending into the outer housing, is fixed by threads, i.e., the outer housing is disposed on the outer periphery of the main housing. A metal tail cover is provided at the threaded front end of the outer housing. The metal tail cover has at least one through hole (preferably, four through holes are evenly distributed on the arc surface of the front end of the metal tail cover, and one through hole is arranged on the end face). The main housing is fixed to the outer housing by the outer threads and dissipates heat to the outer housing through heat conduction. At the same time, the metal tail cover fixed to the front end of the outer housing also dissipates heat to the outer housing. A sealing gasket 5 seals the gap between the seat of the main housing 3 and the seat of the outer housing 6; a sealing gasket 8 seals the gap between the spark plug and the internal combustion engine.

[0034] It is important to note that the distance S from the tip of the outer housing thread to plane B is greater than 17.5mm (a larger contact area between the outer housing and the cylinder head is more beneficial for spark plug heat dissipation); the thermal conductivity λ of the outer housing is higher than that of the main housing, and the thermal conductivity of gaskets 5 and 8 is higher than that of the main housing. For example, the main housing material is low-carbon steel (which has excellent cold heading and machining properties, as well as sufficient strength), the outer housing and metal tail cover material is copper / nickel alloy, and the sealing gaskets 1 and 2 are made of copper alloy or aluminum alloy, etc. The nominal diameter of the thread on the outer surface of the main housing can be M12, M10, M8, etc., and the nominal diameter of the thread on the outer housing can be M14, M12, M10, etc., corresponding to the main housing.

[0035] Define plane A as the plane whose projection of the front end point of the main housing is orthogonal to the axis, and plane B as the plane whose projection of the lower sealing surface of the outer housing is orthogonal to the axis. Define the distance between plane A and plane B as L, and make L satisfy the following formula:

[0036] 50*[H+(Dd) / 2] / λ+T≤L≤324*S / (80+λ)H+2T,

[0037] In the formula, D is the outer diameter of the outer shell thread, d is the outer diameter of the main shell thread, H is the axial projection height of the spark plug side electrode extending out of the main shell end face, T is the height from the sealing surface of the outer shell to its thread start point, λ is the thermal conductivity of the outer shell, and S is the distance from the front end point of the outer shell thread to plane B, where 1.8mm≤H≤8mm, 0mm≤T≤4mm, and 1mm≤(Dd) / 2≤3mm.

[0038] The distance L between plane A and plane B in the pre-combustion chamber spark plug is the core of its structural design. If L is too large, the ignition performance will decrease and the structural advantages of the pre-combustion chamber spark plug cannot be effectively utilized. If L is too small, the spark plug will have poor heat dissipation, which will directly affect the normal use of the spark plug and may even cause it to overheat and burn out. Through extensive experimental data and inductive reasoning, this invention has discovered that the spark plug side electrode extension height H affects the selection of L. A larger H makes the spark plug more prone to overheating. On the other hand, a larger H results in a higher side ignition position, which is beneficial for ignition performance. The wall thickness (Dd) / 2 at the outer shell thread is also a factor affecting the selection of L, showing a positive correlation. The thicker the wall, the longer the heat dissipation distance, and the more prone the spark plug is to overheating. The material selection of the outer shell is a key factor affecting the selection of L. The smaller the thermal conductivity λ of the material, the worse the spark plug's heat dissipation capacity, and the more prone it is to overheating. At the same time, the design of L is also positively correlated with the outer shell thread length S. When S increases, the selection of L can be increased. The height T (relief groove) from the outer shell sealing surface to its thread start point is itself unfavorable for spark plug heat dissipation, but the relief groove is a necessary data point in spark plug manufacturing. Therefore, the design selection of L should be based on T, i.e., T should be added, but the maximum should not exceed 2T. After extensive testing and various combinations of parameters, the heat dissipation performance, ignition performance, and strength were tested. It was found that L, in the lower limit design, is directly proportional to the spark plug side electrode extension height H plus the wall thickness (Dd) / 2 at the outer shell thread, and inversely proportional to the thermal conductivity λ. Calculations and statistics showed a 50-fold relationship between them. Finally, the relief groove height T is added, i.e.: {H+(Dd) / 2}*50 / λ+T≤L. In the upper limit design, L is directly proportional to the outer thread length S, inversely proportional to the side electrode extension height H, and inversely proportional to the thermal conductivity λ plus a constant 80. Experiments showed that when the ratio between S and H, and (80+λ) reaches 324 times, the maximum size for spark plug overheating performance is satisfied. The size of the relief groove also affects overheating performance, and cannot exceed twice the relief groove height, i.e.: 324*S / (80+λ)H+2T. This leads to the following formula:

[0039] 50*[H+(Dd) / 2] / λ+T≤ L ≤324*S / (80+λ)H+2T, (1)

[0040] The parameters H, T, and (Dd) in this formula can be combined arbitrarily to achieve excellent overheating performance. However, the selection of the above parameters should be based on conventional dimensions in this field, namely: 1.8mm≤H≤8mm, 0mm≤T≤4mm, and 1mm≤(Dd) / 2≤3mm.

[0041] Through verification by examples and experimental data, it is shown that when L meets the conditions of this formula, the designed pre-combustion chamber spark plug has superior heat dissipation and ignition performance.

[0042] Example 1

[0043] The mounting thread for the spark plug with pre-combustion chamber and engine is selected as M14, with a thread length S of 17.5mm (i.e., the nominal diameter D of the outer housing thread is 14mm, and the distance from the front end of the outer housing thread to plane B is 19mm). The nominal diameter d of the main housing thread is 10mm, the spark plug side electrode extension height H is 3.5mm, and the outer housing relief groove height T is 1.5mm.

[0044] When the outer shell is made of carbon steel with a thermal conductivity λ of 45W / (mk), the design range of L satisfies equation (1) and should be 7.61~15.96mm.

[0045] Next, the following experiments were conducted to verify the heat dissipation effect and ignition performance:

[0046] (1) A 1.8L gasoline engine was selected as the test machine to compare the side electrode surface temperature (the side electrode surface temperature is the highest temperature of this type of spark plug). Thermocouple temperature measurement was used to conduct temperature comparison tests under the same engine operating conditions. The temperature was set to four levels: low (≤600℃), medium (600℃~700℃), high (700℃~800℃), and ultra-high (800℃~1000℃). The specific comparison is shown in Table 1 below:

[0047]

[0048]

[0049] Table 1

[0050] It is evident that the L value should be above 7.61 mm for temperatures below medium. When designed to meet the current conditions, the spark plug's heat dissipation effect is relatively good. However, increasing the L length leads to poorer fuel economy and significantly increased fuel consumption. Therefore, while meeting heat dissipation requirements, the spark plug must also possess fuel-saving properties. The following tests will assess its fuel consumption performance.

[0051] Ignition performance verification:

[0052] A 1.8L engine was selected for ignition performance verification. The test conditions were that the engine ran at 2000 rpm with the throttle fully open for 1 hour. The better the ignition performance, the lower the fuel consumption rate of the engine. The original spark plug of an engine without a pre-combustion chamber structure was selected as a comparison, and its fuel consumption rate was set to high. The fuel consumption was divided into five levels: ultra-low, low, medium, high, and ultra-high. Ultra-low refers to a fuel consumption rate of less than 210g / (kW.h) under the above test conditions; low refers to a fuel consumption rate between 210 and 218g / (kW.h); medium refers to a fuel consumption rate between 219 and 226g / (kW.h); high refers to a fuel consumption rate between 227 and 234g / (kW.h); and ultra-high refers to a fuel consumption rate of more than 234g / (kW.h).

[0053] The specific comparison data is as follows:

[0054]

[0055]

[0056] Table 2

[0057] In practical applications, considering fuel economy, the fuel consumption of an engine should not exceed moderate levels. Therefore, the fuel consumption of L below moderate levels should not exceed 15.96 mm.

[0058] In Example 1, the length L should be set between 7.61 and 15.96 mm to achieve both good heat dissipation and low fuel consumption.

[0059] Example 2

[0060] Keeping the structural design unchanged in Example 1 (all parameters are the same), but replacing the outer shell with a nickel alloy with a thermal conductivity λ of 80 W / (mk), the design range of L that satisfies equation (1) is 4.94~13.13 mm.

[0061] Similarly, the heat dissipation effect and ignition performance were verified, and the results are shown in Tables 3 and 4, respectively:

[0062] Temperature: Low Temperature: Medium Temperature: High Temperature: Extremely high L＝0 √ L＝2 √ L＝4 √ L＝4.94 √ L＝8 √ L＝10 √ L＝12 √ L＝13.13 √ L＝16 √ L＝18 √ L＝20 √

[0063] Table 3

[0064]

[0065]

[0066] Table 4

[0067] As can be seen, the experimental conclusions are the same as those in Example 1.

[0068] Example 3

[0069] Keeping the structural design unchanged in Example 1 (all parameters are the same), but replacing the outer shell with a copper alloy with a thermal conductivity λ of 330 W / (mk), the design range of L that satisfies equation (1) is 2.33~6.95 mm.

[0070] Similarly, the heat dissipation effect and ignition performance were verified, and the results are shown in Tables 5 and 6 respectively:

[0071] Temperature: Low Temperature: Medium Temperature: High Temperature: Extremely high L＝0 √ L＝2.33 √ L＝4 √ L＝6 √ L＝6.95 √ L＝10 √ L＝12 √ L＝14 √ L＝16 √ L＝18 √ L＝20

[0072] Table 5

[0073] Fuel consumption: Ultra-low Fuel consumption: Low Fuel consumption: Medium Fuel consumption: High Fuel consumption: Extremely high L＝0 √ L＝2.33 √ L＝4 √ L＝6 √ L＝6.95 √ L＝10 √ L＝12 √ L＝14 √ L＝16 √ L＝18 √ L＝20 √

[0074] Table 6

[0075] As can be seen, the experimental conclusions are the same as those of Examples 1 and 2, and the fuel consumption is even lower.

[0076] Example 4

[0077] Keeping the structural design unchanged in Example 1 (all parameters are the same), but replacing the outer shell with copper material with a thermal conductivity λ of 400W / (mk), the design range of L that satisfies equation (1) is 2.19~6.38mm.

[0078] Similarly, the heat dissipation effect and ignition performance were verified, and the results are shown in Tables 7 and 8, respectively:

[0079]

[0080]

[0081] Table 7

[0082] Fuel consumption: Ultra-low Fuel consumption: Low Fuel consumption: Medium Fuel consumption: High Fuel consumption: Extremely high L＝0 √ L＝2.19 √ L＝4 √ L＝6.38 √ L＝8 √ L＝10 √ L＝12 √ L＝14 √ L＝16 √ L＝18 √ L＝20 √

[0083] As shown in Table 8, the conclusions are the same as those in Example 3.

[0084] To ensure reliable installation of spark plugs with pre-combustion chambers, a shell strength verification was designed. Comparative experiments were conducted on the schemes of Examples 1-4, with the shell strength set to high, medium, and low levels. The comparison data is shown in Table 9 below:

[0085] Shell strength: Low Shell strength: Medium Shell strength: High carbon steel √ Nickel alloy √ copper alloy √ copper √

[0086] Table 9

[0087] In summary, considering the strength of the housing, heat dissipation, and ignition performance after installation, the design range of L should meet the requirements, and the material of the outer housing is preferably copper alloy or nickel alloy.

[0088] Example 5

[0089] The mounting thread for the spark plug with pre-combustion chamber and engine is selected as M12, that is: the nominal diameter D of the outer thread is 12mm, the thread length S is 25mm, the nominal diameter d of the main housing thread is 8mm, the side electrode height H is 3mm, and the height T of the outer housing relief groove is 1.5mm. When the outer housing is made of carbon steel with a thermal conductivity λ of 45W / (mk), the design range of L should be 7.06~24.6mm.

[0090] Next, the following experiments were conducted to verify the heat dissipation effect and ignition performance:

[0091] (1) A 1.5L gasoline engine was selected as the test machine to compare the side electrode surface temperature (the side electrode surface temperature is the highest temperature of this type of spark plug). Thermocouple temperature measurement was used to conduct temperature comparison tests under the same engine operating conditions. The temperature was set to four levels: low, medium, high, and ultra-high. The specific comparison is shown in Table 10 below:

[0092]

[0093]

[0094] Table 10

[0095] (2) Ignition performance was verified using a 1.5L engine. Better ignition performance results in lower fuel consumption. The original spark plugs of an engine without a pre-combustion chamber structure were selected for comparison. The fuel consumption was set to high, and the fuel consumption was divided into four levels: ultra-low, low, medium, high, and ultra-high. The specific comparison data is shown in Table 11 below:

[0096] Fuel consumption: Ultra-low Fuel consumption: Low Fuel consumption: Medium Fuel consumption: High Fuel consumption: Extremely high L＝0 √ L＝2 √ L＝4 √ L＝6 √ L＝7.06 √ L＝10 √ L＝12 √ L＝14 √ L＝16 √ L＝18 √ L＝20 √ L＝22 √ L＝24.6 √ L＝26 √ L＝28 √

[0097] Table 11

[0098] Example 6

[0099] Keeping the structural design unchanged in Example 5 (all parameters are the same), but replacing the outer shell with a nickel alloy with a thermal conductivity λ of 80 W / (mk), the design range of L that satisfies equation (1) is 4.63~19.88 mm.

[0100] Similarly, the heat dissipation effect and ignition performance were verified, and the results are shown in Tables 12 and 13, respectively:

[0101] Temperature: Low Temperature: Medium Temperature: High Temperature: Extremely high L＝0 √ L＝2 √ L＝4.63 √ L＝6 √ L＝8 √ L＝10 √ L＝12 √ L＝14 √ L＝16 √ L＝18 √ L＝19.88 √ L＝22 √ L＝24 √ L＝26 √ L＝28 √

[0102] Table 12

[0103]

[0104]

[0105] Table 13

[0106] Example 7

[0107] Keeping the structural design unchanged in Example 5 (all parameters are the same), but replacing the outer shell with a copper alloy with a thermal conductivity λ of 330 W / (mk), the design range of L that satisfies equation (1) is 2.26 to 9.59 mm.

[0108] Similarly, the heat dissipation effect and ignition performance were verified, and the results are shown in Tables 14 and 15, respectively:

[0109] Temperature: Low Temperature: Medium Temperature: High Temperature: Extremely high L＝0 √ L＝2.26 √ L＝4 √ L＝6 √ L＝8 √ L＝9.59 √ L＝12 √ L＝14 √ L＝16 √ L＝18 √ L＝20 √ L＝22 √ L＝24 √ L＝26 √ L＝28 √

[0110] Table 14

[0111] Fuel consumption: Ultra-low Fuel consumption: Low Fuel consumption: Medium Fuel consumption: High Fuel consumption: Extremely high L＝0 √ L＝2.26 √ L＝4 √ L＝6 √ L＝8 √ L＝9.59 √ L＝12 √ L＝14 √ L＝16 √ L＝18 √ L＝20 √ L＝22 √ L＝24 √ L＝26 √ L＝28 √

[0112] Table 15

[0113] Example 8

[0114] Keeping the structural design unchanged in Example 5 (all parameters are the same), but replacing the outer shell with copper material with a thermal conductivity λ of 400W / (mk), the design range of L in Equation (1) is 2.13~8.63mm. However, since a length of L less than 3mm will affect the setting distance of the center electrode and affect the normal operation of the spark plug, the actual distance of L for the spark plug should be set above 3mm.

[0115] Similarly, the heat dissipation effect and ignition performance were verified, and the results are shown in Tables 16 and 17, respectively:

[0116]

[0117]

[0118] Table 16

[0119] Fuel consumption: Ultra-low Fuel consumption: Low Fuel consumption: Medium Fuel consumption: High Fuel consumption: Extremely high L＝0 √ L＝2.13 √ L＝4 √ L＝6 √ L＝8.63 √ L＝10 √ L＝12 √ L＝14 √ L＝16 √ L＝18 √ L＝20 √ L＝22 √ L＝24 √ L＝26 √ L＝28 √

[0120] Table 17

[0121] Comparative experiments were conducted on the schemes of Examples 5-8, with the shell strength set to high, medium, and low levels. The comparative data are shown in Table 18 below:

[0122] Shell strength: Low Shell strength: Medium Shell strength: High carbon steel √ Nickel alloy √ copper alloy √ copper √

[0123] Table 18

[0124] In summary, considering the strength of the housing, heat dissipation effect and ignition performance after installation, the design range of L should meet the requirements of equation (1), and the material of the outer housing is preferably copper alloy or nickel alloy.

[0125] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A spark plug, characterized in that, The system includes a main housing located on the outer periphery of an insulator and an outer housing connected to a metal tail cover. The outer housing is located on the outer periphery of the main housing. A first sealing gasket seals the gap between the seat of the main housing and the seat of the outer housing. A second sealing gasket seals the gap between the spark plug and the internal combustion engine. The main housing has threads. The plane orthogonal to the axis of the projection of the tip of the thread is plane A. The plane orthogonal to the axis of the contact surface between the outer housing and the second sealing gasket is plane B. The distance between plane A and plane B is L, and the dimension L is: 50*[H+(Dd) / 2] / λ+T≤ L ≤324*S / (80+λ)H+2T, In the formula, The outer diameter of the outer shell thread. The outer diameter of the main housing thread. The axial projection height of the spark plug side electrode extending out of the main housing end face. The height from the outer housing sealing surface to the starting point of its thread. The thermal conductivity of the outer shell is... The distance from the front end of the outer shell thread to plane B is 1.8mm≤H≤8mm, 0mm≤T≤4mm, and 1mm≤(Dd) / 2≤3mm.

2. The spark plug according to claim 1, characterized in that, The spark plug includes a center electrode and a side electrode. The insulator has a shaft hole extending along the axis. The center electrode is disposed in the shaft hole. The side electrode is disposed at the front end of the main housing and extends to a position opposite to the discharge surface of the center electrode to form a gap. The main housing with the side electrode end extends into the interior of the outer housing and is fixed by threads.

3. The spark plug according to claim 2, characterized in that, The outer housing is provided with a metal tail cover at the threaded front end, and the metal tail cover is provided with at least one through hole.

4. A spark plug according to claim 3, characterized in that, The distance from the threaded tip of the outer housing to plane B Greater than 17.5mm.

5. A spark plug according to claim 1, characterized in that, The thermal conductivity of the outer shell Higher than the thermal conductivity of the main shell, The range is 45~400W / (mk).

6. A spark plug according to claim 5, characterized in that, The outer housing mounting thread is M14, and the length of L satisfies any of the following values: ① When the power is 45W / (mk), the length of L is 7.61~15.96mm; ② When the power is 80W / (mk), the length of L is 4.94~13.13mm; ③ When the power is 330W / (mk), the length of L is 2.33~6.95mm; ④ When the power is 400W / (mk), the length of L is 2.19~6.38mm.

7. A spark plug according to claim 5, characterized in that, The outer housing has an M12 mounting thread, and the length of L satisfies any of the following values: ① When the power is 45W / (mk), the length of L is 7.06~24.6mm; ② When the power is 80W / (mk), L is set between 4.63 and 19.88 mm; ③ When the power is 330W / (mk), L is set between 2.26 and 9.59 mm; ④ When the power is 400W / (mk), L is set between 2.13 and 8.63mm.

8. A spark plug according to claim 1, characterized in that, The length of L is 3~20mm.

9. A spark plug according to claim 1, characterized in that, The outer shell material is a copper alloy or a nickel alloy.

10. An engine employing any one of the spark plugs described in claims 1-9.

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