EP0102984A1

EP0102984A1 - Arrangement for the injection of fuel, like lpg, in liquid form

Info

Publication number: EP0102984A1
Application number: EP83900855A
Authority: EP
Inventors: Johannes Benjamin Willem Hoebeek
Original assignee: CALCOL BV
Current assignee: CALCOL BV
Priority date: 1982-03-10
Filing date: 1983-03-08
Publication date: 1984-03-21
Also published as: NL8200993A; WO1983003120A1

Abstract

Alimentation commandée d'un carburant qui, dans des conditions ambiantes, se présente sous une forme gazeuse ou de vapeur (telle que LPG), dans un moyen de combustion, comme un moteur à combustion interne. L'exemple décrit l'application du système d'alimentation sur un moteur du type Otto pourvu d'une injection de pétrole et d'une unité de commande électronique (29) d'un type standard. Un injecteur unique (43) de LPG est appliqué, lequel dessert de préférence plus d'un cylindre, en injectant le carburant sous forme liquide dans l'air de combustion en aval du papillon-valve (7). Dans une unité (40), dans laquelle est logé l'injecteur de LPG, est également incorporé un régulateur de pression (48) pour le carburant liquide. La commande et l'activation de l'injecteur LPG a lieu parallèlement et simultanément aux injecteurs de pétrole par le biais de l'unité de commande électronique existante (29). Au choix, l'unité de commande peut être réglée pour actionner soit les injecteurs de pétrole (15) soit l'injecteur LPG (43), soit les deux, de préférence le LPG en tant que carburant principal et le pétrole en petit dosage de 10 % ou moins. Des détails de conception de l'unité injecteur-régulateur sont donnés.Controlled supply of fuel which, under ambient conditions, is in the form of a gas or vapor (such as LPG), in a means of combustion, such as an internal combustion engine. The example describes the application of the supply system to an Otto type engine fitted with petroleum injection and an electronic control unit (29) of a standard type. A single LPG injector (43) is applied, which preferably serves more than one cylinder, by injecting the fuel in liquid form into the combustion air downstream of the butterfly valve (7). In a unit (40), in which is housed the LPG injector, is also incorporated a pressure regulator (48) for the liquid fuel. The control and activation of the LPG injector takes place in parallel and simultaneously with the petroleum injectors via the existing electronic control unit (29). Optionally, the control unit can be adjusted to operate either the petroleum injectors (15) or the LPG injector (43), or both, preferably LPG as the main fuel and petroleum in small doses of 10% or less. Design details of the injector-regulator unit are given.

Description

Arrangement for the injection of fuel, like LPG, in liquid form.

The invention relates to an .arrangement for metered supplying a fuel which under ambient conditions is a gas or vapour, more specially LPG, to a cαribustion means, like an internal ccmbustion engine, gas turbine, oven or the like, in which the fuel before its entry into the ccπibustion space is mixed with the required ccπibustion air.

Fuels of the above type, more specially LPG, are generally transported and held at ambient temperature in liquid form, the pressure in the conta ner rernaining thereby within easily controllable limits between approximately 4 and 12 bar over¬ pressure. Before its supply to the ccmbustion means the fuel is generally evaporated and its pressure generally is reduced con- siderably in a pressure reducing apparatus. The control of the quantity of fiel supplied to the ccmbustion means thus takes place after the evaporation and the pressure reduction, and therefore in the gas- or vapour-phase. In doing so the control becomes much dependent of the temperature and the pressure of the vapour, which in their turn are dependent of the composition of the fuel. As an example it is pointed to the differences in ccmposition of the butane and propane content in the summer- or winter-ccmposition of LPG. It is a known fact that the above control procedure in the vapour phase when for instance applied with internal ccmbustion engines of the Otto-type, leads to difficulties which for instance result in mixtures deviating from the required air/fuel ratio, being too lean or too rich.

The invention aims to solve nearly completely the problems connected with an accurate metering, by having the control of the closely related introduction of the fuel into the combustion air take place in the liquid phase. The above described arrangement is accordingly characterized in that the arrangement is adapted to meter the fuel under pressure and introduce it into the ccmbustion .air in substantially liquid form, the above in such a way that the evaporation of the fuel substantially only will take place in the combustion air.

In itself an accurate, reproduceable and controll<able metering of small fluid quantities is already known from fuel systems like those applied for instance on gas turbines, diesel engines and petrol—injection engines.

Due to the fact that the fuel under consideration is introduced in the supplied ccπibustion air and evaporates therein before the air/fuel mixture enters the ccmbustion means, and because the fuel is metered under comparatively lew pressure and equally does not require a higher pressure for its introduction into the ccmbustion air, an expensive high pressure -'injection system of the type developed for instance for diesel engines, is not required. Applicable are arrangements of the type developed for petrol injection of Otto-engines, which operate with relatively low pressures.

Since the main field of application of the arrangement according to the invention will be the application with piston- ccmbustion engines, in the following the invention will be further explained and illustrated for this application. It is, however, emphasized that the invention is basically applicable as well to for instance gas turbines, ovens and the like ccmbustion means. The arrangement according to the invention, when adapted for a piston-cctribustion engine, is -EurtherrtDre characterized in that the arrangement includes an injector to inject the fuel into the air inlet pipe. The arrangement is both applicable with diesel engines as with spark ignited Otto-engines, the latter including both carburetter-type engines and injection-type engines. Application with hybrid intermediate types are possible as well.

According to a further characteristic the arrangement, adapted for Otto ccmbustion engines, is characterized in that the injector is positioned downstream with regard to the air control valve (throttle valve) . Since a more or less accurate stoichiometric ai /fuel mixture is required in spark ignited Otto engines to get a regular and reproduceable ccmbustion. Otto engines are always equipped with an air control valve which controls the ccmbustion air quantity aspirated by the engine primarily as function of the power demanded from the engine. Both Otto engines with carburetter as with petrol injection are always provided with a throttling valve. Injection of LPG or the like according to the invention, downstream of the throttle valve, is advantageous because of the strong swirl in the airflew downstream the throttle valve, pro¬ moting the evaporation of the liquid fuel and its mixing with the ccmbustion air. Due to the evaporation an important reduction of temperature takes place, whereby water vapour present in the ocrribustion air temporarily can freeze and constitu.snts of the LPG or other fuel temporarily may become solid; this, however, cannot interfere with a free adjustability and a reproduceable use of the throttle valve, since the injection takes place downstream with regard to said throttle valve. From calculations and experiments it was found that the cxarbustion air, even in winter time, contains sufficient heat, together with the heat supplied through the walls of the air inlet pipe, to evaporate the fuel fast enough and cαtpletely, assuring a supply to all cylinders of a sufficiently homogeneous mixture.

From the above it follows that the arrangement is fiirtherπore characterized in that one injector serves more than one cylinder, like for instance 4, 5 or 6 cylinders of a whole engine or a rcw of cylinders in case of V-type engines or still other designs. Although the control of the fuel supply in itself can already take place accurately in the fluid phase, it is nevertheless preferable to dispose of a predetermined supply pressure of the fuel both for the metering as for the injection. The arrangement is therefore preferably characterized in that a pressure regulator is introduced in the supply of the fluid fuel to the injector. In order to keep the injection downstream of the throttle valve as reproduceable as possible, it is preferable to have the pressure regulator regulate the fuel supply pressure to ^' the injector as function of the air pressure prevailing in the air inlet pipe near to the injector. Not only the influence on the air pressure at the injector due to the throttle valve is thereby excluded, but also influences resulting from air filters, pressure charging com¬ pressors, ere. A CGnsr_anτ-. pressure difference between the fuel supply to the injector and the air into -which the injection takes place is thereby provided.

Although experts are of the opinion that the pressure of LPG cannot be reduced without a troublesome formation of vapour

bubbles, a certain pressure reduction - although to a small extent - is applied according to the invention. In doing so, however, certain conditions to be described below, should be answered. Surprisingly little problems proved to arise and had to be solved, for which the explanation will be revealed as well.

The- above arrangements are applicable to all types of internal xxribustion engines. However, a control unit will be required for the metering control of the fuel quantity per unit of time delivered by the injector. It is especi.ally attractive, when the engine to which the arrangement according to the invention will be applied, is already fitted with a control system of this type. Especially this is the case with Otto—engines fitted with petrol injection, in which group the systems are considered which measure the aspirated air quantity and which are fitted with digital control, like for instance is described in the publication in "Bosch Technische Berichte" (5) 1975—1 (Bosch-L-Jetronic) . Although the arrangement according to the invention is also applicable to other injection systems, it is advantageous to adapt the arrangement as much as possible to one of the petrol injection systems with the widest application, including its control system. The following preferred embodiments therefore are described to be used together with the above mentioned Bosch- L-Jetronic systan. The latter comprises a digital electronic control unit, which controls the petrol-injectors. Each cylinder has its own petrol injector which injects the petrol a short distance before the inlet valve into the ccmbustion air inlet pipe concerned. The petrol is supplied under constant pressure to each petrol injector and all injectors are controlled simultaneously through electrcmagnetic means by the control unit. The metering takes place by means of the opening period of the injectors, which all inject simultaneously. A generally adopted control method gives two injections per cycle of the engine, so that the frequency of the injections forms a function of the πχ-*mentary speed of the engine. With the described petrol-injection system the driver controls the air throttle valve in the air inlet pipe for the ccπv- bustion air with his accelerator-pedal. A measuring device placed upstream of the throttle valve provides a signal for the control unit. The position of the throttle valve is sensed and its signa is fed as well into the control unit. Furthermore the speed of the engine, its cooling water temperature, the air pressure downstrea of the throttle valve, eventually the composition of the exhaust gases and the like information is fed into the control unit. From the control unit command signals are directed to the petrol injectors to control their injection rncment and injection period. Petrol injection systems of this kind are described in detail in the relevant literature. The arrangement according to the invention, adapted for an engine provided with an electronically controlled injection system including an air flew measuring means, is fmrthermore characterized in that the injector is of the electrαnagnetic energized type, for which the already available electronic control means govern the opening period and opening frequency of the injector. Without interfering with said electronic control unit, the LPG- or equivalent injector may be controlled with the same signals as the existing petrol injectors. Since the supply pressure of the liquid LPG and the ccmbustion value of the LPG basically is known, also in relation to the required quantity of air for the ccmbustion, the delivery orifice of the LPG injector can be calculated, which results in an equally good air/fuel control when using LPG as when running on petrol.

Change-over to either LPG-operation or petrol-operation can take place in various ways. First the opening signal given by the electronic control unit can only be led to either the LPG-injector or the petrol-injector. Secondly it is possible to actuate both petrol- and LPG-injectors always simultaneously, but to interrupt one or the other fuel supply by means of for instance solenoid valves in the supply lines of each fuel. Thus the arrangement according to the invention is preferably characterized in that the already existing electronic control unit is switchable to control the petrol-injection system and/or the LPG-injector in such a way that each fuel is metered in its liquid form. There are known Otto-engines provided with the above petrol- injection system, which are arranged as well for operation on LPG or equivalent alternative fuel. These engines, however, receive the

- ^jΥ^E OMPI - LPG vaporized in a vaporizer/pressure regulator. Apart frc the above described disadvantages of this system, it is found in practice that after a certain operating period using LPG, without injection of petrol, one or more of the petrol injectors are stuck in the closed position after switching over the system to the petrol operation. The rather sensitive petrol injectors seem not to be able to withstand a longer out-of-use period on a running engine.

An other well-known problem with the use of LPG is the increased wear of the inlet valves on their seats compared to operation on petrol.

The invented arrangement allows in a simple manner to use both fuels siiπultaneously in the engine, whereby a ratio between 0% and 100% is possible thanks to the synchronous energizing of both petrol- and LPG-injectors. Out of all possible mixture ratio's, in general the ratio with high LPG-percentage will be of interest because the LPG serves as the cheaper replacement fuel instead of petrol. For that purpose a preferred embodiment of the invention is such, that the electronic control unit, switched for use of LPG as main fuel, controls the LPG-injector simultaneously with the petrol injectors for the injection of petrol as secondary-fuel, whilst the petrol injection is maintained on a low dose of about 10% or less of the full-load-quantity. This is possible for instance by adjusting the supply pressure of the petrol to the petrol injectors on a lower value. It is therefore not necessary to interfere with the electronic control system. In doing so the advantage is achieved that the constituents contained in the petrol, which are responsible for the "lubrication" of the valve on its seat continue to be uninterruptedly supplied, notwithstanding the fact that LPG is used as main fuel. It has been found that such a small dose of petrol is sufficient to effect the aimed we.ar reduction of the inlet valves. It may be pointed out that the small petrol injection in addition to the use of LPG as main fuel, changes the final air/fuel ratio in the cylinder only slightly and to a neglectable extent in practice, so that neither the ccmbustion nor the com¬ position of the exhaust gases become influenced unacceptably.

The injector and the pressure regulator for the LPG can be of

OMP simple design and of small dimensions, since substantially onl liquid has to be treated. It is preferred that the injecto together with the pressure regulator are ccmbined in one housin into a unit with as small as possible volume of the fuel containin spaces between the outlet of the pressure regulator and the injector. In doing so the risk of the formation of vapour bubbles in the LPG before the injector is reduced to a minimum, also in a period short after shut down of a warm engine. The pressure regulator is preferably adjusted for an outlet pressure which is as high as possible, thus equal to the lowest pressure prevailing in the LPG-tank, which happens in wintertime.

It is possible to use for the injector a valve and tip of the pintle-nozzle type known frcm diesel engines. The seat of the valve is conical and the needle-shaped valve is urged into the closed position by a spring. An armature fitted to the end of the valve extends in a solenoid which lifts the armature when energized against the spring force and opens the valve, allowing the LPG to flow past the conical seat and along the pintle through the delivery orifice to be injected into the ccmbustion air. The application of a pintle, which may be cylindrical, avoids the risk of clogging of the orifice by the formation of ice or solid LPG- constituents. The continuously reciprocating movement of the needle with the pintle prevents ice or other solid particles to build up. Furthermore it was found that preferably the injector is directed such that the fuel will be injected substantially perpendicular to the direction of flow of the ccmbustion air, and tangential along the wall of the air inlet pipe. In doing so two advantages are attained: firstly a fine atαnization of the LPG is not necess-ary, avoiding high r-equirenents in this respect, and secondly some hu idification of the wall of the air intake pipe with the fast vaporizing LPG-liquid prcrnotes a fast and uniform evaporation and prevents the formation of ice and temporarily solid LPG-con- stituents. In case this would not be sufficient for certain applications, according to a preferred embodiment, the housing of the unit in which the injector and the pressure regulator are housed, may be fitted with heating means, more specially in that part of the housing where the injected fuel evaporates on the wall.

-^ J^E

OMPI Heating with the cooling fluid of the engine is here applicable. Even under winter conditions and with a cold engine, said cooling fluid still can release heat to the vaporizing LPG, since during said evaporation temperatures of dozens of degrees below the freezing point may appear. The large required quantity of heat for the evaporation has furthermore an irriportant positive influence with regard to the cooling of the injector-pressure-regulator-unit during engine operation, thanks to the transmission of the heat flew from the unit to the dσwnstre.aπι part of the air inlet pipe which is considerably cooled.

During starting tip a warm engine vapour bubbles may be present in the unit; after a few revolutions of the engine, however, liquid LPG will enter and will, still partly evaporating, reduce the tem¬ perature of the unit very fast, so that soon after substantially liquid LPG is already injected. Otherwise, it was found during tests that up to approximately 10% by volume of vapour bubbles in the liquid LPG before the injector, have no measurable influence on the engine behaviour and the composition of the exhaust gases, since these small vapour quantities have on the one hand an almost negligible influence on the total quantity of injected fuel per injection and on the other hand said 10% vapour are negligible as well compared to the 90% injected liquid in evaporated form in the air inlet pipe.

Furthermore it happens that for the above described possibly appearing evaporation in the unit itself, so much heat is required that also in the warm season the unit remains sufficiently cooled during operation to limit the formation of vapour to a maximum of approximately 10%, as both calculations and experiments have proven. In this connection it is pointed out that, having the liquid LPG evaporate in the aspirated combustion air, this appreciably reduces the temperature of the charge entering the engine also in case of a warm engine compared to two known conditions, i.e. either with petrol injection or with the known use of LPG which first is vaporized in an evaporator and fed as vapour into the ccmbustion air through a common carburetter. In doing so the thermal load of the engine is considerably lower, so that the known power losses

OMPI due to the use of LPG, are ccmpletely avoided with the system and arrangement according to the invention. More specially, also with engines charged for instance with exhaustgas driven turbo-com¬ pressors, the cooling influence of the vaporizing LPG is of con- siderable advantage.

Finally it may be remarked that the applied fuel, like LPG, can have a variable composition, for instance in connection with the different mixing ratio's between butane and propane for summer and winter application. In connection with this both the cptimum air/fuel ratio and the ccmbustion value per mass unit of liquid fuel also change. By adding an adjustable potentiometer to the electronic control unit, for instance in the circuit for the opening period of the injector, this variable value can be fed as well into the unit to achieve an optimal regulation of the air/fuel ratio delivered to the engine. In many cases it is, without more ado, possible to introduce this extra variable into the existing electronic control unit.

In practice with many existing engines an interconnecting flange is already available between the throttle valve and the proper air inlet pipe of the engine. By interposing the housing of the LPG-injector with the unified pressure regulator between said flanges, it is possible to prepare in an extremely simple manner an existing engine provided with petrol injection for use with an alternative fuel like LPG, which is metered and injected into the combustion air in liquid form as well. Applying the arrangement later to existing engines or right at the manufacturer, is very simple therefore and requires in general little or no alteration, apart from fitting and c»nnecrting the ccrπponents concerned.

With the help of the accompanying drawing a preferred embodiment of the injection systβn according to the invention will be explained below in detail.

In the drawing which shews schematically an arrangement according to the invention, a fourstrcke/four cylinder Otto-engine 1 is illustrated in top view. It has four cylinders 2 and a flywheel 3. The exhaustgas manifold 4 extends along one side and the cc bustion .air inlet pipe 5 along the other side of the engine, the latter having branches 6 which are connected with the cylinder

OMPI head for each individual cylinder. The branches 6 of the air inlet pipe 5 continue in the cylinder head to the non-represented inlet valves. Upstreams a throttle valve 7 is fitted in the inlet pipe 5, which throttle valve (schematically illustrated) is connected with an accelerator pedal 8. Since the engine described is fitted with a petrol injection system of the type Bosch-L-Jetronic, upstream with regard to the throttle, valve 7 an air measuring means 9 is fitted, which is provided with a pivotable vane 10, which is urged by a light spring force against the air flew in the closing direction. The vane 10 pivots about a shaft 11 and passes in its rotation along a curved wall 12, providing when the vane 10 is rotated between its end and the curved wall 12 a passage of changing cross section. Thus the position of the vane 10 forms an accurate function of the^' air quantity which is aspirated by the engine at every moment. Upstream with regard to the air quantity measuring means 9, usual means may be placed, like an air filter, a com¬ pressor of a pressure charging group, an air cooler and the like, which schematically are indicated by 13. The ccmbustion air L is aspirated from the environment according to arrow 14. The engine 1, equipped with a petrol injection system, has for each cylinder a petrol injector 15, which schematically is indicated in the drawing and which injects the petrol in the inlet-pipe-branch a short distance before -its inlet valve. Each petrol injector 15 is connected through a pipe 16 with a common petrol supply line 17. This line receives petrol from tank 18 through a pump 19. The supply pressure from the pump 19 is kept constant by a pressure control/overflew valve 20 having a return line 21 to tJne tank 18. A solenoid operated valve 22 is incorpor¬ ated in the petrol supply line 17. The petrol injection system schoratically depicted in the drawing is of the type Bosch-L-Jetronic. With this system each petrol injector 15 is provided with a solenoid which is energized by electric pulses through the connections 23, which all receive simultaneously one and the same electrical signal, so that by energizing the solenoids, all injectors 15 inject simultaneously during the same time equal quantities of petrol. The petrol valve 22 is controlled through the connection 24 and the petrol boost

5Ϊ.FI - pump 19 through the connection 25.

The measuring device 9 for the air quantity is provided with a potentiometer 26 which provides a signal through a connection 27. Equally the position of the throttle valve 7 is sensed through the connection 28. All measurements and signals 27, 28 are fed into a schematically depicted digital electronic control unit 29. This unit is fed frcm the electric system 30 provided with the engine 1. The control unit 29 may receive still further signals or sensor readings, which schematically are indicated with 31 and are con- cerned for instance with the speed n of the engine, its cooling water temperature t and other data, like the air pressure in the air inlet pipe 14, the ambient temperature, the composition of the exhaust gases, etc. Fran the control unit 29 output signals are transmitted to the petrol injectors 15 through the connections 23 with respect to the opening frequency and opening time of the in¬ jectors, through the connection 24 for the opening or closing of the petrol valve 22 and through the connection 25 for the operation of the petrol bcostpurπp 19.

All the above forms part of the normal well-known equipment of a fours-broke Otto engine provided with petrol injection according to the Bosch-L-Jetronic system. To adapt the above described engine for the use of LPG or an equivalent fuel, according to the invent¬ ion, the extra equipment described underneath is added. Between the flanges 41 and 42, in general already available, at both sides of a division in the ccmbustion air inlet pipe 5, a housing 40 is inter¬ posed, being provided with such passage that it corresponds with the passage in the air inlet pipe 5. In the housing 40 an LPG- injector 43 is fitted, which is of the electromagnetic energized solenoid type as well. The nozzle of the injector 43 includes a valve of the needle-type with conical seat and a pintle-shaped pin which extends concentrically through the delivery orifice, as is known in itself frcm pintle-nozzles used with diesel engines. The needle valve is urged into the closed position by spring force and an armature connected to the needle can open the injector by energizing the solenoid. The injector 43 is connected with an LPG- tarik 45 through a pipe 44. The known filters, safety equipment, etc. are not illustrated for clarity's sake. In the LPG supply pipe

£JREALT

O Pl__ 44 a solenoid operable valve 47 is incorporated. In the LPG-in¬ jector housing 40 furthermore a schematically illustrated pressure regulator 48 is incorporated, which maintains the LPG supply pressure to the injector 43 at a constant value as function of the pressure in the air inlet pipe 5 downstream of the throttle valve 7. For that purpose an interconnecting pipe 49 is fitted which influences the action of a spring in the pressure regulator 48 in such a way that the pressure difference over the LPG-injector 43 between the fuel-supply pressure and the air pressure in the air inlet pipe 5 is kept constant. The solenoid of the LPG-injector 43 is connected through a connection 50 with the electronic control unit. The pulse frequency and pulse length produced by the elec¬ tronic control unit is the same as fed into the connection 23 when the unit is adjusted for petrol injection. With the help of a con- nection 51 the electronic control unit can also control the LPG- shut-off valve 47.

According to the invention one single LPG-injector 43 serves all cylinders of the engine, which are connected to one and the same air inlet pipe. Since its opening time and opening frequency are the same as for the petrol injectors 15, it is possible by correct dimensioning of the delivery orifice of the LPG-injector 43 in the same way as with the petrol-injectors, to maintain also in LPG-operation a correct air/fuel ratio over the whole power- and speed range of the engine. There are three different possibilities for the control of the system: both the petrol injectors 15 and the LPG-injector 43 always work in parallel and simultaneously, requiring for petrol operation the opening of the petrol valve 22 and closing of the LPG-valve 47 and contrarily for LPG-operation. In the second mode the electronic control unit controls either exclusively the petrol injectors 15 through the connection 23 or the LPG-injector 43 through the connection 50.

However, it is also possible to inject both fuels simul¬ taneously, in which case more specially the follcwing possibility is of interest, according to which the LPG forms the main fuel, but also small petrol quantities of about 10% or less of the full load quantity are injected. On the one hand the engine then runs on the

GΓΛ Ϊ preferred cheaper fuel, like LPG, but on the other hand the petrol injectors 15 keep working and will not tend to stick, whilst the small supplied petrol quantities have shown to be sufficient to reduce the high inlet valve wear occurring with pure LPG-operation, to normal values when operating on petrol. One of the possible methods to do so, is by reducing the pressure in the petrol supply line 17.

Since the alternative fuel, like LPG, may be of changing com¬ position, like for instance the different winter- and surrnier-c-αm- position, the ccrribustion valve and the required quantity of com¬ bustion air per injected mass unit of fuel is not constant. To allow for this, the electronic control unit may be provided with an extra input 53, controlled by a potentiometer 52, to increase or reduce the duration of the opening of the LPG-injector 43 as function of the characteristics of the fuel in the tank 45.

It has been found to be of advantage to inject the LPG through the injector 43 perpendicular to the direction of the air flow, but approximately -tangential with the wall of the air inlet pipe 5. Thus evaporation of the LPG and the preparation of a homogeneous air/fuel mixture is prcmoted. In general sufficient heat for a fast evaporation will be supplied through the wall and by the aspirated ccmbustion air, but an extra local heat supply is possible on those parts of the wall on which LPG-droplets eventually might hit. This is schematically illustrated in the form of a double wall in the housing 40 with an intermediate space 54 through which for instance the cooling fluid of the engine may be led. An inlet and outlet pipe 55, 56 for this heating fluid are schematically indicated. Since the eventual extra heating of the housing would take place approximately opposite to the injector, the influence of said heating on the injector is small, so that the danger for extra vapour bubble formation in the liquid LPG will not be increased in doing so. In itself, the low air pressure downstream of the throttle valve promotes already the velocity of evaporation. The important cooling of the air inlet pipe 5 due to the evaporation of the LPG has a very positive influence with regard to keeping the injector/pressure regulator unit 40 well cooled, as well as to an eventually occurring evaporation under extra-ordinary circumstances of seme LPG in the unit 40 itself. With a view to a good heat transfer it is preferable to manufacture the housing 40 of an aluminum alloy or so.

Finally it may be remarked that a fine atomization of the injected LPG, as necessary with diesel fuel in diesel engines, is not required. Thanks to the very fast evaporation of the injected liquid LPG jet indeed, this jet disintegrates irrmediately after having left the delivery orifice of the injector into separate pieces which further disintegrate rapidly, so that only part of the liquid still may reach the wall. Therefore requirements with respect to a fine atomization need not to be demanded from the injector.

OMPI

Claims

C A I M S

1. Arrangement for the metered supply of a fuel which unde ambient conditions is a gas or vapour, more specially LPG, to ccrribustion means, like an internal ccmbustion engine, gas turbine, oven or the like, in which the fuel before its entry into th ccrribustion space is mixed with the required ccmbustion air, characterized in that the arrangement is adapted to meter the fue under pressure and introduce it into the ccmbustion air in liqui form, the above in such a way that the evaporation of the fuel sub stantially takes place only in the ccmbustion air.

2. Arrangement according to claim 1, adapted for a piston- combustion engine, characterized in that the arrangement includes an injector, which injects the fuel into the air inlet pipe.

3. Arrangement .according to claims 1 or 2, adapted for an Otto-c*cmbustion engine, characterized in that the injector is placed downstream of the air control valve (throttle valve).

4. Arrangement according to claims 2 or 3, characterized in that one injector serves more than one cylinder, like four, five or six cylinders.

5. Arrangement according to claims 2, 3 or 4, characterized in that a pressure regulator is incorporated in the supply-line of the liquid fuel to the injector, in order to maintain a constant supply pressure in said fuel.

6. Arrangement according to one or more of the preceding claims 2 to 5, characterized in that the pressure regulator controls the fuel supply pressure to the injector as function of the air pressure near to the injector in the air inlet pipe down¬ stream of eventually included means like throttle valve, air filter, pressure charging compressor, etc.

7. Arrangement according to one or more of the claims 3 to 6, adapted for an engine with electronic controlled petrol injection system, including an air flew measuring means, characterized in that the injector is of the solenoid energized type, in which the already available electronic control means controls the opening time and the opening frequency of the injector as well.

8. Arrangement according to claim 7, characterized in that the already available electronic control unit is switchable to control at choice the petrol injection system and/or the LPG-injector, so that each fuel is metered in liquid state.

9. Arrangement according to claims 7 or 8, characterized in that the electronic control unit, adjusted for LPG as main fuel, controls the LPG-injector simultaneously with the petrol-injectors injecting petrol as secondary fuel, under which condition the petrol injection is maintained on a small dose of approximately 10% by volume or less of the full load quantity.

10. Arrangement according to one or more of the preceding claims, characterized in that the injector together with the pressure regulator are combined in one housing into a unit, having as small as possible volume of the fuel contai ing spaces and of the fuel duct between the outlet of the pressure regulator and the inlet of the injector.

11. Arrangement according to one or more of the preceding claims, characterized in that the injector has a pintle fitted to and moving together with the injector valve, which pintle concentrically extends through the injector delivery orifice.

12. Arrangement according to one or more of the preceding claims, characterized in that the injector is directed such, that the fuel substantially is injected perpendicular to the flow direction of the air and tangential along the wall of the air inlet pipe.

13. Arrangement according to one or more of the claims 10, 11 or 12, characterized in that the housing of the injector and the pressure regulator are provided with heating means, more specially in the region in which the injected fuel hits the wall.

14. Arrangement according to one or more of the preceding claims, characterized in that the electronic control unit has a potentictπeter or so incorporated in the control unit for the opening time of the injector, in order to make the opening time also dependent of the ccmposition or the type of fuel, like the winter or sunnier ccmposition of LPG.