NL1041716B1 - Method and device for complete combustion in internal combustion engines. - Google Patents

Abstract

The method according to the invention for optimizing the effect of rotating fuel injection into the combustion chamber of an internal combustion engine comprises controlling the rotational speed within a range that assures that the injected fuel is atomized as quickly, uniformly and efficiently as possible. The method takes advantage of the correlation between the fuel injector nozzle configuration, the fuel injection pressure and the required rotational speed for fine atomization and uniform distribution of the fuel inside the combustion chamber. In addition, the invention comprises an injection device for application of the method.

Description

METHOD AND DEVICE FOR COMPLETE COMBUSTION IN INTERNAL COMBUSTION ENGINES

FIELD OF THE INVENTION

The present invention relates to a method and a device for fuel injection into the combustion chamber of internal combustion engines aimed at increasing the fuel efficiency of and reducing the emissions by such engines.

BACKGROUND OF THE INVENTION

Internal combustion engines of for example power generation equipment, road vehicles, airplanes, boats and ships are important sources of harmful emissions such as C02, NOx and particulate matter (PM).

The main cause of these emissions is the fact that the combustion in the combustion chambers of such engines according to the prior art is incomplete. The combustion pattern mainly consists of flamelet generated manifolds (FGM), which is not the desired and required pattern when the formation of PM and NOx is to be prevented. In the past few decades internal combustion engine manufacturers have been increasing the fuel injection pressure in internal combustion engines in their attempts to improve the combustion. However, the beneficial effect of such fuel injection pressure increases on the emissions have been very limited.

Triggered by the industry's unsuccessful attempts to solve the emission problems, the Dutch patent NL 2001069 discloses an invention comprising a rotating fuel injector for internal combustion engines which is aimed at obtaining essentially complete combustion in internal combustion engines and thereby preventing FGM's.

Not only does the proposed fuel injector rotate, but in a number of preferred embodiments it also includes an impeller to create turbulence inside the combustion chamber. Although it has been demonstrated that rotational injection of fuel into a combustion chamber of an internal combustion engine is very useful, the effects of the fuel injection nozzle configuration and the rotational speed of the nozzle on the combustion process and the way to optimize the combustion through these variables were not properly understood, even not by persons skilled in the art.

SUMMARY OF THE INVENTION

The method according to the invention for optimizing the effect of rotating fuel injection into the combustion chamber of an internal combustion engine comprises controlling the rotational speed within a range that assures that the injected fuel is atomized as quickly, uniformly and efficiently as possible. The method takes advantage of the correlation between the fuel injector nozzle configuration, the fuel injection pressure and the required rotational speed for fine atomization and uniform distribution of the fuel inside the combustion chamber. In addition, the invention comprises an injection device for application of the method. The device comprises a rotatable fuel injection nozzle and impeller, both with a distinguishing configuration.

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 longitudinal section of an embodiment of a fuel injector nozzle according to the invention; - FIG. 2 is a schematic cross-section of a piston inside a cylinder of an internal combustion engine showing the effect of injecting fuel into a combustion chamber under different angles; FIG. 3 is a schematic side view of an embodiment of an injection nozzle assembly of a rotatable fuel injector according to the invention.

Identical or similar parts have been designated with identical or similar reference numbers.

DETAILED DESCRIPTION OF THE INVENTION

If fuel(s) and oxidizing agents (oxygen, OH-groups, peroxides, etc.) can react with each other properly inside a combustion chamber, full combustion will occur without the release of particulate matter (PM). To achieve this with liquid fuels, the fuel will need to be transformed into the gaseous phase as complete and fast as possible. This will have to be achieved without intermediate forms which are created by phenomena such as pyrolysis.

In spite of decades of research and development work by the industry on combustion chamber geometry, injection equipment and the influence of injection pressures, there still are many problems with respect to emissions (PM, NOx, C02, etc.). The recent emission scandals involving Volkswagen and other car manufacturers provide proof for that.

The present invention comprises solutions that prevent or at least substantially reduce such emissions through measures at the source, instead of symptom fighting in the exhaust system through after-treatment.

Static fuel injectors according to the prior art all have the purpose of atomizing the fuel as finely as possible inside a combustion chamber, however, the performance of engines with such static injectors shows that, both in terms of fuel efficiency and emissions, the injectors apparently fail to actually achieve the intended fine atomization. Injection of fuel through static injectors according to the prior art results in massive liquid fuel jet streams inside the combustion chamber of an internal combustion engine and a combustion pattern comprising undesirable so-called flamelet generated manifolds (FGM's), which may also be referred to as separate plumes. The separated areas comprising the fuel injection jet stream and resulting plumes are referred to as FGM's, since each of them can be seen as an isolated area directly related to one of each of the nozzle holes inside the combustion chamber. Studies of these areas led to the insight that these FGM's are the cause of emissions from today's combustion engines. Apart from the intrinsic disadvantages of creating FGM's the injection techniques according to the prior art also fail to utilize the space between individual FGM's efficiently. This will be a thing of the past if the fuel is injected into the combustion chamber rotationally and under conditions as per the present invention.

Due to the high temperature of the gases around the fuel jet streams, evaporation of liquid fuel at the outer surfaces of fuel jet stream is induced and in the core of the jet stream pyrolysis of fuel takes place, which results in the formation of PM and non methane hydrocarbons (NMHC).

When fuel in the jet stream which is still in the liquid phase hits relatively cold engine parts, such as the piston bowl or cylinder wall, the transition from the liquid to gaseous phase is prevented or at least slowed down. In this situation the mixing with gases is almost completely based on the heat release from the ignition phases inside the plume or FGM's. Direct reactive contact with the gases is hindered by the high velocity. The problematic mixing between liquid fuel and gases will continue to exist as long as the principle of FGM's continues to exist.

The liquid fuel that is injected through static fuel injectors constitutes only a few percent of the total volume of the combustion chamber. Emissions are created mainly in areas with a shortage of oxygen, such areas include but are not limited to: a. positions where liquid fuel hits the cylinder wall and where heat release occurs at the cylinder wall; b. positions where oxygen has been consumed or displaced by the reaction products of completed chemical reactions; c. positions where oxygen is displaced due to gas transport;

Swirl and squish play a role in mitigating emissions, however they are not strong enough to prevent emissions.

The spaces between FGM's (plumes) are oxygen rich areas as well as the centre around the injector nozzle.

The majority of NOx is formed around the outer surface of the FGM's due to a non-uniform temperature distribution, whereby the local peak temperatures exceed the critical temperature limit for the formation of thermal NOx by far.

Static fuel injectors may have two distinct types of fuel pressure supply systems, i.e. plunger pumps or Common Rail (CR). When using a plunger pump the injection rate increases during the duration of the injection cycle as a result of the cam drive geometry. When using a plunger pump the injection rate increases if the injection duration is increased.

When using CR the injection rate decreases during the duration of the injection cycle. This is caused by a pressure drop in the rail upon opening of the injector(s). When using CR the injection rate decreases if the injection duration is increased.

An increase of the injection pressure in order to obtain a higher degree of atomization is the method applied most in the prior art. This leads to more liquid fuel hitting engine parts in the combustion chamber with the pertaining undesirable effects discussed above. In addition, higher injection pressures lead to the need for heavier fuel pump drive systems and injector components.

Using a rotating fuel injector instead of a static fuel injector for the introduction of fuel into the combustion chamber of an internal combustion engine has shown to reduce many of the aforementioned shortcomings in the combustion process. However, so far, the effects of the variables involved in rotating fuel injection on the completeness of the combustion process and hence on the emissions were not understood by persons skilled in the art.

In conceptualizing the present invention, the inventor hypothesized that the required rotational speed of a rotating fuel injector for internal combustion engines in order to obtain the best effect on the combustion process and to prevent FGM's, is substantially higher than the rotational speed according to the prior art. The latter is in the order of a few thousand revolutions per minute (rpm) up to approximately 6.000 rpm.

The rotation is aimed at breaking down the fuel streams that exit each of the injector nozzle holes. However: (i) at a rotational speed that is too low the full stream will be deflected but not broken down and therefore the isolated FGM's will still be present, be it that they will show a bent shape as a result of the rotation; (ii) at a rotational speed that is too low but higher than the speed range of (i) above, the FGM's will (partially) merge, which is not an optimal situation either; (iii) at a rotational speed that is desirable/required no FGM's are formed and the fuel is finely dispersed, mixed and distributed uniformly with the gases across the combustion chamber.

At the fuel injection pressures of for example 1500 bar and higher that have become common nowadays the linear speed of the fuel exiting the fuel injector nozzle holes, hereinafter also called fuel exit speed, can easily exceed 100 meters per second (m/s), depending on the injector nozzle configuration and nozzle hole diameter. The method for complete combustion according to the present invention involves rotating the fuel injectors at a rotational speed which results in a peripheral linear speed of a nozzle hole exit that is preferably equal to or higher than the fuel exit speed in order to prevent or minimize the occurrence of massive fuel streams and to create substantial turbulence.

For example rotating fuel injection through an injection nozzle of which the nozzle hole exit openings (with a diameter of 0,22 millimeters) lie on a circle with a radius of 3,1 millimeters around the rotational axis preferably requires a minimum rotational speed of approximately 80.000 rpm in the case of a diesel fuel injection pressure of 600 bar and approximately 300.000 rpm if an injection pressure of 1600 bar is applied. When a rotating fuel injector is used that comprises an impeller, the rotational speeds for optimum combustion may be lower than the aforementioned levels. The invention comprises electric, pneumatic or hydraulic actuators for the rotation of the fuel injector at any rotational speed including speeds in excess of 100.000 rpm if and when required.

Apart from a minimum rotational speed of a rotating fuel injector that is required in order to obtain essentially complete combustion, the method according to the present invention also comprises maximum rotational speeds for fuel injection into a combustion chamber. In the present context, the concept of a maximum rotational speed is counterintuitive. Once being aware of the positive effects of rotational fuel injection on the combustion process, even persons skilled in the relevant art feel that the higher the rotational speed the better the combustion will be. However, according to the present invention there is a maximum rotational speed above which the effectiveness of the rotation may diminish or may even be reversed. For example: a. the maximum rotational speed is reached as soon as liquid droplets reach the piston bowl and/or cylinder wall due to the fact that during the tangential transportation route (=penetration depth) the residence time is less than the time needed for evaporation of complete liquid fuel droplets. Of course, the actual evaporation speed is fuel dependent. b. The maximum speed is reached when the centripetal acceleration forces exerted on the liquid lead to a pressure drop of zero along the nozzle exit bore.

In addition to the above phenomena which may limit or even reverse the effect of rotation when the rotational speed of a fuel injector exceeds a certain maximum, there are other reasons for not increasing the rotational speed above such a maximum. The higher the required rotational speed of a rotating fuel injector the more complex and therefore more expensive the injector will be. So, there is no logic and/or advantage in increasing the rotational speed after reaching the point at which no emissions of PM, CO and NOx occur anymore.

The method according to the invention comprises injecting fuel rotationally into a combustion chamber whereby the rotational speed of the fuel injector is such that the peripheral linear speed of the injector nozzle opening that moves with the lowest peripheral linear speed, i.e. the injector nozzle opening(s) that is (are) the closest to the rotational axis, is at least 25% and maximum 150% of the fuel exit speed.

For a diesel fuel injector nozzle of which the nozzle hole openings (with a diameter of 0,22 millimeter each) are positioned on a circle with a radius 3,1 millimeter operating with an injection pressure of approximately 600 bar the nozzle rotational speed range according to the invention is approximately 30.000 to 120.000 rpm.

The method according to the invention also comprises measures which may include the positioning of objects in the fuel streams exiting the nozzle in order to initiate a breakdown or divergence of the stream as early as possible. Such measures will be beneficial for the intended refined and homogeneous distribution of fuel throughout the combustion chamber. The finer the fuel droplets that are mixed with the oxidizing agents the more complete the combustion will be. Ideally the fuel droplets should have molecular dimensions. This of course is not achievable, but nevertheless can be strived for.

The invention also includes a fuel injector of which at least two nozzle holes are positioned such that fuel exiting each of these holes exits at a different angle relative to the longitudinal axis of the cylinder. FIG. 1 is a schematic longitudinal section of an embodiment of a fuel injector nozzle 1 according to the invention. In this view six sectioned nozzle holes involving in total essentially three different fuel exit angles, also referred to as fuel injection angles, are shown. In this embodiment the bores of each pair of opposite nozzle holes are positioned at an essentially equal angle relative to the longitudinal axis of the nozzle. Another embodiment of the fuel injector nozzle according to the invention comprises an eight hole nozzle in which each of the eight bores of the nozzle holes is placed at a different angle relative to the axis of the nozzle. Of course, the invention also comprises yet other embodiments of the nozzle with less than six or more than eight holes and with a different configuration of the bores and angles.

Even when used as a static injector a rotary fuel injector with a plurality of nozzle injection angles is likely to provide improved fuel and air mixing and improved combustion. A fuel injector with a plurality, i.e. two or more, of nozzle injection angles, may hereinafter also be referred to as multi injection angle nozzle.

Since certain embodiments of the rotary fuel injector that may be used in applying the method according to the invention are redundant, meaning for example that if the rotation would cease the fuel injector can still continue to operate as a static fuel injector, the term rotating or rotary fuel injector used in this description and the claims below, shall be construed to include static fuel injection with respect to the nozzle injection angles. FIG. 2 is a schematic cross-section of an example of a piston 3 inside a cylinder 4 of an internal combustion engine, whereby fuel is injected into the cylinder through a multi injection angle nozzle 1. In the drawing of FIG. 2 the piston is essentially in the top dead center (TDC) position. In moving towards the TDC the gasses are displaced to the piston bowl and are transported towards the center. The latter is also referred to as squish. When the piston moves downwards the reverse takes place. In both cases these gas streams intersect with the fuel injected through the rotating multi injection angle nozzle according to the invention. Due to the different angles the injected fuel follows a number (depending on the number of different injection angles) of different cone shaped patterns, which may be beneficial in limiting the required nozzle rotational speed fora maximum effect on increasing the completeness of the combustion process. FIG. 2 does not show the fuel injector's impeller as used in many embodiments of the fuel injector according to the invention. The impeller will help in creating turbulence and close contacts between the fuel and oxidizing agents. FIG. 3 is a schematic side view of an embodiment of an injection nozzle assembly of a rotatable fuel injector according to the invention. In this embodiment the injection nozzle assembly comprises a nozzle 1 and a cone shaped object 5, hereinafter also called cone 5, that is placed in front of the nozzle hole coaxially with the bore of the nozzle hole and whereby the vertex of the cone is facing the nozzle hole. Fuel exiting the nozzle hole will hit the cone and will be diverged to also adopt a cone like flow pattern as shown schematically by the lines 6, of which only one has been numbered. Since the fuel stream is spread and assumes an essentially hollow cone like pattern, it will subsequently be broken down more quickly and efficiently due the rotation of the nozzle assembly than is the case with a massive fuel stream. Instead of a cone shaped object 5, hereinafter also referred to as a flow diverging object 5, the invention also comprises embodiments of the nozzle assembly with other shapes of flow diverging objects, such as for example a pyramid shape. The flow diverging objects can be attached to the nozzle of a rotating fuel injection device according to the invention in any practicable manner, such as for example integration in an impeller that may be mounted on the nozzle.

In an embodiment of the fuel injection device according to the invention the flow diverging object 5 is also used as an electrode in order to electrostatically influence the fuel and/or the fluid that is injected. Electrostatic influence may help in accelerating the release of free radicals.

In an embodiment, the impeller of the injection device is then used as an electrode with an opposite charge relative to the charge of the flow diverging object. By transferring this opposite charge to the gases, the reaction between the fuel/fluid and the gases is promoted.

In yet another embodiment of the fuel injection device the nozzle is static but the fuel exiting the nozzle hits an object that rotates in front of the nozzle exit end of the injector and the fuel stream will be broken down by this collision with the rotating object and, hence, will be distributed across a substantial part of the combustion chamber. Such a rotating object may comprise an impeller, a crown with blades of any shape and size which is beneficial in breaking down the fuel or fluid stream.

Many changes can be made in the method and device described above without departing from the intent and scope thereof. It is intended therefore that the above description and accompanying drawings be interpreted as illustrative and not in a limiting sense.

Claims (16)

A method for rotating fuel injection into a combustion chamber of an internal combustion engine using a rotary atomizer, characterized in that the rotational speed of the rotary atomizer is adjusted such that the linear speed of the slowest moving atomizer hole of the rotary injector is at least twenty-five percent and at most one hundred and fifty percent of the speed at which the injected fuel exits from a nozzle hole. A method according to claim 1, characterized in that the rotational speed of the rotary atomizer is set such that the linear speed of the slowest moving atomizer hole of the rotary atomizer is at least fifty percent and at most one hundred and twenty five percent of the speed at which the injected fuel exits from a nozzle hole. Method according to claim 1 or 2, characterized in that the speed of revolution of the rotary atomizer is set such that the linear speed of the slowest moving atomizer hole of the rotary atomizer is at least seventy five percent and at most one hundred and ten percent of the speed at which the injected fuel exits from a nozzle hole. Method according to one or more of the preceding claims, characterized in that the fuel is injected into the combustion chamber at at least two different angles with respect to the longitudinal axis of the cylinder or the axis of rotation of the rotary atomizer. A device for applying the method according to one or more of the preceding claims. Device as claimed in claim 5, characterized in that the device comprises a rotary atomizer comprising at least two different fuel outlet angles. Device as claimed in claim 5 or 6, characterized in that the device comprises a rotating atomizer comprising at least three different fuel outlet angles. Device as claimed in one or more of the claims 5-7, characterized in that the device comprises a rotary atomizer comprising at least four different fuel outlet angles. Device as claimed in one or more of the claims 5-8, characterized in that the device comprises drive means which can achieve a rotational speed of the atomizer of at least ten thousand revolutions per minute. Device as claimed in one or more of the claims 5-9, characterized in that the device comprises drive means which can achieve a rotational speed of the atomizer of at least twenty-five thousand revolutions per minute. Device as claimed in one or more of the claims 5-10, characterized in that the device comprises drive means which can achieve a rotational speed of the atomizer of at least fifty thousand revolutions per minute. Device as claimed in one or more of the claims 5-11, characterized in that the device comprises drive means which can achieve a rotational speed of the atomizer of at least one hundred thousand revolutions per minute. Device according to one or more of claims 5-12, characterized in that the device comprises a flow divergent object (5). Device according to claim 13, characterized in that the current diverging object comprises a cone or a pyramid. Device as claimed in claim 14, characterized in that the cone or the pyramid is positioned coaxially with the bore of a spray hole with the top facing the spray hole for the opening of the spray hole. Device according to one or more of claims 13 to 15, characterized in that the current diverging object (5) comprises an electrode.