GB2235950A

GB2235950A - Engine pre-combustion chamber

Info

Publication number: GB2235950A
Application number: GB9017849A
Authority: GB
Inventors: Mario Brighigna
Original assignee: VM Motori SpA
Current assignee: VM Motori SpA
Priority date: 1989-09-12
Filing date: 1990-08-15
Publication date: 1991-03-20
Also published as: IT8903618A0; IT1235594B; GB9017849D0; DE4025997A1

Abstract

The chamber 6 comprises a hemi-spherical portion 6a into which the nozzle of a fuel injector 5 emerges, a substantially spherical portion 6b housing a glow plug 7 and a portion 6c connecting with the main combustion chamber 4 by way of a duct 9. Dimensional relationships are given in the specification. <IMAGE>

Description

1 1 A pre-combustion chamber for compression-ignition engfnes The present

invention relates to a pre-combustion chamber, suitable in particular for compression ignition engines such as the Diesel.

In engines of the type in question, fuel can be injected into the combustion chambers by one of two methods, namely by direct injection or by indirect injection.

With the direct system, the injector is positioned such that its nozzle is oriented straight toward the combustion chamber, which in most instances will be formed in the piston and facing back toward the cylinder head. Thus, the injector squirts the fuel directly into the combustion chamber.

In the indirect system, by contrast, the injector and the main combustion chamber are separated by a further chamber, or pre-combustion chamber; this means in effect that, the space in which combustion occurs is distributed between two chambers, the one formed conventionally in the piston, and the other, the pre-combustion chamber, in the cylinder head.

2 The two chambers are interconnected by one or more pass-ages of relatively narrow section. In this type of structure, the fuel is injected generally toward the end of the compression stroke, by an injector mounted in the pre-combustion chamber and oriented substantially in the direction of the passages that connect the two chambers.

Part of the fuel sprayed from the nozzle burns in the pre-combustion chamber; this causes a rise in pressure, the effect of which being to force the remaining unburned fuel through to the in-piston chamber and thus into contact with the air needed to bring about its full combustion.

Indirect fuel injection is used almost exclusively in engines of small/medium displacement, inasmuch as it allows lower maximum pressures at the piston, hence smoother operation and the possibility of higher running speeds, and by logical extension, higher specific output per unit of displacement.

Conversely, there are objective drawbacks connected with the construction of pre-combustion -chambers, hence the general preference for direct injection, especially when engine dimensions allow; in effect, the inclusion of a pre-combustion chamber involves notable complications in cylinder head design.

3 Following extensive experiment both theoretical and pradtical, the applicant has contrived to embody a pre-combustion chamber in which the particufar geometry and arrangement of the salient features are such as to achieve higher efficiency both at high and at low engine speeds.

Accordingly, the object of the present invention is to overcome the drawbacks mentioned by designing a pre-combustion chamber of which the configuration permits a notable efficiency in operation, as well as facilitating embodiment of the head containing the chamber, precisely by virtue of the design and construction features adopted.

The stated object is realized in a pre-combustion is chamber as characterized in the appended claims, of which the shape, viewed in section, appears as three sectors connected in unbroken continuity one with the next: a first sector of substantially hemispherical shape, into which the nozzle of the injector emerges, a second, fully spherical sector exhibiting a wider radius than that of the first and accommodating a glow plug that extends in a direction substantially transverse to the chamber, and a third sector exhibiting a substantially flat bottom and connected with the combustion chamber by 4 way of a duct that is angled in relation to the longitudinal axis of the pre-combustion chamber.

Among the advantages of the present invention is that the particular geometry of the pre-combustion chamber enables an improved balance of turbulence values at both high and low speeds of rotation, especially with the engine running at full load; moreover, the position of the glow plug ensures better starting of the engine from cold, and the stabilization of combustion at optimum parameters in a particularly short time.

The invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which:

-fig 1 is a section through the pre-combustion chamber according to the invention, incorporated into a cylinder head; -fig 2 is the section through II-II of fig 1, seen on larger scale.

With reference.to the accompanying drawings, the pre-combustion chamber according to the invention is intended for cdmpression-ignition engines, such as Diesels for example, comprising a crankcase 1 accommodating a plurality of pistons 2 reciprocated in the direction denoted F, and a cylinder head 3, fitted over the crankcase 1 and combining therewith to form a corresponding plurality of combustion chambers 4.

denotes a conventional fuel injector accommodated by and mounted to the cylinder head 3, of which the nozzle end emerges into a pre-combustion chamber incorporated into the head 3 and denoted 6 in its entirety. The pre-combustion chamber 6 is located between the injector 5 and the combustion chamber 4 (with which it connects), and accommodates a glow plug 7 serving to warm the pre-combustion enclosure when starting the engine and thus favour combustion of part of the fuel sprayed in by the injector 5.

According to the invention, the pre-combustion chamber 6 appears in axial section (see fig 1) as three sectors denoted 6a, 6b and 6c, connected one to the next with no break in continuity. The first sector 6a exhibits essentially hemispherical shape, and it is into this sector that the nozzle of the injector 5 dispenses. The second sector 6b, a full sphere truncated through two parallel planes, is of radius R2 wider than the radius Rl of the first sector 6a, and supports the transversely disposed glow plug 7. The third sector 6c provides the base of the pre-combustion chamber 6, and presents a 6 flat bottom 8 connecting with the main combustion chamber 4 by way of a duct 9 angled in relation to the longitudinal axis x of the pre-combustion chamber 6; the bottom 8 and the side wall of the third sector 6c are merged at a tight radius R3 such as will ensure that fuel is favoured with a swirling motion internally of the pre-combustion chamber while remaining unaffected by flow to and from the inpiston combustion chamber 4.

The upper part of t he pre-combustion chamber 6, i.e. the first and second sectors 6a and 6b, are integrated into the cylinder head proper, whereas the third sector 6c is formed in an insert 10 that registers in a corresponding socket afforded by the head 3; this insert incorporates the angled duct 9, and is fashioned from a material possessing notable resistance to heat, given that considerably high temperatures will be concentrated along the duct 9 during operation.

A preferred dimensional ratio between the radius R1 of the first sector 6a and the radius R2 of the second sector 6b will be between 0.73 and 0.76.

To reiterate, the injector 5 emerges into the first hemispherical sector 6a, and more exactly, enters from above at a given angle a (350 or thereabouts) 7 from the longitudinal axis x of the pre-combustion chamber 6; the axis 5x of the injector 5 and the axis 9x of the duct 9 are disposed substantially parallel one with the other.

The transverse axis y of the pre-combustion chamber is distanced from the topmost point of the first sector 6a by a dimension B of which the ratio with the radius R2 of the sector 6b is 1.40 approx.

The glow plug 7 is positioned tangential to one of the flanks of the second sector 6b and parallel to the transverse axis y. Clearly enough, the plug 7 might be positioned on either side of the chamber, as indicated by the two phantom circles of fig 2, according to assembly requirements. The distance G that separates the seating of the plug 7 from the longitudinal axis x is equivalent substantially to one third of the radius R2 of the second sector 6b.

By virtue of the arrangement of the injector 5 and the glow plug 7, and of the particular geometry of the pre-combustion chamber 6, the spray from the injector 5 encounters a favourable environment, and one conducive to the following results:

-a better balance of turbulence values occurring at both high and low engine speeds, especially with the engine operating at full load, attributable to 8 the particular embodiment of the bottom part of the pre-_combustion chamber, i.e. of the third sector; -increased turbulence at low engine speeds,.thus ensuring a more efficient and complete combustion, and accordingly, reduced emissions. Also, the positioning of the glow plug is such as to ensure efficient starting and swiftly optimized combustion.

9

Claims

Claims

A pre-combustion chamber for compression ignition engines comprising: -a crankcase housing at least one reciprocating piston; -a cylinder head, fitted to the crankcase and combining therewith to create at least one combustion chamber; -a fuel injection system, comprising at least one injector mounted to the cylinder head and emerging into a precombustion chamber formed in the head, in receipt of fuel from the injector on the one hand and connecting with the combustion chamber by way of a duct on the other, and at least one glow plug located internally of and serving to heat the pre-combustion.chamber, characterized in that the pre- combustion chamber exhibits an axial section comprising three sectors merged one with the next in unbroken continuity and occupying a longitudinal axis parallel with the axis of the piston: a first sector of essentially hemispherical shape into which the injector emerges, a second and fully spherical sector of radius greater thdn the radius of the first sector, by which the glow plug is accommodated in a position substantially transverse to the longitudinal axis, and a third sector affording an essentially flat bottom from which the duct extends angled in relation to the longitudinal axis to connect the pre-combustion chamber with the combustion chamber.

2) A pre-combustion chamber as in claim 1, wherein the dimensional ratio between the radius of the first sector and the radius of the second sector is between 0.73 and 0.76.

3) A pre-combustion chamber as in claim 1, wherein the injector emerges into the first hemispherical sector at an angle of approximately 350 from the longitudinal axis of the chamber.

4) A pre-combustion chamber as in claim 3, wherein the axis of the injector is disposed substantially parallel to the axis of the duct.

5) A pre-combustion chamber as in claim 1, wherein the trarisverse axis of the chamber is distanced from the topmost point of the sphere of the first sector by a dimension of which the ratio with the radius of the second sector is approximately equal to 1.40 6) A pre-combustion chamber as in claim 1, wherein the glow plug is positioned tangential to and in contact with one flank of the second sector and parallel to the transverse axis.

7) A pre-combustion chamber as in claim 1, wherein the distance separating the seating of the glow plug from the longitudinal axis of the chamber is equivalent to approximately one third of the radius of the second sector.

8) A pre-combustion chamber as in claim 1, wherein the bottom and side of the third sector merge through a tight radius designed to favour a swirling motion of the fuel injected into the pre-combustion enclosure.

9) A pre-combustion chamber as in preceding claims, described and illustrated with reference to the 12 figures of the accompanying drawings, and as intended for the stated objects.

Published 1991 at The Patent Office. State House. 66171 High Holbom. London WC1R47P. Further copies rnay be obtained from Sales B. Unit 6, Nine Mile Fbint. Cwrnlelinfach. Cross Krys. Newport NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.