Heating device for exhaust system of internal combustion engine
By designing a labyrinth structure and a static mixer, the problem of low catalyst temperature during cold start in the internal combustion engine exhaust system was solved, resulting in a high-efficiency, low-cost, and miniaturized heating device that improves the heating efficiency of the catalyst.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MARELLI EURO SPA
- Filing Date
- 2021-09-18
- Publication Date
- 2026-06-02
AI Technical Summary
Existing internal combustion engine exhaust systems have low catalyst temperatures during cold starts, resulting in high emissions. Furthermore, existing heating devices suffer from heat loss and overheating issues, increasing costs and size.
The heating device employing a labyrinth structure includes a conveying section and a return section surrounding a tubular body. Combining a static mixer and a labyrinth structure, the labyrinth structure provides thermal insulation and preheats the air, reducing heat loss. The gas temperature is controlled through exchange holes to prevent overheating.
This achieves high energy efficiency heating, reduces heat loss, avoids component overheating, lowers production costs and size, and improves catalyst heating efficiency.
Smart Images
Figure CN114251161B_ABST
Abstract
Description
[0001] Cross-references to related applications
[0002] This patent application claims priority to Italian Patent Application No. 102020000022396, filed on September 23, 2020, the entire disclosure of which is incorporated herein by reference. Technical Field
[0003] This invention relates to a heating device for an internal combustion engine exhaust system. Background Technology
[0004] An exhaust system for an internal combustion engine includes an exhaust pipe along which at least one device for treating exhaust gases from the internal combustion engine is installed; in particular, a catalyst (oxidant or reductant) is always provided, to which a particulate filter may be added. For the catalyst to function (i.e., to perform catalytic conversion), it needs to operate at a relatively high temperature (modern catalysts operate at temperatures close to 800°C) because only after reaching this operating temperature will the chemical reaction that converts unburned hydrocarbons, nitrogen oxides, and carbon monoxide into carbon dioxide, water, and nitrogen occur.
[0005] During the cold start phase (i.e., when the internal combustion engine is started after a prolonged stop, as the various components of the engine have reached ambient temperature), the catalytic converter remains well below its operating temperature for a relatively long period (even during the few minutes the engine idles, which is always or almost always, in winter and on city routes). Therefore, during the cold start phase, i.e., the period before the catalytic converter reaches its operating temperature, emissions at the outlet are high because the catalytic converter's purification effect is zero or, under any circumstances, not very effective.
[0006] To accelerate the reaching of the catalyst's operating temperature, patent documents EP0631039A1, WO2012139801A1, US8006487B2, US5320523A, CN104006394A, WO2014133817A1, US2015300630A1, US2014123632A1, and US2621477A propose installing a heating device along the exhaust pipe to generate a (very) hot airflow through the catalyst via fuel combustion. Specifically, the heating device includes a combustion chamber connected at its outlet to the exhaust pipe (immediately upstream of the catalyst) and at its inlet to a fan that generates an airflow through the combustion chamber. A fuel injector is also provided within the combustion chamber, injecting fuel mixed with air, and a spark plug is provided that cyclically releases a spark to ignite the air-fuel mixture, thereby achieving combustion of heated air.
[0007] Inside the heating element, fuel burns at high temperatures (above 1200°C-1400°C for gasoline); therefore, the combustion chamber walls are heated to temperatures approaching 1000°C, thus tending to release a large amount of heat to everything around the combustion chamber. This heat released from the combustion chamber walls can be problematic because it can overheat components near the combustion chamber. Furthermore, the heat released from the combustion chamber walls represents a "thermal power loss" because it does not contribute to heating the catalyst after it is generated (i.e., it reduces the energy efficiency of the heating element).
[0008] To limit heat diffusion from the combustion chamber walls, it has been proposed to wrap the combustion chamber walls with insulating materials; however, this solution significantly increases the production cost and size of the heating device. Summary of the Invention
[0009] The purpose of this invention is to provide a heating device for the exhaust system of an internal combustion engine that allows for high energy efficiency, is easy and inexpensive to manufacture, and has a small overall size.
[0010] According to the present invention, a heating device for the exhaust system of an internal combustion engine is provided, the heating device comprising:
[0011] The first tubular body provides a combustion chamber within it;
[0012] A fuel injector, which is mounted through the first base wall of the first tubular body, to inject fuel into the combustion chamber;
[0013] At least one air intake, which can be connected to a fan to receive airflow that is directed into the combustion chamber and mixed with fuel;
[0014] A hot air exhaust port is provided to allow hot air to exit the combustion chamber. The exhaust port is located at the second base wall of the first tubular body, which is opposite to the first base wall.
[0015] The outlet pipe originates at the exhaust port;
[0016] A spark plug, which is installed through the side wall of the first tubular body, to trigger the combustion of the air-fuel mixture; and
[0017] The labyrinth, which surrounds the sidewalls of the first tubular body, begins at the air intake and ends at the combustion chamber, and must be traversed by the air traveling from the air intake to the combustion chamber;
[0018] The labyrinth includes a transport section formed around a first tubular body and extending from an inlet at a first base wall of the first tubular body to an annular manifold, which preferably surrounds an outlet channel; and
[0019] The heating device is characterized by:
[0020] The transport section is formed only around half of the first tubular body; and
[0021] The labyrinth includes a return section that forms around the remaining half of the first tubular section that is not connected to the delivery section, has no points of overlap with the delivery section, and extends from the annular manifold to the combustion chamber. Attached Figure Description
[0022] The invention will now be described with reference to the accompanying drawings, which illustrate non-limiting embodiments of the invention, in which:
[0023] • Figure 1 It is a schematic partial view of the exhaust system of an internal combustion engine, which is equipped with a heating device manufactured according to the present invention;
[0024] • Figure 2 yes Figure 1 A longitudinal cross-sectional view of the heating device, with some components removed for clarity;
[0025] • Figure 3 yes Figure 1 A longitudinal cross-sectional view of the heating device, with some components removed for clarity, showing the prominent path of the airflow;
[0026] • Figure 4 yes Figure 1 A three-dimensional view of the heating device;
[0027] • Figure 5 yes Figure 1 Side view of the heating device;
[0028] • Figure 6 yes Figure 1 A longitudinal sectional view of the heating device, and
[0029] • Figure 7 and Figure 8 yes Figure 1 Two different cross-sectional views of the heating device. Detailed Implementation
[0030] exist Figure 1 In the text, the number 1 represents the exhaust system of the internal combustion engine 2.
[0031] The exhaust system 1 includes an exhaust pipe 3 that originates from the exhaust manifold of the internal combustion engine 2 and terminates at a muffler 4, from which exhaust gases are released into the atmosphere. At least one exhaust gas treatment device 5 for the exhaust gases from the internal combustion engine is installed along the exhaust pipe 3; in particular, a catalyst (oxidant or reductant) is always provided, to which a particulate filter may be added. For the catalyst to function (i.e., to perform catalytic conversion), it needs to operate at a relatively high temperature (modern catalysts operate at temperatures close to 800°C) because only after reaching this operating temperature will the chemical reaction that converts unburned hydrocarbons, nitrogen oxides, and carbon monoxide into carbon dioxide, water, and nitrogen occur.
[0032] In order to accelerate the heating of the processing unit 5, that is, to allow the processing unit 5 to reach its operating temperature more quickly, the exhaust system 1 includes a heating device 6, which generates a (very) hot airflow by burning fuel, which passes through the processing unit 5.
[0033] The heating device 6 includes a combustion chamber 7, which is connected at its outlet to an exhaust duct 3 (immediately upstream of the processing device 5) and at its inlet to a fan 8 (i.e., an air pump), which generates an airflow through the combustion chamber 7. A fuel injector 9 and a spark plug 10 are also arranged in the combustion chamber 7. The fuel injected by the fuel injector 9 mixes with air, and the spark plug 10 circulates a spark to ignite the air-fuel mixture, thereby achieving combustion that heats the air. The combustion chamber 7 of the heating device 6 terminates at an outlet duct 11, which connects to the exhaust duct 3 (immediately upstream of the processing device 5).
[0034] according to Figure 2 As shown, the heating device 6 includes a tubular body 12 (e.g., cylindrical, with a circular or elliptical cross-section) having a longitudinal axis 13; the tubular body 12 is defined at both ends by two opposing base walls 14 and 15, and laterally defined by a side wall 16 connecting the two base walls 14 and 15 to each other. The base wall 14 is perforated in the center to accommodate an injector 9, which is coaxial with the tubular body 12 (or with the longitudinal axis 13); in other words, the fuel injector 9 is mounted through the base wall 14 of the tubular body 12 to inject fuel into the combustion chamber 7. Similarly, the base wall 15 is perforated in the center to engage with an outlet pipe 11, which terminates in an exhaust pipe 3; that is, the base wall 15 has a hot air outlet 17 to exhaust hot air from the combustion chamber 7, from which the outlet pipe 11 originates.
[0035] like Figure 2 As shown, at least one air inlet 18 is obtained through the tubular body 12, which is connected to the air inlet pipe 19. Figure 1(As shown) is connected to the fan 8 to receive airflow, which is directed into the combustion chamber 7 and mixed with fuel injected by the fuel injector 9. Preferably, the air flows into the intake port 18 in a tangential direction (relative to the tubular body 12), that is, the intake duct 19 (relative to the tubular body 12) is tangential.
[0036] according to Figure 1 In the possible (but non-limiting) embodiment shown, check valve 20 is located at the air inlet 18, which only allows air to flow into the combustion chamber 7 (i.e., into the tubular body 12). Preferably, check valve 20 is passive (i.e., it does not include an electric, hydraulic, or pneumatic actuator to generate motion), pressure-controlled, and only opens when the pressure upstream of check valve 20 is greater than the pressure downstream of check valve 20. The function of check valve 20 is to prevent exhaust gases from rising out of the air inlet 18 when the heating device 6 is not in use (and therefore when the fan 8 is off), thus preventing them from being dispersed into the environment through the treatment device 5. Alternatively, check valve 20 may be installed along the outlet duct 11, for example at the air outlet 17; in this case, check valve 20 only allows air to flow out of the combustion chamber 7 (out of the tubular body 12) and into the exhaust duct 3, i.e., it prevents exhaust gases from flowing from the exhaust duct 3 into the combustion chamber 7 (into the tubular body 12).
[0037] like Figure 2 As shown, the heating device 6 includes a supply channel 21 that receives air from the air inlet 18, surrounds the end portion of the fuel injector 9, and terminates at a nozzle 22 arranged around the injection point of the fuel injector 9 (i.e., around the nose of the fuel injector 9 from which fuel is ejected).
[0038] Spark plug 10 is installed through the side wall 16 of tubular body 12 to trigger the combustion of an air-fuel mixture generated by the mixing of air and fuel. Air flows into tubular body 12 from intake port 18 and is introduced into combustion chamber 7 through nozzle 22 of supply channel 21, while fuel is injected into combustion chamber 7 by fuel injector 9. Specifically, the side wall 16 of tubular body 12 has a radial through-hole (i.e., perpendicular to longitudinal axis 13), within which spark plug 10 is installed (screwed) (obviously radially); the through-hole of spark plug 10 is as follows: Figure 4 , 5 As shown in Figure 7.
[0039] The heating device 6 includes a static mixer 23 (i.e., without moving parts), which is in the shape of a circular crown, arranged along the supply channel 21 and around the fuel injector 9, and is configured to generate turbulence, in particular vortex motion, in the air flowing toward the nozzle 22.
[0040] According to the preferred but non-limiting embodiment shown in the accompanying drawings, downstream of the static mixer 23, the supply channel 21 has a gradually decreasing cross-sectional area, resulting in an increase in air velocity. Specifically, downstream of the static mixer 23, the supply channel 21 includes an initial portion with a constant cross-sectional area, an intermediate portion with a gradually decreasing cross-sectional area, and a final portion with a constant cross-sectional area extending to the nozzle 22.
[0041] The supply channel 21 is defined externally by an outer conical tubular body 24 and internally by an inner conical tubular body 25 that surrounds and includes the fuel injector 9. That is, the supply channel 21 is defined between the inner conical tubular body 25 and the outer conical tubular body 24. Specifically, the two conical tubular bodies 24 and 25 alternately arrange conical segments (i.e., converging shapes with gradually decreasing dimensions) and cylindrical segments (i.e., shapes with constant dimensions).
[0042] According to a preferred embodiment, air flows into the supply channel 21 in a tangential flow manner so as to exhibit a rotational tendency (which is subsequently increased by the action of the static mixer 23), which is beneficial for mixing with the fuel injected by the fuel injector 9; in other words, the combustion air is introduced into the combustion chamber 7 through a pipe tangential to the combustion chamber 7, allowing for a circumferential motion of the combustion air flow (which is further enhanced by the presence of the static mixer 23) to optimize the air / fuel mixing within the combustion chamber 7.
[0043] The heating device 6 includes a labyrinth 26 surrounding the sidewall 16 of the tubular body 12, starting at the air inlet 18 and ending at the supply channel 21, and must be passed through by air from the air inlet 18 (i.e., from the fan 8) to the supply channel 21.
[0044] The maze 26 includes a transport section 27 which is formed around half of the tubular body 12 (i.e., around about 180° of the tubular body 12) and extends from the base wall 14 to the base wall 15 (also including the initial portion of the outlet pipe 11), and a return section 28 which is formed around the other half of the tubular body 12 (i.e., around 180° of the tubular body 12 in a complementary manner to the transport section 27) and extends from the base wall 15 to the base wall 14.
[0045] In other words, the delivery section 27 is formed around one half of the tubular body 12 and extends from the air inlet 18 at the base wall 14 of the tubular body 12 to the annular manifold 29 surrounding the outlet pipe 11; on the other hand, the return section 28 is formed around the remaining half of the tubular body 12 that does not join the delivery section 27, has no point of overlap with the delivery section 27, and extends from the annular manifold 29 to the combustion chamber 7 (i.e., to the supply passage 21). The annular manifold 29 is an annular environment surrounding the outlet pipe 11 (which is the hottest spot in the entire heating device 6) and connecting the delivery section 27 to the return section 28; that is, air is delivered from the delivery section 27 through the annular manifold 29 (which forms the connection point between the two sections 27 and 28) to the return section 28. Therefore, the manifold 29 forms a transition area (space) between the delivery section 27 and the return section 28, that is, the area where the delivery section 27 ends and the return section 28 begins.
[0046] Figure 3 This shows the airflow path through the tubular body 12 from the air inlet 18 to the air outlet 17; the airflow can be seen from the air inlet 18 to the supply passage 21, then through the static mixer 23, and out of the nozzle 22 surrounding the nose of the fuel injector 9. Figure 3 As shown, air enters from the inlet 18, travels along the conveying section 27 from the base wall 14 to the base wall 15, flows from the conveying section 27 to the return section 28 at the collector 29, passes through the return section 28 from the base wall 15 to the base wall 14, and finally at the base wall 14, it is transferred from the return section 28 to the supply channel 21.
[0047] In other words, the two segments 27 and 28 are arranged side by side around the tubular body 12, covering the sidewall 16 of the tubular body 12 in a complementary manner.
[0048] The presence of the labyrinth 26 between the air intake 18 and the supply passage 21 allows for two positive effects: highly effective thermal insulation of the combustion chamber 7, which is surrounded by the labyrinth 26 (and therefore thermally insulated) (thus the temperature of the heating device 6 is significantly lower) and preheating of the combustion air introduced into the combustion chamber 7, thereby promoting combustion ignition and energy efficiency. In other words, the combustion air passing through the labyrinth is heated by absorbing heat from the combustion chamber 7, thus achieving both (positive) preheating of the combustion air and (positive) thermal insulation of the combustion chamber 7.
[0049] Thus, the heating device 6 is highly energy efficient because the heat released from the wall of the combustion chamber 7 does not represent (complete) "thermal power loss," since most of this heat is absorbed by the combustion air and thus helps to heat the catalyst (i.e., improve the energy efficiency of the heating device 6).
[0050] Typically, the temperature of the combustion air entering the combustion chamber 7 after passing through the maze 26 is about 100-150℃.
[0051] In addition, the delivery section 27 of the labyrinth 26 is located at the spark plug 10, so that the combustion air passing through the delivery section 27 passes around the spark plug 10, thereby producing a beneficial cooling effect on the spark plug 10; in this way, the spark plug 10 (located in the center of the combustion chamber 7) will not overheat because it is constantly cooled by the combustion air passing through the delivery section 27.
[0052] On the other hand, the fuel injector 9 does not require special cooling because it is not located in the center of the combustion chamber 7 (in fact, its nose is always a certain distance from the front of the flame) and is cooled by the fuel flowing inside and the (relatively) fresh air circulating in the supply channel 21 around the fuel injector 9.
[0053] according to Figure 2 and Figure 3 In the possible, but not limiting, embodiment shown, the labyrinth 26 has a plurality of through and aligned exchange holes 30 that directly connect the labyrinth 26 to the outlet duct 11 (at the manifold 29). The function of the exchange holes 30 is to introduce a portion of the air from the fan 8 directly into the outlet duct 11 without passing through (i.e., bypassing) the combustion chamber 7. The direct entry of fresh air downstream of the combustion chamber 7 lowers the temperature of the hot air introduced into the exhaust duct 3 and passing through the processing unit 5, thus preventing the processing unit 5 from overheating. In other words, the presence of the exchange holes 30 allows for control of the temperature of the combustion gases flowing to the exhaust duct 3 (i.e., to the processing unit 5) to prevent the combustion gas temperature from reaching a critical level (too high) for the processing unit 5.
[0054] By appropriately adjusting the size (calibrated) of the exchange orifice 30, it is possible to obtain the optimal temperature of the combustion gases flowing to the exhaust duct 3 (i.e., to the processing device 5): the temperature of the combustion gases flowing out of the combustion chamber 7 is typically 1200°C-1400°C, while the optimal temperature of the combustion gases flowing to the exhaust duct 3 (i.e., to the processing device 5) should be 800°C-900°C; therefore, by appropriately adjusting the size of the calibrated exchange orifice 30, it is possible to allow a sufficient flow of fresh air to mix with the flow of combustion gases flowing out of the combustion chamber 7, thereby obtaining the optimal temperature downstream of the calibrated exchange orifice 30.
[0055] It must be emphasized that by adding fresh air to cool the combustion gases exiting the combustion chamber 7, the temperature of the combustion gases is reduced, while the flow rate of the combustion gases is increased. Therefore, due to the compensating effect between the reduction in the temperature of the combustion gases and the increase in the flow rate of the combustion gases, the overall thermal power generated by the heating device 6 (which can be calculated by multiplying the temperature of the combustion gases by the flow rate of the combustion gases) remains (approximately) constant.
[0056] In the embodiment shown in the accompanying drawings, the heating device 6 includes another tubular body 31 coaxial with and arranged around the tubular body 12. An annular space is defined between the two tubular bodies 12 and 31, in which a labyrinth 26 (i.e., the conveying section 27 and the return section 28 of the labyrinth 26) is obtained. The longitudinal (axial) separation between the conveying section 27 and the return section 28 is achieved by inward deformation of the sidewall 32 of the tubular body 31 (i.e., toward the longitudinal axis 13); that is, the sidewall 32 of the tubular body 31 has two straight grooves 33 (deformation) (e.g. Figure 7 and Figure 8 As shown), it is U-shaped and arranged on opposite sides of the sidewall 32, and terminates in contact with the sidewall 16 of the tubular body 12 so as to form insulation between the transport section 27 and the return section 28 of the labyrinth 26.
[0057] The presence of two grooves 33 on the sidewall 32 of the tubular body 31 allows for insulation between the transport section 27 and the return section 28 of the labyrinth 26 in an extremely simple manner, i.e., without adding any additional components, but only through local variations (deformations) in the shape of the sidewall 32 of the tubular body 31.
[0058] According to a preferred embodiment, the heating device 6 includes a control unit 34 (in... Figure 1 (Illustrated schematically) It is configured to control the entire operation of the heating device 6, namely, to actuate the fan 8, injector 9 and spark plug 10 in a coordinated manner in order to achieve the desired goal in the most efficient and effective way (i.e., to rapidly heat the processing device 5 without damaging the processing device 5 due to excessive temperature).
[0059] In the (non-limiting) embodiment shown in the accompanying drawings, a supply channel 21 is provided that receives air from the labyrinth 26 (i.e., the return segment 28 from the labyrinth 26), surrounds the end of the fuel injector 9, and terminates at a nozzle 22 arranged around the injection point of the fuel injector 9; according to different embodiments not shown, there is no supply channel 21, and the labyrinth 26 (i.e., the return segment 28 of the labyrinth 26) terminates at an opening that flows directly into the combustion chamber 7. That is, in all cases, the labyrinth 26 begins at the intake port 18 and terminates in the combustion chamber 7, with (or possibly even without) the intervention of the supply channel 21 (therefore it is an optional element).
[0060] The embodiments described herein can be combined with each other without departing from the scope of the invention.
[0061] The heating device 6 described above has many advantages.
[0062] First, the heating device 6 described above can achieve high energy efficiency even when its size is drastically reduced.
[0063] In addition, the heating device 6 can generally limit the transfer of heat from the combustion chamber 7 to the components arranged near the heating device 6, thus preventing damage to the components due to overheating.
[0064] The heating device 6 described above also has a high thermal power relative to its overall size; that is, although the heating device 6 is relatively small, it allows for the generation of high thermal power.
[0065] Finally, the heating device 6 described above is simple to manufacture and inexpensive because it consists of several uncomplicated parts and is easy to weld and assemble with standard components.
[0066] List of reference numerals
[0067] 1. Exhaust System
[0068] 2 Internal Combustion Engines
[0069] 3 exhaust pipes
[0070] 4 silencers
[0071] 5 processing devices
[0072] 6 Heating devices
[0073] 7 Combustion Chamber
[0074] 8 fans
[0075] 9 injectors
[0076] 10 spark plugs
[0077] 11 Export Pipelines
[0078] 12 tubular bodies
[0079] 13 Longitudinal axis
[0080] 14 base walls
[0081] 15 base walls
[0082] 16 sidewalls
[0083] 17 air outlets
[0084] 18 air intakes
[0085] 19 Intake pipe
[0086] 20 Check Valve
[0087] 21 supply channels
[0088] 22 nozzles
[0089] 23 Static Mixer
[0090] 24 external tapered tube body
[0091] 25 internal tapered tube body
[0092] 26 Mazes
[0093] 27 Conveyor Section
[0094] 28 Return segment
[0095] 29 manifold
[0096] 30 exchange ports
[0097] 31 tubular body
[0098] 32 sidewalls
[0099] 33 grooves
[0100] 34 control units
Claims
1. A heating device (6) for an exhaust system (1) of an internal combustion engine (2); the heating device (6) comprising: The first tubular body (12) has a combustion chamber (7) inside it; A fuel injector (9) is installed through the first base wall (14) of the first tubular body (12) to inject fuel into the combustion chamber (7); At least one air inlet (18) is provided, which can be connected to a fan (8) to receive an airflow that is directed into the combustion chamber (7) and mixed with fuel. Hot air outlet (17) allows hot air to be discharged from the combustion chamber (7), the outlet (17) being located at the second base wall (15) of the first tubular body (12) opposite to the first base wall (14); Outlet pipe (11), which originates at the outlet (17). Spark plug (10), which is installed through the sidewall (16) of the first tubular body (12) to trigger the combustion of the air-fuel mixture; as well as The maze (26) surrounds the sidewall (16) of the first tubular body (12), begins at the air inlet (18), ends in the combustion chamber (7), and must be passed through by the air from the air inlet (18) to the combustion chamber (7); The maze (26) includes a conveying section (27) formed around the first tubular body (12) and extending from an air inlet (18) at a first base wall (14) of the first tubular body (12) to an annular manifold (29) surrounding an outlet pipe (11); and The heating device (6) is characterized in that... The conveying section (27) is formed only around half of the first tubular body (12); and The maze (26) includes a return section (28) that forms around the remaining half of the first tubular body (12) that is not joined to the delivery section (27), has no points of overlap with the delivery section (27), and extends from the annular manifold (29) to the combustion chamber (7).
2. The heating device (6) according to claim 1, characterized in that The conveying section (27) is formed around one half of the first tubular body (12), and the return section (28) is formed around the other half of the first tubular body (12) in a complementary manner to the conveying section (27).
3. The heating device (6) according to claim 1, characterized in that The annular manifold (29) connects the delivery section (27) to the return section (28), so that air flows from the delivery section (27) to the return section (28) through the annular manifold (29).
4. The heating device (6) according to claim 1, characterized in that The two segments (27, 28) of the maze (26) are arranged side by side around the first tubular body (12), thereby covering the sidewall (16) of the first tubular body (12) in a complementary manner.
5. The heating device (6) according to claim 1, characterized in that The delivery section (27) of the maze (26) is located at the spark plug (10), so that the air flowing through the delivery section (27) flows around the spark plug (10).
6. The heating device (6) according to claim 1, characterized in that A second tubular body (31) is provided, coaxial with the first tubular body (12) and arranged around the first tubular body (12); and An annular space is defined between the two tubular bodies (12, 31), forming a maze (26).
7. The heating device (6) according to claim 6, characterized in that The longitudinal spacing between the conveying section (27) and the return section (28) is obtained by the inward deformation of the sidewall (32) of the second tubular body (31).
8. The heating device (6) according to claim 7, characterized in that The sidewall (32) of the second tubular body (31) has two straight grooves (33) arranged on opposite sides of the sidewall (32) and terminating in contact with the sidewall (16) of the first tubular body (12) to form insulation between the conveying section (27) and the return section (28).
9. The heating device (6) according to claim 1, characterized in that The maze (26) has multiple through-holes (30), which are calibrated and establish a direct connection between the maze (26) and the outlet pipe (11).
10. The heating device (6) according to claim 9, characterized in that The exchange port (30) is obtained at the manifold (29).
11. The heating device (6) according to claim 1, characterized in that Air flows tangentially into the air inlet (18).
12. The heating device (6) according to claim 1, comprising a check valve (20) arranged at the air inlet (18) to allow air to flow only to the exhaust pipe (3) of the exhaust system (1), the check valve being passive and pressure-controlled, and opening only when the pressure upstream of the check valve (20) is higher than the pressure downstream of the check valve (20).
13. The heating device (6) according to claim 1, comprising a supply channel (21) that receives air from an air inlet (18) via a labyrinth (26), the supply channel surrounding an end of a fuel injector (9) and terminating at a nozzle (22) arranged around the injection point of the fuel injector (9).
14. The heating device (6) according to claim 13, characterized in that Includes a static mixer (23) which is circular in shape and is arranged along the supply channel (21) and around the fuel injector (9), and the static mixer (23) is configured to generate turbulence in the air flowing toward the nozzle (22).
15. The heating device (6) according to claim 14, characterized in that The static mixer (23) is configured to generate vortex motion in the air flowing toward the nozzle (22).
16. An exhaust system (1) for an internal combustion engine (2), the exhaust system (1) comprising: Exhaust pipe (3), which begins at the exhaust manifold of the internal combustion engine (2) and ends at the muffler (4), from which exhaust gas is released into the atmosphere; An exhaust gas treatment device (5) is provided along the exhaust pipe (3); and The heating device (6) according to any one of claims 1 to 15 is connected to an exhaust pipe (3) upstream of the processing device (5), and is designed to generate a hot airflow by burning fuel.