GB2109457A - Fuel and water emulsion supply system for diesel engines - Google Patents

Abstract

A heater 204 operated to provide a predetermined viscosity in response to a viscosity controller 207 is located downstream of an emulsifier 202 which receives fuel, water and emulsion not consumed in the engine. Temperature and pressure controllers 211, 212 are provided downstream of the controller 207. Valves 214, 214 and 226 enable fuel alone to be supplied to the engine 215, the excess being returned to the fuel tank. The unconsumed emulsion may pass through a cooler (130), Fig. 1 (not shown), before return to the emulsifier (106). The water flow to the emulsifier may be controlled in dependence on injector rack position, engine torque and speed. A rotor emulsifier is described, Figs. 2 to 4 (not shown). <IMAGE>

Description

SPECIFICATION Fuel supply systems The present invention relates to the supply of fuel to combustion processes and in particular to internal combustion engines.

Our earlier British Patent No. 1 572698 discloses an emulsifier by which by mechanical means alone, without the need for surfactants, emulsions of water and oil can be produced.

Investigations since the filing of that application have revealed that it produces micron size water droplets each carrying a coating of the oil with which the water has been mixed.

Subsequent work has corroborated that the device is effective in mixing water and a wide range of hydrocarbon fuels and it will be appreciated that blends with alcohols such as methanol or ethanol can also be emulsified.

The present invention is concerned particularly with the supply of fuel and water emulsions to large recirculation flow fuel systems, such as petrol and diesel injection engines for example certain fuel injection diesel engines such as the Cummins (Registered Trade Mark) diesel engine.

Large recirculation flow fuel system are particularly prevalent in American designs of medium and high speed engines. A substantial proportion of the fuel provided by the fuel pump is designed to bypass the fuel injection stage and is returned to the fuel tank. The prime objective of this approach is to use the surplus fuel as a coolant thereby maintaining sensible operating temperatures of the injection equipment. The penalties involved including the requirement for an oversize fuel pump, additional power consumption and system complexity.

With a 'conventional' fuel system all the fuel provided by the fuel pump is passed through the injectors and hopefully burned to produce power.

Consequently the addition of an emulsifier is relatively straightforward. The fuel line may be cut between the lift and main fuel pumps and the device added. A water-supply system provides the necessary quantity of water to the device at this junction point which, in turn, produces the emulsion which passes through the main fuel pump to the injectors.

With large return spill engines certain problems arise. Thus if the "contaminated" return fuel is taken to the fuel tank precipitation is liable to occur in the fuel tank as the water separates out or alternatively the ratio of water to fuel will continue to rise at each pass of the mixture through the emulsifier.

According to one aspect of the present invention a fuel supply system for a spill return engine, e.g. a high spill return engine, comprises first means for receiving the spill return from the engine and second means for returning the spill return to the engine, heater means and viscosity sensing means being located in association with the second means whereby the viscosity can be controlled in a predetermined manner.

In another aspect of the present invention a fuel supply system for a spill return engine (215) e.g. a high spill return engine, comprises fuel supply means (229, 230) and diluent (e.g. water) supply means (200, 201), an emulsifier (202), first (227) and second means (225) for supplying fuel to the engine or to the emulsifier respectively under the control of first valve means (226), third means (203, 4, 5, 7, 8, 213) for supplying fuel/diluent mixture from the emulsifier to the engine under the control of second valve means (214), fourth means (220, 1,2, 3) and fifth means (218) for returning the spill return from the engine to the emulsifier (202) or to the fuel supply (219) respectively under the control of third valve means (217), the first, second and third valve means being arranged to be operable so that when diluent is being used, the spill return is returned to the emulsifier, none being returned to the fuel supply which thus remains uncontaminated with diluent, and when pure fuel is being used the spill return is returned direct to the fuel supply and bypasses the emulsifier.

Preferably this second aspect of the present invention is combined with the first aspect and heater means (204) and viscosity sensing means (207) are located in association with the third supply means whereby the viscosity can be controlled in a predetermined manner.

The viscosity sensing means are preferably located downstream of the heater and provide feed back control of the heater so as to maintain the viscosity within preset limits.

The third supply means may also be under the control of a temperature regulator (211), or under the control of a pressure regulator (212), or both.

A controllable connection (208, 210) between the third and fourth supply means is preferably provided whereby the emulsifier can be run, even when the engine is being supplied with pure fuel, or a proportion of the emulsifier output can be diverted from the engine and returned to the emulsifier when the engine is being supplied with a fuel/diluent mixture.

The third supply means may be provided with a flow meter (222) so that the spill return flow can be determined.

A flow controller (201) may be located in the diluent supply to the emulsifier.

According to another aspect of the present invention a fuel supply system for a spill return engine, e.g. a high spill return engine, comprises an emulsifier, first means for supplying fuel and second means for supplying diluent (e.g. water) to the emulsifier, third means for supplying fuel/diluent mixture from the emulsifier to the engine, means for receiving the spill return from the engine, means for cooling the said spill return, preferably means for smoothing out variations in the flow rate of the spill return liquids and means for delivering the cooled and preferably smoothed spill return to the emulsifier or to a point on the input side of the emulsifier e.g. in the diluent or fuel supply to the emulsifier.

Control means are preferably provided to ensure that the fuel supply system provides a stipulated quantity of emulsion of defined fuel to diluent content dependent on the amount of fuel burnt as opposed to the amount of emulsion fed to the engine.

Sequential control, which may be by electronic means, is thus desirably provided to enable the fuel to water ratio to be kept at an optimum level either fixed by reference to a particular load condition or varying as the load on the engine varies for example so that at low load the proportion of water is high and decreases as the load on the engine increases.

The means for cooling the spill return may comprise an intercooler located in the spill return line so that the primary function of a high fuel bypass system is maintained.

The means for smoothing out variations in the flow rate of the spill return liquids may comprise a vented tank located in the spill return line, preferably after the cooling means.

Alternatively the means for smoothing out variations in the flow rate of the spill return liquids may comprise an accumulator located in the spill return line, preferably after the cooling means.

In another aspect of the invention a fuel supply system for a spill return engine e.g. a high spill engine which comprises an emulsifier, first means for supplying fuel and second means for supplying diluent to the emulsifier, third means for supplying fuel/diluent mixture from the emulsifier to the engine, means for receiving the spill return from the engine, an accumulator and means for delivering the smoothed spill return from the accumulator to the emulsifier or to a point on the input side of the emulsifier.

The smoothing means compensate for transient load demand and fuel system performance. Level control means are desirably also provided.

The water supply to the emulsifier can conveniently be obtained from a header tank at a height sufficient to overcome pressure vagaries in the fuel line. Alternatively an accumulator, e.g.

centrifugally charged by the water pump of the engine, may be used as the water suply. As a further less preferred option a constant displacement pump could be used.

Filters, limit switches, solenoid trips and failsafe mode controls are desirably also included in the circuit.

This fuel supply system can be used with naturally aspirated and with turbocharged engines such as those produced by British Leyland and Ford as well as Cummins.

The invention may be put into practice in various ways and one specific embodiment will be described to illustrate the invention with reference to the accompanying drawings in which: Figure 1 is a flow diagram of a fuel supply system in accordance with the present invention for use with a high spill return fuel injection engine; Figure 2 is a longitudinal cross-section of a preferred embodiment of an emulsifier for use in the system of the invention; Figure 3 is a cross-section on the line Ill-Ill of Figure 2, on a reduced scale, showing the mixing chamber and, diagrammatically, the outline of the rotor; Figure 4 is a cross-section on the line IV--IV of Figure 2, on an enlarged scale showing in detail the shape of the passages in one form of the rotor.

The particular form of rotor to be used depends on the fuel being used and attention is directed to G.B. Patent No. 1 572698 for directions on this aspect.

Referring now to Figure 1 reference 100 denotes the fuel injection system of the engine, 101 being the inlet line thereto and 102 being the outlet therefrom to the high spill return line 103.

The inlet 101 to the injector 100 is fed by a line 104 and main fuel pump 105. The main fuel pump 105 draws the fuel and water emulsion via a line 107 from an emulsifier 106 of appropriate type such as that described below with reference to Figures 2 to 4.

The emulsifier is fed with fuel from a fuel tank 110 having a filter 111 in its outlet by a lift pump 112 via a further filter 113 and a line 114.

The emulsier is fed with water from a water supply 120 via a filter 121 and a line 122. The water supply may be a header tank, an accumulator driven by the engine e.g. by its water pump or may be a constant displacement pump. The first two options are preferred.

The spill return line passes through a cooler 130 e.g. provided with forced cooling by a cooling water inlet 131 and outlet 132. The cooled spill return then passes via a line 133 to the smoothing means which are shown as a tank 140 having a vent 141 to atmosphere. The smoothed spill return then passes by the line 142 to the emulsifier 106.

The structure of a preferred form of emulsifier will now be described.

The emulsifier shown in Figures 2 to 4 consists of an inlet chamber housing 10 and a seal housing 11 bolted together by bolts 12 and provided with an 'O' ring seal 13. The housings 10 and 11 between them provide a mixing chamber 1 5.

Located in the mixing chamber for free rotation therein is a rotor 20 having radial passages 1 9, the rotor being supported on a shouldered drive shaft 21 which extends out through an aperture 23 to an external drive (not shown).

Interposed between the rotor 20 and the aperture 23 is a mechanical seal of conventional type, the aperture 23 being part of the seal. The seal is located within a seal chamber 35 formed in the seal housing 11. The seal chamber 35 is separated from the mixing chamber 1 5 by the rotor 20 except for a small clearance, c, between the outer edge of the rotor and the inner peripheral wall 37 of the mixing chamber 1 5.Liquids are prevented from passing directly through into the chamber 35 by the provision of a recirculation flow of the emulsion which is introduced through an orifice (not shown) into the seal housing 11 and which provides a cooling effect for the seal and then recombines with the emulsion in the chamber 1 5. The housing 10 provides an inlet chamber 50 which is fed by three inlet passages, a water inlet passage 51, a fuel inlet passage 52 and a spill return passage 57. Each supply line 114, 1 22, and 1 42 to these passages is provided with an on-off valve (150, 152, 152 respectively (not shown)) adjacent the emulsifier.

The inlet chamber comprises the substantially cylindrical chamber 53 at the confluence of the passages 51 and 52, plus the disc shaped chamber 49 located between the central end face 54 of the rotor 20, the inner wall 55 of the passages 1 9 and the end face 56 of the chamber 53.

The mixing chamber 1 5 is defined as being bounded by a front wall 60, an inner wall extending from the inside edge of the front wall parallel to the longitudinal axis of the device, an outer side wall, of which part, 37, is circular and part, 66, is spiral, and a rear wall extending parallel to the front wall 60 from the rear of the outer side wall. The mixing chamber communicates with an outlet passage 65 disposed tangentially to the rotor (see Figure 2) and transverse to its axis.

The circular wall extends around the chamber for 2400 and the spiral wall 66 extends outwardly from the point 70 to the outer edge of the outlet passage 65. The mixing chamber includes this part crescent shaped region extending from point 70 to the line 72 across the opening 65. The mixing chamber is largely occupied by the rotor 20.

The clearance, C, between the wall 37 and the outer space of the rotor is preferably in the range 0.001" to 0.005", e.g. 0.002". The radius, R, of the rotor is 2.8".

The generally crescent shaped region may have a flat outer wall as shown in Figure 3. However, one convenient way of making this part of the housing is to mill out the cylindrical mixing chamber and drill the circular outlet opening 65 tangentially to the circular chamber down to the point 78. One can then pick out the region 1 5 with a milling machine from a line 72 down to the point 70 so as to smooth out the transition between the hole 65 and the circular wall 37 of the mixing chamber to form the curved region extending from the line 72 to the point 70. In this arrangement, the wall 66 need not be flat.The maximum clearance, C2, between the wall 66 and the periphery of the rotor at the point 78 is many times that of the clearance C between the wall 37 and the rotor and the ratio C2/C is preferably at least 10:1 and more desirably at least 50:1 or 100:1 and particularly in the range 50:1 to 200:1 or 500:1.

Referring now to Figure 4, the rotor 20 in this embodiment has twelve radial passages 1 9 equally spaced apart through 300 and extending from the inlet wall 55 to the outer periphery 36 of the rotor 20. The radial length of each passage 19 is 0.6 times the radius of the rotor.

In this form of the invention the inlet end of each passage is a V shaped slot 1 72 including an angle of 600 and the outlet end is a V shaped slot 73 including an angle of 200: these angles are such that the slots would intersect even if the passage was not broadened in this region to form a parallel sided throat portion 71, 1/12" wide.

In operation the liquids to be mixed are drawn from the inlet chamber by the centrifugal force on the liquid in the passages 19 and thrown out radially through the passages 1 9 and caused to hit the wall 37. The outer wall 36 of the rotor is broken up into twelve solid portions 77, each about twice the circumferential length of the outlets 73, and the solid portions 77 may be considered to act as vanes.

They thus have the function both of shearing the fuel and water mixture in the gap between the wall 37 and the wall 36 and propelling it around the circumference of the mixing chamber through the part crescent shaped region 78, where turbulent mixing may be expected to occur and then ejecting it through the outlet passage 65.

In the embodiment of Figure 4 the constriction 71 has the function of impeding the flow of fluid along the passage 1 9 and thus increasing its velocity outwardly and the diverging outlet slots then cause a pressure drop in the fluid resulting in vaporisation of the fuel in the mixture.

The rotor shown in Figure 4 is best used for fuels having viscosities from 35 Redwood seconds up to 3000 Redwood seconds and rotor speeds of 2800 to 7000 r.p.m. The rotor is thought to work by vaporisation of the fuel as it goes through the throat of the passages 1 9 producing cavitation in the fuel/water mixture, the water droplets are thought to be sheared by the wall 37 and the vanes 77 and the fuel is thought to condense on the surface of the water droplets in the turbulent flow region 78.

Mention has been made earlier of sequential control of the amount of return fluids fed to the emulsifier.

Figure 5 shows a circuit for achieving this as applied to a marine diesel engine. The circuit of Figure 5 can be used to replace the components 120 and 121 of Figure 1. The input line 300 in Figure 5 is connected to a ship board source of engine grade water and the output line 31 7 in Figure 5 is connected to the line 122 in Figure 1.

The emulsor 316 in Figure 5 is the same as the emulsifier 106 in Figure 1.

Thus referring to Figure 5 a supply tank 302 provided with a vent to atmosphere 324 is fed via an input control valve 301 from the line 300. An output line 322 runs from the bottom of the tank 302 via an "on-off" check valve 320 via a filter 321 to a water pump 307. The water pump is driven at constant speed by an appropriate power source or take off from the engine to which the emulsion is being fed. The pump 307 feeds a line 308 which takes the supply flow via a filter 306, a flow meter 309, and a control valve 310 to a solenoid operated valve 311 and thence via the lines 313 and 317 to the line 122 (of Figure 1) and thence to the emulsor 316 (or 106 of Figure 1). A line 314 leads via a solenoid operated valve 312 to a drain 315 from the junction of the lines 313 and 317.

In another embodiment the solenoid valve 311 is in the line 317 rather than the line 313.

A return line 303 branches from the line 308 between the pump 307 and the filter 306 and feeds into the top of the tank 302 via an "on-off" or check valve 305.

In a further modification (not shown) a solenoid valve controlled drain arrangement analogous to that afforded by components 311,312 and 31 5 in Figure 5 may be provided in the line 142 in Figure 1. This facilitates draining of the system for maintenance. Also should the spill return flow rise to too high a level some of it can be diverted to drain (which may be a holding tank) whilst maintaining some spill return to the emulsifier.

The operation of the system is such as to prescribe the amount of water and oil which is applied to the emulsifier. The water fuel ratio is dependent on the characteristics of the engine, which is its power versus speed versus fuel consumption characteristics. The control system needs to know the power generated by the engine which can be obtained by measuring the r.p.m.

and the torque and sensing the fuel rack position.

On a diesel engine instead of having a throttle, one has a rack and the rack turns the injectors and as it turns the injectors it either increases or decreases the amount of fuel which is supplied to the engine.

Having determined these three variables one can by comparison with prior measurements of the optimum water fuel ratios at different loadings of the engine match the water fuel ratio to the load to which the engine is being subjected from moment to moment. When the water and the fuel which has been recirculated is returned to the emulsifier the amount of water which requires to be fed to the emulsifier from the water supply 1 20 (or 302) needs to be controlled in relationship and dependency on the amount of fuel which is actually being burnt in the engine not the amount of fuel which has,passed through the emulsifier, since the spill return already contains some water.

Consequently one still needs to measure the torque, the speed, and the fuel rack position of the engine to be able to put in the correct quantity of water from the tank 120 (or 302) to meet the optimum requirements for the load, current at that moment. A controller or comparator is desirably also provided which generates the characteristic of the water to fuel ratio which is an optimum, for the current load.

The comparator may thus have a memory store prepared from prior trials on the engine.

Alternatively in a simpler arrangement the characteristics of the control valve 310 can be made to provide the desired non-linear response to match the water fuel ratio to the load characteristics of the engine. Thus the valve ports can be shaped so that when the valve opens the flow that goes through it is not linearly displaced according to the fuel valve opening position. The shape of the valve port can be arranged to afford a cubic characteristic, or a quartic characteristic, or whatever characteristic is required for the particular type of engine.

Reference has been made above to the sequential control provided to enable the fuel to water ratio to be kept at an optimum level varying as the load on the engine varies for example so that at low load the proportion of water is high and decreases as the load on the engine increases.

It will be appreciated that the most desirable arrangement is for the control to match the characteristics of the diesel engine involved whatever those characteristics may be.

Thus the control could be such that at low load the proportion of water is low and increases as the load on the engine increases.

Also the relationship need not vary linearly in either of these possibilities and can follow any sequence of values determined by the engine itself.

The cooler 1 30 plays a critical part with these systems in which a high spill return flow is used.

Thus, the spill return is used to cool the injectors and it has been worked on by the pumps and a variety of other heat inputs act on it.

The spill return flow temperature is therefore liable to rise to a level significantly above the optimum at which the fuel should be supplied to the injectors and moreover its temperature is also liable to fluctuate. Such problems as this are not met with where the spill return is pure fuel because there it can be returned to the main fuel tank and the bulk of unused fuel cools the spill return.

The provision of a cooler in accordance with the present invention overcomes these problems and enables a more compact system to be built which is particularly necessary for land vehicles.

Referring now to Figure 6 this is an alternative to Figure 1 and is suitable for use with marine diesels e.g. of horse power ratings which are multiples of 1000 H.P.

A typical engine with which the control system can be used is a type MAK 551 shown by reference numeral 215.

This is fed from a conventional fuel supply system indicated by 230 via a flow meter 229 (e.g. a Helix positive displacement flow meter type 241) a three way valve 226, a pure fuel line 227 and a three way valve 214. The spill return from the engine 21 5 is via a line 216 and a three way valve 217 to a return line 218 and from thence to a mixing tank 219. This spill route being used when pure fuel only is being used. This arrangement so far described is conventional apart from the presence of the three way valves 226, 214 and 21 7 which are ganged together as indicated by 228 so as only to be operable in certain predefined ways which will be described in more detail below. It will be observed that the valves 226,214 and 21 7 are in fact set in Figure 6 so as not to supply pure fuel.

They are set so as to supply emulsion in accordance with the invention.

Thus the valve 226 directs the fuel supply from 229 to the line 225 and thence to an emulsifier 202 (e.g. as described in Figures 2 to 4) which is fed from a water tank 200 via a preset flow meter 201. This is set by reference to the flow through the flow meter 229 so as to achieve the desired fuel to water ratio. The emulsion has a higher viscosity than pure fuel. The emulsion from the emulsifier thus passes via a viscosity temperature and pressure control system to the valve 214 which directs it to the engine 21 5 (e.g. its injector). This viscosity control is needed to ensure proper atomisation in the engine.

The viscosity, temperature and pressure control system consists of a heater 204 under feedback control 206 of a viscosity controller 207 which measures the viscosity and feeds a signal to the heater via a line 205. The output line 208 feeds a pressure and temperature control line 213 which feeds the valve 214. The line 213 has a temperature sensor and controller 211 (e.g. set to 118 to 1 280C) and a pressure sensor and controller 212 (e.g. set to 45 bar pressure).

The spill return from the engine passes via the line 216 via the valve 217 to the return line 220 and thence either to a return line 221 and thence via a flow meter 222 to a line 223 which feeds the emulsifier 202 at the junction of lines 225 and 224 or via a line 210 and a check valve 209 feeds to the junction of the lines 208 and 213.

Coolers and water supply control systems as described for Figures 1 and 5 can if desired be inserted respectively in the line 221 or replace the components 200 and 201.

The ganging 228 of the valves 226, 214 and 217 ensures that when emulsion is being supplied to the engine the spill return goes back to the engine or to the emulsifier and not to the main fuel supply and that when pure fuel is being used the spill return goes to the pure fuel tank and not to the emulsifier.

This enables the emulsifier to be ieft running recirculating emulsion e.g. when the engine is switched to pure fuel such as may occur before entering port.

Thus according to a broader aspect of the invention a flow meter is located in the spill return line to sense the amount of emulsion which is being recirculated to the emulsifier.

Claims (19)

1. A fuel supply system for a spill return engine, e.g. a high spill return engine, comprising first means for receiving the spill return from the engine and second means for returning the spill return to the engine, heater means and viscosity sensing means being located in association with the second means whereby the viscosity can be controlled in a predetermined manner.

2. A fuel supply system for a spill return engine e.g. a high spill return engine, comprising fuel supply means and diluent supply means, an emulsifier, first and second means for supplying fuel to the engine or to the emulsifier respectively under the control of first valve means, third means for supplying fuel/diluent mixture from the emulsifier to the engine under the control of second valve means, fourth means and fifth means for returning the spill return from the engine to the emulsifier or to the fuel supply respectively under the control of third valve means, the first, second and third valve means being arranged to be operable so that when diluent is being used, the spill return is returned to the emulsifier, none being returned to the fuel supply which thus remains uncontaminated with diluent, and when pure fuel is being used the spill return is returned direct to the fuel supply and bypasses the emulsifier.

3. A fuel supply system as claimed in Claim 2 in which heater means and viscosity sensing means are located in association with the third supply means whereby the viscosity can be ccontrolled in a predetermined manner.

4. A fuel supply system as claimed in Claim 1 or Claim 3 in which the viscosity sensing means are located downstream of the heater and provide feedback control of the heater so as to maintain the viscosity within preset limits.

5. A fuel supply system as claimed in Claim 2, 3 or 4 in which the third supply means is also under the control of a temperature regulator.

6. A fuel supply system as claimed in Claim 2, 3, 4 or 5 in which the third supply means is also under the control of a pressure regulator.

7. A fuel supply system as claimed in any one of Claims 2 to 6 in which a controllable connection between the third and fourth supply means is provided whereby the emulsifier can be run, even when the engine is being supplied with pure fuel, or a proportion of the emulsifier output can be diverted from the engine and returned to the emulsifier when the engine is being supplied with a fuel/diluent mixture.

8. A fuel supply system as claimed in any one of Claims 2 to 7 in which the third supply means is provided with a flow meter so that the spill return flow can be determined.

9. A,fuel supply means as claimed in any one of Claims 2 to 8 in which a flow controller is located in the diluent supply to the emulsifier.

10. A fuel supply means as claimed in Claim 1 substantially as specifically described herein with reference to Figure 6 of the accompanying drawings.

11. A fuel supply system for a spill return engine, e.g. a high spill return engine, which comprises an emulsifier, first means for supplying fuel and second means for supplying diluent to the emulsifier, third means to supplying fuel/diluent mixture from the emulsifier to the engine, means for receiving the spill return from the engine, means for cooling the said spill return, preferably means for smoothing out variations in the flow rate of the spill return liquids and means for delivering the cooled and preferably smoothed spill return to the emulsifiedr or to a point on the input side of the emulsifier, e.g. in the diluent of fuel supply to the emulsifier.

12. A fuel supply system as claimed in Claim 11 in which control means are provided to ensure that the fuel supply system provides a stipulated quantity of emulsion of defined fuel to diluent content dependent on the amount of fuel burnt as opposed to the mount of emulsion fed to the engine.

13. A fuel supply system as claimed in Claim 12 in which sequential control, which may be by electronic means, is provided to enable the fuel to diluent ratio to be kept at an optimum level either fixed by reference to a particular load condition or varying as the load on the engine varies for example so that at low load the proportion of diluent is high and decreases as the load on the engine increases.

14. A fuel supply system as claimed in Claim 11, 12 or 13 in which the means for cooling the spill return comprise an intercooler located in the spill return line so that the primary function of a high fuel by-pass system is maintained.

1 5. A fuel supply system as claimed in Claim 11,12, or 14 in which the means for smoothing out variations in the flow rate of the spill return liquids comprise a vented tank located in the spill return line, preferably after the cooling means.

1 6. A fuel supply system as claimed in any one of Claims 11 to 14 in which the means for smoothing out variations in the flow rate of the spill return liquids comprise an accumulator located in the spill return line preferably after the cooling means.

1 7. A fuel supply system for a spill return engine e.g. a high spill engine which comprises an emulsifier, first means for supplying fuel and second means for supplying diluent to the emulsifier, third means to supplying fuel/diluent mixture from the emulsifier to the engine, means for receiving the spill return from the engine, an accumulator and means for delivering the smoothed spill return from the accumulator to the emulsifier or to a point on the input side of the emulsifier.

18. A fuel supply system as claimed in any one of Claims 2 to 17 in which an accumulator, e.g.

centrifugally charged by the water pump of the engine, is used as the diluent supply.

19. A fuel supply system as claimed in Claim 11 or Claim 17 substantially as specifically described herein with reference to Figure 1 or Figure 5 of the accompanying drawings.