GB2206378A

GB2206378A - Fuel injection arrangement

Info

Publication number: GB2206378A
Application number: GB08714451A
Authority: GB
Inventors: Ian Chirnside Finlay; Raymond John Boyle
Original assignee: UK Secretary of State for Trade and Industry
Current assignee: UK Secretary of State for Trade and Industry
Priority date: 1987-06-19
Filing date: 1987-06-19
Publication date: 1989-01-05
Also published as: GB8714451D0

Abstract

A fuel jet from an injector nozzle 18 is caused to contact an electric heater 10 by air supplied through bores 21, 23 during passage of the jet through the tube 12 to a manifold. The air is supplied at starting and low engine speeds and may be under pressure or drawn in due to manifold vacuum. The air may be heated by engine coolant or exhaust. <IMAGE>

Description

FUEL INJECTION SYSTEMS The present invention relates to fuel injection systems, and in particular to systems for injecting gasoline into internal combustion engines.

It is becoming increasingly important to optimise the combustion of fuel in fuel/air mixtures, both to improve fuel consumption and, quite often even more importantly, to minimise noxious emissions.

To this end, fuel injection systems are increasingly being used in place of the one time universal carburettor system. With a fuel injection system the amount of fuel supplied, proportional to the air intake1 two an engine can be accurately controlled to optimise the fuel/air ratio for any set of engine operating conditions.

Unfortunately1 even with fuel injection, hoped for combustion efficiencies and ignition levels can prove disappointing under certain engine operating conditions. This is believed to result from ineffective mixing of the fuel and air prior to ignition, and is particularly noticeable with cold engines and at light-load conditions. There is, therefore, a need for devices which can improve the mixing of fuel and air prior to ignition.

According to the present invention apparatus for use in a fuel injection system includes means for conveying a fuel jet directly from a fuel injector to a manifold and means for dispersing the jet and causing at least a substantial proportion of the fuel to contact a surface of a heater.

One form of the invention includes a cylindrical conduit having, in series extending from a point connectable to the fuel injector, a first bore by which the inside of the conduit can be diametrically connected to an air supply, a pair of second parallel bores exten- ding tangentially and in the same sense from the inside of the conduit and connectable to an air supply, and a heater element.

An alternative embodiment of this form of the invention has a single pair of parallel bores extending chordwise and in the same sense from the inside of the conduit and connectable to an air supply.

The heater element may include temperature measuring means such as a thermo-couple. Alternatively the heater element may be formed of a material of the type known as Positive Temperature Coefficient (Pv whose electrical resistance increases rapidly with temperature.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which: Figure 1 is an elevation, in section, of a heater unit accord to the invention.

Figure 2 is a section along line BB of 1, and Figure 3 is a section along line AA of 1.

A heater unit (Figure 1) has a heater element 10 on an inner surfac 11 of a cylinder 12. The cylinder 12 may conveniently be formed of material such as Tufnol. One end-13 of the cylinder is connectable to a manifold (not shown) and the other 14 is enclosed in a recess 15 in a block 16. A cylindrical conduit 17, of diameter equal to tl inside diameter of the cylinder 12, and coaxial therewith, connects the cylinder 12 to a nozzle 18 of a fuel injector. The nozzle 18 it positioned in a recess 19 in the block 16 and is kept fuel tight wit respect to atmosphere by means of a O-ring 20.

A first bore 21 (see also Figure 2) extends diametrically from the conduit 17 to an air connection point 22. Downstream, relative to the fuel injector nozzle 18, of the hole 21 a pair of second parallel bores .23 extend tangentially and in the same sense, illustrated as clockwise in Figure 3, from the conduit 17 to air connection points 24.

A thermo-couple 25 is connected to the heater 10.

In use, the air connection points 22, 24, are connected to a compressed air supply, a fuel injector (not shown), of which the nozzle 18 is a part, is connected to a fuel supply, and the end 13 of the cylinder 12 is connected to a manifold (not shown) where fuel passing through the cylinder 12 can be mixed with an air supply.

Fuel is supplied through the nozzle 18 and passes through the cylinder 12 to the manifold. On engine start, and at low engine speeds, compressed air is supplied through the air supply points 22, 24 and bores 21, 23 respectively. Air through the bore 21 breaks up the fuel jet emerging from the nozzle 18 and air passing through the bores 23 imparts a strong swirl to the fuel flow. As a result of the svirl most of the fuel impacts on the heater element 10, which has energy supplied to it (means not shown) to raise fta temperature to, for example, 90 C under control of thetermo-couple 25. A8 a result a substantial fraction of the fuel is evaporated prior to entry to the manifold and fuel/air mixing is greatly enhanced.At high engine apeeds and with the engine wared up a dieproportlonate amount of energy would be required to break up the fuel jet, impart swirl, and evaporate the fuel impinging on the heater 10, and in consequence under these engine conditions the heater is switched off and the air supply disconnected. Under these engine conditions, the extra efforts to improve mixture are not necessary. The fuel jet then passes directly to the manifold without impinging on the heater 19.

As an alternative to the first bore 21 and second bores 23 a pair of parallel bores extending chordwise and in the same sense from the conduit 17 may be used. Air passing through these bores both breaks up the fuel jet and imparts swirl thereto.

As an alternative to using compressed air advantage may be taken of the manifold vacuum pressure to draw atmospheric air through bores such aa 21, 23.

It will be realised that the temperature of the heater 10 must be carefully controlled to prevent premature ignition of the fuel. As an alternative to using a temperature measuring device such as thermocouple 25 and electrical control means the heater may be formed of a PTC material whose resistance rises rapidly with temperature, its maximum temperature for a given electrical current and voltage thus being self regulating.

It will be realised that the jet of air from the first hole must impinge on the fuel stream from the nozzle 18. The first hole 21 is therefore advantageously positioned close to the nozzle 18.

The air passing through bores 21, 23 may advantageously be pre-heated, using, for example, engine coolant or exhaust, to reduce the electrical power required by heater 10.

Claims

Claims

What is claimed is: 1. Apparatus for use in a fuel injection system including means for conveying a fuel Jet directly from a fuel injector to a manifold and means for dispersing the Jet and causing at least a substantial proportion of the fuel to contact a surface of a heater.
2. Apparatus as claimed in claim 1 including a cylindrical conduit connectable between the fuel injector and the manifold and having leading therein a plurality of bores through which air can be passed to disperse the jet and to impact swirl thereto.
3. Apparatus as claimed in Claim 2 wherein the bores include in series extending from a point connectable to the fuel injector, a first bore by which the inside of the conduit can be diammetrically connected to an air supply, and a pair of second parallel bores extending tangentially and in the same sense from the inside of the conduit.
4. Apparatus as claimed in Claim 2 wherein the bores are a pair of parallel bores extending chordwise and in the same sense from the inside of the conduit.
5. A heater unit as claimed in any one of Claims 1 to 4 wherein the heater includes temperature measuring means.
6. A heater unit as claimed in Claim 5 wherein the temperature measuring means includes a thermo-couple.
7. A heater unit substantially as herein described with reference to the acconpanying drawings.
8. An internal combustion engine including a heater unit as claimed in any one or Claims 1 to 7.