AU672495B2 - Recirculation of fuel - Google Patents

Description

40086DIV(2) AWT:MH P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

.I

Name of Applicant: 0(rV Wi.v-, Srr, M Name of inventor: MANOS KAVARNOS Address for Service: COLLISON CO.,117 King William Street, Adelaide, S.A. 5000 Invention Title: RECIRCULATION OF FUEL Details of Associated Applications: 90155/91 and 90192/91 made by BIOCOM PTY LTD The following statement is a full description of this invention, including the best method of performing it known to us: FIELD OF THE INVENTION This invention relates to an apparatus and a method of fuel injection and more particularly to the injection of low boiling point liquid fuels into an engine in liquid form.

As an example of a low boiling point liquid fuel Liquid Petroleum Gas is a good fuel for motor vehicles as it has a high calorific value per unit volume at high pressures and is particularly good in the liquid form as it does not So require very high pressure tanks to store it. The liquid does have a relatively high vapour pressure and particularly at very high engine operating Si: temperatures there is a danger that the LPG can vaporize and exhibit poor injection characteristics. It is desirable therefore to maintain injectors at a temperature at which the fuel is liquid and to inject LPG into a motor vehicle engine at a pressure which ensures the LPG is in liquid form at the highest ambient temperatures but this may require a very large pump to maintain a high constant pressure because of the low vapour pressure of the LPG in cold weather. Such a large pump can be relatively heavy and have a very high power draw so that in fact it may be necessary to actually drive the LPG pump directly from the engine rather than as an electric pump.

It is the object of this invention to provide an apparatus and a method of injecting low boiling point liquid fuels which does not require such an energetic pump but maintains the fuel in liquid form.

BRIEF SUMMARY OF THE INVENTION In one form therefore the invention is said to reside in a fuel injection arrangement for an internal combustion engine comprising a fuel rail system supplying LPG to at least one injector to inject LPG into an inlet manifold of the engine and an electronic control unit SRA4, 1$(TO arrangement acting upon engine parameters and demand parameters for the LPG to determine injector timing for the LPG, and the or each injector is of a bottom feed type of injector and excess LPG is recirculated through the or each injector, wherein the fuel rail system comprises a tank for the LPG, a fuel pump to raise the pressure of the LPG a fixed differential above the vapour pressure of the LPG in the tank, a LPG supply line from the pump to the or each injector, a return LPG line from the or each injector to the tank and a 10 LPG pressure regulator in the return LPG line.

ae The or each injector may be a flow through type.

*eo.

The fuel rail system may be of a low heat capacity construction so it can be easily cooled by the recirculating flow of the fuel.

The fuel pressure regulator in the return fuel line may be incorporated in the non-return valve in the second fuel outlet.

In an alternative form the invention may be said to reside in a method 'of operating a fuel injection system for an internal combustion engine including a fuel rail system supplying LPG to at least one injector to inject LPG into an inlet manifold of the engine and an electronic control unit arrangement acting upon engine parameters and demand parameters for the LPG to determine injector timing for the LPG wherein the LPG is stored in a tank and has a vapour pressure in the tank dependant upon ambient temperature, the method including the steps of recirculating excess LPG through the at least one injector to maintain cooling of the at least one injector, pumping the LPG to ,n operating pressure a fixed differential above the vapour pressure and monitoring the absolute pressure of the LPG and varying LPG injection timing for the LPG dependant upon the absolute pressure determined.

Preferably the fuel is a low boiling point liquid fuel.

The absolute pressure of the fuel may be determined directly by the use of a pressure transducer or alternatively it may be determined by indirect methods such as to monitor the temperature and the density of the fuel and this will enable a determination of the absolute pressure.

In a preferred form of the invention the low boiling point liquid fuel may be Liquid Petroleum Gas (LPG) and the invention will be discussed in relation to this fuel. Petrol may also be used with the method of the invention in a :10 closed fuel system which will prevent the release of hydrocarbons into the a o atmosphere.

It will be seen that by this invention there is provided an arrangement by which only a relatively small pump is required to raise the pressure of the low boiling fuel such as LPG a fixed amount above that vapour pressure thereby 15 ensuring that the LPG will stay liquid at operational temperatures and flow rates.

*o.

This invention preferably provides that the injectors are of a bottom feed flowthrough type so that with a considerable excess to the amount of fuel a necessary for supplying to the engines flowing through the injectors there is considerable absorbing of heat which is taken away to the fuel tank. This will assist in prevention of vaporisation of the fuel in the injector.

In one particular example for instance using petrol the ratio of circulating to used flow may range from 100:1 for idling to 3:1 at full power.

For LPG there may be 230:1 circulating to used flow at idle and 7:1 circulating to used flow at full power. The actual flow rate of LPG in the system may be 270 litres per hour of liquid LPG.

In one particular example LPG may have a vapour pressure of from 300 to 1500 kilopascals dependant on ambient temperature and the differential pressure may be 150 to 300 kilopascals. This means that the absolute 10 pressure of the LPG can range from as low as 450 kilopascals up to as "high as 1800 kilopascals and hence the LPG injection timing can be varied to ensure that the correct amount of LPG is injected dependent upon that absolute pressure.

The advantage of this arrangement is that a fixed size and power output pump is needed and in fact a relatively low pressure and high flow rate pump is needed to at all times ensure that sufficient LPG entering the injectors is in liquid form and recirculated.

For the present invention there may be used an electric fuel pump of a constant speed roller cell, positive displacement gear or turbine type.

Such pumps deliver a constant pressure and volume of fuel which is always more than the engine needs. The operating pressure variation of the system therefore is due to the vapour pressure changes of LPG inside the tank and not solely to the discharge pressure of the pump. Therefore the pressure variation depends on the absolute pressure of the liquid in the suction side of the pump i.e. tank pressure.

In an alternative form the invention may be said to reside in a fuel injection system for an internal combustion engine operating on a low boiling point liquid fuel comprising a tank for storage of liquid fuel, a pump means to raise the pressure of the fuel in fuel rail means, the fuel rail means extending to an injector or injectors for the fuel, the pump means adapted to raise the pressure of the fuel to a fixed pressure differential ahove the tank pressure, fuel return means extending from the injector or injectors to the tank and pressure regulation means in the fuel return means to regulate the pressure of the fuel in the fuel rail means.

As in the earlier form of the invention in a preferred form of the invention the low builing point liquid fuel may be Liquid Petroleum Gas (LPG).

The pressure in the fuel rail may be monitored by a pressure sensor which feeds back to a control unit for the engine for adjusting the injection timing from a series of look up tables that correspond to various operating *10 pressures. Alternatively the control unit may include a processing unit S• using a formula to calculate from the operating pressure and other variables.

The fuel pressure regulator may be incorporated in a non-return valve with a fixed spring of a certain cracking pressure.

15 It will be seen that by this invention there is provided a way of economically ensuring that LPG is maintained in a liquid state in injectors by raising the pressure only a certain amount above the vapour pressure at the ambient temperature.

DETAILED DESCRIPTION 20 This then generally describes the invention but the invention will now be discussed in relation to a preferred embodiment as shown in the accompanying drawing in which: FIGURE 1 shows a stylized fuel recirculation and injection system for an internal combustion engine.

In the drawing, FIGURE 1, it will be seen that an engine 1 has cylinders 2,3,4 and 5. Combustion air enters by means of inlet manifold 6 and exhaust exits through exhaust manifold 7. A low boiling point liquid fuel such as LPG is injected into each inlet manifold for each cylinder by means of injectors 8, 9, 10 and 11. A fuel rail means consists of a inlet rail extending to the injectors and a outlet fuel rail 16 withdrawing fuel from each injector. The injectors provide an essentially open flow path between the inlet rail 15 and the outlet rail 16 thereby allowing recirculating flow of fuel.

A fuel tank 17 has a fuel exit 18 and a fuel withdrawl line 19 extending to a fuel pump 20. The fuel pump 20 pumps fuel to the fuel inlet rail 15 via line 21 and filter 22. A pressure gauge 23 measures the absolute pressure of fuel in the fuel rail means and a pressure regulator 24 in the outlet fuel rail 16 allows a desired pressure differential between the tank pressure and 9.-.the rail pressure to be maintained. Return line 26 extends from the "°°pressure regulator 24 to the fuel tank 17.

The pressure of the fuel in the fuel tank 17 is determined by the vapour pressure of the fuel in the tank which in turn is determined by the ambient temperature surrounding the fuel tank. The vapour pressure may be from 300 to 1500 kilopascals. The pump 20 is of sufficient power to raise the S°pressure of the fuel by 150 to 300 kilopascals and hence the absolute pressure in the fuel rails may be from 450 to 1800 kiiopascals. The actual 20 timing of the injectors 8, 9, 10 and 11 can be determined by the usual 9 engine parameters as well as the absolute pressure of fuel in the inlet rail as determined by the pressure gauge 23.

99 9 o•