DE102019122559A1 - Externally ignited reciprocating internal combustion engine with a prechamber ignition system - Google Patents

Abstract

Externally ignited reciprocating internal combustion engine with a prechamber ignition system in a cylinder head of the reciprocating internal combustion engine, the prechamber ignition system having a cavity in which an ignition device with an ignition electrode is arranged, the cavity being covered with a cover opposite a combustion chamber of the reciprocating internal combustion engine, wherein the cover has at least one opening that connects the cavity and the combustion chamber with each other in a gas-conducting manner, the cover having at least one second opening, the cross section of which is smaller than a cross section of the first opening Gas exchange significantly improved, which significantly improves the ignition properties at low loads and speeds of the internal combustion engine.

Description

The invention relates to an externally ignited reciprocating internal combustion engine with a prechamber ignition system with the features from the preamble of claim 1.

For the technical environment, for example, the German Offenlegungsschrift DE 10 2014 111 897 A1 pointed out. From this an ignition device for igniting fuel-air mixtures in a combustion chamber of an internal combustion engine by means of a corona discharge is known, with an ignition electrode, an outer conductor surrounding the ignition electrode, which has a front and a rear end and one between the ignition electrode and the outer conductor arranged electrical insulator, from which at least one tip of the ignition electrode protrudes. The at least one tip of the ignition electrode is in a space which is shielded by a cap assigned to the insulator, which has an inside facing the insulator and an outside facing away from the insulator, as well as one or more holes through which the shielded space and one on the outside the space lying on the cap, the combustion chamber.

• eine Zündelektrode,
• eine elektrische Versorgungsleitung, an welche die Zündelektrode angeschlossen ist,
• einen Isolatorkörper, durch den die Versorgungsleitung hindurchgeführt ist,
• ein Gehäusekopf, der dichtend auf dem Isolatorkörper sitzt und ein Außengewinde zum Einschrauben in einen Verbrennungsmotor,
• ein Rohrgehäuse, das an dem Gehäusekopf befestigt ist, den Isolatorkörper umgibt und einen Sechskant trägt,
• wobei das Rohrgehäuse eine Isolatorkörper-Halterung umgibt, die über eine Schweißnaht mit dem Gehäusekopf verschweißt ist und den Isolatorkörper mit einer Vorspannung gegen den Gehäusekopf presst.

Next is from the international patent application with the international publication number WO 2008/031482 A2 a spark plug for igniting a combustible gas mixture in an internal combustion engine is known, comprising:

• an ignition electrode,
• an electrical supply line to which the ignition electrode is connected,
• an insulator body through which the supply line is passed,
• a housing head that sits sealingly on the insulator body and an external thread for screwing into an internal combustion engine,
• a tubular housing which is attached to the housing head, surrounds the insulator body and carries a hexagon,
• wherein the tubular housing surrounds an insulator body holder which is welded to the housing head via a weld seam and presses the insulator body against the housing head with a prestress.

For further technical information, please refer to the German Offenlegungsschrift DE 10 2016 120 984 A1 pointed out. A prechamber spark plug for a gas-operated internal combustion engine and a method for its production are known from this laid-open specification.

Further is from the German Offenlegungsschrift DE 10 2016 206 992 A1 , from which the present invention is based, a spark plug is known. The spark plug is in particular a prechamber spark plug with a housing, an ignition electrode and a ground electrode, the ignition electrode being able to be subjected to an electrical voltage via a supply line and the supply line running at least partially within an insulator, with at least one discharge area of the housing is made of a material with a thermal conductivity of over 150 W / mK.

The disadvantage of these known prechamber ignition systems is that in the low load and / or speed range of an internal combustion engine there is little or no gas exchange within the prechamber ignition system, so that reliable ignition of the fuel-air mixture is not always guaranteed in these load and / or speed ranges is.

The object of the present invention is to provide a measure with which the ignitability of a prechamber ignition system can be ensured in a low load and / or speed range of an internal combustion engine.

This object is achieved by the feature in the characterizing part of claim 1.

Advantageous further developments of the invention are described in the subclaims.

Due to the design of the prechamber ignition system according to the invention, a fresh air / fuel mixture is conveyed through all openings directly into the area of the ignition electrode of the ignition device and residual gas is displaced during a charge change during operation of the internal combustion engine. Thus, especially at low load and / or speed ranges of the internal combustion engine, there is always an ignitable fresh air / fuel mixture in the ignition range of the ignition device. Safe ignition is therefore always guaranteed. The second openings are so small, however, that no ignition jets can penetrate through them into the combustion chamber.

The orders of magnitude according to claims 2 and 3 are particularly preferred orders of magnitude for round openings. The overlap area comes about because the size of the openings must be adapted to the respective internal combustion engine, depending on the prevailing pressure and temperature conditions.

The configuration according to claim 4 improves the escape of the ignition beams from the first breakthrough in the lid of the prechamber ignition system.

The configuration according to claim 5 prevents the ignition jets from escaping from the second opening in the cover of the prechamber ignition system.

The embodiment according to claim 6 avoids coking of the first and second openings in the cover of the prechamber ignition system.

• 1 zeigt schematisch einen Schnitt durch ein erfindungsgemäßes Vorkam merzü ndsystem.
• 2 zeigt in einem Diagramm den Einfluss der Durchbruchsgröße.

The invention is explained in more detail below with reference to two figures.

• 1 shows schematically a section through an antechamber according to the invention.
• 2 shows in a diagram the influence of the opening size.

1 shows schematically a section through an antechamber ignition system according to the invention 1 . The pre-chamber ignition system 1 is arranged in a cylinder head of an externally ignited internal combustion engine. The internal combustion engine is preferably for a motor vehicle such. B. provided a car or a single-track vehicle. In the prechamber ignition system 1 is a cavity 3 , in which an igniter 4th with an ignition electrode 5 is arranged. Next is the cavity 3 from a lid 6th opposite a combustion chamber 7th the internal combustion engine covered. The lid 6th has at least a first breakthrough 8th and a second breakthrough 9 on that the cavity 3 and the combustion chamber 7th Connect gas leading together. In the present exemplary embodiment there are two first openings 8th and four second breakthroughs 9 shown. The number of first and second breakthroughs 8th , 9 may differ significantly in other exemplary embodiments.

According to the invention is a cross section Q1 of the first breakthrough 8th larger than a cross section Q2 of the second breakthrough 9 , this applies to all possible cross-sectional shapes. Preferably the openings are 8th , 9 however round.

The first cross section preferably has Q1 a diameter between 0.5 mm and 2.5 mm and the second cross section Q2 a diameter between 0.1 mm and 1.0 mm. How the diameters result becomes 2 explained in more detail.

In a particularly preferred embodiment, the first breakthrough 8th a nozzle shape through which the pilot jets can pass with lower losses.

In a further preferred embodiment, the second breakthrough is 9 Sharp-edged so that the ignition jets are prevented from passing through.

The cover particularly preferably has 6th a catalytic coating, such as. B. platinum. This measure causes the lid to coke 6th avoided by combustion residues.

2 shows in a diagram the influence of the opening size. There is a discharge figure over a Y-axis µ in the range of 0 and 1.

The discharge number µ is a fluid mechanical correction factor that determines the ratio of the amount of gas or liquid that actually escapes when flowing out of openings to that which is released when there is no friction and there is no jet contraction (if liquid passes through a sharp-edged hole, the cross-section of the free jet measures only about 60% of the hole cross-section) would flow out of the opening. The flow velocity determined with the help of Bernoulli's equation must be multiplied by the outflow number in order to take into account the two corrections mentioned. For liquid flows, the outflow number is µ between 0 and 1.

About an X axis is a Reynolds number re shown from 0.

The Reynolds number is a dimensionless number named after the physicist Reynolds. It is used in fluid dynamics and can be understood as the ratio of inertia to viscosity forces. The turbulence behavior of geometrically similar bodies is identical with the same Reynolds number. This property allows z. B. realistic model tests in water or wind tunnels.

The aim of the invention is a prechamber ignition system 1 , which forms a fluidic "one-way street", which during the gas exchange of the internal combustion engine cooler and slower fuel / air mixture into the cavity 3 but offers resistance to hotter and faster combustion gas so that most of the combustion gases pass through the larger, first breakthroughs 8th of the lid 6th into the combustion chamber 7th is directed.

Hierbei ist A der Strömungsquerschnitt des Durchbruchs 8, 9 und µ die Ausflusszahl, die zusammen den effektiven Düsenquerschnitt bilden.
Bei ausreichend hohem Druckverhältnis (kritisches Druckverhältnis) wird in den Durchbrüchen 8, 9 Schallgeschwindigkeit erreicht.
Die Ausflusszahl µ hängt von der Geometrie der Durchbrüche 8, 9 sowie der Reynolds-Zahl der Strömung ab. Hierbei gilt qualitativ der in 2 dargestellte Verlauf des unbezifferten, einzigen Graphen.The mass flow through the breakthroughs 8th , 9 follows the nozzle flow, which in this context can be summarized as: $$\dot{m}=\mathrm{A.}\cdot \mathrm{\mu }\cdot f\left(p_{\text{cavity}},p_{\text{cylinder}}\right)$$

Here A is the flow cross section of the opening 8th , 9 and µ the number of outflows, which together form the effective nozzle cross-section.
If the pressure ratio is high enough (critical pressure ratio), the openings 8th , 9 Speed of sound reached.
The discharge number µ depends on the geometry of the breakthroughs 8th , 9 and the Reynolds number of the flow. The in 2 Represented course of the unquantified, single graph.

A design of the prechamber ignition system is advantageous 1 where the first breakthroughs 8th for the pilot jets from the cavity 3 in the cylinder (combustion chamber 7th ) a very large discharge number µ , ie close to the ideal value 1 , have, optimally even form a nozzle, in particular a Laval nozzle. This discharge number µ is plotted in area B of the diagram over the X axis.

On the other hand, the additional second breakthroughs should 9 , the flushing openings, the lowest possible number of outflows µ which is strongly dependent on the flow velocity and can therefore be found in area A of the diagram above the X axis. This is possible because the Reynolds number is directly proportional to the flow velocity and the cross section Q2 is. With a sufficiently high number of additional flushing openings, the second breakthroughs 9 , the disadvantage of the small diameter could be compensated for by a sufficient flow cross-section Q2 for gas exchange in the cavity 3 to create.

• • Ersten Durchbrüchen 8, den Zündstrahlbohrungen, mit typisch 0,5 - 2,5 mm Durchmesser, optional und optimal in Form einer Laval-Düse.
• • Sowie mit zweiten Durchbrüchen 9, den Spülöffnungen
• • Mit typischen Durchmesser zwischen 0,1 und 1 mm, optimal kleiner oder deutlich kleiner 0,1 mm, geometrisch strömungsungünstig, z. B. scharfkantig ausgebildet.

oder

• • Ausformung des Deckels 6 porös und gasdurchlässig mit Porengrößen bis maximal der oben genannten Größenordnung.

Designs with:

• • First breakthroughs 8th , the pilot bores, typically 0.5 - 2.5 mm in diameter, optionally and optimally in the form of a Laval nozzle.
• • As well as with second breakthroughs 9 , the irrigation openings
• • With a typical diameter between 0.1 and 1 mm, optimally smaller or significantly smaller 0.1 mm, geometrically unfavorable for flow, e.g. B. sharp-edged.

or

• • Shape of the lid 6th porous and gas-permeable with pore sizes up to a maximum of the size mentioned above.

A gas-permeable lid 6th would then be a sintered filter or made of a material similar to a sintered filter. In the case of sintered filters or materials similar to sintered filters, the (hydraulic) diameter of the second openings 9 also be smaller than 0.1 mm in the material. 0.1 mm = 100 µm are the coarsest sintered filters, the diameter of the second openings 9 can also have a size of less than 10 µm in the case of sintered filters. Here a material such as copper or steel would be useful as a base, its heat conduction to the design of the prechamber ignition system 1 fits and to optimize this over a thin surface layer (e.g. galvanically applied) for use in the combustion chamber, while still guaranteeing gas permeability.

In a further embodiment, in the case of non-sintered filter materials, the second openings 9 also be designed such that their second cross-sectional areas Q2 reduce at higher temperatures and are therefore easier to flow through for cold gas than with hot gas. This can be achieved, for example, by a bi-metal effect.

It is also advisable to have a catalytically active layer (e.g. platinum) on the lid 6th to ensure that deposits of combustion residues do not arise or that they clean themselves again quickly.

Finally, it should be said that the embodiment of the prechamber ignition system according to the invention 1 both for passive prechamber ignition systems, as shown here, and for active prechamber ignition systems with their own introduction of fuel into the cavity 3 , can be used.

List of reference symbols

1.

Pre-chamber ignition system

2.

Cylinder head

3.

cavity

4th

Ignition device

5.

Ignition electrode

6th

cover

7th

Combustion chamber

8th.

First breakthrough

9.

Second breakthrough

Q1

Cross-section of the first breakthrough

Q2

Cross-section of the second breakthrough

µ

Discharge number

re

Reynolds number

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102014111897 A1 [0002]
• WO 2008/031482 A2 [0003]
• DE 102016120984 A1 [0004]
• DE 102016206992 A1 [0005]

Claims (7)

Externally ignited reciprocating internal combustion engine with a prechamber ignition system (1) in a cylinder head (2) of the reciprocating internal combustion engine, the prechamber ignition system (1) having a cavity (3) in which an ignition device (4) with an ignition electrode (5) is arranged , wherein the cavity (3) is covered with a cover (6) opposite a combustion chamber (7) of the reciprocating piston internal combustion engine, the cover (6) having at least one opening (8), which the cavity (3) and the combustion chamber ( 7) connects to one another in a gas-carrying manner, characterized in that the cover (6) has at least one second opening (9) whose cross-section (Q2) is smaller than a cross-section (Q1) of the first opening (8). Externally ignited reciprocating internal combustion engine after Claim 1 , characterized in that the first cross section (Q1) has a diameter between 0.5 mm and 2.5 mm. Externally ignited reciprocating internal combustion engine after Claim 1 or 2 , characterized in that the second cross section (Q2) has a diameter between 0.1 mm and 1.0 mm. Externally ignited reciprocating internal combustion engine according to one of the Claims 1 to 3 , characterized in that the first opening (8) has a nozzle shape. Externally ignited reciprocating internal combustion engine according to one of the Claims 1 to 4th , characterized in that the second opening (9) is sharp-edged. Externally ignited reciprocating internal combustion engine according to one of the Claims 1 to 5 , characterized in that the cover (6) has a catalytic coating. Externally ignited reciprocating internal combustion engine according to one of the Claims 1 to 6th , characterized in that the cover (6) is a sintered filter or made of a sintered filter-like material.

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