WO1992012340A1

WO1992012340A1 - Method and device for atomising a liquid fuel

Info

Publication number: WO1992012340A1
Application number: PCT/SE1991/000908
Authority: WO
Inventors: Lars Erling Elias Westerlund; Jan Bertil Hermodsson
Original assignee: Creative Power Development In Malmö Ab
Priority date: 1990-12-28
Filing date: 1991-12-27
Publication date: 1992-07-23
Also published as: SE9004180D0; SE467704C; SE467704B; AU9124391A; SE9004180L

Abstract

The invention relates to a method and a device for atomising a liquid fuel during the supply thereof to a combustion chamber (10). According to the invention, a liquid fuel is mixed with a combustion-promoting gas and, in this context, set in high-frequency vibration, the mixture is conducted past an inwardly directed, peripheral edge (16) in said chamber, and a secondary flow of combustion-promoting gas is sucked into the chamber adjacent or immediately after this edge in an amount controlled by the negative pressure or vacuum in the chamber, when the negative pressure in the chamber is lower than a settable limit value. According to the invention, use is preferably made of a check valve (19) whose degree of opening varies depending on the prevalent negative pressure in the chamber and which is settable to a desired limit value.

Description

METHOD AND DEVICE FOR ATOMISING A LIQUID FUEL

The present invention relates to a method and a device for atomising a liquid fuel during the supply thereof to a combustion chamber according to the preamble of claim 1 and claim 3, respectively.

When burning liquid fuel in internal combustion engines and combustion chambers of other combustion appa¬ ratuses it is common to atomise the fuel by injection thereof through nozzles in the form of jets. It is also common that, during or after the injection into a combus¬ tion-promoting gas, the fuel is set in high-frequency vibration in order to obtain a thorough mixing of fuel and gas. Examples of this technique are to be found in the publications EP-A-0,202,100, DE-A-2,450,801, DE-A- 2,430,415 and FR-A-1,259,494. By using vibration means, the atomising of the fuel in the combustion-supporting gas is improved, i.e. the fuel droplets become small and comparatively uniformly distributed in the mixture. However, to obtain good results, high pressures and a high velocity of the fuel jet and also an excess of com¬ bustion-promoting gas (usually air) are required. Prior art devices, however, have appeared not to yield optimum results when using this technique for internal combustion engines, independently of whether they operate by car¬ burettors or by direct injection. It has thus appeared that, owing to surface tension, the liquid droplets are frequently collected as a film of liquid which moves along the wall of the throughflow chamber. As a result, the fuel forming the film of fuel is inadequately burnt.

The object of the present invention therefore is to improve prior art methods and devices for atomising a liquid fuel durinq the supply thereof to a combustion chamber, and when using the invention, a liquid fuel should be mixed with a combustion-promoting gas and, in this connection, be set in high-frequency vibration, and the mixture should be conducted past an inwardly directed, peripheral edge in the chamber, and a secondary flow of combustion-promoting gas should be sucked into the chamb adjacent or immediately after this edge in an amount con trolled by the negative pressure ( "vacuum") in the cha - ber, when the negative pressure in the chamber is lower than a settable limit value. When using the invention, u is preferably made of a check valve whose degree of open¬ ing varies depending on the prevalent negative pressure the chamber and which is settable to a desired limit value. The intake of the secondary flow of combustion- supporting gas after the edge should thus occur in a con¬ trolled manner and in an amount which is dependent on the negative pressure prevailing in the chamber after this edge, the sucked-in air providing a redispersion of liqui fuel on the walls of the throughflow chamber.

The characteristic features of the method according to the invention are stated in claim 1, while the charac¬ teristic features of the device according to the inventio are stated in claim 3. When using the invention, a most pronounced reduc¬ tion of the content of carbon monoxide (CO) and hydrocar¬ bons (HC) is obtained. The content of nitric oxides (NO ) is also reduced, particularly since there is a consider¬ able decrease in fuel consumption in consequence of a more effecient combustion.

US-A-3,834,367 discloses the insertion of a flat plate after a carburettor, said plate forming a wall in the throughflow chamber and having inlet openings for taking in secondary air. This intake of secondary air occurs in a completely uncontrolled manner and is not affected by anything else but the engine speed and load.

German publication DE-A-3,411,094 discloses a device for supplying secondary air to the intake duct of an Ot o engine. In this case, the supplied amount of secondary ai is controlled by a throttle valve whose degree of opening is regulated by a separate regulating means in such a man¬ ner that the throttle valve is closed when idling and open at full speed. Thus, this device operates quite contrary to the device and the method according to the present invention.

US-A-3,659,575 discloses a device for reducing the negative pressure in the intake manifold of an engine and supplying additional air to said engine. This device comprises a normally closed, spring-loaded one-way valve which is adapted to be controlled by the negative pressure in the manifold and which is substantially loaded by a constant counterforce means in the form of a weight and to a smaller extent by spring force, said valve being damped against vibrations. The additional air is introduced into the throughflow duct by a number of radially directed inlet apertures which open into the wall of the through- flow duct. The function of this prior art device is depen¬ dent on the mounted position of the device, and moreover it can be affected by inertia forces when the device is used in a vehicle engine. Further, the shown embodiments of this prior art device have no means for providing, in the manner according to the present invention, a redisper- sion of liquid fuel forming a film of liquid on the wall of the throughflow duct.

Consequently, the invention distinguishes from all prior art in that a combination is obtained of atomisation by vibration and intake of secondary air, controlled by negative pressure, after an inwardly directed flange for forced reatomisation of fuel which flows as a layer along the walls of the throughflow duct.

Two embodiments of the invention will be described in more detail below with reference to the accompanying draw¬ ing. Fig. 1 illustrates, partly in section, a secondary air supply plate in a first embodiment of the inventive device. Fig. 2 is a cross-sectional view along the line II-II in Fig. 1 and neighbouring portions of the through- flow chamber. Fig. 3 is a cross-sectional view, corre¬ sponding to the one in Fig. 2, of a second embodiment of the device according to the invention. In the two illustrated embodiments of the device according to the invention, a throughflow chamber 10 comprises a first section 11 and a second section 12 between which a secondary air supply plate 13 is inserte A fuel injection nozzle 14 extends into the throughflow chamber and is connected with a schematically shown vibr tion means 15 for setting the fuel nozzle in high-fre¬ quency vibration. However according to the invention, us can be made of a stationary fuel injection nozzle togeth with a separate vibrator, the vibrating body of which extends in the throughflow chamber for setting the fuel- gas mixture in high-frequency vibration.

The secondary air supply plate 13 forms an edge 16 which is inwardly directed in the throughflow chamber 10 and which breaks a film of liquid formed on the chamber wall and moving in the direction of the gas flow along th wall. After the edge 16, there is formed a peripheral recess 17 into which a secondary air inlet duct 18 opens substantially tangentially in order that the sucked-in ai should be set in a whirling motion for improving the redispersion of liquid fuel moving along the wall of the throughflow chamber in the form of a film of liquid.

The secondary air inlet duct 18 is connected to a check valve means 19 which is mounted in a bore 20 in the plate 13. The check valve comprises a valve seat componen 21 which is screwable to different axial positions in the bore 20, thereby changing the position of the seat 22 of the check valve. A valve member 23 is contained in the check valve and is spring loaded in the direction of the seat 22 by a compression spring 24 resting against an annular abutment 25 in the bore 20. The secondary air is sucked in through an air cleaner 26, when the negative pressure in the throughflow chamber 10 exceeds a limit value which is settable by adjusting the bias of the spring 24 by varying the axial position of the valve seat component 21 in the bore 20. The embodiment according to Fig. 3 distinguishes fro the embodiment according to Figs. 1 and 2 only in that th recess 17 has been formed as a screw thread, so that the sucked-in secondary air, to an even higher extent, is set in a helical whirling motion for whirling the fuel and redispersion of liquid fuel moving along the wall of the throughflow chamber.

When using the invention, air is not supplied in a greater amount than in normal operation of the engine, bu the air is admitted in a different manner, so that the combustion is improved and the exhaust gases become con¬ siderably cleaner. If a greater amount of air should be supplied than is normally the case under the same operat¬ ing conditions, a leaner mixture would be obtained. This would, in turn, have negative effects, such as an increas¬ ed risk of burnt valves.

According to the invention, it is also important that the secondary air supply plate 13 does not form a drastic contraction in the throughflow chamber 10, since such a contraction would yield a pressure drop which, in turn, would result in a greater intake of secondary air and, thus, a leaner fuel-air mixture bringing the above-men¬ tioned drawbacks. Preferably, the edge 16 of the plate 13 is aligned with the wall of the throughflow chamber or extends slightly beyond this, so that a peripheral (pos¬ sibly helical) groove is formed adjacent the plate. Expe¬ riments have shown that the best results are obtained in these cases, but that a slight projection (1-2 mm at most) can be tolerated. The above-described embodiments of the invention are intended for an internal combustion engine fitted with a carburettor. However, the invention is also useful in internal combustion engines having direct injection of the fuel and in diesel engines. An expert can readily apply the inventive principles and provide such engines with secondary air inlets and a redispersing means of the type described above. In these embodiments of the invention, only one sub stantially tangentially directed secondary air inlet is used. However, if desired, use can be made of two or mor substantially tangential inlets distributed along the periphery, which receive the air from the check valve.

Claims

1. A method for atomising a liquid fuel during the supply thereof to a combustion chamber, in which method the fuel is effectively mixed with a combustion-promoting gas, especially air, in that, at an injection position (14), the fuel is fed to a chamber (10) through which the gas flows and, during or after said injection, the fuel is set in high-frequency vibration to be thoroughly mixed with said combustion-promoting gas, c h a r a c t e r ¬ i s e d in that the mixture of fuel and combustion-pro¬ moting gas is conducted past an inwardly directed, peri¬ pheral edge (16) in said chamber (10), and that a secon- dary flow of combustion-promoting gas is sucked into said chamber (10) adjacent or immediately after this edge in an amount controlled by the negative pressure or vacuum in said chamber, when the negative pressure in the chamber is lower than a settable limit value.

2. The method according to claim 1, c h a r a c ¬ t e r i s e d in that the intake of the secondary flow is controlled by a check valve (19) which has means (21) for setting said limit value for varying the degree of opening of said check valve depending on the prevalent negative pressure in said chamber (10).

3. A device for atomising a liquid fuel during the supply thereof to a combustion chamber, said device com¬ prising a throughflow chamber (10) for feeding a combus¬ tion-promoting gas to the combustion chamber and a fuel supply nozzle (14) which opens into said chamber (10) at an injection position and which serves to inject the fuel for mixing together with the combustion-promoting gas, and a vibration means (15) for setting, during or after supplying the fuel, the mixture of fuel and gas in vibra- tion, said throughflow chamber (10) having an inwardly directed, peripheral edge (16) after the injection posi¬ tion and a secondary inlet (18) for a secondary flow of combustion-promoting gas adjacent or immediately after this edge, c h a r a c t e r i s e d in that said device comprises an intake-controlling means (19) which is arranged to permit the intake of combustion-promoting gas through the secondary inlet (18) in an amount which is dependent on the prevalent negative pressure or vacuum in the throughflow chamber (10) at the secondary inlet.

4. The device according to claim 3, c h a r a c ¬ t e r i s e d in that the intake-controlling means (19) comprises a check valve (19) which has adjusting means (21) or setting a limit value pressure for opening the check valve and, thus, varying the degree of opening of the check valve depending on the prevalent negative pres¬ sure in said chamber (10).