Method for determining the bulk modulus of fuels

Abstract

A method for determination of the bulk modulus of fuels in a fuel system of a combustion engine (2) with a common rail injection system (6), with a high pressure volume (16) including the high pressure side of a high pressure pump (9) and a fuel accumulator (8) with injectors (7) for injection of fuel into the cylinders of the combustion engine. The method including: first determining the volume of the high pressure volume by supplying a fuel with a known bulk modulus to the fuel system and by controlling the high pressure pump (9) so that it performs a pump stroke with the volume of the high pressure volume closed. The value of the determined volume is later used with another fuel in order to determine the latter fuel's bulk modulus.

Claims

1. A method for determining a bulk modulus of fuels in a fuel system of a combustion engine, the engine having cylinders and having a common rail fuel injection system, with a high pressure volume comprising the high pressure side of a high pressure pump and a fuel accumulator with injectors for injecting fuel into the cylinders of the combustion engine or for being closed; the method comprising the steps: 1) determining a volume (V) of the high pressure volume by: a) supplying a fuel with a known bulk modulus (B.sub.0) to the fuel system; b) controlling the high pressure pump to perform a pump stroke to supply a given amount (M) of fuel to the high pressure volume while keeping the injectors closed; c) measuring the fuel pressure (P.sub.1) in the high pressure volume before and the fuel pressure after said pump stroke (P.sub.2), and as a result, determining the fuel pressure increase (P) achieved by the pump stroke; d) measuring the temperature (T) of the fuel; and e) calculating the volume (V) of the high pressure volume, based on the values of the temperature (T), the fuel pressure increase (P), the amount (M) of fuel supplied and the fuel's bulk modulus (B.sub.0); and 2) subsequently, with other fuel in the high pressure volume, carrying out the steps b)-d) and then calculating the bulk modulus (B) of the fuel, based on the fuel's temperature (T), the pressure increase (P) and the volume (V) of the high pressure volume calculated in step 1).

2. A method according to claim 1, further comprising performing steps 1) a first time the fuel system of the combustion engine starts operation, in order to calculate a value for the volume (V) of the high pressure volume to be used at the performance of step 2) during the subsequent operation of the combustion engine.

3. A method according to claim 1, performed in a fuel system of a combustion engine in a motor vehicle.

4. A method according to claim 1 further comprising performing step 2) in connection with fuel being filled into a fuel tank of the fuel system.

5. A method according to claim 4, further comprising performing step 2) each time fuel has been filled into the fuel tank.

6. A computer program product comprising: a data storage medium which is readable by a computer; a computer program stored in a non-volatile internal memory of a computer, the computer program comprises a computer program code configured to cause the computer to control the method steps according to claim 1, when the computer program is executed in the computer.

7. An electronic control device configured for determining a bulk modulus of fuels in a fuel system of a combustion engine including a common rail fuel injection system, the device comprising: an execution means, a non-volatile memory connected to the execution means and a data storage medium connected to the execution means, the computer program code in the computer program product according to claim 6 being stored on the data storage medium.

8. A motor vehicle comprising the electronic control device according to claim 7, and the vehicle is a wheeled motor vehicle, a truck or a bus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Below are descriptions of example embodiments of the invention with reference to the enclosed drawings, in which:

(2) FIG. 1 is a schematic drawing of a combustion engine with a common rail fuel injection system in which a method according to the invention may be applied,

(3) FIG. 2 is a flow chart showing a method according to one embodiment of the invention, and

(4) FIG. 3 is a diagram of an electronic control device for the implementation of a method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS ACCORDING TO THE INVENTION

(5) With reference to FIG. 1, a fuel system in a combustion engine, with a common rail injection system to which the method according to the invention is applicable, is described below. A driveline 1 in a motor vehicle comprises a combustion engine 2, e.g. a diesel engine, which is connected to driving wheels (not displayed) of the vehicle via a coupling 3 and a gearbox 4.

(6) The combustion engine 2 comprises several, for example four, schematically indicated cylinders 5. The number of cylinders may naturally be different. Fuel is supplied to the cylinders with the help of a common rail fuel injection system 6, comprising a plurality of electrically controlled injectors 7. Each cylinder of the combustion engine 2 is assigned its own injector. The injectors 7 are connected to a fuel accumulator 8 in the form of a so-called common rail, which includes an accumulator for accumulation of high pressure fuel to be supplied to the injectors. The fuel accumulator 8 is supplied with pressurised fuel by a high pressure pump 9, which receives fuel from a fuel tank 10 of the vehicle 11. The injectors 7 are connected to the fuel accumulator 8 via fuel conduits 12, which branch from the fuel accumulator in order to inject fuel accumulated in the fuel accumulator 8 into the respective cylinders.

(7) An electronic control device 13 is configured for control of the injectors 7 for fuel injection into the respective cylinders. The electronic control device is also adapted to control the high pressure pump 9. A pressure sensor 14 is configured to measure the fuel pressure in the fuel accumulator 8 and send information regarding the measured fuel pressure to the electronic control device 13. Further, a temperature sensor 15 is configured to measure the temperature of the fuel in the fuel accumulator.

(8) A high pressure volume 16 of the fuel system is defined by the volume containing fuel, and lies between the high pressure side of the high pressure pump and the injectors. In order to calculate the volume of this high pressure volume, the electronic control device 13 is configured to control the high pressure pump 9 so that it carries out pump strokes with closed injectors, which means that, via known data of the high pressure pump, the amount of fuel fed into the high pressure volume is thus known. If this has not been done previously, it should be carried out for a fuel with a known bulk modulus B.sub.0.

(9) FIG. 2 shows a flow chart illustrating a method according to one embodiment of the invention for determination of the bulk modulus of fuels in a fuel system of the type described above. In a first step S.sub.1 the question is asked, if it is the first time the fuel system is taken into operation. If the answer to this question is yes, in a second step S.sub.2 a fuel with a known bulk modulus B.sub.0 is supplied to the fuel system, whereupon the fuel pressure P.sub.1 is measured via the sensor 14 in the high pressure volume. Subsequently, the high pressure pump 9 is controlled so that it carries out a pump stroke to supply the amount M of fuel to the high pressure volume, whereupon the fuel pressure P.sub.2 in the high pressure volume is again measured in step S.sub.5. Subsequently, the fuel pressure increase P achieved by the pump stroke is calculated in step S.sub.6. Subsequently, or in parallel with or in connection with the previous step, the temperature T of the fuel is measured in step S.sub.7. Then the question is asked again, if it is the first time the fuel system is taken into operation. If the answer to this question is yes, in step S.sub.9 the volume V of the high pressure volume is calculated based on B.sub.0, P, T and M. If, however, the answer to the question is no, the fuel's bulk modulus B is calculated in step S.sub.11, based on V, P, T and M.

(10) When, subsequently, the fuel system is filled up with new fuel, and the volume V of the high pressure volume is already determined, the answer to the question in step S.sub.1 will be no, and fuel with an unknown bulk modulus B will be supplied in order to subsequently have its bulk modulus calculated in step S.sub.11.

(11) A computer program code for the implementation of a method according to the invention is suitably included in a computer program, loadable into the internal memory of a computer, such as the internal memory of an electronic control device of a combustion engine. Such a computer program is suitably provided via a computer program product comprising a data storage medium readable by an electronic control device, which the data storage medium has the computer program stored thereon. The data storage medium is e.g. an optical data storage medium in the form of a CD-ROM, a DVD, etc., a magnetic data storage medium in the form of a hard disk drive, a diskette, a cassette, etc., or a Flash memory or a ROM, PROM, EPROM or EEPROM type memory.

(12) FIG. 3 illustrates very schematically an electronic control device 13 comprising execution means 17, such as a central processor unit (CPU), for the execution of a computer software. The execution means 17 communicates with a memory 18, e.g. a RAM memory, via a data bus 19. The control device 13 also comprises a data storage medium 20, e.g. in the form of a Flash memory or a ROM, PROM, EPROM or EEPROM type memory. The execution means 17 communicates with the data storage means 20 via the data bus 19. A computer program comprising computer program code for the implementation of a method according to the invention, e.g. in accordance with the embodiment illustrated in FIG. 2, is stored in the data storage medium 20.

(13) The invention is obviously not limited in any way to the embodiments described above, but numerous possible modifications thereof should be obvious to a person skilled in the area, without such person departing from the spirit of the invention as defined by the appended claims.

(14) It is implicit that the high pressure volume must be pressurised before carrying out step b) of the method according to the invention.