Patent Description:
An exhaust system of an internal combustion engine comprises an exhaust duct, along which there is installed at least one device for the treatment of the exhaust gases coming from the internal combustion engine; in particular, there always is a catalytic converter (either an oxidation catalytic converter or a reduction catalytic converter), to which a particulate filter can be added. The catalytic converter, in order to work (namely, in order to carry out a catalytic conversion), needs to operate at a relatively high operating temperature (a modern catalytic converter works at temperatures even close to <NUM>), since the chemical reactions for the conversion of unburnt hydrocarbons, nitrogen oxides and carbon monoxide into carbon dioxide, water and nitrogen take place only once the work temperature has been reached.

During a cold start phase (i.e. when the internal combustion engine is turned on after having been turned off for a long time, thus causing the temperature of the different components of the internal combustion engine to reach ambient temperature), the temperature of the catalytic converter remains, for a relatively long amount of time (even some minutes in winter and during a city travel, along which the internal combustion engine idles or runs very slow), significantly below the operating temperature. As a consequence, during the cold start phase, namely for the amount of time in which the catalytic converter has not reached its operating temperature yet, polluting emissions are very high, since the purification effect of the catalytic converter is close to zero or, anyway, is scarcely effective.

In order to speed up the reaching of the operating temperature of the catalytic converter, patent documents <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT> suggest installing, along the exhaust duct, a heating device, which, by burning fuel, generates a (very) hot air flow, which flows through the catalytic converter. In particular, the heating device comprises a combustion chamber, which is connected, at the outlet, to the exhaust duct (immediately upstream of the catalytic converter) and is connected, at the inlet, to a fan, which generates an air flow flowing through the combustion chamber; in the combustion chamber there also are a fuel injector, which injects fuel to be mixed with air, and a spark plug, which cyclically produces sparks to ignite the air-fuel mixture in order to obtain the combustion that heats the air.

A further heating device is disclosed in the late <CIT>.

In known heating devices, the combustion of fuel is not always complete in all operating conditions and, therefore, it can happen (especially when a large quantity of fuel is injected in order to develop a large quantity of heat) that unburnt fuel reaches the exhaust duct and burns inside the exhaust duct, thus locally determining sudden, unexpected and undesired temperature rises.

The object of the invention is to provide an exhaust system of an internal combustion engine having a heating device permitting a complete fuel combustion (namely without introducing unburnt fuel into the exhaust duct) and, furthermore, being simple and economic to be manufactured.

According to the invention, there is provided an exhaust system of an internal combustion engine having a heating device according to the appended claims.

The appended claims describe preferred embodiments of the invention and form an integral part of the description.

The invention will now be described with reference to the accompanying drawings, which show some non-limiting embodiments thereof, wherein:.

In <FIG>, number <NUM> indicates, as a whole, an exhaust system of an internal combustion engine <NUM>.

The exhaust system <NUM> comprises an exhaust duct <NUM>, which originates from an exhaust manifold of the internal combustion engine <NUM> and ends with a silencer <NUM>, from which exhaust gases are released into the atmosphere. Along the exhaust duct <NUM> there is installed at least one device <NUM> for the treatment of the exhaust gases coming from the internal combustion engine; in particular, there always is a catalytic converter (either an oxidation catalytic converter or a reduction catalytic converter), to which a particulate filter can be added. The catalytic converter, in order to work (namely, in order to carry out a catalytic conversion), needs to operate at a relatively high operating temperature (a modern catalytic converter works at temperatures even close to <NUM>), since the chemical reactions for the conversion of unburnt hydrocarbons, nitrogen oxides and carbon monoxide into carbon dioxide, water and nitrogen take place only once the work temperature has been reached.

In order to speed up the heating of the treatment device <NUM>, namely in order to allow the treatment device <NUM> to reach its operating temperature more quickly, the exhaust system <NUM> comprises a heating device <NUM>, which, by burning fuel, generates a (very) hot air flow, which flows through the treatment device <NUM>.

The heating device <NUM> comprises a combustion chamber <NUM>, which is connected, at the outlet, to the exhaust duct <NUM> (immediately upstream of the treatment device <NUM>) and is connected, at the inlet, to a fan <NUM> (namely, to an air pump), which generates an air flow flowing through the combustion chamber <NUM>; in the combustion chamber <NUM> there also are a fuel injector <NUM>, which injects fuel to be mixed with air, and a spark plug <NUM>, which cyclically produces sparks to ignite the air-fuel mixture in order to obtain the combustion that heats the air. The combustion chamber <NUM> of the heating device <NUM> ends with an outlet duct <NUM>, which leads into the exhaust duct <NUM> (immediately upstream of the treatment device <NUM>).

According to <FIG>, the heating device <NUM> comprises a tubular body <NUM> (for example, with a cylindrical shape and having a circular or elliptical cross section) having a longitudinal axis <NUM>; the tubular body <NUM> is delimited, at the two ends, by two opposite base walls <NUM> and <NUM> and is laterally delimited by a side wall <NUM>, which connects the two base walls <NUM> and <NUM> to one another. The base wall <NUM> is perforated at the centre so as to accommodate the fuel injector <NUM>, which is mounted coaxially to the tubular body <NUM> (namely, coaxially to the longitudinal axis <NUM>); in other words, the fuel injector <NUM> is mounted through the base wall <NUM> of the tubular body <NUM> so as to inject fuel into the combustion chamber <NUM>.

Similarly, the base wall <NUM> is perforated at the centre so as to be fitted onto the outlet duct <NUM>, which ends in the exhaust duct <NUM>; namely, the base wall <NUM> has an outlet opening <NUM> to let hot air out of the combustion chamber <NUM> from which the outlet duct <NUM> originates.

According to <FIG>, through the tubular body <NUM> there is obtained (at least) part of an inlet opening <NUM>, which is connected to the fan <NUM> by means of an inlet duct <NUM> (shown in <FIG>) in order to receive an air flow, which is directed towards the combustion chamber <NUM> and is mixed with the fuel injected by the fuel injector <NUM>. Preferably, air flows into the inlet opening <NUM> with a flow that is oriented tangentially (relative to the tubular body <NUM>), namely the inlet duct <NUM> is oriented tangentially (relative to the tubular body <NUM>).

According to a possible, though non-binding embodiment shown in <FIG>, in the area of the inlet opening <NUM> there is a non-return valve <NUM>, which allows for an air flow only towards the combustion chamber <NUM> (namely, flowing into the tubular body <NUM>). Preferably, the non-return valve <NUM> is passive (namely, does not comprise electric, hydraulic or pneumatic actuators generating a movement), is pressure-controlled and opens only when a pressure upstream of the non-return valve <NUM> is higher than a pressure downstream of the non-return valve <NUM>. The function of the non-return valve <NUM> is that of preventing, when the heating device <NUM> is not used (namely, when the fan <NUM> is turned off), exhaust gases from flowing back until they flow out of the inlet opening <NUM> and, hence, are released into the atmosphere without going through the treatment device <NUM>. Alternatively, the non-return valve <NUM> could be mounted along the outlet duct <NUM>, for example in the area of the outlet opening <NUM>; in this case, the non-return valve <NUM> allows air to only flow out of the combustion chamber <NUM> (out of the tubular body <NUM>) towards the exhaust duct <NUM>, namely it prevents exhaust gases from flowing from the exhaust duct <NUM> towards the combustion chamber <NUM> (into the tubular body <NUM>).

According to <FIG>, the heating device <NUM> comprises a feeding channel <NUM>, which is entirely contained inside the tubular body <NUM>, receives air from the inlet opening <NUM>, surrounds an end portion of the fuel injector <NUM> and ends with a nozzle <NUM>, which is arranged around an injection point of the fuel injector <NUM> (namely, around a spray tip of the fuel injector <NUM>, from which fuel flows out).

The spark plug <NUM> is mounted through the side wall <NUM> of the tubular body <NUM> in order to trigger the combustion of an air and fuel mixture, which is obtained because of the mixing of air, which flows into the tubular body <NUM> from the inlet opening <NUM> and is introduced into the combustion chamber <NUM> by the nozzle <NUM> of the feeding channel <NUM>, and fuel, which is injected into the combustion chamber <NUM> by the fuel injector <NUM>. In particular, the side wall <NUM> of the tubular body <NUM> has a through hole, which is oriented radially (namely, perpendicularly to the longitudinal axis <NUM>) and accommodates, on the inside (screwed into it), the spark plug <NUM> (which is obviously oriented radially).

The heating device <NUM> comprises a static mixer <NUM> (namely, without moving parts), which has the shape of an annulus, is arranged along the feeding channel <NUM> and around the fuel injector <NUM> and is configured to generate turbulences, in particular a swirling motion, in the air flowing towards the nozzle <NUM>.

According to a preferred, though non-binding embodiment shown in the accompanying figures, downstream of the static mixer <NUM>, the feeding channel <NUM> has a progressive reduction of the area of the cross section, so as to determine an increase in the air speed. In particular, downstream of the static mixer <NUM>, the feeding channel <NUM> has an initial portion having a constant cross section area, an intermediate portion having a progressively decreasing cross section area and an end portion having a cross section area that is constant up to the nozzle <NUM>.

The feeding channel <NUM> is delimited, on the outside, by an (at least partially conical) outer tubular body <NUM> and is delimited, on the inside, by an (at least partially conical) inner tubular body <NUM>, which surrounds the fuel injector <NUM> and contains, on the inside, the fuel injector <NUM> (namely, serves as container for the end part of the fuel injector <NUM>). Namely, the feeding channel <NUM> is defined between the inner tubular body <NUM> and the outer tubular body <NUM>. In particular, the two tubular bodies <NUM> and <NUM> alternate conical portions (i.e. having a converging shape that progressively decreases its size) with cylindrical portions (i.e. having a shape with a constant size); preferably, the end part of the inner tubular body <NUM> has a converging taper (namely, which progressively reduces its size towards the nozzle <NUM>), whereas the end part of the outer tubular body <NUM> has a cylindrical shape.

According to a preferred embodiment, air flows into the feeding channel <NUM> with a tangentially oriented flow so as to have a swirling motion (subsequently increased by the action of the static mixer <NUM>), which helps it get mixed with the fuel injected by the fuel injector <NUM>; in other words, the introduction of oxidizing air into the combustion chamber <NUM> through a duct oriented tangentially to the combustion chamber <NUM> allows the oxidizing air flow to gain a circular motion (further enhanced by the presence of the static mixer <NUM>) so as to optimize the mixing of air and fuel inside the combustion chamber <NUM>.

According to <FIG>, the fuel injector <NUM> is configured to spray at least <NUM>% (and preferably at least <NUM>-<NUM>%) of the fuel against an inner surface <NUM> of the feeding channel <NUM>; namely, the fuel injector <NUM> does not directly direct the fuel towards the outside of the feeding channel <NUM>, but, on the contrary, directs the fuel against the inner surface <NUM> of the feeding channel <NUM>, so that the fuel flowing out of the fuel injector <NUM> preliminarily hits the inner surface <NUM> before flowing out of the feeding channel <NUM> through the nozzle <NUM>. The impact of the fuel against the inner surface <NUM> allows the fuel droplets emitted by the fuel injector <NUM> to be atomized in a very effective manner and, by so doing, the mixing of said fuel with the air flowing along the feeding channel <NUM> is significantly improved; an improvement in the mixing between air and fuel ensures an ideal and, especially, complete combustion of the fuel, thus preventing part of the unburnt fuel from flowing out of the combustion chamber <NUM>.

According to a preferred embodiment, the fuel injector <NUM> is configured to emit a fuel jet <NUM> having a centrally hollow conical shape, namely having a cross section shaped like an annulus, in which fuel gathers in the periphery; in particular, according to the embodiment shown in <FIG>, an outer surface of the fuel jet <NUM> has an opening angle α of approximately <NUM>° (for example, ranging between <NUM>° and <NUM>°) and an inner surface of the fuel jet <NUM> has an opening angle β of approximately <NUM>° (for example, ranging from <NUM>° to <NUM>°). In other words, the fuel injector <NUM> generates a fuel jet <NUM> having a conical shape (with the vertex of the cone close to the injection nozzle) and having, at the centre, a hole (namely, an area without fuel) also with a conical shape (with the vertex of the cone close to the injection nozzle); hence, the fuel jet <NUM> generated by the fuel injector <NUM> has the shape of a conical shell due to the presence of the central hole, namely has an internally hollow conical shape.

It should be pointed out that when we say that the fuel jet <NUM> generated by the fuel injector <NUM> has the shape of a conical shell (namely, has an internally hollow conical shape) we mean that the large majority of the fuel flowing out of the fuel injector <NUM> spreads in the space within a conical shell, but a very small (residual) part of the fuel can spread differently. Furthermore, depending on the how the fuel outlet opening is made, the fuel jet <NUM> flowing out of the fuel injector <NUM> can have a more symmetrical distribution around the longitudinal axis <NUM> (as shown in <FIG>) or a less symmetrical distribution around the longitudinal axis <NUM> (as shown in <FIG>). In particular, the fuel jet <NUM> flowing out of the fuel injector <NUM> has the conformation shown in <FIG> when the fuel injector <NUM> is of the "swirl" type, whereas the fuel jet <NUM> flowing out of the fuel injector <NUM> has the conformation shown in <FIG> when the fuel injector <NUM> is of the "multihole" type (<FIG> shows a "multihole" fuel injector <NUM> with six outlet holes, but the number of outlet holes could be different).

According to a preferred embodiment, the fuel injector <NUM> is of the "swirl" type, namely imparts a rotary swirling motion to the injected fuel (namely, a swirling motion in which fuel rotates around the longitudinal axis <NUM> of the tubular body <NUM>).

As mentioned above, the feeding channel <NUM> is delimited, on the outside, by the outer tubular body <NUM> (having the inner surface <NUM> of the feeding channel <NUM>) and is delimited, on the inside, by the inner tubular body <NUM>, which surrounds the fuel injector <NUM> and contains, on the inside, the fuel injector <NUM>.

According to <FIG>, the outer tubular body <NUM> comprises a conical portion <NUM>, which reduces its size towards the nozzle <NUM>; furthermore, according to a preferred embodiment shown in the accompanying figures, the outer tubular body <NUM> also comprises a cylindrical portion <NUM>, which is arranged downstream of the conical portion <NUM> and ends with the nozzle <NUM>. According to a different embodiment which is not shown herein, the outer tubular body <NUM> has no cylindrical portion <NUM> and, therefore, comprises the sole conical portion <NUM>. According to a further embodiment which is not shown herein, the cylindrical portion <NUM> could be replaced by a further conical portion having a smaller taper (convergence) than a taper (convergence) of the conical portion <NUM>.

In the embodiment shown in the accompanying figures, the fuel injector <NUM> is configured to spray at least part of the fuel against the cylindrical portion <NUM> (or against the further conical portion) of the outer tubular body <NUM>; in particular, the fuel injector <NUM> is configured to spray the largest part (almost the entirety) of the fuel against the cylindrical portion <NUM> (or against the further conical portion) of the outer tubular body <NUM>. According to a different embodiment, the fuel injector <NUM> is configured to spray at least part of the fuel against the cylindrical portion <NUM> (or against the further conical portion) of the outer tubular body <NUM> and at least part of the fuel against the conical portion <NUM> of the outer tubular body <NUM>; for example, the fuel injector <NUM> is configured to spray approximately half the fuel against the conical portion <NUM> of the outer tubular body <NUM> ad approximately half the fuel against the cylindrical portion <NUM> (or against the further conical portion) of the outer tubular body <NUM>. According to a further embodiment, the fuel injector <NUM> is configured to spray at least part of the fuel against the conical portion <NUM> of the outer tubular body <NUM>; in particular, the fuel injector <NUM> is configured to spray the largest part (almost the entirety) of the fuel against the conical portion <NUM> of the outer tubular body <NUM>.

According to <FIG>, an axial distance X (namely, measured along the longitudinal axis <NUM> of the tubular body <NUM>) between the spray tip of the fuel injector <NUM> from which fuel flows out (namely, the injection point of the fuel injector <NUM>) and a longitudinal axis <NUM> of the spark plug <NUM> ranges from <NUM>% to <NUM>% of an inner diameter D of the tubular body <NUM> (namely, of the diameter D of the combustion chamber <NUM>); preferably, the axial distance X ranges from <NUM>% to <NUM>% of the inner diameter D of the tubular body <NUM> and, in particular, the axial distance X ranges from <NUM>% to <NUM>% of the inner diameter D of the tubular body <NUM>. It should be pointed out that the tubular body <NUM> preferably has a circular cross section and, therefore, there are no doubts on how the inner diameter D of the tubular body <NUM> has to be measured in order to assess the axial distance X; if, on the contrary, the tubular body <NUM> had an elliptical cross section, the larger size would be one to be taken into account as diameter D of the tubular body <NUM> in order to assess the axial distance X.

According to <FIG>, the spark plug <NUM> has one single inner electrode <NUM> and one single outer electrode <NUM>; according to variants shown in <FIG>, the spark plug <NUM> has one single inner electrode <NUM> and two outer electrodes <NUM> (<FIG>) or one single inner electrode <NUM> and four outer electrodes <NUM> (<FIG>); according to a further variant which is not shown herein, there could be three outer electrodes <NUM>.

According to <FIG>, the outer tubular body <NUM> has a through opening <NUM> (namely, a slit), through which the spray tip of the fuel injector <NUM> from which fuel flows out (namely, the injection point of the fuel injector <NUM>) directly aims at the electrodes <NUM> and <NUM> of the spark plug <NUM>. Thanks to the presence of the through opening <NUM>, a limited part <NUM> of the fuel jet <NUM> emitted by the fuel injector <NUM> does not hit the outer tubular body <NUM>, but goes through the outer tubular body <NUM> until it directly reaches the electrodes <NUM> and <NUM> of the spark plug <NUM>. In other words, thanks to the presence of the through opening <NUM>, the limited part <NUM> of the fuel jet <NUM> directly "wets" the electrodes <NUM> and <NUM> of the spark plug <NUM> so as to create, around the electrodes <NUM> and <NUM> of the spark plug <NUM>, a local fuel excess (namely, a locally richer mixture), which favours the ignition of the flame and, hence, supports a quicker propagation of the flame to the rest of the mixture.

According to <FIG>, the through opening <NUM> is shaped like a slit, namely has a circumferential size that is greater than an axial size; preferably, the circumferential side of the through opening <NUM> angularly ranges from <NUM>° to <NUM>°.

According to <FIG>, <FIG>, the outer electrode <NUM> (or the outer electrodes <NUM>) of the spark plug <NUM> is oriented so as not to obstruct (intercept) the limited part <NUM> of the fuel jet <NUM> moving towards the inner electrode <NUM>; namely, the outer electrode <NUM> (or the outer electrodes <NUM>) of the spark plug <NUM> is oriented so as not to shade (screen) the inner electrode <NUM> from the limited part <NUM> of the fuel jet <NUM>. As a consequence, the spark generated between the two electrodes <NUM> and <NUM> is hot shaded (screened) by the outer electrode <NUM> relative to the limited part <NUM> of the fuel jet <NUM>. <FIG> and <FIG> show both parts <NUM> of the fuel jet <NUM> that have a correct orientation relative to the electrode <NUM> (namely, which are not screened by the electrode <NUM>) and parts <NUM> of the fuel jet <NUM> that have a wrong orientation relative to the electrode <NUM> (namely, which are screened by the electrode <NUM>) and, for this reason, are "cancelled" by means of an "X".

In the embodiments shown in <FIG> and <FIG>, the fuel jet <NUM> emitted by the fuel injector <NUM> is perfectly symmetrical relative to the longitudinal axis <NUM> of the tubular body <NUM> (and of the fuel injector <NUM>); namely, the longitudinal axis <NUM> of the tubular body <NUM> coincides with a central symmetry axis <NUM> of the fuel jet <NUM>. On the other hand, in the embodiment shown in <FIG>, the fuel jet <NUM> emitted by the fuel injector <NUM> is asymmetrical relative to the longitudinal axis <NUM> of the tubular body <NUM> (and of the fuel injector <NUM>) and, hence, the fuel jet <NUM> is inclined towards the electrodes <NUM> and <NUM> of the spark plug <NUM>; namely, the central symmetry axis <NUM> of the fuel jet <NUM> forms an angle γ (other than zero) with the longitudinal axis <NUM> of the tubular body <NUM>. According to a preferred embodiment, the central symmetry axis <NUM> of the fuel jet <NUM> is inclined towards the electrodes <NUM> and <NUM> of the spark plug <NUM> so as to form, with the longitudinal axis <NUM> of the tubular body <NUM>, the angle γ having a width ranging from <NUM>° to <NUM>° and preferably equal to approximately <NUM>-<NUM>°. Inclining the fuel jet <NUM> towards the electrodes <NUM> and <NUM> of the spark plug <NUM> permits the creation, around the electrodes <NUM> and <NUM> of the spark plug <NUM>, of a local fuel excess (namely, a locally richer mixture), which favours the ignition of the flame and, hence, supports a quicker propagation of the flame to the rest of the mixture.

According to a preferred embodiment, the heating device <NUM> comprises a control unit <NUM> (schematically shown in <FIG>), which is configured to control the entire operation of the heating device <NUM>, namely to control the fan <NUM>, the injector <NUM> and the spark plug <NUM> in a coordinated manner so as to reach, as efficiently and effectively as possible, the desired object (namely, quickly heating the treatment device <NUM> without damaging the treatment device <NUM> due to an excess temperature).

According to a possible embodiment shown in <FIG>, the heating device <NUM> comprises a temperature sensor <NUM>, which is arranged along the outlet duct <NUM> so as to measure the temperature of the hot air flowing through the outlet duct <NUM>; alternatively, the heating device <NUM> comprises a temperature sensor <NUM>, which is arranged along the exhaust duct <NUM> downstream of the point in which the outlet duct <NUM> branches off (and upstream of the treatment device <NUM>) so as to measure the temperature of the mixture of exhaust gases and hot air flowing through the exhaust duct <NUM>. Generally, there is only one of the two temperature sensors <NUM> and <NUM>, even if, in special applications, both temperature sensors <NUM> and <NUM> could be present. The control unit <NUM> uses the reading of the temperature sensor <NUM> or <NUM> in order to control (if necessary, by means of a feedback control) the combustion in the combustion chamber <NUM> so as to quickly heat the treatment device <NUM> without damaging the treatment device <NUM> due to an excess temperature.

The embodiments described herein can be combined with one another, without for this reason going beyond the scope of protection of the invention.

The heating device <NUM> described above has numerous advantages.

First of all, the heating device <NUM> described above ensures, in all operating conditions (especially when a large quantity of fuel is injected in order to develop a large quantity of heat), a complete fuel combustion (namely, without introducing unburnt fuel into the exhaust duct <NUM>) thanks to an ideal mixing between the oxidizing air introduced by the nozzle <NUM> of the feeding channel <NUM> and the fuel injected by the fuel injector <NUM>.

Furthermore, the heating device <NUM> described above has a high thermal power in relation to its overall dimensions; namely, even though it is relatively small, the heating device <NUM> described above generates a high thermal power.

Claim 1:
An exhaust system (<NUM>) of an internal combustion engine (<NUM>); the exhaust system (<NUM>) comprises:
an exhaust duct (<NUM>), which originates from an exhaust manifold of the internal combustion engine (<NUM>) and ends with a silencer (<NUM>), from which exhaust gases are released into the atmosphere;
an exhaust gas treatment device (<NUM>), which is arranged along the exhaust duct (<NUM>);
a heating device (<NUM>), which is connected to the exhaust duct (<NUM>) upstream of the treatment device (<NUM>) by means of an outlet duct (<NUM>) coming out of the exhaust duct (<NUM>) and is designed to generate, by burning fuel, a hot air flow;
a temperature sensor (<NUM>, <NUM>), which is arranged along the outlet duct (<NUM>) or along the exhaust duct (<NUM>) downstream of the point in which the outlet duct (<NUM>) branches off; and
a control unit (<NUM>), which adjusts the combustion in the heating device (<NUM>) also depending on the measure provided by the temperature sensor (<NUM>, <NUM>);
wherein the heating device (<NUM>) comprises:
a tubular body (<NUM>), where a combustion chamber (<NUM>) is obtained on the inside;
a fuel injector (<NUM>), which is mounted through a base wall (<NUM>) of the tubular body (<NUM>) so as to inject fuel into the combustion chamber (<NUM>);
at least one inlet opening (<NUM>), which can be connected to a fan (<NUM>) so as to receive an air flow, which is directed to the combustion chamber (<NUM>) and gets mixed with the fuel;
a feeding channel (<NUM>), which is entirely contained inside the tubular body (<NUM>), receives air from the inlet opening (<NUM>), surrounds an end portion of the fuel injector (<NUM>) and ends with a nozzle (<NUM>), which is arranged around a spray tip of the fuel injector (<NUM>); and
a spark plug (<NUM>), which is mounted through a side wall (<NUM>) of the tubular body (<NUM>) so as to trigger the combustion of a mixture of air and fuel;
wherein an axial distance (X), namely measured along a longitudinal axis (<NUM>) of the tubular body (<NUM>), between the spray tip of the fuel injector (<NUM>) and a longitudinal axis (<NUM>) of the spark plug (<NUM>) ranges from <NUM>% to <NUM>% of an inner diameter (D) of the tubular body (<NUM>);
wherein the fuel injector (<NUM>) is configured to spray at least part of the fuel against an inner surface (<NUM>) of the feeding channel (<NUM>).