EP1576282A1

EP1576282A1 - Fuel injection nozzle

Info

Publication number: EP1576282A1
Application number: EP03781188A
Authority: EP
Inventors: Jerzy Chomiak
Original assignee: Stiftelsen Chalmers Industriteknik
Current assignee: STIFTELSEN CHALMERS INDUSTRITEKNIK
Priority date: 2002-12-06
Filing date: 2003-12-05
Publication date: 2005-09-21
Also published as: WO2004053326A1; AU2003287121A1; SE0203625D0

Abstract

A fuel injection nozzle (10) for internal combustion engines provided with a valve, in particular a needle valve (24), and a nozzle sac (20) below the valve which includes plural injection orifices (22) distributing the fuel in combustion space. A swirl flow is induced upstream the nozzle sac, for instance by using a swirl fluid passage (34). A free ball (32) from a material of higher density than the fuel is located in the nozzle sac (20) moved by the swirling flow around the sac and following a track (36) in the form of a rounded corner of a radius slightly larger than the ball and connecting the injection orifices with entrances in the center of the rounded corner. The ball sequentially covers the injection orifices so that it provides multiple fuel injection pulses during a single opening of the fuel valve i.e. per single cylinder firing. The multiple injections provide substantially improved fuel atomization, air entrainment into the fuel spray and better air utilization in the engine, increasing power density, combustion and cycle efficiency and reducing emissions. For best effects the fuel swirl rate in the sac shall be three to four times the air swirl rate in the combustion chamber. The ratio of the ball diameter to the sac diameter is preferably between 0.6 and 0.8.

Description

Fuel injection nozzle

TECHNICAL FIELD

The present invention relates to a fuel injection nozzle primarily for internal combustion engines.

BACKGROUND OF THE INVENTION

In the majority of internal combustion engines liquid fuel is used which is injected in the air in the inlet manifold as in typical spark ignition (SI) engines or more or less compressed air in the cylinder as in direct injection (Dl) homogeneous and stratified charge (SI) engines or compression ignition engines i.e. Diesel and homogeneous charge compression ignition (HCCI) engines. Rapid fuel atomization, evaporation and fuel-air mixing must be achieved in the engines for proper operation and low emissions. Therefore a leading issue in engine development is improving fuel atomization.

In order to achieve the best results, a very large number of solutions have been proposed. Orifice injectors with multiple small and ultra-small, circular and non-circular injection orifices, swirl injectors, pintle injectors, liquid-liquid and liquid-surface impingement injectors, vibratory injectors, air assisted injectors, heated tip injectors, and many others have been developed for the SI engines, as discussed extensively in the SAE Technical Paper No. 950506 by Fu Quan Zhao et al., "The Spray Characteristics of Automotive Fuel Injection - A Critical Review", 1995. For compression injection engines currently almost exclusively multiple, small diameter injection orifices are used.

To achieve the growing demands concerning atomization and fuel-air mixing quality, injection pressures have been raised and smaller and smaller injection orifices used. The benefits of the very high pressure, small and ultra-small orifice injection have been discussed for instance in the SAE Technical Paper No. 900438 by T. Minami et al., "Analysis of Fuel Spray Characteristics and Combustion Phenomena under High Pressure Fuel Injection", 1990. In contemporary Diesel engines pressures up to 2200 bar and orifice diameters down to 0.1 mm are used. Clearly this requires expensive pumps, seals, conduits and filtering devices, and makes the system more prone to failure due to mechanical stresses, erosion of pumping elements and injector blockage, the probability of which increases as the injector orifices become smaller.

One way to achieve finer fuel atomization, evaporation and mixing with air is to use multiple, short sequential injections. The improvement of combustible mixture formation by multiple sequential injections leads to reduction of pollutant emissions as explained e.g. in the SAE Technical Paper No. 940897 by T. Tow et al., "Reducing Particulate and NOx Emissions Using Multiple Injection in a Heavy Duty Dl Diesel Engine", 1994. Second generation high pressure common rail injection systems using piezoelectric control of the injector needle allowing 7 sequential injections during one cylinder firing are already available on the market as reported in the January 2002 issue of the "Automotive Engineer" magazine. Again, this is a rather expensive technology as it also requires elaborate control and actuator systems. Consequently there is a need for an improved fuel injection system, much less complicated and expensive.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a multihole fuel injection nozzle (or "injector"), which is capable of generating multiple sequential injections at much lower cost. Another object of the present invention is to provide a high performance multishot injector simple in construction and capable of being easily manufactured and assembled. Yet another object of the present invention is to provide a multishot injector which does not require multiple opening of the needle valve per cylinder firing. A still further object of the invention is to provide an injector minimizing emissions, especially of nitrogen oxides and particulate matter (soot) by modification of the injection process. Another object of the present invention is to provide an injector which at lower injection pressures and for larger injector orifices generates fuel sprays of quality satisfying the demands of contemporary internal combustion engines. A still further object of the invention is to provide an injector which in spite of increased nozzle sizes prevents engine wall wetting by the fuel leading to larger unbumed hydrocarbon and soot emissions.

At least one of the above objects is achieved by the fuel injection nozzle as claimed in appended claim 1.

By providing a multihole injector of classic design where, in the nozzle sac distributing the fuel between the individual injection orifices, an interruption means, preferably in the form of a ball, is placed which is operable by the fuel flow, sequential opening and closing of the orifices is attainable without recourse to further extrinsic means. Preferably, a swirl flow of fuel is generated. Under the influence of the imposed swirl the ball moves around in the sac, sequentially covering the injection orifices and thus generating multishot injections in rapid sequence from each of them. The injections are regular and can be synchronized with the air swirl in the combustion chamber to secure uniform fuel distribution in the combustion air.

Thus, the invention provides a simple, yet overwhelmingly effective solution to a long standing problem particularly in the art of compression ignition (Diesel) engines. Similarly it is imaginable, that the same technology could also be applied to other injection systems of internal combustion engines in particular direct injection SI engines and HCCI engines as well as in liquid atomization devices used in other application fields.

Preferred embodiments of the present invention are detailed in the dependent claims. BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in the following in greater detail by way of example only and with reference to the attached drawings, in which:

FIG. 1 is a schematic perspective view of a fuel injection nozzle according to the present invention;

FIG. 2 is a schematic cross-sectional view of the lower end of the fuel injection nozzle illustrated in Fig. 1, with the left-hand side of the drawing illustrating the nozzle in a closed condition and the right-hand side of the drawing illustrating the nozzle in an open condition;

FIG. 3 is a schematic cross-sectional view of the nozzle sac of the fuel injection nozzle according to the present invention on a relatively large scale, and

FIG. 4 is a sectional view along line IV-IV of Fig. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the drawings, reference numeral 10 denotes a fuel injection nozzle in accordance with the present invention. With particular reference to Fig. 2, the fuel injection nozzle comprises a nozzle body 12 having a guide passage 14 extending along a longitudinal axis L. The guide passage has a first end 16 connectable to a (not shown) fuel source and a second end 18. The nozzle body 12 further comprises a nozzle sac 20 having a plurality of orifices 22, of which two are shown in the drawings. The nozzle sac 20 communicates with the second end of 18 of the guide passage 14. The fuel injection nozzle 10 also comprises valve means 24 for opening and closing in a conventional manner the second end 18 of passage to thereby control fuel flow to the nozzle sac 20. Preferably, and as illustrated in Fig. 2, the valve means is a needle valve having a tip 26. The needle valve is provided with a frusto-conical end portion 28 adjacent to the tip 26. As shown to the left in Fig. 2, the frusto-conical end portion 28 of the needle valve is adapted to rest against a frusto-conical valve seat 30 in the nozzle body 12 when the valve is in its closed position. When fuel injection is to take place, and as shown to the right of Fig. 2, the needle valve is lifted such that the frusto-conical end portion 28 leaves the valve seat 30 to thereby place the guide passage 14 in liquid communication with the nozzle sac 20. Accordingly, the needle valve controls the opening and closing of the injection nozzle 10 i.e. the injection timing and duration.

In accordance with the present invention, the nozzle sac 20 of the fuel injection nozzle 10 accommodates interruption means 32 operable by the fuel flow to sequentially open and close the plurality of orifices 22. By the expression "sequentially open and close the plurality of orifices" it is meant that the fuel flow effects displacement of the interruption means such that an orifice which has been closed and thereafter opened by the interruption means will not be closed again until another orifice has been closed. Such opening and closing of the orifices takes place during the open phase of the valve means 24.Thus, the term "sequentially" does not necessarily imply that all of the orifices are opened and closed one after the other in a completely preset order, even though this is obviously preferable.

So that the interruption means 32 may be easily influenced, and hence, operable by the fuel flow, in one embodiment of the invention the interruption means is a freely displaceable member, preferably a ball having a diameter d. A person skilled in the art will appreciate that, in order to operate reliably, the freely displaceable member must be made from a material of higher density than the fuel.

Although flow of fuel over the valve seat 30 and into the nozzle sac 20 is often sufficient to create flow turbulence which is adequate to operate the interruption means 32, such operation is chaotic in its nature. It may therefore be advantageous to provide the fuel injection nozzle 10 with swirl-inducing means. Thus, in one embodiment, the guide passage 14 may be provided with means, such as a groove, for generating swirl in the fuel flow as the fuel enters the nozzle sac. In an alternative embodiment, or indeed in combination with the means in the guide passage, the valve means 24 may be provided with means, such as a groove 34, for generating swirl in the fuel flow as the fuel enters the nozzle sac. In either case, the groove 34 is inclined at an angle Θ relative to the longitudinal axis L of the fuel injection nozzle. It is also contemplated that multiple tangential grooves may be provided. Thus, the groove or grooves 34 act as a swirl passage for the fuel. The combination of the swirl flow imposed by the grooves 34 and straight flow imposed by the passage 14 provides flexibility to obtain a global fuel swirl of desired intensity below the needle when the injection nozzle is opened and fuel injection occurs. The fuel swirl is enhanced due to conservation of angular momentum when the fuel moves along the frusto-conical valve seat 30 (vortices rotate faster when their diameter decreases) and enters the sac. Thus fuel rotation in a wide range of rotational speeds can be realized easily in the sac. Also other ways of inducing fuel swirl in the sac are possible even if they may be more complicated.

During injection, the interruption means 32 is forced by the fuel flow to move around the nozzle sac 20 causing sequential opening and closing of the injection orifices 22, thus producing a number of sequential injections from each of them i.e. realizing the required multishot operation. It is not necessarily essential that the orifices be uniformly distributed around the nozzle sac. Nevertheless, in one embodiment of the present invention, the plurality of orifices 22 are uniformly distributed around the nozzle sac and are at least five in number, preferably between five and ten in number. The multiple injections provide substantially improved fuel atomization, air entrainment into the fuel spray and better air utilization in the engine, increasing power density, combustion and cycle efficiency and reducing emissions. With particular reference to Figs. 3 and 4, the nozzle sac 20 comprises a track, generally denoted by 36, along which the plurality of orifices 22 is arranged. The track 36 presents a guide surface 38 for the interruption means 32. The guide surface 38 delimits an internal diameter D of the nozzle sac and the nozzle sac comprises a substantially planar bottom surface 40 bordered by the guide surface 38. Preferably, the base of the sac has internal radii close as possible to, though slightly larger than, the radius of the interruption means, in the shown example in the form of a ball. The location of the inlets to the orifices 22 are advantageously arranged in the middle of the contact of the ball with the guide surface 38. According to the above, the corner radii at the sac bottom are nominally equal to d/2 where d is the diameter of the ball, the diameter of the flat part is δ=D-d where D is the internal diameter of the sac and α=45 deg.

In practice, three types of sprays have been observed when the ball 32 passes an orifice 22: hollow non-circular, non-circular, and non-circular with changing orientation (targeting). Occasionally, when the ball is further away from the orifice two sprays occurred. Finally a standard spray is formed when the ball is further away from the orifice. The above processes cause a wide variation in spray angle and targeting and result in more uniform fuel distribution in the combustion air. In addition the penetration of the fuel jets is decreased, which can reduce fuel deposition on the combustion chamber walls which is a problem for engines with compact combustion chambers. In the engine, reduced fuel consumption, reduced NOx and soot emission can be achieved as a substantial amount of fuel is burnt in lean flames and the rich fuel zones are dispersed faster. The frequency of injections is controlled by the fuel swirl in the sac and/or by the fuel flow turbulence. To achieve best results the frequency shall be synchronized with the air swirl in such a way that the sequential injections occur when the air has moved around the combustion chamber 12-15 deg. Then the fuel is always injected in fresh air and not in the oxygen depleted wake of the previous injection leading to substantial combustion improvements. This would require the fuel swirl number in the sac to be typically about four times larger than the swirl number of the air in the combustion chamber.

The ratio of injection interval to the injection time in a single shot depends on the ball to sac diameter ratio d/D. Good combustion results are obtained for the interval duration of about 0.3 of the single shot duration which can be achieved for d/D of about 0.75-0.8. Smaller balls provide shorter intervals which are also beneficial. Thus typically the preferred d/D value is in the range of from 0.5 to 0.9, preferably from 0.6 to 0.8, and most preferably about 0.75 to 0.8. Larger balls cause a decrease of the overall discharge rate of the injector which, if necessary, can be restored by increasing the diameters of the injection orifices.

Typically for a ball of the diameter equal to 0.8 of the internal sac diameter and six injection orifices the discharge rate is reduced about 30 % which can be compensated by increase of the injection orifice diameters by 14 %. The ball also reduces the volume of fuel in the sac and thus in the same proportions reduces the unburned hydrocarbons (UHC) emissions of the engine. The ball prevents also formation of coke deposits in the sac caused by fuel decomposition which sometimes leads to blockage of the injector.

In case of injectors with so-called "minisacs" where the sac volume is minimized so that the needle tip enters deeply into the sac, cutting of the needle tip may be necessary to assure enough space for the ball. However, this does not increase the fuel volume in the sac. On the contrary the amount of fuel in the sac is still reduced by the presence of the ball and because the hydrocarbons are released from the sac just after end of injection due to inertia of the still moving ball.

In the above, the present invention has been described in connection with an intermittent fuel injection nozzle for an internal combustion engine. However, the skilled person will recognize that the principle of operation, i.e. using interruption means operable by a liquid flow to thereby effect multishot injections, may be applied to any liquid atomization nozzle for any application, in particular using continuous flow. For example, using the nozzle described above, with a continuously open needle will provide continuous multishot operation providing improved atomization and fuel air mixing. In a further example, by using a liquid nozzle having a cylindrical chamber with liquid being admitted to the chamber through a plurality of spaced-apart, inclined slots, and an interruption means having a cylindrical shape, for example in the form of a roller, passing over the slots sequentially, improved liquid atomization can be attained in a continuous flow nozzle. Such nozzles could have applications in gas turbine engines, stationary power plants and burners. Similar arrangements are conceivable In agricultural watering equipment.

Claims

1. A fuel injection nozzle (10) for an internal combustion engine, said nozzle comprising: a nozzle body (12) comprising a guide passage (14) having a first end (16) connectable to a fuel source and a second end (18), said nozzle body further comprising a nozzle sac (20) having a plurality of orifices (22), said nozzle sac communicating with said second end (18) of said guide passage (14); and valve means (24) for opening and closing said second end of said passage to thereby control fuel flow to said nozzle sac (20), wherein said nozzle sac (20) accommodates interruption means (32) operable by said fuel flow to sequentially open and close said plurality of orifices (22).

2. The fuel injection nozzle (10) as claimed in claim 1, wherein said interruption means (32) is a freely displaceable member.

3. The fuel injection nozzle (10) as claimed in claim 2, wherein said freely displaceable member is a ball having a diameter (d).

4. The fuel injection nozzle (10) as claimed in any one of the preceding claims, wherein said fuel injection nozzle is provided with means for generating swirl (34) in the fuel flow as the fuel enters the nozzle sac (20).

5. The fuel injection nozzle (10) as claimed in claim 4, wherein said means for generating swirl is provided in the guide passage (14).

6. The fuel injection nozzle (10) as claimed in claim 4, wherein said means for generating swirl is provided on the valve means (24).

7. The fuel injection nozzle (10) as claimed in claim 6, wherein said valve means (24) is a needle valve.

8. The fuel injection nozzle (10) as claimed in any one of claims 4 to 7, wherein said means for generating swirl comprises at least one groove (34) in said guide passage (14) and/or in said valve means (24).

9. The fuel injection nozzle (10) as claimed in any one of the preceding claims, wherein said plurality of orifices (22) is non-uniformly distributed around the nozzle sac (20).

10. The fuel injection nozzle (10) as claimed in any one of claims 1 to 8, wherein said plurality of orifices (22) is uniformly distributed around the nozzle sac (20).

11. The fuel injection nozzle (10) as claimed in claim 9 or 10, wherein said plurality of orifices (22) is at least five in number, preferably between five and ten in number.

12. The fuel injection nozzle (10) as claimed in any one of the preceding claims, wherein said nozzle sac (20) comprises a track (36) along which said plurality of orifices (22) are arranged, said track presenting a guide surface (38) for said interruption means (32).

13. The fuel injection nozzle (10) as claimed in claim 12, wherein said guide surface (38) delimits an internal diameter (D) of the nozzle sac.

14. The fuel injection nozzle (10) as claimed in claim 13, wherein said nozzle sac comprises a substantially planar bottom surface (40).

15. The fuel injection nozzle (10) as claimed in claim 13 or 14, wherein the ratio of the diameter of the interruption means (32) to the internal diameter of the nozzle sac (d/D) is from 0.5 to 0.9, preferably from 0.6 to 0.8, most preferably about 0.75 to