Field of the invention

The present invention is concerned with improving charge preparation in an internal combustion engine.

Background of the invention

In an engine in which fuel is injected into the intake port there is a tendency for the fuel to collect as a pool on th back of the intake valve. Despite the high temperature of the valve, the fuel is not vaporised as the air in the port is stagnant when the valve is closed.

Air assisted sprays have been proposed, for example in US-A-4,475,486, in which an air gallery supplies air to blo the spray in the direction of the intake port. However, despite these and other attempts to produce a fine spray by the injector, the charge entering the combustion chamber when the intake valve opens is far from homogeneous. The accumulation of fuel in the intake port also produces hysteresis effects which cause emission problems during transient operation.

Object of the invention

The present invention seeks to vaporise the fuel that tends to collect in the intake port in order to mitigate the foregoing disadvantages.

Summary of the invention

According to the present invention, there is provided an internal combustion engine having an intake valve, an injector for directing a metered jet of fuel into the intak port and means for directing a jet of air at the back of th intake valve to assist in vaporisation of any fuel

collecting in the intake port, wherein the means for directing a jet of air comprises a fluidic ejector formed o an external air supply jet, an entrainment section and a diffuser.

To inject enough external air to ensure complete fuel vaporisation would interfere significantly with the engine speed control, especially at idle. The present invention relies on a known device, a fluidic ejector sometimes also termed a jet pump, to amplify a small external air flow. The energy in the external air jet is used to entrain a large volume of air flow through the ejector causing an internal air recirculation within the intake port.

A jet pump or fluidic ejector consists of three parts. The first is the supply nozzle which provides the kinetic energ for initiating the mass air flow. The second is a mixing tube or entrainment section. This section comprises an elongate tube wider than the supply jet which is aligned with but spaced from the supply jet. The mixing tube widen gradually into a conical diffuser section. The jet flowing in the mixing tube causes entrainment of air from within th intake port causing a total flow down the length of the diffuser which is directed at the intake valve and which ha several times (typically four to six times) the air mass flow in the supply jet. The smaller the diameter of the jet relative to the diameter of the mixing tube, the greater will be the entrained flow.

The jet pump of the invention allows the air to be discharged close to the inlet valve so that saturation of the vapour above the inlet valve when the latter is closed can be avoided. The recirculating flow around the diffuser and mixing tube also tends to scour the surface of the intake port to promote more rapid evaporation.

It is preferred to direct the fuel jet or spray from the injector along the centre of the mixing tube and diffuser.

If desired it may be introduced through the supply jet. I this way, fuel deposited on the internal walls of the jet pump will be evaporated very efficiently by the rapid air flow and this may if desired be assisted by heating the je pump. Alternatively, the fuel jet may be a pencil jet aim along the jet pump directly at the intake valve so that fu is not allowed to land on the relatively cold surfaces of the intake port.

The supply jet air may either be drawn in by the manifold vacuum or it may be supplied under pressure. The air form part of the metered air supply and does not therefore redu the mixture strength. If ambient air is drawn in, the tot amount entering through the supply jet must be smaller tha the air flow rate during idling in order not to interfere with the engine tick over.

When the air is supplied by a compressor, if the intake of the compressor is downstream from the intake throttle, the the total air charge to the engine is not at all affected the rate of flow in the supply jet. However, in this case, the compressor forms a further recirculation loop and if fuel is allowed to pass around this entire loop then the compressor will form part of the manifold system and will upset the fuel metering by acting as a fuel reservoir. Th problem can however be avoided if the connections of the compressor to the manifold are sufficiently far apart as there will not be sufficient time for the fuel vapours to re-enter the compressor before they are sucked into the engine cylinders. The compressor will then not receive fue vapours and will not disturb the fuel metering.

Brief description of the drawing

The invention will now be described further, by way of example, with reference to the accompanying drawing in whi the single figure is a diagrammatic representation of an intake port of an engine of the present invention.

Description of the preferred embodiment

An internal combustion engine has a cylinder head 10 with a intake port 16 controlled by a poppet intake valve 12 drive by cams in the usual manner. Combustion air is supplied to intake port by a duct 14 of the induction manifold in which duct there is mounted an injector 40.

As so far described, the engine is conventional. Fuel is sprayed into the intake port by the injector 40 where it would normally be partially vaporised by the heat of the valve 12 but most would collect as a pool on the head 18 of the poppet valve 12.

In order to improve charge preparation and supply a homogeneous mixture to the engine in which the fuel is full vaporised, the present invention provides a jet pump 32 fixed to a cup 20 which is used for mounting the injector 4 in the intake manifold duct 14. The cup 20 has a connectio for ambient air or air compressed by a compressor having it intake connected downstream of the main intake throttle but at a location as far removed from the jet pump 32 as possible. The air entering the cup 20 passes along a supply jet 22 and is directed along the jet pump 32. The jet pump 32 has an entrainment section 24 in which the air from the supply jet 22 causes more air to be drawn in from the intak port through apertures 28 surrounding the supply jet 22. The total flow, which has a significantly greater mass flow than the air from the supply jet 22 passes along a diffuser section 26 the mouth of which is positioned close to the head 18 of the poppet valve 12.

The fuel jet 42 from the injector 40 is also directed along the jet pump and may be either a pencil jet or a spray.

Fuel is now directed along the jet pump towards the valve head 18 and no portion of the fuel is allowed to wet the intake port. Such fuel as lands on the jet pump itself will

be rapidly evaporated by the high rate of air flow and evaporation may be assisted by heating the jet pump. Th remaining fuel will land directly on the hot intake val and will be evaporated rapidly. The air in the vicinit the intake valve head 18 forms a convection current aro the jet pump and is not stagnant as in the prior art. vapour pressure in the air near the valve head does not reach saturation point and any pool of fuel collecting the valve head 18 is scoured directly by the air flow.

The invention can thus be seen to provide improved fuel preparation without significant alteration to the intake system and it can be implemented inexpensively by a moun cup for the injector integrated with the jet pump.