GB2226659A

GB2226659A - Fuel injection system

Info

Publication number: GB2226659A
Application number: GB8829531A
Authority: GB
Inventors: John Allen
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-12-17
Filing date: 1988-12-17
Publication date: 1990-07-04
Also published as: GB8829531D0

Abstract

An internal combustion engine fuel injection system is controlled in accordance with the colour of the light of combustion in a cylinder by a probe (11) preferably of quartz with a multi-facetted end (14) and a plane face (15) abutting three glass light guides. In one embodiment, one of the light guides has a filter of one colour, another a filter of another colour and the third no filter at all. Respective photo detectors are provided for each light guide and the photo detectors are connected to a spectrum analyser (21) in which the outputs of the photo detectors are added and subtracted and used by a servo unit (26) to produce a signal to control the supply of fuel to the engine. The unit (26) may also respond to engine speed, throttle setting and engine temperature. <IMAGE>

Description

Fuel Injection System The present invention relates to a fuel injection system for an internal combustion engine.

Conventional fuel injection systems have sought to match the quantity of fuel injected to engine conditions by means solely of an alogorithm. Typically the engine conditions are: speed; throttle setting; and temperature.

The object of the present invention is to provide a fuel injection system responsive to measured combustion conditions.

According to a first aspect of the invention, a fuel injection system for an internal combustion engine comprises: an optical probe adapted to be mounted in the engine to transmit light from combustion within the engine; an optical transducer adapted to receive the engine-combustion light and arranged to produce a signal indicative of the colour of the light; and a servo-control device controlling fuel supply to the engine in accordance with the combustion colour.

According to a second aspect of the invention, a fuel injected internal combustion engine includes: a combustion chamber; means for supplying fuel to the combustion chamber; means for supplying air to the combustion chamber; an optical probe mounted in a wall of the combustion chamber for transmission of light from combustion within the combustion chamber; an optical transducer mounted at an end of the optical probe remote from the combustion chamber for reception of engine-combustion light and arranged to produce a signal indicative of the colour of the light; and a servo-control device for controlling the fuel supply means to supply fuel to the engine in accordance with the colour of the combustion of the fuel and air in the combustion chamber.

According to a third aspect of the invention, a method of controlling fuel injection to an internal combustion engine consists in the steps of: measuring the colour of the fuel/air combustion in the engine; and producing a servo signal dependent upon the measured combustion colours and controlling fuel supply in accordance with the servo signal.

The invention enables the quantity of fuel injected to be controlled to optimise the combustion temperature achieved, that is increase the temperature to an optimum.

The higher the temperature, the whiter the light will be and the greater the thermodynamic efficiency. Accordingly the servo-control will normally be arranged to increase or decrease the fuel supply to produce a combustion of a colour corresponding to an optimum for an optimum mixture.

The invention is applicable to all forms of internal combustion engine, in particular but not only LPG, petrol and diesel reciprocating piston engines. As appropriate, either direct fuel injection into the combustion chamber or indirect fuel injection into one or more air passages to the fuel chamber can be employed.

The optical transducer can be a spectrum analyser. A simple optical transducer and probe includes a parallel split light path with a colour filter in one of the light tracks and photo detectors at the remote ends of the tracks.

If the filter is towards the red end of the spectrum, its photo-detector will receive comparatively less light at low combustion temperatures when red light predominates. If the filter is towards the blue end of the spectrum, its photo-detector will receive comparatively less light at higher combustion temperature when the light is more evenly distributed in the visible spectrum.

The optical transducer can be rendered substantially insensitive to fouling by solid combustion products on its combustion chamber end by feeding the outputs from the photo-detectors to an additive/substractive circuit in which the outputs are both added and substracted, and the ratio of the subtracted result divided by the added result is the final output. This is substantially independent of overall intensity.

Alternatively a three (or more) light path arrangement can be used. One light path includes a red light filter, another a blue light filter and the third no filter. The outputs from photo-detectors receiving the resultant light is compared in two pairs, each including a respective one of the filtered lights and the unfiltered light. The resultant subtractive signals are subtractively compared. This signal is independent of light intensity and is non-linearly proportional to the spectral balance of the light and the temperature of the combustion. In an alternative to the light guides and filters, a prism may be employed, the prism acting both as a light guide to the photo-detectors and to spectrally separate the light.

To further guard against fouling, the combustion chamber end of the probe may be multi-faceted. Suitably the probe is of quartz.

Where engine is expected to be constantly on load, the servo-control device may be a simple feed back device.

Where the engine is expected to experience widely differing loadings, as in a vehicle, the servo-control device may be an alogorithmic micro-processor control device taking account of: speed; throttle setting; engine temperature and other engine parameters as appropriate.

To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic cross-sectional view of a cylinder of an internal combustion engine equipped with a fuel injection system according to the invention; Figure 2 is a block diagram of the fuel injection system; and Figure 3 is a block diagram of an optical probe and transducer of the fuel injection system.

Referring to Figure 1, the engine has a conventional block 1, inlet and outlet valves 2,3, piston 4 and head 5.

Air inlet is via a tube 6 having a centrally pivotted throttle plate 7 and an air cleaner - not shown. A spark plug 8 is provided in the head.

Petrol is fed to the engine from a variable flow pump 9 to an indirect injection pipe 10 passing through the head 5 into the air inlet passage immediately up-stream of the inlet valve 3. In the head, close to the block, an optical probe 11 is provided. Suitably it is of quartz with a sealing screw fitting 12 provided on the outside of the block. The inner end of the probe 11 is multi-facetted to provide that if one facet tends to collect swirling solid combustion products, other facets remain exposed to receive combustion light and transmit it along the probe. It is provided high in the cylinder in order to be as close as reasonable to the combustion. It could be provided in the block. The screw fitting 12 enables the probe to be removed for cleaning of its facets. Where the engine is a multi-cylinder engine, more than one of the cylinders may be equipped with a probe.

Along its length, the probe divides into three light paths. Suitably this is arranged by providing a head 13 having the facets 14 on one end and a plane face 15 on the other end against which are abutted the ends 16 of three glass light guides 17.

At the opposite ends of these, one has a red light filter 18R, another a blue light filter 18B and the other no filter. The filters and the filterless end are each abutted against respective photo-detectors 19 conveniently photo-diodes or photo-transistors. These are indentical broad spectrum devices, which would give an identical output in the absence of the filters, but whose output is biased by the filters. The photo-detectors comprise an optical transducer and are housed with the screw fitting 12, which has an output lead 20 extending from it.

The lead 20 is connected to an spectrum analysis unit 21, which includes three difference circuits 22,23,24. The first two 22,23 have as their respective inputs the output from the red filter photo-detector and the unfiltered photo-detector on the one hand and the output from the blue filter photo-detector and the unfiltered photo-detector on the other hand. The third difference circuit 24 has as its input the outputs from the other two. The result is that where the combustion occurs with a red bias - i.e. a rich mixture - the red filter passes this and its photo-detector gives a similar output to the unfiltered one. The blue filter removes the red light so that its photodetector's output differs from the unfiltered one. The circuit 23 will therefore give a higher output and the circuit 24 will give an output of one sign. When the combustion is occurring with a blue light bias, i.e. a weak mixture, the reverse will occur; and a signal of the other sign will be produced.

The size of the signal will vary in accordance with the degree of red or blue light bias, i.e. the temperature of combustion which is dependent on the richness of the petrol air mixture.

The difference circuits can be biased to produce a zero output for a colour corresponding to an optimum mixture. A positive signal would then indicate the requirement for more (or less) fuel and a negative signal would indicate the need for less (or more) fuel, according to the connection of the circuits. The output is fed on a line 25 to a servo unit 26.

In a simple arrangement, the servo-unit would control the fuel pump 9 to increase or decrease fuel flow to the engine in accordance with the detected mixture strength, to optimise this to a fixed value.

However the optimum value varies in practice with: (i) engine temperature - a richer mixture being required when the engine is cold; (ii) engine speed - a leaner mixture being required at high speed and to promote rapid combustion; (iii) engine torque - a lean mixture being required on over-run or engine braking and a transiently richer than usual mixture after throttle opening movements.

Accordingly inputs from an engine temperature sensor 27, a tachometer 28, and a torque sensor 29, conveniently an engine displacement sensor - the engine being mounted on mounts which deflect resiliently with engine torque.

Conveniently, the throttle setting is also fed via a throttle position detector to the servo unit to bias it to cause more or less fuel to be pumped in anticipation of a requirement for more fuel from the combustion colour servo or feed-back loop 30. The servo unit is preferably of the type having a memory in which it can memorize as an algorithm the fuel pump settings for varying engine conditions. This has the advantage that should the probe become fouled, the system can still inject close to the optimum quantity of fuel in accordance with the learned algorithm. The servo unit is conveniently a microprocessor.

The invention is not intended to be restricted to the details of the above described embodiment. For instance the variable flow fuel pump can be replaced by a constant flow pump pressurising a fuel reservoir from which fuel is fed under control of a variable flow valve. The three light paths in the optical probe can be replaced by a prismatic light path in which the spectrum is split and the need for filters obviated. Photo-detectors are placed along the spectral separation to detect relative intensities therealong.

Claims

1. A fuel injection system for an internal combustion engine comprising: an optical probe to be mounted in the engine to transmit light from combustion within the engine; an optical transducer to receive the engine-combustion light and to produce a signal indicative of the colour of the light; and a servo-control device to control fuel supply to the engine in accordance with the colour of the combustion light.

2. A fuel injection system according to claim 1, in which the optical transducer is a spectrum analyser.

3. A fuel injection system according to claim 1, in which the optical transducer and the probe include a parallel split light path with a colour filter in one of the light tracks so formed and photo detectors at the remote ends of the tracks.

4. A fuel injection system according to claim 3, in which the filter is towards the red end of the spectrum whereby its photo-detector will receive comparatively less light at low combustion temperatures when red light predominates.

5. A fuel injection system according to claim 3, in which the filter is towards the blue end of the spectrum whereby its photo-detector will receive comparatively less light at higher combustion temperature when the light is more evenly distributed in the visible spectrum.

6. A fuel injection system according to any one of claims 3 to 5, in which the optical transducer can be rendered substantially insensitive to fouling by solid combustion products on its combustion chamber end by feeding the outputs from the photo-detectors to an additive/subtractive circuit in which the outputs are both added and subtracted, with the ratio of the subtracted result divided by the added result as the final output.

7. A fuel injection system according to claim 1, utilising a three light path arrangement wherein one light path includes a red light filter, a second a blue light filter and the third no filter, the outputs from photo-detectors receiving the resultant light is compared in two pairs, each including a respective one of the filtered lights and the unfiltered light, the resultant subtractive signals are subtractively compared, to give a signal which is independent of light intensity and is non-linearly proportional to the spectral balance of the light and the temperature of the combustion.

8. A fuel injection system according to claim 1, utilising a prism acting both as a light guide to photo-detectors and spectrally to separate the light.

9. A fuel injection system according to claim 1, in which further to guard against fouling, the combustion chamber end of the probe is multi-faceted.

10. A fuel injection system according to any one of claims 1 to 9, in which the probe is of quartz.

11. A fuel injection device according to any one of claims 1 to 10, in which the servo-control device is an algorithmic micro-processor control device taking account of; speed; throttle setting; engine temperature and other engine parameters as appropriate.

12. A fuel injected internal combustion engine including: a combustion chamber; means for supplying fuel to the combustion chamber; means for supplying air to the combustion chamber; an optical probe mounted in a wall of the combustion chamber to transmit light from combustion within the combustion chamber; an optical transducer mounted at an end of the optical probe remote from the combustion chamber to receive engine-combustion light and to produce a signal indicative of the colour of the light; and a servo-control device to control the fuel supply means to supply fuel to the engine in accordance with the colour of the light of combustion in the combustion chamber.

13. A method of controlling fuel injection to an internal combustion engine comprising the step of: measuring the colour of the fuel/air combustion in the engine; producing a servo signal dependent upon the measured combustion colours; and controlling fuel supply in accordance with the servo signal.

14. A fuel injection system for an internal combustion engine substantially as hereinbefore described and illustrated with reference to the accompanying drawings.