WO2013108281A2

WO2013108281A2 - Two-stroke internal combustion engine with reduced thermal dispersion

Info

Publication number: WO2013108281A2
Application number: PCT/IT2013/000014
Authority: WO
Inventors: Roland HOLZNER
Original assignee: ASPA Srl
Current assignee: ASPA Srl
Priority date: 2012-01-16
Filing date: 2013-01-16
Publication date: 2013-07-25
Anticipated expiration: 2014-07-16
Also published as: WO2013108281A3

Description

TWO-STROKE INTERNAL COMBUSTION ENGINE WITH REDUCED THERMAL DISPERSION

Field of the invention

This invention relates to an improved two-stroke internal combustion engine, namely an internal combustion engine in which the control of the suction fluid obtained in the engine is carried out in way to limit the exchange of thermal energy of the engine, in such a way to improve the volume and mass of the fluid sucked at all the operating conditions, especially at high load and at high rotation conditions.

Prior art

The background art includes some types of internal combustion engine in which the fluid insulating effect is searched, both at the suction and at the exhaust, but with very different aims. In the art is known since a long time, as visible in the prior art document GB 478,471 , that the suction duct is cooled in order to maintain the sucked fluid with greater density and have greater combustion-air in the cylinder at the moment of the burst. In similar way, in the document DE 10 2007 045 634 a thermal insulation is placed in an entry zone of the inlet valve of the fluid sucked in the cylinder by the suction collector. The thermally insulating coating is pre-formed in single piece and inserted within the channel in the assembly even if with profile not in contact with the wall.

In the art, as further said, also the insulation of the exhaust duct to avoid that the exhaust gases exiting from the heated cylinder impregnate the cylinder and decrease the amount of air that, if heated, enters the engine, is known. An example of the aforementioned embodiment is shown in the document US 5,438,825 in which the exhaust duct is coated with metallic insert to create an air space between the exit hot gases and the part of the main cylinder. Moreover, from the document US 5,372,176 is shown the method of production of cylinders for two-stroke engines with insulating metallic insert in the exhaust duct by the lost-foam melting process. So, always from the prior art document GB 1 561 528 an exhaust duct coating for dump valves in an internal combustion engine head is described where the prefabricated coating is made up of metallic sheets or by melting and is introduced in the exhaust ducts to avoid the heat transfer to the head, leaving an air space with the seats of these ducts in the head.

Moreover, even if the insulator is placed on the surface of the engine parts in contact with the hot gases or with the insulator in the suction ducts with inserted piece, the execution is complex and specially expensive in the cooling of the air being sucked in such a way to make it not much economical and of difficult application in an effective way with directed application in the directly touched engine part.

In conclusion, none of these prior documents proposes to carry out an engine that though in the constructive simplicity of a two-stroke engine, namely with no controlled valves, allows to carry out a significant improvement of the thermal exchange between the fluids, in suction and in exhaust, that limits the heat, namely the energy released by the fluids to the engine parts, especially if these must work at high loads.

This background art is susceptible of important improvements with regard to the possibility of carrying out an improved two-stroke internal combustion engine, that overcomes the aforementioned drawbacks and makes functional a significant improvement of the yield to prevent the heat transmission between the housing and the fluid being sucked and with the reduced thermal heat dispersion of the exhaust gases in the members of the same engine.

The technical problem, therefore, that is at the base of the present invention is to carry out a two-stroke internal combustion engine with reduced thermal dispersion in the members of the same engine and with reduced release of the heat present in the members to the fluid being sucked.

An additional aim of the present invention is to insulate the fluids inside the engine so that the fluid can perform evolutions in engine and at the same time is not exchanged with the parts by which heat is collected, receiving it at the suction or yielding it at the exhaust.

Moreover, a further part of the more above exposed technical problem is to make functional and practical the insulating protections for the suction and exhaust ducts on the motor application or assembling. An additional, and further, aim of the present invention is to insulate the fluids inside the engine with the parts with which it is in contact by the heat in particular the one released at the suction on the fluid entering the pumps housing that conditions the capacity and speed of the fluid being sucked to differentiate itself at the different engine regimes so as to make it modifiable at will of a mechanical preparer.

Finally, a further part of the above exposed technical problem is to obtain easiness in the assembling and in the replacement of the insulation coating in order to satisfy also, but not only, the variable needs of a skilled mechanic of competition engines.

Summary of the invention

This problem is solved, according to the present invention, by an improved two-stroke internal combustion engine with reduced thermal dispersion, comprising a cylinder, a piston and a motor shaft; characterised in that it presents a suction insert with insulating coating, inserted or made in the engine housing or in the housing pumps to coat the air suction duct; the insulating coating of the fluid sucked towards the duct metallic wall extends also in the initial part of the transfer ducts.

Moreover, in a specific execution, the coating in insulating material is made up of material with resin base resisting to the etching of oils and fuels.

Furthermore, in an additional constructive form the suction insert extends in the engine housing part lower than the cylinder, to protect the sucked fluid also in the housing pumps and before entering the transfer ducts.

Moreover, in a preferred execution, the insulating suction insert can be replaced with a similarly insulating insert and having an internal shape different in diameter or section or bending in such a way to change the characteristics of the engine as desired by the preparer. The replaceability also allows to make the insulating insert in the suction duct in at least two parts, in such a way to allow shape changes of the internal duct according to the wish and experience of the mechanic of competition engines.

Even more, advantageously, the insulating insert in the replaceable suction duct is made in two halves, on average symmetrical on a dividing plane.

Moreover, in a different constructive form, in at least one of the feeding ducts or exhaust of the fluids there is an insulating coating of the fluid passing towards the metallic wall of the duct.

Moreover, a two-stroke internal combustion engine; includes in the cylinder body at least one exhaust duct and at least one transfer duct and presents, to obtain a reduced thermal dispersion, from the burnt gas exiting towards the fluid in entry to the cylinder, an insulating insert placed in the exhaust duct.

Moreover, a two-stroke internal combustion engine; comprises in the cylinder body at least one exhaust duct, at least one transfer duct and presents, to obtain a reduced thermal dispersion, from the burnt gas in exit towards the fluid in entry to the cylinder, an insulating insert placed in the transfer duct.

Moreover, a two-stroke internal combustion engine; comprises in the cylinder body at least one exhaust duct, at least one transfer duct and a stratification duct and presents, to obtain a reduced thermal dispersion, from the burnt gas in exit towards the fluid in entry to the cylinder, an insulating insert placed in the stratification duct.

Moreover, a cylinder for a two-cycle internal combustion engine; comprises in the cylinder body at least one exhaust duct and at least one transfer duct and presents, to obtain a reduced thermal dispersion, from the burnt gas in exit towards the fluid in entry to the cylinder, an insulating insert placed in the transfer duct.

Moreover, a cylinder for a two-cycle internal combustion engine; comprises in the cylinder body at least one exhaust duct, at least one transfer duct and a stratification duct and presents, to obtain a reduced thermal dispersion, from the burnt gas in exit towards the fluid in entry to the cylinder, an insulating insert placed in the stratification duct.

Moreover, in the execution of the insulating coatings, the insulating material used for the execution is made up of two-component resin; or, the coating in insulating material is made up of ceramic material.

Finally, an engine or cylinder, for a two-stroke internal combustion engine, comprising in the cylinder body: at least one exhaust duct, at least one transfer duct, a stratification duct, and a suction duct, presents in more than one of these ducts an insert in insulating material, as described later, in the suction duct; an insulating insert in the exhaust duct; an insulating insert in the transfer duct and an insulating insert in the stratification duct, to obtain a reduced thermal dispersion from the gas in entry to the cylinder.

The characteristics and the advantages of the present invention, in the execution of a two-stroke internal combustion engine with reduced thermal dispersion, are mentioned in the description made in the following, of some schematic examples of execution supplied as indication and not as limitative, with reference to eight enclosed drawing tables.

Brief description of the drawings

Figure 1 represents a schematic section on a plane axial to the cylinder of a two-stroke internal combustion engine in which in the suction duct and in the exhaust duct inserts are provided insulating the fluids towards the wall of the same ducts, according to the invention;

Figure 3 represents a schematic view axial to the motor shaft of the internal combustion engine of Figure 2 limited to the single pump housing and of the insulating insert in the suction duct, subdivided in a plane axial to the cylinder;

Figure 4 represents a schematic view in perspective of the pump housing and of the suction duct insulating insert, of the engine of Figure 2, that are both advantageously subdivided on the plane axial to the cylinder of the internal combustion engine;

Figure 5 represents a schematic view axial to the motor shaft, of the internal combustion engine of Figure 1 , of the single pump housing and of the suction insulating insert complete also with the coating of the pump housing, subdivided in a plane axial to the cylinder; Figure 6 represents a schematic view axial to the cylinder of the engine housing of Figure 1 as represented in the previous Figure of one single half;

Figure 7 represents a schematic perspective view of an insulating insert of one half of the pump and suction housing, intended to be introduced in the half of pump housing of Figure 8, according to the invention, that is the schematic picture of this half of the pump housing of an engine as represented in Figure 1 ;

Figure 9 represents an external sideway schematic view of a cylinder for internal combustion engine of Figure 1 , according to the invention;

Figure 10 represents an X-X schematic section of Figure 9 of the exhaust duct of the burnt gases in which the insulating insert of the gases from the duct walls is visible;

Figure 1 1 represents a schematic view axial to the cylinder from the top of a cylinder for the engine of Figure 1 ;

Figure 12 represents a XII-XII schematic section of Figure 1 1 on the axial plane of the cylinder and on the plane containing the axis of the exhaust duct of the exhaust gases, in which the insert insulating the walls of the exhaust duct from the burnt gases coming from the cylinder, as well as an insulating insert in the duct of the stratification port of the fluid in suction is visible;

Figure 13 represents a schematic view axial to the cylinder from below a cylinder for the engine of Figure 1 in which the insulating inserts in the ducts and transfer ports are visible;

Figure 14, finally, represents a schematic section XIV-XIV of Figure 13 on the axial plane of the cylinder and containing two of the ducts and transfer ports with insulating inserts in the transfer ducts.

Detailed description of a preferred embodiment

In Figure 1 , in a constructive form of single-cylinder endothermic engine 1 endowed with the insulating inserts of the invention, with two-stroke cycle, is visible an engine housing 2: here represented in two halves on an axial plane containing the axis of the cylinder, and in which a crank 3 is made rotating on the motor shaft 4, a connecting rod 5 connects a piston 6 to the crank in its reciprocating motion in the cylinder 7 in the known way. The cylinder is endowed with pressed-in barrel 8, or alternatively it can be endowed with internal surface hardening as known. The suction duct 9 and the pump housing 10 are coated with a suction insert 1 1 , in insulating material, to avoid the contact of the fluid in entry with the internal walls of the engine housing. A stratification duct 12 is provided downstream of the suction duct 9 and is endowed with insert 13 in insulating material in the cylinder 7. The fluid in entry possibly being the comburant/combustible mixture prepared in one of the known ways, with carburettor or fuel injector in the suction duct or only air if the engine is endowed with direct injection in the head, here not represented as being of known type. In the exhaust duct 14, present in the cylinder 7, an exhaust insert 15 is housed being held in the housing by the collector 16 of the exhaust pipe. The exhaust insert 15 being made of insulating material and resistant to high temperatures, allows the hot burnt gases, exiting from the cylinder, not to yield heat to the walls of the exhaust duct, in practice to preserve the cylinder from the strong heating due to gases discharged from the engine. Moreover, in the following Figures from 5 to 8 a half of the engine housing 2 is represented separated or joined to the corresponding half of the suction insert 11 , separated in the Figures 7 and 8 and joined in the Figures 5 and 6. Also the configuration of the pump housing 10, for the transfer ports 17, has a ramp 18 in the engine housing 2 and a corresponding inclined shape 19 in the suction insert 1 1 , insulating; so also the stratification port presents an enlarging 20 of the suction duct 9 and a corresponding axial channel 21 right away downstream of the suction duct 9 in the suction insert 1 1.

In similar way, the engine housing presents one half almost mirror-like the one represented and which also presents an insulating internal insert similar to the suction insert 1 1 , represented, but provided for the specific configuration of that engine housing further half.

In the Figures from 10 to 12 the exhaust port 22, the transfer ports 17, present on each side of the cylinder 7 and the pressed-in barrel 8 as well as the stratification port 23 at the mouth end of the stratification duct 24 are visible.

Moreover, in a cylinder 28, in the Figures 13 and 14, are visible the transfer ducts 27 coated with inserts 29 in insulating material made by cast in transfer ducts of greater section suitable to house the insulator thickness. In Figure 2, in an improved constructive configuration of single cylinder endothermic engine 41 , with two-stroke cycle, an engine housing 42 is visible: here represented in two halves on an axial plane containing the cylinder axis, and in which a crank 43 is made rotating on the motor shaft 44; a connecting rod 45 connects in the known way a piston 46 to the crank in its reciprocating motion in the cylinder 47. The cylinder is endowed with suction duct 49 and the pump housing 50 presents a suction insert 51 , in insulating material, to avoid the contact of the fluid in entry with the internal walls of the duct in the engine housing. A stratification duct 52 is provided downstream of the suction duct 49 of the cylinder 47. In the Figure are also visible with 54 an exhaust duct of the burnt gases from the cylinder and with 65 a suction reed pack placed, as known, in said suction duct 49.

Moreover, in the following Figures 3 and 4 of one half of the engine housing 42 and of the ensemble of the two halves of the engine housing in separate and exploded configuration, the two corresponding halves of the suction insert 51 are visible. The configuration of the pump housing 50, for the transfer ports 57, presents a ramp 58 in the engine housing 42 and a corresponding inclined shape 59 in the suction insert 51 , insulating; so also the stratification port presents an enlarging 60 of the suction duct 49 and a corresponding axial channel 61 right away downstream of the suction duct 49 in the suction insert 51 in insulating material, towards the represented stratification duct.

In similar way, the engine housing 42 presents, in Figure 4, one half almost mirror-like to the one represented in Figure 3 and that also presents an insulating internal insert similar to the suction insert 51 , represented, but provided for the specific shape of that further engine housing half. So, the two parts of the suction insulating insert 51 , right 70 and left 71 , when moved away allow the intervention of the mechanical skilled engine mechanic on the side-walls 72 and on the upper and lower surface 73 74 of the duct internal to the insert that determines the geometry of the suction duct 49 for the conveying of the sucked fluids in the pump housing 10.

The application and the assembling of the above described inserts occur as follows. The inserts are preformed with appropriate dies or forms suitable to provide the internal shape of the duct to be coated, when it is an exhaust one, advantageously with a ceramic material, or when it is a suction one with insulating material, generally plastic or obtained by melting or cast in the aforementioned form or die. The insert is then introduced in its seat in the cylinder 7 in such a way to remain stopped by the cylinder assembling in the engine, for example as represented for the stratification insulating insert 12 or for the exhaust insulating insert 15.

Another way of execution of the insulating inserts in particularly curved ducts, namely with under-cuts, as the transfer ducts 27 in the cylinder 28: they are made directly in the ducts by previous coating with the still soft and just preformed insulating material, as a two-component resin, and the introduction of a mould in soft and flexible material, to make the inside wall of the duct insulating coating, but sufficiently rigid to maintain the position of the bi-component resin layer and give the desired shape to the duct. At the end of the hardening the shape internal to the duct is removed due to its flexibility also in the presence of the aforementioned under-cuts.

In similar way, but as already known in the art the insulating coating 11 of the suction duct and of the pump housing 10 is formed or pre-formed in a special die that recopies the necessary shape of the engine housing part and duct in which it must be inserted and placed in the assembling before the internal members of the engine.

The suction insulating insert 51 further described, in its execution, application and assembling, is pre-formed with appropriate dies or forms suitable to provide the internal configuration of the suction duct with insulating material, generally plastic, resisting to the etching of oils and fuels, and obtained by melting or cast in the aforementioned form or die. The insert 51 in two halves is then introduced in its seat in the engine housing 42 in such a way to remain tightened by the engine assembling.

The production die of the insulating insert 11 or 51 , of the suction duct 9 or 49 in the pump housing 10 or 50, is formed or pre-formed in a special die that recopies the necessary configuration of the engine housing part 2 or 42 in which it must be inserted and placed in the assembling whilst assembling the internal members of the engine.

Moreover, the change or the replacement of the insulating insert 51 in the suction duct can occur in moments successive to the assembly; in fact, a mechanical preparer may have more inserts 51 available, but having shape different from the suction duct internal 49 to them. Furthermore, the execution in two parts, 70 and 71 , of the suction duct allows the skilled engine mechanic to modify manually the duct inside as desired exploiting the effect on the sucked fluid flow, air/combustible or even only air for direct injection engines, that a different configuration of the duct generates on the power curve and/or torque of the engine so prepared for a specific use.

The change of the internal shape of the insulating insert 11 , in the portion that covers the suction duct 9, can occur as shown for the suction insert 51. Or the insulating insert 11 of the suction duct 9 and of the pump housing 10 can be made separate in such a way to allow the mechanical preparer to intervene only on the insulating coating part of the insert 11 of said suction duct 9.

The operating of a two-stroke internal combustion engine, with reduced thermal dispersion according to the invention, occurs as known in the art for the two-stroke engines in the operating phase with volumetric behaviour of the fluids in suction and exhaust, while in the engine described in the invention the operation can occur as follows. Once reached a high rotational state, it is well known that the propagation of the flame is so fast, that the volumetric cycle is not anymore distinguishable in its characteristic phases, and the pump housing 10 or 50 does not make anymore the function of treating all the fluid passing in the cylinder. Namely the speed of the fluid in the entry in the exhaust port and in exit from the transfer and stratification ports is such as to increase considerably the temperature in the combustion chamber. In these conditions the heat collected by the walls of the cylinder, especially from the exhaust duct, is transmitted to the fresh fluids in the suction, so the engine efficiency decreases for decreased amount of comburant air that enters the engine. The possibility, as further described, to coat the ducts internal to the transfer and stratification cylinder, for the fluids in suction and of exhaust for the exhaust gases in exit, allows to further limit this thermal exchange, beyond what provided in the only suction duct, with undoubted positive effects in the greater density for the fluid lower temperature or combustion-air that is sucked.

Moreover, in the Figures a single cylinder engine is represented, but for a most profitable execution also in the multi-cylinder engines the insulating coating of the ducts in the respective cylinders can be inserted, made or generated by cast as described more over.

Finally, in the Figures the cylinder 7 or 28 presents a pressed-in barrel 8, but the execution and assembling of the described inserts both in suction and in exhaust may occur in similar way in a cylinder with the integral barrel, namely made with a coating in hard material as known in the art.

Even if in the Figures a water cooled engine is represented, the application of an insulating insert in the suction duct is much more effective in an air-cooled engine, due to the minor cooling capacity of the air on the hot parts of the engine, specially at the base of the cylinder, just where the insulating insert 11 or 51 of the suction duct 9 or 49 is housed, also in case the effect of intake valve was automatic, as with the reeds block 65, but was carried out by the underside of the piston in its reciprocate motion. The advantages in the execution and use of a two-stroke internal combustion engine with reduced thermal dispersion can be summarized in the greater difference in temperature between the fluid in entry and the burnt gas in exit that the engine can support. This, as known in the art makes increase the limits of the Carnot cycle in which the motor can operate and in consequence obtains a greater yield using the same combustible.

Even if the greater advantages can be summarized in the greater density of the fluid in entry for the minor heat transmission to the fluid sucked in the passage in the suction duct, the most evident advantages are obtained with the use of all the described insulating inserts. In fact, if the insulating insert in the pump housing is known in the art, the use of the further inserts in the suction and exhaust ducts even of just one of them, allows the reaching of best engine performances. The best result is however obtained with the use of all the described insulating coatings in the suction, transfer, stratification and exhaust ducts, provided in a two-stroke endothermic engine.

Moreover, the constructive way used, in carrying out the suction insulating insert 51 , allows to produce at a reasonable cost the suction duct 49 configurations that results most advantageous in the specific use of the engine to be made. In this way, the replaceability of the insert also successively to the engine construction, for maintenance or for specific preparation of the same to uses in the sporting competitions, makes very practical and cheap the change of the performances in the engine power and torque also to a skilled mechanic. Finally, the execution in separable parts, as visible in Figure 4, allows a skilled mechanical preparer to intervene as desired on the shape of the side-walls and on the upper and lower surfaces of the suction duct modifying its profile. A not- negligible advantage in this practice is the very low application cost inasmuch as the insulating insert 51 of the suction duct 49 can be bought in bulk at the original state or even rough, with the internal part of the duct grossly shaped, so the engine mechanic can carry out the experimentations he wants at very low cost to obtain the engine performance desired. The cost of this experimentation will not depend any more on the cost of the material, being the insert cost very low, and will allow moreover to possibly avoid interventions on the metallic part of the engine housing to modify with scrapings or welds its internal suction duct. Finally, after each experimentation it is always disposable: in fact, when carried out an even an unsatisfactory experimentation, it is always possible to bring back the engine to known performances of torque or power that, obviously, are related to a well precise configuration of the suction duct that, due to the effect of the invention, is not minimally damaged, but simply replaced with the one modified for the experimentation.

Obviously, to the two-stroke internal combustion engine with reduced thermal dispersion, described above, a technician skilled in the art, in order to satisfy specific and contingent needs, can bring numerous changes, all moreover contained in the protection range of the present invention which is defined by the following claims. So, the subdivision of the insulating insert 51 of the suction duct can occur on one or more planes different from the one axial to the cylinder, as represented, but though always intended to make accessible to the engine mechanic the internal surface of the duct run by the sucked fluid.

Claims

1 . Improved two-stroke internal combustion engine with reduced thermal dispersion, comprising a cylinder, a piston and a motor shaft; characterised therein, that presents a suction insert (1 1 , 51 ) with insulating coating, inserted or made in the engine housing (2, 52) or in the pump housing (10, 50) to coat the suction duct of the air (9, 49); the insulating coating of the fluid sucked towards the metallic wall of the duct also extends in the initial part of the transfer ducts.

2. Internal combustion engine, according to claim 1 , in which the coating in insulating material is made up of a material with resin base resistant to the etching by oils and fuels.

3. Internal combustion engine, according to one of the claims 1 or 2, in which the suction insert (11) extends in the part of the engine housing (2) lower than the cylinder, to protect the fluid sucked also in the pump housing (10) and before the entry in the transfer ducts.

4. Internal combustion engine, according to one of the preceding claims, in which the insulating suction insert (11 , 51 ) can be replaced with a similarly insulating insert and having different internal shape in diameter or section or bending in such a way to change the characteristics of the motor as desired by the engine mechanic.

5. Internal combustion engine, according to claim 4, in which the insulating insert in the suction duct is replaceable and made in at least two parts in such a way to allow changes of shape of the internal duct according to the wish and experience of the mechanic of competition engines.

6. Internal combustion engine, according to claim 5, in which the insulating insert in the replaceable suction duct is made in two halves, on an average symmetrical on a dividing plane.

7. Internal combustion engine, according to claim 1 , in which in at least one of the feeding ducts or exhaust of the fluids there is an insulating coating (15, 13) of the fluid passing towards the metallic wall of the duct.

8. Two-stroke internal combustion engine; comprising in the body of the cylinder (7) at least one exhaust duct (14) and at least one transfer duct (17); characterised in that it presents, to obtain a reduced thermal dispersion, from the burnt gas in exit towards the fluid in entry to the cylinder, an insulating insert placed (15) in the exhaust duct.

9. Two-stroke internal combustion engine; comprising in the body of the cylinder (7) at least one exhaust duct (14) and at least one transfer duct (17); characterised in that it presents, to obtain a reduced thermal dispersion, from the burnt gas in exit towards the fluid in entry to the cylinder, an insulating insert (29) placed in the transfer duct (27).

10. Two-stroke internal combustion engine; comprising in the body of the cylinder (7) at least one exhaust duct (14), at least one transfer duct (17) and a stratification duct (12); characterised in that it presents, to obtain a reduced thermal dispersion, from the burnt gas in exit towards the fluid in entry to the cylinder, an insulating insert (13) placed in the stratification duct.

1 1. Cylinder for two-stroke internal combustion engine; comprising in the body of the cylinder (7) at least one exhaust duct (14) and at least one transfer duct (17); characterised in that it presents, to obtain a reduced thermal dispersion, from the burnt gas in exit towards the fluid in entry to the cylinder, an insulating insert (29) placed in the transfer duct (27).

12. Cylinder for two-stroke internal combustion engine; comprising in the cylinder body (7) at least one exhaust duct (14), at least one transfer duct (17) and a stratification duct (12); characterised in that it presents, to obtain a reduced thermal dispersion, from the burnt gas in exit towards the fluid in entry to the cylinder, an insulating insert (13) placed in the stratification duct.

13. Internal combustion engine, according to one of the preceding claims from 1 to 12, in which the insulating material used for the execution is made up of two-component resin.

14. Internal combustion engine, according to one of the preceding claims from 1 to 12, in which the coating in insulating material is made up of ceramic material.

15. Cylinder of two-stroke internal combustion engine comprising in the cylinder body (7, 28, 47): at least one exhaust duct (14, 54), at least one transfer duct (17, 57), a stratification duct (12, 52), and a suction duct (9, 49), it presents in more of one of these ducts an insert in insulating material, as described in the preceding claims, in the suction duct (1 1 , 51 ); an insulating insert (15) in the exhaust duct; an insulating insert (29) in the transfer duct (27) and an insulating insert (13) in the stratification duct (12), to obtain a reduced thermal dispersion from the gas in entry to the cylinder.