GB2167491A

GB2167491A - C.I. engine fuel supply system

Info

Publication number: GB2167491A
Application number: GB08429965A
Authority: GB
Inventors: Louis Barnbas Bodo; Donald Francis Walter Power
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1984-11-28
Filing date: 1984-11-28
Publication date: 1986-05-29
Also published as: GB8429965D0

Abstract

To maintain the viscosity of fuel flowing to an injection pump substantially constant a fuel heater is controlled in response to the signal from a viscosity sensor. The sensor comprises an electrically vibrated annular member (17, Fig. 2) in a housing 14 through which the fuel flows, the electrical power for a constant member displacement or member displacement for a constant power input provides a viscosity signal.

Description

SPECIFICATION Fuel supply system This invention relates to a fuel supply system for a compression ignition engine, the system being of the kind comprising a high pressure pump which is driven in timed relationship with the engine to which fuel is supplied.

A substantial number of the high pressure pumps on the market utilize in some way or other the fuel which is being pumped by the pump as a lubricant for a part or parts of the pump. For example, it is common for the pump to comprise a plunger reciprocable within a bore and some pumps also have a rotary distributor member mounted in a bore in the body of the pump. In order to minimise the leakage of fuel along the working clearance defined between the working surfaces of the plunger and the wall of the bore, and where provided between the distributor member and its bore, the clearance should be kept as small as possible. However, in order to lubricate the working surfaces some leakage must be allowed and hence a compromise working clearance is established which provides the minimum leakage while at the same time ensuring adequate lubrication.Unfortunately, the leakage of fuel along the working clearance depends amongst other things upon the viscosity of the fuel and if the pump is designed to operate with fuel of a particular viscosity the leakage may be excessive if the viscosity is reduced and the lubrication may be inadequate if the viscosity is increased. The viscosity of a given fuel depends upon its temperature and it is therefore possible if the fuel temperature is too high, for there to be so much leakage along the working clearance as to make it difficult to start the associated engine. If the fuel temperature is too low then there may be inadequate lubrication due to insufficient fuel flow along the working clearance. A further problem arises if the type of fuel is changed since different fuels have different viscosities at the same temperature.

The object of the invention is to provide a fuel supply system of the kind specified in a simple and convenient form.

According to the invention a fuel supply system of the kind specified includes fuel heating means disposed in a fuel supply line to said pump and sensing means for sensing the viscosity of fuel flowing in said supply line the signal provided by said sensing means being utilized to control said heating means, A fuel supply system in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of the fuel system, and Figure 2 is a diagrammatic view of part of the system shown in Figure 1.

Referring to Figure 1 of the drawings the fuel system comprises a high pressure pump 10 which may be of the rotary distributor type having a fuel inlet 11 and a plurality of outlets not shown for connection in use to the injection nozzles of an associated engine. The pump 10 is driven in timed relationship by the engine in known manner. The fuel inlet 11 is connected to a source of fuel by way of a fuel treatment unit (not shown), the fuel treatment unit incorporating filter medium whereby the fuel which is supplied to the pump is filtered.

Upstream of the pump inlet 11 is a heater 12 which conveniently is an electrical heater although other forms of heater may be employed such for example as a heater which receives heat from the engine cooling system. Intermediate the heater and the pump is a viscosity sensing device 13. The sensing device has associated therewith electrical circuit means whereby a signal can be obtained indicative of the viscosity of the fuel flowing to the inlet 11. The signal obtained from this circuit means is utilized to control the heat supplied to the fuel during its passage through the heater 12. By this arrangement it is possible to control the viscosity of the fuel supplied to the pump 10. The pump can therefore be designed with a particular fuel viscosity in mind.It is not envisaged that any form of fuel cooling will be employed so that the pump should be designed to operate with fuel of low viscosity to take acount of the fact that at high ambient temperatures the fuel will be less viscous.

The continuous adjustment of the viscosity will effect an improvement in the operation of any high pressure injection pump which is sensitive to viscosity.

The measurement of fuel viscosity on a continuous basis is not easy and the device 13 which is shown in greater detail in Figure 2, is provided for this purpose. The device 13 comprises a housing 14 into which and from which the fuel flows from the heater 12 to the pump 11. Within the housing there is mounted an electrical vibrator 15 having an output member 16 which is coupled to a moving body generally indicated at 17. In the illustrated example the body comprises an annular member which is movable axially in an oscillatory manner by the vibrator 15. The body may however be of any convenient shape and surface finish so as to generate a high rate of shear within the fuel and a high skin friction preferably with minimum fuel movement and minimum turbulence.Preferably the volume of fuel contained within the device 13 should be as small as possible so that it is as sensitive as possible to changes in the viscosity of the fuel as a result of operation of the heater and/or as a result of a change in the type of fuel.

As shown the vibrator 15 is located within the chamber but it may be positioned outside the chamber if so desired.

In order to derive a signal representative of the viscosity of the fuel the average power which has to be supplied to the vibrator to effect a given displacement may be measured or alternatively, the power supplied to the vibrator may be kept constant and the displacement of the output member 16 measured by means of a transducer 18. As the viscosity of the fuel increases, the power required to maintain a given displacement will increase. Al ternatively, if the power supplied to the vibrator is maintained constant, then the actual displacement will decrease.

In Figure 1 the heater 12 and the sensing device 13 have been shown as separate items. They may however be located in the same housing particularly in the case where the heating device is electrically powered. It is envisaged that they could be located in the housing of the fuel treatment unit which forms part of the fuel supply system.

Although the sensing device 13 is shown as part of a fuel system for an engine it is envisaged that it could be used in other sytems for the measurement of the viscosity of liquids flowing therein. For example, it could be used to measure the viscosity of opaque liquids, suspensions or emulsions and also to liquids in continuous streamline flow.

Claims

1. A fuel supply system for a compression ignition engine comprising a high pressure pump which is driven in timed relationship with the engine to which fuel is supplied, fuel heating means disposed in a fuel supply line to the pump and sensing means for sensing the viscosity of the fuel flowing in said supply line the signal provided by said sensing means being utilized to control said heating means whereby the viscosity of the fuel supplied to the pump can be maintained substantially constant.

2. A fuel supply system according to Claim 1 in which said sensing means is disposed intermediate the heating means and the pump.

3. A fuel supply system according to Claim 1 or Claim 2 in which said viscosity sensing means includes a housing through which fuel can flow to the pump, a body movable in the fuel in the housing, electrical means for moving said body in the housing, the power supplied to said electrical meanslor the displacement of the body being maintained constant and an indication of the viscosity of the fuel being obtained by measuring the displacement of the body/or the power supplied to the electrical means.

4. A fuel supply system for a compression ignition engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.