Patent Application
20140083391
The present invention concerns a pre-chamber system for an internal combustion engine as set forth in claim 1 as well as an internal combustion engine having such a pre-chamber system.
In operation of an internal combustion engine—in particular a gas engine—with a substantially stoichiometric ratio of fuel and air very high temperatures can occur, which is detrimental to the exhaust gas behavior of such an engine. It is possible to counteract that situation by exhaust gas recycling. That however leads to a worsening in terms of the ignition characteristics.
Using a pre-chamber to be filled with combustion gas for ignition purposes in that case, as is a standard solution adopted in regard to large-volume lean-burn engines, is initially problematic. For the mixture which upon compression is urged out of the main combustion chamber into the pre-chamber does not in fact have an air excess, whereby a fuel-air mixture which can be well ignited does not prevail in the pre-chamber.
In DE 35 06 217 A1 that problem is avoided by a near-stoichiometrically mixed fuel gas already being fed to the pre-chamber. A disadvantage in that respect, besides the increased structural complication and expenditure, is that when the injection valve of the pre-chamber suffers from wear there is the possibility of back-ignition of the pre-chamber mixture into the supply passages. That represents a safety risk which should be avoided.
The object of the present invention is to provide a pre-chamber system which even in a stoichiometric mode of operation of a large-volume engine with substantial exhaust gas recycling allows good ignition of the fuel-air mixture in the pre-chamber without at the same time introducing a safety risk due to the presence of an ignitable fuel-air mixture outside the combustion chambers.
That object is attained by a pre-chamber system having the features of claim 1 and with an internal combustion engine having such a pre-chamber system.
Dividing the pre-chamber volume into an ignition region and a flow transfer region which is at least partially separated from the ignition region by an intermediate wall and introducing air through the air feed passage into the flow transfer region provides that a minimum of exhaust gas-bearing combustion mixture passes out of the main combustion chamber into the ignition region during the compression phase. At the same time that main chamber gas urges the air introduced through the air feed passage into the ignition region, thereby affording there a mixture which can enjoy good ignition. In that way a lambda value of between 0.8 and 1.2 can be achieved in the ignition region of the pre-chamber, wherein the lambda value relates to the ratio of air to fuel and the lambda value of 1 represents the ideal, that is to say stoichiometric, ratio.
DE 10 2008 062 574 A1 discloses a spark plug for an internal combustion engine, which has a post-chamber volume region, wherein that post-chamber volume region at least partially surrounds a combustion chamber-side end region of the spark plug. That however only serves to increase the volume of the pre-chamber and does not attain the present object. For, the absence of an intermediate wall does not prevent the mixture from passing from the main combustion chamber to the ignition region upon compression.
Further advantageous embodiments of the invention are defined in the dependent claims.
To make it easier for the ignition flame produced by ignition in the pre-chamber to reach the main combustion chamber, a connecting passage can be provided in the intermediate wall, the connecting passage connecting the ignition region to the flow transfer region.
To achieve uniform cooling of the entire pre-chamber by virtue of the injected air it can be provided that the intermediate wall is of a substantially peripherally extending configuration in relation to a longitudinal axis of the pre-chamber system, wherein the flow transfer region substantially surrounds the ignition region—separated by the peripherally extending intermediate wall.
A preferred embodiment is one in which by way of the air feed passage a—preferably cooled—charge air of the internal combustion engine and/or a compressed air—preferably compressed to between 6 bars and 10 bars—can be introduced into the flow transfer region. That further contributes to effectively keeping the exhaust gas-bearing mixture away from the ignition region.
In that case for energy reasons it can be provided that firstly charge air which is typically available at a pressure of between 2 and 3 bars from a turbocharger is fed and then, as soon as the pressure in the pre-chamber exceeds the pressure of the charge air, compressed air is fed.
For precise control or regulation of the period of time of the air feed or the amount of air which is fed, it can be provided that arranged at the air feed passage is a valve which is preferably electronic.
For optimum propagation of the fed air it can be provided that a peripherally extending annular passage is provided in the flow transfer region in relation to a longitudinal axis of the pre-chamber system, wherein preferably the air feed passage opens into the annular passage. To permit a rolling-like inflow of the air, in that case a peripherally extending annular gap can be provided between the annular passage and the rest of the flow transfer region, wherein considered radially with respect to the longitudinal axis the annular passage has an annular passage width and the annular gap has an annular gap width, wherein preferably the annular gap width is less than the annular passage width.
So that there is a sufficiently large available volume for pressure equalization a flow transfer volume of the flow transfer region can be larger than an ignition volume of the ignition region.
It can be provided that the connecting passage has a connecting passage opening, wherein the connecting passage opening opens into the flow transfer region. As it is advantageous in terms of fluid mechanics it is particularly preferably provided that in relation to a longitudinal axis of the pre-chamber starting from the connecting passage opening a sub-volume of the flow transfer region, that faces away from the ignition region, is smaller than the remaining residual volume of the flow transfer region.
To achieve particularly directed discharge of the flow the ratio of a passage diameter of the flow transfer passage to a passage length of the flow transfer passage can be at a maximum 0.25. Thus it can be provided both that the flow transfer passage of the pre-chamber system is of an inclinedly extending configuration with respect to the longitudinal axis, and also the flow transfer passage with its flow transfer passage opening which opens into the flow transfer region is substantially tangential in relation to an inside wall of the pre-chamber system. As a result the flow of the fuel-air mixture which flows into the pre-chamber due to the compression effect faces away from the ignition volume of the pre-chamber.
In order in comparison to guarantee a directed flow of the ignition flame into the flow transfer passage, it can be provided that the connecting passage opening—or at least a part of its cross-section—extends in the direction of the flow transfer passage opening.
Further advantages and details of the invention will be apparent from the Figures and the related specific description. In that respect
The present invention is not limited to the foregoing embodiments. For example the flow transfer passage can be arranged centrally along the longitudinal axis. In that respect it may be advantageous for the connecting passage opening to be arranged to face away from the flow transfer passage opening. A mixture, for example with a lambda value of 0.3, could also be supplied by way of the fuel gas passage 7.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1048/2012 | Sep 2012 | AT | national |
