GB2138496A

GB2138496A - Reducing fuel pressure rise at i.c.engine injectors

Info

Publication number: GB2138496A
Application number: GB08310210A
Authority: GB
Inventors: Rupert Maurice Taylor
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1983-04-15
Filing date: 1983-04-15
Publication date: 1984-10-24
Also published as: EP0122802A2; EP0122802A3; ES8503788A1; JPS59206669A; GB8310210D0; ES531493A0

Abstract

A filter 14 in each fuel line between a fuel injection pump and an injector has an internal chamber 28 within which pressure waves generated by the pump and travelling from an inlet 26 to an outlet 27 will be reflected to produce interference. The pressure pulse resulting from the reflection has a reduced rate of pressure rise at its leading end. <IMAGE>

Description

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GB 2 138 496 A 1

SPECIFICATION

Reducing combustion noise in a fuel-injected engine

5 This invention relates to the reduction of combustion noise from a fuel-injected engine, particularly a diesel engine. The invention provides a method and an apparatus for reducing this noise.

In a diesel engine, a fuel-injection pump produces a 10 pressure wave pulse in the high pressure fuel pipe which travels down the pipe to the injector where it causes a volume of fuel to be injected into the cylinder. The instantaneous mass flow of fuel into the cylinder depends on the pressure in the injector sac and, as it 15 burns, gives rise to pressure fluctuations in the cylinder which are related to those inthe high pressure fuel pipes. Inthisway, pressure fluctuations in the high pressure pipes aretranformed into and heard as combustion noise from the engine. 20 Thefrequency range of the combustion noise which isthe mostsignificant part of the sound spectrum is around 2000 Hz. This component of noise derives from the change of slope of the cylinder pressure atthe very start of combustion.

25 According to the present invention, there is provided a method of reducing combustion noise in a fuel injected engine, by including a wave filter in each fuel line between the injection pump and the injector, the filter being adapted to reduce the rate of rise of fuel 30 pressure atthe injector.

The invention also provides apparatusfor reducing combustion noise from a fuel-injected engine, the apparatus comprising a filterfor inclusion in a fuel line between the injection pump and an injector, the filter 35 having a chamber with an inletthereto and an outlet therefrom, and an internal wall against which pressure waves can be reflected, the distance between the inlet and the internal wall being greaterthan the distance between the inlet and the outlet, so that 40 pressure waves reflected by the internal wall will meet and interfere with incoming pressure waves from the inletto produce a resultant pressure wave which leaves the cham ber th roug h the outlet.

The invention will now be further described, byway 45 of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram showing the progress of a pressure wave pulse through a fuel injection system; and 50 Figure 2 shows a cross section through a filter according to the invention.

Figure 1 shows a fuel injection pump 10,afirstfuel line portion 12,afilter14,asecondfuel line portion 16 and an injector 18. In practice a number of injectors 18 55 areconnectedtoonefuel pump,through appropriate fuel lines and filters.

Below this hardware, the wave forms produced at the various stages of thefuel pipe are indicated. The plungers in thefuel injection pump produce a sharply 60 defined pressure wave 20. This pressure wave is modified by discontinuities in the pump and emerges into the high pressure fuel line portion 12 as a pressure pulse 22 with a high frequency oscillation superimposed. This oscillation, at about 12,000 Hz, does not make a significant contribution to the combustion noise. Instead it isthe initial slope of this pressure pulse which is the important parameter, and this slope is modified as the wave propagates down thefuel pipe.

In the classical anaylsis of pressu re waves in a fluid, it is assumed that thefuel is compressible. However, due to the high pressure levels obtaining in a system of this nature, it is not possible to make this assumption. The speed at which pressure waves propagate (the speed of sound) is greater at high pressures than at low pressures. This means that the high pressure part of the pulse moves faster than the low pressure part and the leading edge of the pulse steepens up into a Shockwave, as can be seen at 24. It is th is shock wave th at the filter 14 seeks to modify.

The filter itself is shown in more detail in Figure 2. It has an inlet 26 and an outlet 27. Both inlet and outlet are provided with nipples onto which the fuel lines 12 and 16can be fitted. The filter has a chamber 28. The inlet through passage 26 opens into one end of this chamber. The outlet 27 leaves the chamberthrough a pipe 29 which extends across the chamber 28 nearly to the position of the inlet 26. The actual dimensions of the chamber 28 and the position of the end of the tube 29 relative to the inlet 26 will be determined in accordance with the characteristics of the pressure waves to be filtered. The incoming pressure wave 24 spreads out in the chamber 28 and is reflected between the end faces 30 and 31. The reflected waves will then interfere with unreflected waves entering through the inlet 26, to produce a new, transmitted pulse 32 constructed from reflected waves. This pressure pulse is smooth and has a reduced rate of rise of pressure atthe leading edge.

This new pulse 32 travels to the injector and steepens as it is propagated to a shape 34, but still has a lower rate of rise than normal. As a consequence, the rate of rise of pressure in the engine cylinder is reduced, because the initial fuel mass flow rate into the cylinder is reduced. The result is less noise. CLAIMS

1. A method of reducing combustion noise in a fuel injected engine, by including a filter in each fuel line between the injection pump and the injector, the filter being adapted to reduce the rate of rise of fuel pressure atthe injector.

2. An apparatusfor reducing combustion noise from a fuel-injected engine, the apparatus comprising a filter for inclusion in a fuel line between the injection pump and the injector, thefilter comprising a chamber having an inletthereto and an outlet therefrom, and an internal wall against which pressure waves can be reflected, the distance between the inlet and the internal wall being greater than the distance between the inlet and the outlet, so that pressure waves reflected by the internal wall will meet and interfere with incoming pressure waves from theinlet to produce a resultant pressure wave which leaves the chamberthrough the outlet.

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The drawing(s) originally filed was/were informal and the print here reproduced is taken from a later filed formal copy.

Claims

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GB2 138 496 A
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3. An apparatusfor reducing combustion noise fr Dm a fuel injected engine, substantially as herein described with reference to the accompanying drawing.

Printed in the United Kingdom for Her Majesty's Stationery Office, 8818935, 10/84,18996. Published at the Patent Office, 25 Southampton Buildings, London WC2A 1AY, from which copies may be obtained.

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