AU2011204939A1 - Fuel rail - Google Patents

Abstract

A fuel injection system 10 for supplying a low boiling point fuel and a second fuel to an engine, the system including one or more injectors 12 for injecting low boiling point fuel as a liquid; a supply conduit 26A upstream of the injectors for supplying liquid low 5 boiling point fuel from a source to the injectors, and a return conduit 26B downstream of the injectors for returning low boiling point fuel to the source, the return conduit 26B being thermally coupled to the supply conduit to cool the supply conduit; 26A, one or more further injectors 12' for injecting the second fuel; and a controller 30 controlling the injectors to supply a selected one or both of the low boiling point fuel and the second 10 fuel to the engine. ~(D w (00 >14 00 b I

Description

P100/011 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Fuel rail The following statement is a full description of this invention, including the best method of performing it known to us: 2 Fuel rail Field of the invention The invention relates to supplying a low boiling point fuel and second fuel to an engine. Background of the invention 5 From time to time it is desirable that an engine be capable of alternately or simultaneously running on more than one type of fuel. Recently, there has been an increasing interest in transport fuels which can be used in conjunction with or as an alternative to conventional petroleum liquid fuels. By way of example, vehicles including conventional spark ignition engines intended to consume 10 conventional petroleum (hereinafter 'petroleum') are sometimes supplied with petroleum blended with a large proportion of ethanol. Due to the similar nature of these fuels, the substitution of one for the other is typically unproblematic and does not require any change to the vehicles' conventional fuel injection systems. In contrast to fuels such as petroleum, ethanol and diesel which are liquids at normal 15 atmospheric conditions. Low boiling point fuels such as liquid petroleum gas (LPG) are gaseous at normal atmospheric conditions . Petroleum is typically stored in a tank at more or less atmospheric pressure and supplied to the manifold of the engine, or more recently directly to the cylinder bores, via injectors. Low boiling point fuels are typically stored within high pressure tanks in liquid 20 form. Thus, supplying a low boiling point fuel and another fuel such as petroleum, ethanol or diesel to an engine presents a range of challenges due to the different characteristics of the fuels. Various prior art approaches to using low boiling point fuels have involved supplying the 25 fuel in vapour form to the induction path of the engine. Such systems are referred to as 3 vapour systems'. Vapour systems have the draw back that the gaseous fuel supplied to the engine has a relatively large volume compared to an equivalent amount of petroleum. As such, the calorific value of an air fuel mixture which can be drawn into a cylinder for each intake stroke is relatively less than when petroleum is used. This 5 results in engines equipped with vapour systems producing less power than equivalent engines operating on petroleum. A more recent approach to the supply of low boiling point fuels involves supplying the fuel to the engine manifold via fuel injectors which produce a finely metered spray of liquid. It has been found that fuel so injected expands resulting in the intake charge 10 being cooled. This offsets the larger volume occupied by the fuel itself. As such, liquid injection systems are generally viewed as an improvement over vapour systems. However, liquid injection systems are not without their problems. Low boiling point fuels by their very nature require relatively high pressures in order to be kept in their liquid state. The task of maintaining the fuel in its liquid state is made more difficult by the 15 elevated temperatures about an operating engine. As such, a range of approaches for dealing with this problem have been developed. International patent application no. WO 2002/081895 Al describes an engine which operates on diesel and LPG. The diesel is injected directly into the cylinder bore. Liquid LPG is injected into the intake manifold via an injector. Upstream of the injector, 20 vapour is separated from the liquid LPG and directed over an exterior of the injector to cool the injector. The vapour is subsequently delivered to the intake manifold, or in some variants of the system to another location for use or storage. It is an object of the invention to provide an improved fuel injection system or at least to provide alternatives for those concerned with fuel injection. 25 It is not admitted that any of the information in this specification is common general knowledge, or that the person skilled in the art could reasonably be expected to have ascertained, understood, regarded it as relevant or combined it in any way at the priority date.

4 Summary of the invention Accordingly in its various aspects the invention provides fuel injection systems, components therefor and methods of injecting fuel. One aspect of the invention provides a fuel injection system for supplying a low boiling 5 point fuel and a second fuel to an engine, the system including one or more injectors for injecting low boiling point fuel as a liquid; a supply conduit upstream of the injectors for supplying liquid low boiling point fuel from a source to the injectors, and a return conduit downstream of the injectors for returning low boiling point fuel to the source, the return conduit being thermally coupled 10 to the supply conduit to cool the supply conduit; one or more further injectors for injecting the other fuel; and a controller controlling the injectors to supply a selected one or both of the low boiling point fuel and the second fuel to the engine. Optionally one or both of the supply conduit and the return conduit is defined by a 15 tubular structure carrying the low boiling point fuel injectors. The system may include a pump and/or a restriction device controlling pressure in the return conduit to boil the low boiling point fuel. Optionally, the injectors are arranged in parallel to connect the supply conduit to the return conduit, in which case an or the restriction device may be provided to connect the supply conduit to the return conduit in 20 parallel to the injectors. Preferably, one of the supply conduit and the return conduit substantially embraces, surrounds,is contained within or is concentric with the other of the supply conduit and the return conduit. The supply conduit and the return conduit may be substantially defined by an integrally formed structure.

5 Brief description of the figure Figure 1 is a schematic view of a fuel supply system including a fuel injection system in accordance with an embodiment of the invention; Figure 2 is a more detailed schematic illustration of a portion of the fuel supply system 5 of Figure 1; Figure 3 is perspective view of a fuel rail portion and an injector; and Figure 4 is a perspective cutaway view of the components of Figure 3. Detailed description of the embodiments Figure 1 shows a fuel supply system 1 for alternately supplying a selected one of LPG 10 and petroleum. The supply system 1 includes a fuel injection system 10, fuel tanks 16, 16' and fuel lines 18, 18', 20, 20'. The supply system 1 includes an LPG supply system 2 and a petroleum supply system 2'. It is also contemplated that according to other variants of the system 1, that the supply system 2' might instead supply diesel. 15 The LPG supply system 2 is illustrated in more detail in figure 2. It includes the tank 16 in which is mounted a pump 14. The pump 14 drives LPG in liquid form from the tank 16 along supply line 18 towards the supply side of fuel rail 26. Fuel rail 26 includes supply conduit 26A and return conduit 26B. Fuel injectors 12 are 'flow through injectors' meaning that only a portion of the fuel they receive is injected, the remainder flows 20 through the injector, typically to a fuel return line. The injectors 12 and a restriction device in the form of damper 28 are mounted in parallel between the supply conduit 26A and the return conduit 26B so that the supply conduit is on their upstream side and the return conduit 26B is on their downstream side. In the described embodiment the injectors 12 are top feed injectors so no injector housing is required. 25 Fuel from return conduit 26B is returned to the tank 16 via the return path 20 to complete a fuel circuit 22. The pump 14 drives fuel about the circuit 22 and damper 28 6 restricts flow about the circuit 22. The pump is preferably a variable speed pump to assist with controlling the pressure in the supply system. The flow path may further include a flow restriction 40 on the return side of the tank 16 to control pressurein the return line. The flow restriction may be a fixed orifice or a variable orifice. 5 The petroleum supply system 2' similarly includes injectors 12', pump 14', tank 16', lines 18' & 20', and fuel rail 26'. A controller 30 coordinates the operation of the LPG injectors 12 and the petroleum injectors 12'. Some embodiments of the invention can take the form of a 'retro fit system'; e.g. the LPG supply system 2 and control components might be added to an engine having a 10 petroleum supply system 2'. The added control components may replace or cooperate with existing control components to form the controller 30. By way of example, the added control components may intercept a signal from a pre existing controller to the injectors 12', and apply logic to signal to control the injectors 12. Figures 3 and 4 illustrate a preferred form of the fuel rail 26 and an injector 12. 15 The fuel rail 26 is predominately formed from an extruded alloy body which is integrally formed and defines supply conduit 26A and return conduit 26B. The alloy is selected for its relatively high thermal conductivity. The supply conduit 26A is a cylindrical aperture formed centrally within the rail 26. The return conduit 26B is an annular space formed in rail 26. The conduit 26B circumferentially surrounds a substantial portion of the 20 supply conduit 26A and as such substantially embraces the supply conduit 26A. The supply conduit 26A and the return conduit 26B are thermally coupled by the tubular wall separating the conduits 26A and 26B. This has the significant advantage in that fuel in the return conduit 26B cools the fuel in the supply conduit 26A by heat exchange. Desirably, the pressure drop between the fuel conduits 26A and 26B is selected or 25 controlled so that fuel from the injectors 12 vapourises to have a refrigerant effect to cool the supply fuel. In this embodiment the pressure drop is up to 6 bar. Generally the greater the pressure drop the greater the refrigerant effect.

7 According to this embodiment, the injectors 12 include an internal restriction selected so that the fuel starts to boil as it passes through the injectors. As such, both the injectors (including their windings) and incoming fuel are cooled by boiling fuel. Desirably the cross sectional area of the return conduit 26B is larger than the supply conduit to 5 accommodate the expanding fuel. In this embodiment the ratio of the cross sectional areas are about 1.9, say between 1.7 and 2.1. It is also contemplated that embodiments of the invention might include a fuel rail formed of other materials having relatively lower thermal conductivity. By way of example, the fuel rail 26 might be formed of plastic. This would of course reduce the 10 efficiency of the heat exchange between the supply conduit 26A and the return conduit 26B, but this reduction in efficiency is offset by the improved insulation between the supply conduit 26A and the elevated under bonnet temperatures to which an exterior of the fuel rail 26 is exposed. A desirable arrangement would involve an outer wall of the rail 26 being formed of a material having low thermal conductivity (eg plastic) and the 15 wall of the supply conduit 26A being formed of a material having high thermal conductivity (eg an alloy). As shown in figure 3, the cylindrical wall defining the supply conduit 26A is carried by a vertical web of material 27 radially spanning the return conduit 26B. As shown in figure 4, the injector 12 communicates with the supply conduit 26A via a vertical aperture 29 20 through the vertical web 27. The injector 12 includes a nipple embraced by two 0-rings by which it is sealingly engaged with the vertical aperture 29. The rail 26 includes at its lower extent a pair of short horizontal flanges extending in opposite directions to define a pair of side grooves 32. The injector is carried in a housing 33. A retaining ring 30 embraces the rail 26 and engages with the housing 33. 25 This engagement together with the engagement of injector 12 with the vertical aperture 29 restrains the injector 12 against moving away from or along the rail 26. The housing 33 includes a pair of hooks 34 on each of it sides. The hooks 34 engage with side grooves 32 to restrain the injector against pivotal movement about the engagement with the vertical aperture 29.

8 Desirably, in this embodiment, the supply conduit 26A and the return conduit 26B respectively communicate with the fuel lines 18 and 20 at the same end of the rail, and the other end of the rail is capped by the damper 28. As such the rail 26 forms a counter-flow heat exchanger. 5 It is preferred that the fuel lines 18 and 20 take the form of separate flexible conduits. It is thought that concentric fuel lines are generally less flexible and therefore more difficult to route through an engine bay. It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features 10 mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims (11)

1. A fuel injection system for supplying a low boiling point fuel and a second fuel to an engine, the system including one or more injectors for injecting low boiling point fuel as a liquid; 5 a supply conduit upstream of the injectors, for supplying liquid low boiling point fuel from a source to the injectors, and a return conduit downstream of the injectors for returning low boiling point fuel to the source, the return conduit being thermally coupled to the supply conduit to cool the supply conduit; one or more further injectors for injecting the other fuel; and 10 a controller controlling the injectors to supply a selected one or both of the low boiling point fuel and the second fuel to the engine.

2. The system of claim 1 wherein one or both of the supply conduit and the return conduit is defined by a tubular structure carrying the low boiling point fuel injectors.

3. The system of claim 1 or 2 further including a pump and/or a restriction device 5 controlling pressure in the return conduit to boil the low boiling point fuel.

4. The system of claim 1, 2 or 3 wherein the low boiling point fuel injectors are arranged in parallel to connect the supply conduit to the return conduit.

5. The system of claim 4 including an or the restriction device connecting the supply conduit to the return conduit in parallel to the low boiling point fuel injectors. 20

6. The system of any one of claims 1 to 5 wherein one of the supply conduit and the return conduit substantially surrounds, is contained within or is concentric with the other of the supply conduit and the return conduit. 10

7. The system of any one of claims 1 to 6 including an integrally formed structure substantially defining the supply conduit and the return conduit.

8. The system of any one of claims 1 to 7 wherein the low boiling point fuel is LPG.

9. The system of any one of claims 1 to 8 wherein the other fuel is petroleum. 5

10. The system of any one of claims 1 to 8 wherein the other fuel is diesel.

11. The system of any one of claims 1 to 10 wherein the cross sectional area of the return conduit is about 1.9 times the cross sectional area of the supply conduit.