NL1041741B1 - Improved internal combustion engine. - Google Patents

Abstract

The present invention provides an improved, efficient and clean internal combustion engine with rotating fuel injectors and an optimized combustion chamber geometry in order to promote an homogeneous mixture of the injected fuel and the combustion air. The engine according to the invention comprises a piston head and/or cylinder head geometry that is adapted to create a gas flow pattern inside the combustion chamber that promotes thorough mixing of the gases (fuel and combustion air) and that reduces heat losses through the cylinder wall.

Description

IMPROVED INTERNAL COMBUSTION ENGINE

FIELD OF THE INVENTION

The present invention relates to an internal combustion engine with a high fuel efficiency and no or very low emissions of particulate matter (PM) and NOx. The engine comprises rotating fuel injectors and a piston crown and/or cylinder head geometry adapted to optimize mixing of the injected fuel and the combustion air inside the combustion chamber.

BACKGROUND OF THE INVENTION

Internal combustion engines according to the prior art are highly inefficient. Net efficiencies in general do not exceed approximately 30%. Moreover, prevention of the emission of NOx and PM is confined to 'end of pipe' measures such as catalytic converters and soot filters. When trying to tackle these issues by changing the operating parameters of the prior art internal combustion engine there is always a trade-off between NOx and PM emission. Changes in the operating conditions that reduce the formation of NOx tend to increase the formation of PM. An example of such a change in operating condition is retarding the fuel injection timing.

The fuel efficiency of a reciprocating internal combustion engine, either operating according to the two-stroke or the four-stroke principle, highly depends on the efficiency of the combustion process. In addition, the more efficient the combustion the lower the formation of pollutants such as NOx and PM will be.

It has been proposed to introduce the fuel into the combustion chambers of internal combustion engines through a rotating fuel injection device in order to obtain an homogeneous mixture of fuel and air that will result in complete and clean combustion. Such a rotating fuel injection device is disclosed in WO 2009/075572 A2 and NL 2001069. By applying such rotating fuel injection devices while leaving the prior art cylinder head and piston head geometries unchanged, the benefits of the rotating fuel injection devices will not be reaped to the full extent. The prior art piston head geometries are based on attempts to infuence the formation and deflection of flamelet generated manifolds (FGM) inside a combustion chamber in which fuel is injected through prior art static fuel injectors at ever higher fuel injection pressures. However, so far, the effect has been negligible.

In an internal combustion engine with rotating fuel injectors the formation, and hence, the emission of PM and thermal NOx can essentially be reduced to zero. But even in such an engine adaptation of the piston head design can still result in added advantages, such as further improvement in fuel efficiency.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an improved, efficient and clean internal combustion engine with rotating fuel injectors by optimizing the combustion chamber geometry in order to promote an homogeneous mixture of the injected fuel and the combustion air. The engine according to the invention comprises a piston head and/or cylinder head geometry that is adapted to create a gas flow pattern inside the combustion chamber that promotes thorough mixing of the gases (fuel and combustion air) and reduces heat losses through the cylinder wall.

The engine according to the invention and the method of operating assure that the lambda value, the actual amount of air relative to the theoretically required amount of air for complete combustion, essentially does not have to be greater than 1, i.e. allowing stochiometric operation. With the absence of the need for excess air intake the need for a valve timing overlap is eliminated, hence, no fresh fuel is lost through the exhaust valve which results in a higher efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a schematic sectional view of a part of an embodiment of an engine according to the invention with a prior art cylinder head configuration; FIG. 2 is the schematic sectional view as shown in FIG. 1 with a schematic representation of the gas flow pattern; - FIG. 3 is a schematic bottom view of the cylinder head of an engine according to the invention with a prior art cylinder head configuration; FIG. 4 is a schematic sectional view of a part of an embodiment of an engine according to the invention with a novel cylinder head configuration; FIG. 5 is the schematic sectional view as shown in FIG. 4 with a schematic representation of the gas flow pattern; FIG. 6 is a schematic sectional view of a part of an embodiment of an engine according to the invention with a novel cylinder head configuration as shown in FIG. 4 and FIG. 5 with the piston in a slightly different position.

Identical or similar parts have been designated with the same or similar reference numbers in all drawings.

DETAILED DESCRIPTION OF THE INVENTION

The internal combustion engine according to the invention comprises rotating fuel injectors and a piston head geometry, either or not in the form of a piston bowl or piston crown, that is adapted to the cylinder head configuration and to the rotary injection of the fuel, whereby 'cylinder head configuration', refers to, among other aspects, the position and geometry of the valves. In this description and in the attached claims the designation rotating fuel injector may refer to embodiments of fuel injectors comprising injection nozzles that actually rotate or to static, i.e. nonrotary injection nozzles, which spray the fuel into the suction side of an impeller or other rotary displacement component that rotates around or in front of the static fuel injection nozzles.

The cylinder head configuration may either comprise conventional poppet valves or novel annular valves. An annular inlet valve promotes a more uniform distribution of the combustion air, particularly if it is combined with a ring-shaped impeller inside the combustion chamber. This should normally result in an almost complete combustion. An annular exhaust valve facilitates and improves the emptying of the combustion products from the chamber without losing fuel with the exhaust gases. FIG. 1 is a schematic sectional view of a cylinder 1 of an embodiment of an engine according to the invention with a prior art cylinder head 2. The piston 3 which is essentially in or almost in its top position comprises a piston bowl 4, formed in the head of the piston. FIG. 1 further shows a schematic cross section of a rotatable fuel injector 5 inside a housing 6 that is installed in the cylinder head 2. The rotatable fuel injector 5 comprises an impeller 7 which, during operation of the engine, will rotate at a high rotational speed inside the cylinder or combustion chamber in order to create a turbulent flow pattern resulting in an homogeneous mixture of injected fuel and combustion air.

In view of the relatively small diameter of the anticipated embodiments of this type of impeller 7 adaptation of the shape of the cylinder bowl 4 may have a significant effect on the fuel/air mixing dynamics and hence on the combustion process. FIG. 2 is the schematic sectional view as shown in FIG. 1 with a schematic representation of the gas flow pattern. Forced by the rotating impeller the turbulent gas flow follows essentially the path shown by the two bold arrows in the piston bowl. So, the gases are forced to flow towards the cylinder wall. However, since, in this piston position the upper wall section of the piston bowl covers the cylinder wall the gases follow the contours of the bowl and flow back towards the centre of the chamber. An added advantage of the shape of the bowl which protects the cylinder wall from direct impingement of hot gases is the fact that it reduces the risk that the lubrication oil film on the cylinder wall burns which would create particulate matter. Contrary to what the drawing in FIG. 2 may suggest the rotating fuel injector combined with the piston bowl shapes which are envisaged by the present invention the flow pattern is three dimensional and covers essentially the entire combustion chamber. Fuel is dispersed uniformly and no agglomeration of fuel drops will normally occur. FIG. 3 is a schematic bottom view of the cylinder head of an engine according to the invention with a prior art cylinder head configuration. This view clearly illustrates that the maximum diameter of the impeller 7 is limited due to the intake and exhaust valves. FIG. 4 is a schematic sectional view of a part of an embodiment of an engine according to the invention with a novel cylinder head configuration. This embodiment of the cylinder head does not comprise separate, conical intake and exhaust poppet valves, but instead one annular (ring-shaped) intake valve 8 and one annular exhaust valve 9. In this embodiment the two annular valves are positioned essentially concentric with the cylinder and piston, whereby the exhaust valve 9 has the largest diameter of the two valves. In the embodiment shown in FIG. 4 the assembly comprises an impeller 10 with vanes arranged in a ring between the outer diameter of the intake valve 8 and the inner diameter of the exhaust valve 9. When the intake valves opens the air directly enters the suction side of the impeller 10 and is forced out from the pressure side towards the cylinder wall. As shown in FIG. 4 the exhaust valve 9 comprises a deflection shield 11, which shields off the cylinder wall in order to prevent the gases, that are forced by the impeller to flow towards the cylinder wall, from actually hitting the cylinder wall. In the embodiment shown in FIG. 4 the defection shield 11 has a concave shape when viewed from the centre of the cylinder. The embodiment of the piston shown in FIG. 4 has a bowl size with an outer diameter that essentially matches that of the inner diameter at the bottom end of the defection shield 11, forming an essentially continuous flow path for the gases when the piston is in or close to its top position.

The invention also includes many embodiments of the annular exhaust valve without a defection shield 11 or with a deflection shield with another shape than the shape shown in FIG. 4. FIG. 5 is the schematic sectional view as shown in FIG. 4 with a schematic representation of the gas flow pattern, while the piston is close to its top position. As was the case in the earlier flow pattern example, the gas mixture flows outwards from the impeller along the top of the chamber and then follows the contour of the deflection shield and flows back along the bottom of the piston bowl towards the centre of the impeller. FIG. 6 is a schematic sectional view of a part of an embodiment of an engine according to the invention with a novel cylinder head configuration as shown in FIG. 4 and FIG. 5 while the piston has slightly moved downwards. In a prior art internal combustion engine with a static fuel injector the flow pattern, definitely during the inlet stroke and the exhaust stroke, depends on: - the position of the piston in the combustion chamber, - the vortexes which are dependent on the geometry of the intake and exhaust channels - the position and geometry of the piston crown.

In an engine according to the invention the flow pattern is essentially independent of these factors and maintains the favored shape irrespective of the piston position.

The deflection of the impeller induced flow towards the piston bowl (instead of letting it hit the cylinder wall) and leading it back to the centre of the impeller assures continuous turbulent three dimensional looped flow of the gases. The forced flow resulting from the rotating impeller of the rotating fuel injector and the shape of the piston bowl and the shape of the deflection shield 11, if the latter is present, assure this continuity of the flow. All geometrical measures incorporated in components inside the combustion chamber that will create the desired flow pattern according to the invention may be referred to in the claims as geometrical measures that promote a three dimensional looped flow. In essence, a number of embodiments of a cylinder with such geometrical measures will exhibit a combustion chamber with a longitudinal section resembling a lemniscate, be it slightly flattened and a-symmetrical in the vertical direction. Therefore, a combustion chamber in a cylinder with such geometrical measures may also be referred to as a combustion chamber with the shape of a lemniscate.

The internal combustion engine according to the invention also includes pistoris with thermal barriers in order to limit the transfer of heat through conduction from the piston head to the remainder of the piston and engine structure. In an embodiment the thermal barrier of the piston head, in this case in the form of a bowl, comprises a ceramic coating with a very low thermal conductivity. However, the invention is not limited to thermal barriers comprising a ceramic coating and includes any suitable way of creating a piston that comprises a thermal barrier.

In another embodiment the thermal barrier involves a separate piston crown comprising a low thermal conductivity material that is fitted on top of a piston. This embodiment also may include one or more intermediate ceramic layers, between the piston crown and the base structure of the piston.

To facilitate uniform flow patterns inside the combustion chamber it is beneficial if the surface of the piston crown or bowl has a smooth finish. In embodiments of the internal combustion engine according to the invention the Ra surface roughness of the piston crown or bowl equals 0,2 micrometers or smoother.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims (10)

An internal combustion engine with one or more cylinders wherein at least one cylinder is provided with a rotating fuel atomizer, characterized in that one or more components in at least one cylinder comprise geometrical measures which effect a 3-dimensional loop-shaped flow. An internal combustion engine according to claim 1, characterized in that the geometric features comprise a piston bowl. Internal combustion engine according to claim 1 or 2, characterized in that at least one cylinder comprises an annular valve (8,9). An internal combustion engine according to claim 3, characterized in that the annular valve comprises a deflection shield (11). Internal combustion engine according to claim 4, characterized in that the deflection shield (11) has a concave shape. Internal combustion engine according to one or more of the preceding claims, characterized in that the combustion engine comprises a combustion chamber which, at a piston position in the immediate vicinity of the upper dead center, comprises the shape of a lemniscate in longitudinal section. Internal combustion engine according to one or more of the preceding claims, characterized in that the combustion engine comprises a piston which comprises a thermal barrier. The internal combustion engine according to claim 7, characterized in that the thermal barrier comprises a ceramic coating applied to the piston. The internal combustion engine according to claim 7 or 8, characterized in that the thermal barrier comprises a separate piston crown mounted on the piston. Internal combustion engine according to one or more of the preceding claims, characterized in that the engine comprises a piston with a piston bowl or piston crown whose surface roughness is at most Ra 0.2 micrometer.