DK177936B9

DK177936B9 - A method of operating an internal combustion engine, and an internal combustion engine

Info

Publication number: DK177936B9
Application number: DK201370641A
Authority: DK
Inventors: Flemming M B Andersen
Original assignee: Man Diesel & Turbo Deutschland
Priority date: 2013-11-01
Filing date: 2013-11-01
Publication date: 2015-05-11
Also published as: JP2015096727A; KR20150051180A; DK177936B1; KR101733730B1; CN104612836A

Abstract

In a method of operating an internal combustion engine (1) with at least one cylinder (2) and a reciprocating piston (15) in the cylinder (2), connected with a crank shaft rotating at full load of the engine at 1200 rpm or less, to reciprocate between a top dead centre (TDC) and a bottom dead centre (BDC), the cylinder (2) having air passage openings (10, 12) for intake air and exhaust gas, said openings being closed during at least a major part of a compression stroke of the piston (15) towards TDC, a liquid non-auto-igniting fuel is injected into the cylinder (2) during the compression stroke, while said air passage openings (10, 12) are closed, at crank angles at least 30° before TDC, thereby lowering the pressure in the cylinder and accordingly the compression work performed by the piston thus increasing the efficiency of the engine.

Description

The present invention relates to a method of operating an internal combustion engine, said engine having at least one cylinder with a piston in the cylinder, which piston is connected with a crank shaft and is reciprocating during operation of the engine between a top dead centre (TDC) and a bottom dead centre (BDC), said cylinder having air passage openings for intake air and exhaust gas, and where liquid non-auto-igniting fuel is injected into the cylinder during the compression stroke from an injection position at a cylinder liner of the cylinder while said air passage openings are closed and the piston is located below the injection position, and an ignition device is activated to ignite the liquid non-auto-igniting fuel.

GB 651,526 A discloses a method of this kind in an engine running at 1800 rpm where knocking is suppressed by initiating injection of fuel in the range of 75° to 30° before TDC, and generally from 70° to 30° before TDC, from a fuel injector located in the top of the cylinder next to a spark plug. The injection of fuel in the latter part of the compression stroke from a position close to the spark plug is said to cause prompt ignition of the first portion of injected fuel and vapour-air mixture to establish a flame front travelling counter to a direction of swirl in the cylinder, and thus avoid knocking.

The invention especially relates to engines operating at rotational speeds below 1000 rpm at 100 % engine load.

DK-B-176118 and the corresponding JP-B-3908855 relate to enhancement of the possibilities of running a turbocharged dual fuel internal combustion engine of the diesel type on low pressure supplied gas, and disclose a turbocharged dual fuel internal combustion engine of the diesel type, in which a strong water injection is made directly into the entire cylinder contents during the compression stroke in amounts by weight comparable to or exceeding the amounts of fuel. This renders it possible to operate even large two-stroke diesel engines on low-pressure injected gas fuel as the main fuel so that high-pressure injected fuel is to be used only as an ignition aid, because the injection of water provides for better mixing of the gas fuel and the air in the cylinder thus lowering the risk of local auto-ignition and because the injected water evaporates, which lowers the temperature and the pressure in the cylinder both of which factors delay chemical reaction and contribute to lowering the risk of auto-ignition. Further, it is mentioned to be possible to achieve better combustion conditions in small gas/diesel engines running at higher speeds.

US-B-7 284 506 discloses a method of timing auto-ignition in operation of an internal combustion engine on a substantially homogeneous mixture of a first fuel comprising diesel fuel and a second fuel comprising a low cetane fuel such as methanol or ethanol whereby the amounts of the first and the second fuel are varied to adjust the timing of auto-ignition. In the embodiments described the low cetane fuel is applied in the intake manifold, whereby the low cetane fuel will be introduced into the combustion cylinder during the intake stroke, but it is mentioned that possibly the fuel injector for injecting the low cetane fuel may be configured to inject fuel directly into the combustion cylinder.

The object of the present invention is to increase the engine economy and/or efficiency of an internal combustion engine.

This is obtained by a method as mentioned by way of introduction wherein the liquid non-auto-igniting fuel is injected at crank angles at least 90° before top dead centre (TDC) from an injection position being alternately covered by the piston during operation of the engine, and that the crank shaft rotates at 100 % engine load at a rotational speed in the range of 40 to 1200 rpm. By injecting a liquid non-auto-igniting fuel during the compression stroke the temperature and thereby the pressure of the air inside the cylinder is reduced due to heat consumption by evaporation of the liquid non-auto-igniting fuel, whereby the work performed by the piston during the compression stroke is reduced because the downward pressure on the piston is reduced. When injection occurs of the liquid non-auto-igniting fuel the pressure in the cylinder is also considerably lower than the cylinder pressure at the end of the compression stroke, and the injected liquid non-auto-igniting fuel replaces fuel that would otherwise have been injected at the end of the compression stroke against the higher pressure prevailing at the end of the compression stroke.

The reduction of the work performed by the piston compared to an engine without the injection of a liquid non-auto-igniting fuel during the compression stroke enhances the efficiency of the engine. Alternatively, this effect of the invention may be exploited when designing an engine with an intake air cooler by providing a smaller and thus cheaper intake air cooler thereby obtaining a more economic overall design of the engine.

The earlier during the compression stroke the liquid non-auto- igniting fuel is injected the more the compression work is reduced and thus the liquid non-auto-igniting fuel is injected into the cylinder during the compression stroke at crank angles at least 90° before top dead centre (TDC).

When the injection of liquid non-auto-igniting fuel is performed immediately after the air passage openings for intake air and exhaust gas are all closed at the beginning of the compression stroke at least theoretically the largest reduction of the compression work performed by the piston is obtained. However, depending on the actually liquid non-auto-igniting fuel used and other engine parameters, such as the temperature of the intake air, a delay of the injection may be beneficial to obtain a certain elevation of the temperature of the air inside the cylinder due to compression before the injection of liquid non-auto-igniting fuel to facilitate the evaporation thereof.

In an embodiment, the liquid non-auto-igniting fuel is injected from an injection position at a cylinder liner of the cylinder, said injection position being alternately covered by the piston, and the injection taking place when the piston is located below the injection position. Hereby it is obtained that an injector for the liquid non-auto-igniting fuel may be placed at a point of the cylinder, which is not most stressed.

In an embodiment the internal combustion engine is a low speed, two-stroke, crosshead, diesel type internal combustion engine, in which said least one cylinder comprise a cylinder liner and having scavenge air ports providing said air passage openings for intake air, and the liquid non-auto-igniting fuel is injected while the scavenge air ports are closed. Hereby is obtained that the cylinder is closed when the liquid non-auto-igniting fuel is injected to lower the temperature and the pressure in the cylinder. By "low speed engine" should be understood an engine running at 100 % engine load at rotational speeds in the range from 40 to 300 rpm, especially at rotational speeds in the interval 40 to 250 rpm. The expression "diesel type" should be understood to comprise engines operating according to the Diesel cycle, and the engines can as an example run on diesel fuel, heavy fuel oil, gas fuel such as methane or natural gas, or dual fuel, i.e. an auto-igniting fuel and a non-auto-igniting main fuel.

In an embodiment the internal combustion engine is a medium speed, four-stroke, internal combustion engine, in which said at least one cylinder comprises at least one intake valve and at least one exhaust valve providing said air passage openings for intake air and exhaust gas, respectively, and the liquid non-auto-igniting fuel is injected while said valves are closed. Hereby is obtained that the cylinder is closed when the liquid nonauto-igniting fuel is injected to lower the temperature and the pressure in the cylinder. By medium speed engine should be understood an engine running at 100 % engine load at rotational speeds in the interval 300 to 1200 rpm, especially at rotational speeds in the interval 400 to 1000 rpm.

In an embodiment the liquid non-auto-igniting fuel is injected during the compression stroke at crank angles at least 20° from BDC, while the respective ports and valves forming air intake openings are in closed position.

The liquid non-auto-igniting fuel may be a fuel with a low cetane number that will not auto-ignite during operation at the relevant operation parameters. In an embodiment methanol is used as the liquid non-auto-igniting fuel. Other contemplated liquid non-auto-igniting fuels are ethanol and i-propanol. The liquid non-auto-igniting fuel should preferably have a relatively high heat of evaporation to ensure that the reduction of the pressure in the cylinder because of the reduction of the temperature due to the evaporation of the liquid non-auto-igniting fuel is greater that the raise of the pressure because of the addition of the liquid non-auto-igniting fuel to the charge in the cylinder.

In an embodiment the ignition device is selected from a group comprising a fuel injector for an auto-igniting fuel, a thermal igniting element, and an electric spark element. Thus several possibilities are available to the skilled person to provide for ignition of the liquid non-auto-igniting fuel.

The invention may in an embodiment be applied in a dual fuel solution to a diesel engine whereby the liquid non-auto-igniting fuel may be added as a portion of the overall amount of fuel supplied to the cylinder during an operating cycle. The liquid non-auto-igniting fuel may constitute a smaller or larger portion of the overall amount of fuel supplied to the cylinder during operation, and thus the liquid non-auto-igniting fuel may constitute a minor portion of the fuel or the liquid non-auto-igniting fuel may constitute a main fuel and auto-igniting fuel, like diesel fuel, may be used only as a fuel for igniting the non-auto-igniting fuel at the end of the compression stroke.

In another embodiment a gas fuel is let into the cylinder, as a portion of an overall amount of fuel supplied to the cylinder during operation, during filling the cylinder with intake air prior to closure of the air passage opening for intake air. This embodiment may e.g. be applied to an engine running on natural gas e.g. in a vessel for transporting liquid natural gas (LNG). Thereby natural gas evaporated from a transport tank of the vessel may be introduced in the cylinder together with intake air and liquid natural gas may be injected as the liquid non-auto-igniting fuel according to the invention.

The present invention further relates to an internal combustion engine having at least one cylinder with a piston in the cylinder, which piston is connected with a crank shaft, said piston reciprocating between a top dead centre (TDC) and a bottom dead centre (BDC), said cylinder having air passage openings for intake air and exhaust gas, said openings being closed during at least a major part of a compression stroke of the piston towards the top dead centre (TDC), which internal combustion engine has at least one liquid non-auto-igniting fuel injector for injecting a liquid non-auto-igniting fuel into the cylinder and means for controlling said injector to inject said liquid non-auto-igniting fuel into the cylinder during the compression stroke, while said air passage openings are closed. According to the present invention the at least one liquid non-auto-igniting fuel injector is positioned in the cylinder liner at a position covered by the piston when the piston is in an interval of crank angles from 50° after top dead centre (TDC), through BDC, and to 50° before top dead centre (TDC), the engine having at 100 % engine load a rotational speed in the range of 40 to 1200 rpm. Hereby is obtained an internal combustion engine suited for operation according to the method of the present invention, with the above-mentioned advantages and effects. As the at least one liquid non-auto-igniting fuel injector is positioned in the cylinder liner at a position alternately covered by the piston when the piston is in an interval of crank angles from 50° after TDC, through BDC, and to 50° before TDC, it is obtained that an injector for the liquid non-auto-igniting fuel is placed at a point of the cylinder, which is not most stressed. Due to heat and pressure developments in the combustion chamber during the combustion, the stress level in the wall of the cylinder liner is higher in the upper portion of the cylinder liner.

In an embodiment wherein the cylinder liner is supported by an engine frame at an intermediate position intermediate axial ends of the cylinder liner, and the cylinder liner comprises scavenge air ports positioned between a lower end of the cylinder liner and said intermediate position, the at least one liquid non-auto-igniting fuel injector is positioned between the scavenge air ports and said intermediate position. Hereby it is obtained that an injector for the liquid non-auto-igniting fuel may be placed at a point of the cylinder, which is only little stressed compared to the parts of the cylinder liner extending between the intermediate position and a cylinder cover closing the cylinder at its end opposite the end comprising the scavenging ports. Cylinder bolts hold the cylinder cover in place on top of the cylinder liner, and the portion of the cylinder liner extending between the intermediate position and the cylinder cover is thus affected by the clamping forces transferred from the cylinder bolts via the cylinder cover to the cylinder liner and down to the intermediate position where the clamping forces are taken up by the engine frame. It is thus an advantage to locate the liquid non-auto-igniting fuel injectors at a lower level in the cylinder liner than the intermediate position.

The internal combustion engine in the embodiments is typically pressure charged, such as by providing pressurized inlet air by an electrically driven blower and/or a turbocharger. It is further a possible option according to the invention to use exhaust gas recirculation (EGR) or exhaust gas bypass (EGB) which are also generally known in the art.

In the following the invention will be explained in further detail by way of example with reference to the highly schematic drawings, in which

Fig. 1 illustrates a side view of a diesel engine according to the invention,

Fig. 2 illustrates a vertical sectional view through a cylinder in the engine of Fig. 1, and

Fig. 3 illustrates a segmental view of a lower area of the cylinder.

In Fig. 1 the outline is illustrated of a two-stroke crosshead engine 1 of the diesel type for propulsion of a vessel, like a container ship or a bulk carrier, or for power production in a stationary power plant. The engine 1 has several cylinders 2, such as from 4 to 15 cylinders arranged in line on an engine frame 3. A high-pressure supply pump 4' and a common feed pipe 4 for auto-igniting fuel, such as diesel oil or heavy fuel oil, supply ignition devices 9 in form of fuel injectors mounted in the top of the cylinder with auto-igniting fuel via control devices 5, which may be piston pumps or electron!- cally controlled valves. Control devices 5 activate the ignition devices and initiate combustion in combustion chamber 6 at a desired timing of the engine cycle, corresponding to the traditional timing of fuel injection. The activation may as an example take place in the range of 10° before to 10° after the top dead centre (TDC). The ignition devices are typically activated with an adjustable timing in the engine cycle depending on the current engine load in a well known manner for initiation of combustion in accordance with well-known combustion principles. Other types of ignition devices may be used, such as a thermal igniting element or an electric spark element, like an ignition plug known from Otto-cycle engines.

In case it is desired also to supply the cylinder with gaseous fuel it is possible to supply gas at low pressure, such as a pressure of below 10 bar, to the inlet air in the cylinder prior to injecting the liquid non-auto-igniting fuel during the compression stroke. Such gas is also non-auto-igniting so that the timing of ignition is controlled by the activation of the ignition device.

The internal combustion engine 1 has a feeding system for liquid non-auto-igniting fuel, e.g. methanol, comprising a source, such as a not shown storage tank, of liquid non-auto-igniting fuel, which is supplied via a supply line 7 with a pressure device 8, which may, for example, be a traditional pressure pump, such as a piston pump driven by an electric motor, or a hydraulic or cam shaft driven pump, or at least one tank, which tank is periodically supplied with liquid non-auto-igniting fuel and pressurized by compressed inert air at a pressure corresponding to the desired liquid non-auto-igniting fuel feeding pressure to liquid non-auto-igniting fuel injectors 26. The tank system pressurized by inert gas may be preferable if the non-auto-igniting fuel has very poor lubricating ability. The liquid non-auto-igniting fuel and inert air in the tank may be separated from each other by a membrane or in another manner, such as the tank being provided with floaters, such as air-filled balls floating on the liquid non-auto-igniting fuel and transmitting the inert air pressure to it. In this manner it is possible to produce very high liquid non-auto-igniting fuel pressures and to deliver large amounts of liquid non-auto-igniting fuel to the cylinder without having to take into account the lubrication conditions in a pump cylinder where the piston runs partially in liquid non-auto-igniting fuel.

The liquid non-auto-igniting fuel may be supplied to the liquid non- auto-igniting fuel injectors 26 on a cylinder by opening and closing a control valve time-controlled in dependency of the engine cycle. The control valve may be electronically controlled by a control unit that receives signals for the current angular position of the crankshaft. The injection of the liquid nonauto-igniting fuel may occur quickly and at an overpressure compared to the pressure in the cylinder while the injection takes place. In case it is desired to inject over a longer period, it is possible to take into consideration the increasing compression pressure during the injection by making variable the liquid non-auto-igniting fuel pressure so that this pressure also increases during a compression stroke.

In a well-known manner, each liquid non-auto-igniting fuel injector 26 may comprises a valve housing with an internal seat and a movable slider pressed against the seat by a spring for cutting off the connection between a liquid non-auto-igniting fuel supply and an atomizer nozzle. When the valve is actuated for initiation of the liquid non-auto-igniting fuel injection, the slider is displaced away from the seat, which may be effected, for example, by a control valve opening for the effect of the liquid non-auto-igniting fuel pressure on a downward slider surface, whereby the liquid non-auto-igniting fuel pressure displaces the slider away from the seat. An alternative possibility is to use control oil to displace the slider away from the seat, and in this case the opening-closing function of the valve may be independent of the liquid non-auto-igniting fuel pressure. The atomizer nozzles near the end of the injector are directed so that the injected liquid non-auto-igniting fuel does not hit the cylinder wall or the piston. Several liquid non-auto-igniting fuel injectors 26 may be mounted to the cylinder 2, such as the three indicated in Fig. 2, each having an atomizer nozzle. The various atomizer nozzles may have different orientations in order to distribute the liquid non-auto-igniting fuel relatively evenly in the cylinder contents. The nozzle holes in the atomizer nozzles are typically located in a recess close to - but radially outside - the inner surface of the cylinder liner. The injection may suitably be oriented in directions leading away from the inner surface of the cylinder.

The engine may be provided with scavenge and charging air at a pressure which may vary with the engine load. The scavenge and charging air may be delivered by one or more turbochargers, possibly supplemented by driven auxiliary blowers when the engine is running at part load or low load.

The engine may be a medium-speed engine, but in the embodiment shown it is a low-speed engine having an exhaust valve 10 located at the top of the cylinder in a cylinder cover 11 and a row of scavenge air ports 12 located in the cylinder liner 2' in a lower cylinder section surrounded by a scavenge box 13 which, via an opening 21 communicates with a supply of pressurized scavenge air, such as a scavenge air receiver 30, which is an elongated pressure vessel common to several cylinders. The scavenge boxes 13 may be separate for each cylinder, i.e., be mutually separated by transverse walls between the cylinders, and may be delimited downwards by an intermediate bottom 14 in the engine frame so as to provide an effective separation of the crank housing and the air supply. A piston 15 in the cylinder is mounted on a piston rod 16 passing through the intermediate bottom in a piston rod stuffing box 17. In another embodiment, the scavenge box may be common to several or all cylinders.

In another embodiment illustrated in Fig. 3 the liquid non-auto-igniting fuel injector 26 is mounted in a bore in the cylinder liner 2' at a position below the position of support of the engine frame 3 on the cylinder liner 2' as it is seen in Fig. 2. This part of the cylinder liner 2' is not as heavily loaded as the part of the cylinder liner 2' above the position of support of the engine frame 3, and as seen in Fig. 2 the wall-thickness of the cylinder liner 2' is smaller below the position of support of the engine frame 3. Due to the smaller load and the location closer to the scavenging air ports 12 it is beneficial to place the liquid non-auto-igniting fuel injector 26 in this area and to direct the atomizer bores to that the injection takes place in the upward direction in the cylinder. With a long distance to the top of the cylinder it is possible to inject a large volume of non-auto-igniting fuel while directing the complete injection in directions away from the piston 15.

The individual liquid non-auto-igniting fuel injector 26 is preferably arranged to provide a spray of fine droplets that will evaporate before reaching the inner wall of the cylinder liner 2' opposite the fuel injector 26.

The two-stroke engine has an engine cycle, which in principle is beginning at 0° crank angle at the top dead centre TDC. The major part of the combustion occurs during the combustion stroke from 0° crank angle towards 180° at bottom dead centre BDC. The compression stroke occurs in principle from 180° to 360° crank angle, but the exhaust valve has to be closed and the piston has to cover the the scavenging air ports 12 before the compression actually begins. Crank angles at least 30° before the top dead centre TDC during the compression stroke are thus crank angles in the interval of 180° to 330°, and crank angles at least 50° before the top dead centre TDC during the compression stroke are thus crank angles in the interval of 180° to 310°, and crank angles at least 90° before the top dead centre TDC during the compression stroke are thus crank angles in the interval of 180° to 270°.

When the engine is embodied as a four-stroke engine, the relevant compression stroke is located in the engine cycle from 540° crank angle to 720° crank angle. In the four-stroke engine crank angles at least 30° before the top dead centre TDC during the compression stroke are thus crank angles in the interval of 540° to 690°, and crank angles at least 50° before the top dead centre TDC during the compression stroke are thus crank angles in the interval of 540° to 670°, and crank angles at least 90° before the top dead centre TDC during the compression stroke are thus crank angles in the interval of 540° to 630°.

An example of a non-auto-igniting fuel is methanol having the properties of a cetane number in the range of 2 to 5 and a lower heating value of 19.9 MJ/kg and a heat of evaporation of 1.104 MJ/kg. Another, non-preferred example is ethanol having a cetane number of about 12 and a lower heating value of 28.9 MJ/kg and a heat of evaporation of 0.93 MJ/kg.

Though above an embodiment has been described, comprising provisions for letting in gas in the cylinder as a part of the fuel it should be understood that the invention is applicable also to engines omitting such provisions. Thus the invention is applicable to engines fuelled only by a liquid nonauto-igniting fuel injected into the cylinder(s) of the engine, and a an auto-igniting fuel, such as oil, providing for ignition, whereby the auto-igniting fuel may constitute a substantial portion of the overall fuel amount or only a minor portion sufficient to provide for ignition. The invention is also applicable to engines fuelled only by a liquid non-auto-igniting fuel injected into the cylinders of the engine to be ignited by means of another heat source than auto-igniting fuel, such as an electrically actuated ignition device.

Further it should be understood that the inventive principle of injecting a liquid non-auto-igniting fuel into a cylinder while the openings for intake of air and outlet of exhaust gas, i.e. combustion products, are closed and during specific intervals of the compression stroke, is applicable to four stroke engines both of Diesel and Otto cycle type having intake valves and exhaust valves as well as to two stroke engines as described above with reference to the drawings.

Claims

A method of operating an internal combustion engine (1) having at least one cylinder (2) with a piston (15) in the cylinder, which piston (15) is connected to a crankshaft and performs a reciprocating movement between a peak dead center (TDC) and bottom dead center (BDC) when the engine is running where the cylinder (2) has air passage openings (10, 12) for intake air and exhaust gas, and where liquid non-self-igniting fuel is injected into the cylinder (2) during compression stroke. from an injection position at a cylinder liner (2 ') in the cylinder (2), while the air passage openings (10, 12) are closed and the piston is at a lower level than the injection position, and an ignition device is activated to ignite the liquid, not self-igniting fuel, characterized in that the liquid non-self-igniting fuel is injected at crank angles of at least 90 ° before the peak dead center position (TDC) from an injection position ion, which is alternately covered by the piston (15) as the engine is running, and that the crankshaft rotates at 100% engine load at a speed ranging from 40 to 1200 rpm.

A method according to claim 1, characterized in that the internal combustion engine (1) is a slow-moving, two-stroke cross-head internal combustion engine in which the at least one cylinder (2) comprises a cylinder liner (2 ') with rinsing air ports (12), which provides the air passage openings (10, 12) for intake air.

Method according to claim 1, characterized in that the internal combustion engine (1) is a medium-speed, four-stroke internal combustion engine, in which the at least one cylinder comprises at least one suction valve and at least one exhaust valve which provide the air passage openings for the suction air and exhaust gas respectively. .

Method according to any one of claims 1 to 3, characterized in that the ignition device (5 ') is selected from the group comprising a fuel injector for a self-igniting fuel, a thermal ignition element, and an electric spark element.

Process according to any one of claims 1 to 4, characterized in that the liquid non-self-igniting fuel forms part of a total amount of fuel supplied to the cylinder during an operating cycle, wherein the liquid non-self-igniting fuel ignites. this is by injecting self-igniting fuel into the cylinder near the end of the compression stroke.

An internal combustion engine (1) having at least one cylinder (2) having a piston (15) in the cylinder, said piston (15) being connected to a crankshaft, the piston (15) being reciprocating between a top dead center (TDC) and a bottom dead center (BDC), wherein the cylinder (2) has air passage orifices (10, 12) for intake air and exhaust gas, which openings are closed during at least most of the piston's compression stroke in the direction of the top dead center (TDC), and the combustion engine having at least one liquid non-self-igniting fuel injection valve (26) for injecting a liquid non-self-igniting fuel into the cylinder (2) and means for controlling this injection valve (26) for injecting the liquid non- self-igniting fuel in the cylinder (2) during the compression stroke while the air passage openings are closed, characterized in that the at least one liquid form non-self-igniting fuel injection valve il (26) located in a cylinder liner (2 ') at a position covered by the piston (15) when the piston is in a range of crank angles from 50 ° after the peak dead center position (TDC), via BDC, to 50 ° leading to the top dead center position (TDC) ), which has a speed at 100% engine load in the range of 40 to 1200 rpm.

Combustion engine according to claim 6, characterized in that the cylinder liner (2 ') is supported by a motor frame (3) at an intermediate position located between the axial ends of the cylinder liner (2'), the cylinder liner (2 ') comprising rinsing air ports (12). ) located between a lower end of the cylinder liner (2 ') and said intermediate position, the at least one liquid non-self-igniting fuel injection valve (26) being located between the purging air ports (12) and said intermediate position.