GB2078298A

GB2078298A - Heated fuel supply for diesel engines

Info

Publication number: GB2078298A
Application number: GB8116959A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-06-06
Filing date: 1981-06-03
Publication date: 1982-01-06
Also published as: SE8103563L; FR2484023A1; NL8102731A

Abstract

The system includes an injection pump with a high pressure section 4 immediately upstream of which in the fuel supply path is an electrical heating device 1 including a thermostat 22. The heating device 1 has a housing 12 defining a passage 13 in which is situated a heating rod 16. A helical spring 18 extends around the heating rod 16 and defines a helical fuel flow path. The heating device preheats the fuel thus improving cold starting of the engine and saving fuel. In a modified construction, Figures 3 and 4 (not shown), the heating device 1 affords a passage (30) connected by means of a thermostatic valve (39) to a line (35) of the engine cooling system so that once the engine coolant has warmed up preheating of the fuel is effected by the coolant. <IMAGE>

Description

SPECIFICATION Fuel supply system for internal combustion engines The invention relates to a fuel supply system for internal combustion engines, in particular diesel engines, and is concerned with the preheating of fuel before supplying it to such engines.

It is an object of the present invention to provide a fuel system by means of which fuel can be preheated in an economical and controlled manner andover- heating of the fuel is reliably avoided, particularly during cold starting of diesel engines.

According to the present invention there is provided a fuel supply system for an internal combustion engine including an injection pump upstream of which in the fuel flow path is an electrical heating device connected to a temperature control device.

Preferably the heating device is immediately adjacent the high pressure section of the injection pump.

With the system according to the invention heating of the fuel can be carried out very precisely and, in particular, overheating can be reliably avoided. At the same time, however, during cold starting the fuel is warmed up rapidly and, because of the arrangement adjacent to the injection pump, also effectively, which facilitates cold starting. In addition, a considerable saving of fuel is made possible by preheating the fuel.

The heating device preferably includes a heating rod located within a fuel supply passage, preferably immediately in front of the high-pressure section.

Such a heating rod can be easily arranged in the fuel supply and ensures that heating of the fuel is efficient and because of the short distance to the injection nozzle thermal losses are low.

In one embodiment of the invention the flow passage in which heating occurs is helical and preferably a helical member, e.g. a helical spring, extends around the heating rod within the fuel supply passage thereby defining a helical flow passage for the fuel. This does not significantly affect the fuel supply, but does lengthen the fuel flow path in the region of the heating rod, so that a substantial thermal transfer can occur, even with comparatively short heating rods. The helical spring around the heating rod conveniently engages or terminates adjacent the wall of the flow passage, thereby defining a helical flow path.

The electrical heating device preferably has a thermally insulating casing to minimise heat loss and preferably includes a thermostat arranged adjacent its downstream end.

In the system according to the invention, the excess fuel collecting on the high-pressure side of the injection pump is advantageously returned to the injection pump circuit rather than to the fuel tank.

Thus the system preferably includes a fuel delivery pump and a fuel return line extending between the high pressure section of the injection pump and the inlet line to the delivery pump. The fuel return line is preferably connected to the inlet line to the delivery pump by means of a Connector upstream of which in the fuel return line is an excess pressure valve.

The excess quantity of fuel preheated in the electrical heating system which is not injected into the engine is thus immediately drawn in again without being returned to the fuel tank and again supplied to the electrical heating system and to the highpressure section of the pump. Thus a considerable proportion of the fuel is circulated in a warm state and as a result a large proportion of the heating power can be saved. The excess pressure valve ensures that the back-pressure which is necessary for proper functioning of the injection pump is maintained in the return passage and in the highpressure section of the injection pump.

The invention also embraces an internal combustion engine having such a fuel supply system, and when the engine has a fluid coolant circuit the electrical heating device preferably has a heating passage in thermal communication with the fuel flow passage and connected to the coolant circuit by means of a thermostatic valve. Excess heat is available in the fluid circuit of the engine cooling system in large quantities and at a temperature which can be readily used for preheating of a fuel. In this way electrical energy can be saved. After the engine running temperature has been reached the electrical heating system can be completely shut off as it is only necessary in the warm-up phase.

The engine preferably includes a first thermostatic valve arranged to open when the coolant temperature is above the switch-off temperature of the electrical heating device and situated at the point where the heating passage in the heating device communicates with the fluid coolant circuit. As soon as the opening temperature of the first thermostatic valve is reached in the fluid circuit, this opens the fluid supply to the heating device. Since the opening temperature of this thermostatic valve lies above the cut-off temperature of the electrical heating system, it is reliably ensured that the electrical heating system is completely shut off whilst the fuel is heated by the coolant fluid.Since the thermostatic valve is closed before its opening temperature is reached, the passage of low-temperature fluid through the heating device, which would otherwise cool the heating device and consume additional electrical energy, is avoided.

The engine preferably also includes a second thermostatic valve arranged to close the heating passage in the heating device at a temperature above the opening temperature of the first thermostatic valve. In this way overheating of the fuel is avoided.

A second thermostatic valve may be arranged at the downstream end of the heating passage in the heating device or the first and second thermostatic valves may constitute a single structural unit and the second thermostatic valve is arranged to pass a restricted volume of coolant fluid when it is closed in order to reduce the manufacturing and assembly costs.

Further features and details of the invention will be apparent from the following description of certain specific embodiments which is given by way of example with reference to the accompanying schematic drawings in which: Figure l is an axial sectioon through a first embodiment of an electrical heating device for a fuel supply system according to the invention; Figure 2 is a schematic representation of a fuel supply system of a diesel engine incorporating a heating device as shown in Figure 1.

Figure 3 is a view similar to Figure 1 of a second embodiment of an electrical heating device; and Figure 4 is a schematic representation similar to Figure 2 of a fuel supply of a diesel engine in which excess fuel is returned to the injection pump.

The fuel supply system shown in Figure 2 is connected between a diesel engine 3 and a fuel tank 2. The system comprises a fuel injection pump 5 having a high-pressure section 4 connected immediately upstream of which is an electrical heating device 1 which will be described in more detail below. The heating device 1 is connected to the fuel tank 3 by a fuel line 7 which includes a fuel delivery pump 8 which forms part ofthe injection pump 5 and upstream of which is a filter 6.

Since the quantity of fuel delivered by the pump 8 is roughly suited to the maximum requirement of the engine 3, excess fuel is delivered when the engine is on partial load or idling. The excess fuel is led back by means of a conduit 9 (indicted by broken lines) from the filter 6 into the tank 2. By arranging the heating device 1 immediately adjacent the highpressure section 4 of the injection pump 5, it is ensured that the proportion of fuel delivered which is actually supplied to the engine 3 is heated. This is particularly economical of heating energy, for which reason the heating device 1 is preferably provided with an insulating casing. This casing is optionally also integral with the injection pump housing.

When the engine is running under partial load, the injection pump 5 runs at throttled power and not tali the fuel delivered to the high-pressure section 4 of the injection pump is injected into the engine 3. Thus excess fuel collects in the high-pressure section 4 and is returned via a return line 11,which is connected to the line 9, to the fuel tank 2.

The heating device 1 is shown in more detail in Figure 1 and is preferably an integral part of the fuel system, e.g. part of an exchangeable intermediate pipe member or the like. It has a housing 12 with a passage 13 extending through it with an axial inlet opening 14 at one end and a substantially radial outlet 15 at the other end. A heating element in the form of a rod 16, which is supplied by electrical leads 17, is arranged within the passage 13. The heating rod 16 is arranged within a helical flow channel for the fuel, and in this embodiment the flow channel is defined by a compression spring 18 surrounding the heating rod 16. This engages or terminates adjacent the internal wall 19 of the passage 13. The helical flow path for the fuel is thus formed between the individual loops ofthe compression spring 18.Thus with a relatively short axial length of the passage 12 and thus a low overall length of the device 1 the flow path for the fuel is relatively long so that the fuel is uniformly heated. The heating rod 16 is fixed to a screw coupling which is screwed into an axial threaded section of the passage 13.

Atemperature regulating device 21 associated with the heating device 1 includes a thermostat 22 which is located in the region of the outlet bore 15 and thus also of the fuel inlet of the injection pump 5 (seen in Figure 2). The temperature of the heated fuel in the end region of the heating passage and thus also at the point at which the fuel is at its highest temperature is measured by this thermostat. In practice it has been shown that heating the fuel to approximately 60"C is desirable, particularly for cold starting, and results in more economical running of the diesel engine and reduced exhaust fumes.On the other hand, it must be borne in mind that diesel fuel vapourises at 80"C and it must therefore be ensured that this upper temperature limit is not reached, since this would lead to disruption of the operation of the engine. In the heating device 1 the temperature at which the thermostat 22 switches on is approximately 60 , and the two thermostat temperatures at which the heating rod 16 is switched on and off are comparatively close to each other, the difference between them being of the order of 1"C.

This ensures that the desired heating temperature of the fuel can be very accurately maintained. In a simple modified construction, a bimetal contact which directly switches the heating rod 16 serves as the thermostat 22. In this case the maximum difference between the switching temperatures can be approximately 1 5 C. A connecting terminal for electrical supply leads is indicated at 23.

Instead of a bimetallic thermostat another type of measuring sensor, e.g. a resistance of either negative or positive temperature coefficient could be provided, which is connected to an associated electronic control circuit.

The temperature regulating device 21 may conveniently include a monitoring device, e.g. a check light or the like, which is arranged where it can be seen by a user, in the case of a motor vehicle in the dashboard. In this way heating of the fuel can be properly monitored. Current can be conveniently supplied to the preheating device 1 via the ignition lock, so that this device is switched on upon preliminary heating during the starting procedure.

The first pumping strokes of the high-pressure section of the injection pump 5 thus deliver preheated diesel oil for cold starting, and this considerably facilitates cold starting. This is particularly so because of the arrangement of the heating device in immediate proximity to the high-pressure section of the injection pump 5.

The whole preheating device 1 shown for example in Figure 1 can also be subsequently installed in an existing fuel supply of a diesel engine, particularly at the point shown in Figure 2, thereby converting the fuel supply system to one in accordance with the invention.

A second embodiment of the heating device is shown in Figure 3. The parts which correspond to those shown in Figure 1 are designated by the same reference numerals.

In this embodiment the fuel also passes an electrical heating device including a heating rod 16 in the same way as in the embodiment shown in Figure 1. The electrical heating device is provided with a thermostat which is controlled by a sensor 22 and regulates the temperature.

However, the heating device 1 affords an additional fluid heating system constituted by a heating passage 30 defined between the housing 12 of the heating device and a further inner wall which surrounds the heating roll 16. A supply hose 32 is connected to the passage 30 by an inlet olive 31 and a discharge hose 34 is connected to the passage 30 by an outlet olive 33, and the direction of flow in the passage 30 is indicated by arrows.

The supply hose 32 and the discharge hose 34 are connected at suitable points to the fluid circuit (not shown) of the engine cooling system. The supply hose 32 branches off from a line 35 forming part of the fluid circuit, at which point a thermostat valve housing 36 is provided. An expansion member 37 which is exposed to fluid flowing in the line 35 and connected to a valve stem 38 of the thermostatic valve is positioned in this thermostat housing and arranged so that when the liquid temperature increases it moves the valve stem downwards.

Afirst upper valve plate 39 and a second lower valve plate 40 are connected to the valve stem 38 and cooperate with respective valve seats normally positioned above and below them respectively.

When the cooling liquid temperature is low the first valve plate 39 is in the closed position and the second valve plate 40 is in the open position. When the cooling fluid temperature begins to rise, the valve stem begins to move downwards. At a first lower temperature the first valve plate 39 opens and remains open at all higher temperatures. At a second temperature which is higher than the first the second valve plate 40 closes. Between the two temperatures the cooling liquid can flow through the two valve seats and a throttle opening 41 in the second valve plate 40 permits a throttled flow of coolant liquid into the passage 30 even when the second valve plate 40 is closed.

The dimensions of the illustrated thermostat device are adapted to the design of the electrical thermostat 22 of the heating device so that the first valve plate 39 opens at a temperature above the switching-offtemperature of the electrical thermostat 22. Consequently in the warming up phase of the engine heating of the fuel is carried out exclusively by electrical means. Thus coolant fluid which would otherwise cool the fuel in the heating device is prevented from flowing through the heating channel 30. When the first valve plate 39 opens, the fuel in the heating device is heated via the heating channel 30 at a temperature at which the electrical heating system is reliably switched off. Thus electrical heating power is no longer required during continuous running of the engine.

An excessively high temperature of the heating device should be avoided, for example to prevent vapour bubbles in the heated fuel. Therefore when the temperature exceeds the desired operating temperature the second valve plate 40 of the thermostat closes and permits only a limited coolant fluid flow through the throttle opening 41, which heats the heating device to a sufficient extent and the electrical heating system is optionally also switched on for accurate temperature regulation.

The valve plates 39 and 40 each constitute a thermostat together with their associated valve seat, and these two thermostats can be constructed separately in a manner which is not illustrated. In this case the thermostat 39 which shuts off at low temperature is advantageously situated at the point shown in Figure 3 where the supply hose 32 branches off from the line 35 of the fluid circuit. The second thermostat (corresponding to the second valve plate 40) which closes at the higher temperature is then advantageously situated at the outlet of the heating channel 30 from the heating device, that is to say, for example, on the outlet olive 33 or in the discharge hose 34. It thus monitors the temperature in the heating device.With this arrangement the throttle opening 41 can be omitted, since when the fluid temperature at the second thermostat drops below the required temperature this thermostat immediately reopens the channel.

In this way electrical heat energy can be saved to a considerable extent and is only necessary for cold starting of the engine when the engine coolant fluid has not yet reached its running temperature.

Figure 4 shows a further embodiment of the fuel supply by means of which the heating energy, particularly electrical heat energy, required can be further reduced.

In the conventional construction of the injection pump 5 in accordance with the Bosch (Registered Trade Mark) principle the injection pump is regulated by rotation of the high-pressure piston in the high-pressure section 4. When the engine is on partial load a considerable quantity of excess fuel is collected and has to be removed. Other conventional designs of injection pumps also accumulate excess fuel, which must be removed, in the partial load range.

In the embodiment of Figure 4 the excess fuel is not returned by the excess fuel line 11 to the fuel tank as in the simpler embodiment shown in Figure 2, but is delivered by means of a return line 111 to a T-piece 130 in the inlet pipe 7 of the delivery pump 8.

The excess fuel, which has already been heated, from the high-pressure section 4 of the injection pump is therefore again returned by the delivery pump 8 to the heating device 1 still in a warm state, so that heat losses are avoided. It will however be appreciated that this modification is equally applicable to the embodiment shown in Figure 2.

In order to maintain the back-pressure in the high-pressure section 4 which is necessary for operation a spring-loaded excess pressure valve 131 which opens in the direction of fuel flow shown by the arrow is provided in the return line 111. The spring of the excess pressure valve is set at the necessary back-pressure and ensures opening, for example, only above a back-pressure pressure of 0.5 bar.

The excess pressure valve 131 is advantageously integrally constructed, in a manner which is not shown, with the T-piece 130. In this manner manufacturing costs and assembly times can be reduced.

Claims

1. Afuel supply system for an internal combus tion engine including an injection pump upstream of which in the fuel flow path is an electrical heating device connected to a temperature control device.

2. A system as claimed in Claim 1 in which the heating device is immediately adjacent the high pressure section ofthe injection pump.

3. A system as claimed in Claim 1 or Claim 2 in which the heating device includes a heating rod located within a fuel supply passage.

4. A system as claimed in Claim 3 in which a helical member extends around the heating rod within the fuel supply passage thereby defining a helical flow passage for the fuel.

5. A system as claimed in any one of the preceding claims in which the electrical heating device includes a thermostat arranged adjacent its downstream end.

6. A system as claimed in any one of the preceding claims in which the electrical heating device has a thermally insulating casing.

7. A system as claimed in any one of the precdeding claims including a fuel delivery pump and a fuel return line extending between the high pressure section of the injection pump and the inlet line to the delivery pump.

8. A system as claimed in Claim 7 in which the fuel return line is connected to the inlet line to the delivery pump by means of a T connector upstream of which in the fuel return line is an excess pressure valve.

9. A fuel supply system substantially as specifically herein described with referenceto Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.

10. An internal combustion engine having afuel supply system as claimed in any one of the preceding claims.

11. An engine as claimed in Claim 10 having a fluid coolant circuit, the electrical heating device having a heating passage in thermal communication with the fuel flow passage and connected to the coolant circuit by means of a thermostatic valve.

12. An engine as claimed in Claim 11 including a first thermostatic valve arranged to open when the coolant temperature is above the switch-off temper- ature ofthe electrical heating device and situated at the point where the heating passage in the heating device communicates with the fluid coolant circuit.

13. An engine as claimed in Claim 12 including a second thermostatic valve arranged to close the heating passage in the heating device at a temperature above the opening temperature of the first thermostatic valve.

14. An engine as claimed in Claim 13 in which the second thermostatic valve is arranged at the downstream end of the heating passage in the heating device.

15. An engine as claimed in Claim 13 in which the first and second thermostatic valves constitute a single structural unit and the second thermostatic valve is arranged to pass a restricted volume of coolant fluid when it is closed.