DE19809618C2 - Two-stroke engine - Google Patents

Description

The invention relates to a two-stroke engine, in particular a two-stroke engine. Large diesel engine with turbocharger, with at least one cylinder with an inlet slot assembly controllable by the associated piston tion for feeding the filling medium and with one for an egg NEN predetermined crank angle range extending opening time span open outlet arrangement for discharging the exhaust gas verse hen is.

In known arrangements of this type, for example in the two-stroke Large diesel engines from the applicant, contains the exhaust arrangement single Lich a large exhaust valve. The result is only an exhaust gas flow which contains all impurities and environmental toxins and which is a medium one Has temperature that is significantly lower than that of the expanding Ver combustion gases is released during the pre-exhaust period (the opening period of time of the exhaust valve before opening the intake Slot arrangement) can be drained, and much higher than that of Almost clean purge air that is released during the post-exhaust period (the off flow period after closing the inlet slot arrangement) is drained.

For the arrangements of this kind, compare the unpublished one German patent application 197 45 068.7, are therefore for cleaning and  Detoxification of the exhaust gas requires comparatively large aggregates that can handle a volume flow corresponding to the total amount of exhaust gas must, which is unfavorable due to the given installation conditions can impact.

Furthermore, the relatively low mean temperature of the Ab gases that contain the units for cleaning the exhaust gas from here NEN oxides between the exhaust gas tank and the inlet of the Turbocharger turbine must be attached so that the required ka analytical process can proceed. After the turbocharger turbine that would be Temperature too low.

In addition, part of the exhaust gas energy is lost because a Vermi the total amount of exhaust gas in a container, that the relatively high pressure in the cylinder during the preliminary Exhaust throttled to the pressure in the exhaust gas tank is, without this can be exploited for mechanical work, which can has an adverse effect on the overall economy. That scowl Losing loss means that in modern two-stroke diesel engines Energy potential of about 8% of the shaft power of the motor is lost goes.

It is known from DE-AS 10 04 861, the Zy in a two-stroke engine linder to group together and the exhaust gas of each cylinder group pe to lead to their own exhaust gas turbine. It should between the Ab gas lines of two adjacent cylinders of a cylinder group one Cross connection may be provided. This measure is for comparison moderate the exhaust pressure in the exhaust pipes. A split of the Exhaust gas flow in partial flows, which are fed to different targets, is not scheduled.  

In US-PS 4 807 571 a two-stroke engine with one and Exhaust slots described, in which in the outlet slot two over the entire width of which can be pivoted together flaps are arranged. With these control flaps access to the Ver exhaust gases to the exhaust pipe at an earlier or later time be placed. With this arrangement, too, is a division of the Ab gas flow and supply of exhaust gas partial flows to different Ag gregates not possible.

Proceeding from this, it is therefore the object of the present invention an engine of the type mentioned at the beginning with simple and inexpensive Means to improve so that a comparatively high environmental friend efficiency and economy are achievable.

This object is achieved in that the outlet on order has several outlets that operate independently of one another Tigbare outlet valves are assigned, which during different Teilöff opening times and the total exhaust gas volume in several exhaust gases Subdivide sub-streams that can be fed to different goals.

With these measures, the disadvantages described at the beginning can be eliminated minimize or avoid entirely. The distribution of the total exhaust gas ge in several exhaust gas partial streams advantageously allows indi viduelle Usen adapted to the conditions in each exhaust gas partial flow dung or after-treatment of the exhaust gas, which is advantageous to the Er aiming for a high degree of purity and good economy affects.  

Advantageous refinements and expedient further developments of the overriding measures are specified in the subclaims. So the outlet arrangement can advantageously have at least two outlet groups each have at least one outlet. This already enables at comparatively low construction costs an optimization in one or the other other direction.

It can be provided that the partial opening time of at least one off let it at least partially, preferably entirely in the area after the Discharge of the inlet slot arrangement falls. This partial exhaust gas flow be sits a comparatively high degree of purity and a comparatively low temperature. This partial exhaust gas stream can therefore either directly or indirectly through a separate cooling / cleaning unit or through the engine's own purge air cooler to the inlet slot assembly managed and thus recirculated. If the recirculated exhaust gas partial flow passed through a radiator, this causes an increase in engine Flushing, with a resulting reduction in the occasion engine compression temperature, resulting in an improvement in the us efficiency of the engine. Because the purity of the purge air through this recirculation is reduced, the possibilities are reduced to form NO formations during combustion. A wide one Another advantage is that the need for clean charge air, delivered by the compressor of a turbocharger, which reduces can also reduce the size of the compressor. Because during this phase of the engine cycle, the intake slot assembly of the engine is closed is the upward movement of the comm provides in an advantageous manner compression hubs that the exhaust gas to the charge air storage of the engine is pumped on. If you want to enlarge the recirculating Amount, it may be necessary to change the opening time of the Extend the outlet so that it is already before closing the  Slot arrangement of the engine is opened by the piston. Do this gently further that this partial flow with a compressor for Transport of the exhaust gas in the system must be provided. This ver however, it becomes denser with a much lower pressure ratio than the Ver operate more densely of a turbocharger and thus the power requirement to the Er Reduce generation of the purge air (gas) significantly.

According to another development of the overarching measures can be provided that the partial opening time of at least one outlet valve at least partially preferably completely in the area before the up control of the inlet slot assembly falls. Because in this period of time Engine cycle no direct connection between this exhaust gas flow and the charge air reservoir, the pressure in the assigned Ab gas tank higher than in the charge air storage, without this going back will flow. This partial exhaust gas flow has a proportionate high pressure and a relatively high temperature and thus one high energy content. Because of the relatively high pressure in the assigned exhaust gas storage increases the potential for implementing the Energy in the exhaust gas in mechanical work. This potential can be practical used in a connected turbocharger turbine and / or power turbine become. Furthermore, this exhaust gas flow, which is only a limited one Part of the total amount of exhaust gas, a substantial part of the Contain total amount of contaminants and environmental toxins. A big one Most of the total amount of pollution and environmental toxins from the Motors can thus be cleaned in a relatively small unit, which is both before and after a turbocharger turbine or Power turbine because the temperature is still high enough that the catalytic processes both before and after the expansion in can run off the turbines.  

In any case, it can be provided that the partial opening time at least of an exhaust valve at least partially in the area between opening and Discharge of the inlet slot arrangement falls, or this area entirely covers. The resulting partial exhaust gas stream expediently turns a own exhaust gas turbocharger driven, which together with one the above-mentioned partial exhaust gas flow, the partial opening time of which at least partially falls before the control of the inlet slot arrangement, beatable exhaust gas turbocharger, the engine's need for filling air volume more than can cover. This creates the possibility that the excess amount of energy in the total exhaust gas flow for driving ir used in the form of a suitably connected power turbine can be increased, which increases the overall efficiency of the engine. The parallel connection has the advantage that a comparative one small size results.

Further advantageous configurations and expedient further developments The overriding measures are in the remaining subclaims Chen specified and from the example description below can be seen from the drawing.

In the drawing described below:

Fig. 1 is a schematic representation of a large two-stroke diesel engine according to the invention with several outlets.

Fig. 2 is a diagram of the exhaust gas and filling volume flow over the crank angle or the time.

The basic structure and mode of operation of two-stroke large diesel engines, such as those that can be used, for example, as ship propulsion systems, are known per se and therefore require no further explanation in the present context. Such engines usually contain a plurality of cylinders 1 arranged in a row next to one another, of which only one cylinder 1 is shown in FIG. 1. Each cylinder 1 is associated with a piston 2 , which acts together with the crankshaft, not shown, and which delimits a combustion chamber 3 . The combustion chamber 3 is supplied with fuel and air. The fuel, here diesel oil, is injected. The injection device is not shown in FIG. 1 for reasons of clarity. The air is supplied via inlet slots 4 which are arranged in the region of the cylinder wall and are run over by the piston 2 in the region of the lower piston dead center and are thus driven up and down.

The charge air is pre-compressed using the energy of the exhaust gas. For this purpose, an arrangement with two exhaust gas turbochargers 5 , 6 is provided, which is followed by a common charge air cooler 7 , through which the temperature of the charge air is reduced. Downstream of the cooler 7 is a charge air accumulator 8 which extends through all cylinders 1 and from which branch lines 9 to the individual cylinders 1 depart.

The exhaust gas generated during combustion is expelled from the combustion chamber 3 via a plurality of outlets 10 , 11 , 12 arranged in the cylinder head. In the example shown, three outlets 10 , 11 , 12 are provided. Each outlet 10 , 11 , 12 can be closed or opened by means of an associated outlet valve 13 , 14 , 15 . Each outlet 10 , 11 , 12 is connected to an associated exhaust manifold 19 , 20 , 21 via an associated outlet connector 16 , 17 , 18 . The corresponding outlets 10 or 11 or 12 of all cylinders 1 are each closed to the same exhaust manifold 19 or 20 or 21 .

The outlet valves 13 , 14 , 15 can be actuated independently of one another. The actuating devices provided for this purpose are not shown for reasons of clarity. The control of the actuation lines of the exhaust valves 13 , 14 , 15 is set up so that the outlets 10 , 11 , 12 of each cylinder 1 are successively open. Overlaps are possible. The result is accordingly indicated in the graph of FIG. 2 with T _a opening time period within which the outlets 10, 11 open, 12. This period extends here beyond the period designated T _e , within which the inlet slots 4 are open, towards the front and the rear. In individual cases, an extension of T _a compared to T _e can only be provided in one direction.

In FIG. 2, the times t ₁ t _2, t _3, t ₄ indicated that divide the opening time of clamping ne T _a of the outlets 10, 11, 12 into three partial opening times T _10, T ₁₁ and T _12. During T ₁₀ , the outlet valve 13 assigned to the outlet 10 is open. This period coincides in whole or in part with the period in which the inlet slots 4 , represented by the area curve V _e , are open. During T ₁₁ the outlet 11 assigned to the outlet valve 14 is open. During T ₁₂ the outlet 12 assigned to the outlet valve 15 is open. There are accordingly several, here three, in Fig. 2 indicated by the curves V ₁₀ , V ₁₁ and V ₁₂ from partial gas flows. The area under the curves mentioned corresponds to the associated opening area of the valve in question. The opening area of the inlet slots 4 passing through the combustion chamber 3 to the filling volume flow is indicated by the curve V _e .

The outlet 10 is, as was stated above, during the flushing of the combustion chamber 3 which takes place via the inlet slots. The exhaust gas stream V ₁₀ is accordingly the largest exhaust gas stream. This serves to drive the first exhaust gas turbocharger 5 . Accordingly, from the gas manifold 19 is connected via a line 22 to the turbine 5 a of the exhaust gas boladers 5 , the compressor 5 b, as already mentioned above, is connected via a line 23 to the charge air cooler 7 . A power turbine 28 is driven here simultaneously by means of the exhaust gas partial volume flow V ₁₀ . This is here to achieve small sizes in terms of flow parallel to the turbine 5 a of the exhaust gas turbocharger 5 angeord net. A serial arrangement would of course also be conceivable.

The outlet 11 is, as can be seen from Fig. 2, opened before the start of the flushing mentioned before. Before the purging of the combustion chamber 3 , the exhaust gas has a comparatively high temperature and a comparatively high pressure and a high content of impurities and environmental toxins. The associated exhaust gas partial flow V ₁₁ therefore contains a comparatively large amount of energy, which is also used here to drive an exhaust gas turbocharger. In order to be able to fully utilize this energy, a dedicated exhaust gas turbocharger, here the second exhaust gas turbocharger 6 , is provided, the turbine 6 a of which is connected via a line 24 to the exhaust gas manifold 20 . The compressor 6 b of the exhaust gas turbocharger 6 is connected here via a line 25 to the charge air cooler 7 . Here, too, as can be seen from FIG. 1, an additional, expediently connected power turbine 29 can be acted upon at least a little.

In the exhaust manifolds 19 and / or 20 , catalysts can be arranged, each containing soot filters and No _X catalyst elements. The amount of impurities and environmental toxins that are released into the environment thus depends on whether catalysts flow in both parts V ₁₀ and V ₁₁ , only in one or none of these partial flows.

Compared to the total amount, the partial flow V _{11 is} small, but, as mentioned above, contains a large amount of contaminants and environmental toxins. Thus, a significant reduction in the total amount of contaminants and environmental toxins released into the environment can be achieved by placing a relatively small catalyst in this substream. Furthermore, the temperature of the partial stream 20 will be high enough that the necessary catalytic processes in egg ner arranged after the turbine catalyst can run smoothly. With this principle it becomes possible, by treating less than 25% of the total exhaust gas flow, to reduce the amount of contaminants released to the environment by more than 50%.

In the example shown in FIG. 2, the opening period for exhaust gas flow V ₁₁ falls before the time at which the inlet slot arrangement 4 is opened . As mentioned above, this causes that in the exhaust manifold tube 20 a higher pressure than in the charge air reservoir 8 is present, where the expansion work to be carried out by the turbines 6 a and 29 is increased. If a greater reduction in the total amount of contaminants and environmental toxins than the above-mentioned 50% is desired, the opening period of the exhaust gas flow V _{11 can be} extended so that it overlaps the opening period of the inlet slot arrangement 4 . Since the amount of exhaust gas V _{11 is} increased and the amount catalytically processed by the catalytic converter arrangement provided in the exhaust pipe 20 increases.

The outlet 12 is open after completion of the above-mentioned flushing process. The associated exhaust gas partial flow V ₁₂ therefore contains only comparatively little contamination and has a comparatively low temperature. The exhaust gas partial flow V ₁₂ can therefore be fed back to the combustion chamber 3 together with fresh charge air. This Rezirku lation reduces the amount of charge air required, so that there is a comparatively small size of the exhaust gas turbocharger 5 and 6 .

The partial exhaust gas flow V ₁₂ can be fed directly to the charge air reservoir 8 . In the example shown, the exhaust gas partial flow V _{12 is} fed into the charge air cooler 7 , as indicated by a line 26 leading from the exhaust gas manifold 21 leading to the charge air cooler 7 . It would also be conceivable to use your own cooler. In line 26 , a cleaning device in the form of a soot filter 27 is arranged, which removes particles contained in the exhaust gas partial flow V ₁₂ . By using this principle, ie the conduction of the exhaust gas partial flow V ₁₂ through the charge air cooler 27 or through a separate cooler, it can be achieved that the total flushing quantity flowing through the inlet slot arrangement 4 is increased, with a resultant improvement in the flushing of the Engine with cold air / cold gas and a reduction in the temperature in cylinder 3 at the beginning of the compression (closing of the exhaust valve 15 ). A reduced temperature at the beginning of the compression leads to an improved efficiency of the engine process.

In the example shown in Fig. 2, the opening period of the partial flow V ₁₂ falls after the timing of the deactivation of the inlet-slot arrangement 4 , so that the piston 2 can push the exhaust gas through outlet 12 , collecting tube 21 , soot filter 27 and purge air cooler 7 to the charge air reservoir 8 . The opening period of the partial flow V ₁₂ can begin under ge circumstances before the control of the inlet slot arrangement 4 , whereby the recirculating amount can be increased. However, this requires the installation of a induced draft fan 30 in the area of the line 26 in FIG. 1 with broken lines. When using an induced draft fan in the line 26 , a separate cooler 31 is advantageously installed in front of the latter, as is further indicated in FIG. 1.

Through a mixture of clean charge air and recirculated exhaust gas which the temperature and the oxygen content in the cylinder charge on The beginning of the compression is reduced, which reduces the possibility for the formation of NO formations during combustion process is achieved.

As described above, the total amount of fresh air that flows through the compressors 5 b and 6 b is reduced compared to the amount that flows through the compressor in known arrangements with a common exhaust valve. Furthermore, the amount of energy supplied to the reduced mass flow is almost unchanged compared to the known arrangements. This ratio means that a larger amount of energy is required for the expansion in the turbines 5 a and 6 a than for driving the compressors 5 b and 6 b, which can be used in the illustrated power turbines 28 and / or 29 . With the help of the power turbine 28 or 29 , aggregates of all kinds, for example power generators etc., can be driven.

The above description shows that with the measures according to the invention, the special properties of each partial exhaust gas stream can be used particularly effectively, so that overall a high increase in engine performance can be achieved. This can easily be 3-5% higher than in the known engines with only one exhaust valve. In the example shown, three partial exhaust gas flows are seen before, two of which are upstream or downstream of the purging process. Particularly good results can be achieved here. However, it can be seen that a considerable increase would be achieved if only one or the other of the two exhaust gas streams V ₁₁ or V _{12 were} provided.

In the example shown, each exhaust gas partial flow is supplied with one outlet arranges. But it would also be conceivable to have a group with each exhaust gas partial flow assignable to several outlets. It would also be conceivable to overlap the partial opening times.

The example shown is based on a large two-stroke diesel engine. The However, the invention can also be used in other two-stroke engines, for example Gas engines, diesel gas engines, Otto gas engines and Otto engines with Advantage can be applied.

Claims (18)

1. Two-stroke engine, in particular two-stroke large diesel engine, with at least one cylinder ( 1 ), which with a by the assigned piston ( 2 ) controllable inlet slot arrangement ( 4 ) for supplying the filling medium and with one for a predetermined crank angle range the first opening period (T _a ) of the opening arrangement for discharging the exhaust gas is provided, as characterized in that the outlet arrangement has a plurality of outlets ( 10 , 11 , 12 ) which, independently of one another, of the actuatable outlet valves ( 13 , 14 , 15 ) are assigned, which are open during different partial opening times (T ₁₀ , T ₁₁ , T ₁₂ ) within the opening time span (T _a ) and subdivide the total exhaust gas quantity into several partial exhaust gas streams (V ₁₀ , V ₁₁ , V ₁₂ ) that different goals are feasible. 2. Two-stroke engine according to claim 1, characterized in that the outlet arrangement contains at least two outlet groups each containing at least one outlet ( 10 or 11 or 12 ). 3. Two-stroke engine according to one of the preceding claims, characterized in that the outlet arrangement has three at least one outlet ( 10 or 11 or 12 ) ent-holding outlet groups. 4. Two-stroke engine according to one of the preceding claims, characterized in that the partial opening time (T ₁₀ ) of at least one outlet ( 10 ) at least partially, preferably completely, in the area (T _e ) between the up and down control of the inlet Slot arrangement ( 4 ) falls and that at least one associated turbine ( 5 a, 28 ) can be driven by the associated partial exhaust gas flow (V ₁₀ ). 5. Two-stroke engine according to claim 4, characterized in that the exhaust gas partial flow (V ₁₀ ) is assigned its own exhaust gas turbocharger ( 5 ). 6. Two-stroke engine according to claim 4 or 5, characterized in that the exhaust gas partial flow (V ₁₀ ) at least one preferably in terms of flow parallel to the turbine ( 5 a) of the exhaust gas turbocharger ( 5 ) arranged power turbine ( 28 ) is assigned. 7. Two-stroke engine according to one of the preceding claims, characterized in that the partial opening time (T ₁₁ ) at least one outlet ( 11 ) at least partially, preferably completely before, falls in the area before the control of the inlet slot arrangement ( 4 ) and that by the assigned partial exhaust gas flow (V ₁₁ ) at least one assigned turbine ( 6 a, 29 ) can be driven. 8. Two-stroke engine according to claim 7, characterized in that the exhaust gas partial flow (V ₁₁ ) is assigned its own exhaust gas turbocharger ( 6 ). 9. Two-stroke engine according to claim 7 or 8, characterized in that the partial exhaust gas flow (V ₁₁ ) at least one preferably in terms of flow parallel to the turbine ( 6 a) of the exhaust gas turbocharger ( 6 ) arranged power turbine ( 29 ) is assigned. 10. Two-stroke engine according to one of the preceding claims, characterized in that the partial opening time (T ₁₂ ) at least one outlet ( 12 ) at least partially, preferably completely before, falls in the area after the control of the inlet slot arrangement ( 4 ) and that the associated partial exhaust gas flow (V ₁₂ ) can be fed directly or indirectly to the inlet slot arrangement ( 4 ). 11. Two-stroke engine according to claim 10, characterized in that the exhaust gas partial flow (V ₁₂ ) is assigned a blower ( 30 ), preferably before induced draft fan. 12. Two-stroke engine according to claim 11, characterized in that the fan ( 30 ) is assigned a cooler ( 31 ). 13. Two-stroke engine according to one of claims 10 to 12, characterized in that in the of the inlet-slot arrangement ( 4 ) feedable partial exhaust gas flow (V ₁₂ ) assigned line ( 26 ), a cleaning device ( 27 ) is arranged. 14. Two-stroke engine according to one of the preceding claims, characterized in that each outlet group is associated with an egg gene, over all cylinders ( 1 ) extending exhaust manifold ( 19 , 20 , 21 ). 15. Two-stroke engine according to one of the preceding claims, characterized in that at least the first Abga steep current (V ₁₁ ) is assigned a catalyst arrangement. 16. Two-stroke engine according to one of the preceding claims, characterized in that at least each non-recirculating exhaust gas partial flow (V ₁₁ , V ₁₀ ) is assigned a catalyst arrangement. 17. Two-stroke engine according to claim 15 or 16, characterized in that the catalyst arrangement is integrated in the associated exhaust gas manifold ( 19 , 20 ). 18. Two-stroke engine according to one of the preceding claims, characterized in that a common charge air accumulator ( 8 ) extending over all cylinders ( 1 ) is provided, which is preceded by a common charge air cooler ( 7 ), at least of which by means of at least one Exhaust gas turbocharger ( 5 , 6 ) provided charge air, preferably also by the exhaust gas partial flow (V ₁₂ ) that can be added to the inlet slot arrangement ( 4 ), can be acted upon.