DE102014013611B4 - Method for implementation with a piston engine - Google Patents

Abstract

Method for execution with a piston internal combustion engine as part of a four-stroke cycle with the stroke sequence working stroke, exhaust stroke, intake stroke and compression stroke, the piston internal combustion engine comprising at least one cylinder (1) with an intake tract (5) and an exhaust tract (7) and a cylinder piston (3); wherein within the four-stroke cycle:- in a first step, a cylinder charge is compressed and heated for the first time before the compression stroke;- in a second step, compressed, heated cylinder charge in the first step is discharged from the cylinder (1) with expansion;- in a third step in second step, heated and expanded cylinder charge mixed with fresh charge is subsequently returned to the cylinder (1) and compressed again in the compression stroke; wherein- the method is repeated over a first number of iterations, wherein a respective power stroke of the four-stroke cycle is completed without combustion; and- the cylinder charge compressed and mixed with fresh charge in the third step is charge air.

Description

The present invention relates to a method for execution with a piston internal combustion engine, in particular with a compression-ignited piston internal combustion engine according to patent claim 1, and a piston internal combustion engine set up for carrying out the method according to patent claim 10.

The general state of the art is defined by the publications DE 600 21 901 T2 , U.S. 2005/0 268 609 A1 and WO 2003/008785 A1 educated. The publication US 2006/0 207 257 A1 also discloses an engine in which excess energy is stored in the form of compressed air, for which purpose compression strokes of the cylinders are used.

Furthermore, from the WO 2001/079 675 A1 a method for filling control in an internal combustion engine is known, which consists in that by controlling the closing times (AS) of at least one exhaust valve of the respective cylinder and by opening (EÖ1) at least one intake valve in the area of top dead center (TDC) of the piston, internal residual gas recirculation in Cylinder with temporary expulsion of residual gas in front of the at least one intake valve is initiated, and that at least one intake valve is opened within a gas exchange in the cylinder in at least two separate phases (EÖ1, ES1, EÖ2, ES2).

the US 2003/0 005 898 A1 shows a diesel engine with variably actuated valves in which the cam that controls each intake valve is shaped to cause the respective intake valve to open during the normal exhaust phase of the engine, thus realizing exhaust gas recirculation within the engine due to that during During the normal exhaust phase, part of the exhaust gas from the cylinder enters the intake port, from where it returns to the cylinder during the next intake phase, while part of the exhaust gas that previously flowed into the exhaust port returns to the cylinder during the intake phase, due to the additional opening of the exhaust valve , whereby the exhaust gas charges flowing back into the cylinder are subjected to further combustion in the next engine cycle.

From the DE 943 439 B a method is known for facilitating the starting of internal combustion engines, particularly high-performance diesel engines, in which fresh air is drawn into cylinders of the engine, pushed out into a closed exhaust pipe and passed through a connecting pipe into an intake pipe and then back into the cylinders, the air in each cylinder of the internal combustion engine (i) fuel is mixed with each compression stroke and this fuel-air mixture is circulated in the cylinder-exhaust pipe-connecting pipe-intake pipe-cylinder circuit until it has reached its ignition temperature and ignites.

In the US 2008/0 060 609 A1 discloses a method of operating an engine having at least one cylinder and a piston disposed within the cylinder, the method including injecting fuel into the cylinder during a first condition and then operating the piston to perform a compression stroke prior to combustion of the injected fuel, and during a second condition, injecting fuel into the cylinder and then operating the piston to perform at least two compression strokes before combusting the injected fuel.

In the case of compression-ignited engines, such as diesel engines, the ability to start cold depends largely on the temperature of the cylinder charge at the time of injection. High compression ratios ensure a high charge temperature at the time of injection, but there is a discrepancy with the desired power density (peak pressure). In the case of EGR engines, the problem is further aggravated by the inert charge component. In this respect, there is a conflict of objectives with regard to power density and fuel consumption at high load points with the cold start capability of the internal combustion engine. Furthermore, with a low compression ratio and a cold engine, there is the problem of white smoke due to incomplete combustion. Depending on the engine, this "white smoke problem" can last for several minutes until a sufficient engine operating temperature is reached.

To improve the cold start behavior, it is from the publication DE 10 2005 015 852 A1 It is also known to resort to internal exhaust gas recirculation after the start of combustion operation.

Proceeding from the known state of the art, the present invention is based on the object of proposing a method for implementation with a piston internal combustion engine, with which the cold start capability of the internal combustion engine can advantageously be further improved in a simple manner.

This object is achieved by a method having the features of claim 1.

Advantageous developments and embodiments of the invention are specified in the further claims.

According to the invention, a method is proposed for implementation with a piston internal combustion engine as part of a four-stroke cycle (working cycle) thereof, i.e. as part of a four-stroke cycle with the stroke sequence power stroke, exhaust stroke, intake stroke and compression stroke.

The piston internal combustion engine provided for carrying out the method, preferably in the form of a reciprocating piston internal combustion engine, has at least one (working) cylinder with an inlet tract (and at least one inlet valve) and an outlet tract (with at least one outlet valve) and a cylinder piston. Charge air can be selectively supplied to a combustion chamber of the cylinder via the intake tract (with intake valve(s)), and exhaust gas can be selectively discharged from the combustion chamber of the cylinder via the exhaust tract (with exhaust valve(s)). A piston internal combustion engine that can be used with the method can preferably have a plurality of cylinders configured as above - for example 4, 6, 8, 12, 20 or even more cylinders, i.e. in particular each operable according to the four-stroke cycle.

The piston internal combustion engine is also preferably a compression-ignited piston internal combustion engine, preferably e.g. a diesel engine (also heavy fuel oil, bio-oil, etc.), e.g a stationary application, e.g. in an industrial environment, in a combined heat and power plant or a power generator.

The method according to the invention provides a sequence of steps within the four-stroke cycle or a working cycle, in which, in a first step, a cylinder charge is compressed for the first time before the compression stroke and is thus heated (i.e. in particular inside the cylinder, preferably during a cylinder piston stroke). In a subsequent second step of the method, compressed, heated cylinder charge is discharged from the cylinder with expansion in the first step (i.e. in particular via at least one gas exchange valve, in particular in the intake tract). In a third process step, heated and expanded cylinder charge is mixed with fresh charge in the second step and subsequently returned to the cylinder and compressed again in the compression stroke. The method is repeated over a first number of iterations, with a respective power stroke of the four-stroke cycle being completed without combustion and the cylinder charge compressed and mixed with fresh charge in the third step being charge air.

The method characterized as above provides for two-time or two-stage compression as part of a working cycle or the four-stroke cycle, which enables multi-stage compression, the temperature of the cylinder charge or the charge air before the working stroke of the subsequent working cycle compared to the previously known single compression (in the compression stroke ) to increase significantly. As a result, an intended operating temperature of the internal combustion engine can advantageously be reached more quickly, which means that the problems described at the outset can be reduced. The proposed method can—for internal charge air preheating—in particular be carried out outside of a hot operation or internal combustion operation of the piston internal combustion engine (i.e. without combustion), in addition in particular during a cold start or when the piston internal combustion engine is tow-started.

The method generally provides that the heated cylinder charge is discharged from the cylinder in the second step with (approximately) adiabatically throttled expansion, i.e. while maintaining the temperature while lowering the pressure level (expansion), i.e. without doing any (additional) work. As a result, the charge, which was compressed and thus heated in the first step, advantageously retains an increased temperature level in the second step after being discharged from the cylinder, i.e. a higher initial temperature level with regard to the subsequent compression in the third step.

In a preferred embodiment of the proposed method, the compression is effected in the first step, like an intermediate compression or pre-compression (before the actual compression in the compression stroke), by means of the exhaust stroke or an exhaust piston stroke, furthermore in particular in conjunction with an advance of an exhaust valve timing (e.g. with a phase shift in the range from - 30° to - 45 °NW), or - alternatively or additionally - an early exhaust closing. If the exhaust is closed early, for example by shifting the exhaust valve control curve proportionately into the power stroke (advancement) or by reducing the exhaust valve opening lift (early exhaust closing), part of the cylinder charge remains in the combustion chamber during the exhaust stroke and is - towards it - during the exhaust stroke End - compacted (first compaction), therefore also heated.

The in the first step - compressed for the first time - cylinder charge can now according to the preferred embodiment of the method in the context of be exhausted from the cylinder subsequent intake stroke, ie with the transition from the exhaust stroke to the intake stroke. With the opening of the intake tract (via an intake valve) at the beginning of the intake stroke, the heated and compressed cylinder charge is allowed to initially escape into the intake tract, ie the cylinder charge is discharged from the cylinder according to the second method step. In this case, the cylinder charge ideally relaxes under the adiabatic throttling explained above, ie while maintaining its higher temperature level resulting from the first step.

In the preferred embodiment of the method, the cylinder charge that escaped into the intake tract in the second step can now be fed back to the cylinder from the intake tract in the third step, mixed with fresh charge, in order to be subsequently compressed in the compression stroke. This is advantageously caused simply by the continuous intake stroke piston stroke, which generates a vacuum which is suitable for sucking in the cylinder charge mixed with fresh charge again, i.e. while the intake is or remains open (piston stroke in particular towards bottom dead center UT).

As already mentioned above, the method according to the invention can already be carried out before the piston internal combustion engine is started, for example as part of tow-starting or starting. According to the invention, as already described above, the method is repeated over a first number of iterations, with a respective working cycle being completed without combustion. Furthermore, the cylinder charge compressed in the third step and mixed with fresh charge is essentially pure charge air (which is preheated with the method).

After the piston internal combustion engine has started, particularly during warm-up, the method can be repeated over a second number of iterations, with each power stroke being completed in a four-stroke cycle with combustion, particularly during injection operation. As combustion begins within the second number of iterations, exhaust timing advance and/or early exhaust closing may be reduced as the number of iterations increases (towards less early).

In particular when starting the internal combustion engine via a starting device, e.g. cold start, with a subsequent warm-up phase, the method can advantageously be repeated first for the number of first iterations without combustion and then for the number of second iterations with combustion each in the power stroke (whereby in the context of the second iterations can in turn be switched to normal control times with an increasing number of iterations).

A possible strategy for a starting process in the case of particularly poor starting conditions can, for example, provide for the first number of iterations (without fuel injection) - within the framework of the respective work cycles - to first heat the charge air, with the with an early, particularly very early, position of the exhaust profile Strong temperature increase effect can be used to advantage here to increase the temperature significantly (with little fresh charge being sucked in). With the onset of combustion or fuel injection, the exhaust valve position or the exhaust control curve can be set less early over the second number of iterations, so that the cylinder is supplied with sufficient fresh air mass for combustion (in addition to the hot exhaust gases and their recirculation via the intake valves in advantageously cause additional heating of the combustion chamber).

For the advantageously simple adjustment of the exhaust valve timing—in particular advanced or back to normal—an exhaust cam with a phase adjuster can be provided according to the invention, which is assigned to the exhaust tract or an exhaust valve of the same for adjusting the timing. Such a phase adjuster is associated with little structural effort, in addition to which the phase adjuster can also be used advantageously for controlling an HCCI engine, e.g. for retaining an internal residual gas mass.

According to the invention, a piston internal combustion engine is also proposed, which is set up to carry out the method explained above. Such an internal combustion engine can, for example, have control information for carrying out the method and a valve control device, in particular a phase adjuster as explained above, which interact to allow outlet control times—for the intermediate compression—to be controlled according to the method. The control information can be stored in a control unit of the internal combustion engine.

Further features and advantages of the invention result from the following description of exemplary embodiments of the invention, with reference to the figures of the drawings, which show details essential to the invention, and from the claims. The individual features can each be implemented individually or together in any combination in a variant of the invention.

• 1 exemplarisch und schematisch eine Ansicht, welche das Verfahren anhand von Gaswechsel- und Zylinderkolbenzuständen veranschaulicht.
• 2 exemplarisch und schematisch ein Diagramm, welches eine Endtemperatur im Zylinder in Abhängigkeit einer Auslasssteuerzeitverschiebung darstellt.

Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Show it:

• 1 exemplary and schematic view that illustrates the method based on gas exchange and cylinder piston states.
• 2 as an example and schematically a diagram which shows a final temperature in the cylinder as a function of an outlet control time shift.

1 illustrates the method according to the invention for execution with a piston internal combustion engine as part of a four-stroke cycle with the stroke sequence power stroke, exhaust stroke, intake stroke and compression stroke. The strokes are plotted over crankshaft degrees [°KW] between 0° and 720°. continue in 1 applied - in the upper part of the diagram - are an intake control curve A and exhaust control curves B and C, ie gas exchange valve lift over [°KW].

In the lower part of 1 - based on the partial views a) to d) - is also shown as an example of a cylinder 1 with cylinder piston 3 guided therein of the piston internal combustion engine, furthermore an intake or inlet (tract) 5 and exhaust or outlet (tract) 7 of the same or their Gas exchange valves 9 (inlet valve) and 11 (outlet valve). In the lower part of 1 a) to d) illustrate, in particular, gas exchange states and piston positions which occur during the method or as part of the respective method steps.

The reciprocating internal combustion engine used with the method is set up to be able to adjust at least the exhaust valve timing variably, in particular to be able to adjust the exhaust valve timing from "normal" to "advanced" (and vice versa), in particular to shift an exhaust valve control curve B proportionately into the power stroke. For this purpose, a phase adjuster can be provided for the exhaust cam of an exhaust valve 11 - with advantageously little effort - in addition, other devices for phase adjustment are of course conceivable, e.g. a fully variable valve train.

With the method according to the invention, which is intended in particular for cylinder-internal charge air heating, within one as in 1 Four-stroke cycle or working cycle shown, a multi-stage compression can be realized, comprising a first, intermediate compression (2nd compression, Fig. Lb), which precedes a compression in the actual compression stroke. In this way, the temperature level of the cylinder charge can be significantly increased compared to the previously known single-stage compression, ie before a subsequent power stroke of the next four-stroke cycle.

The first, the compression stroke preceding compression and heating of the cylinder charge - according to a first step - is at the 1 illustrated preferred embodiment of the method realized by means of the piston stroke of the exhaust stroke, while still according to the exhaust timing 1 is advanced, i.e. via the phase adjuster of the exhaust cam.

With the advanced exhaust control time, accompanied by a shift of the exhaust control curve B into the power stroke (illustrated by curve C in 1 , which shows an example of an exhaust control curve advanced by -45° NW compared to the normal exhaust control curve B), the exhaust 7 is already blocked during the exhaust stroke before the cylinder charge has all been pushed out, so that a part of the cylinder charge is released with the exhaust stroke of the cylinder piston 3 or .compressed in the exhaust stroke and thus heated, 1b .

In the second step that follows according to the method, compressed, heated cylinder charge is discharged from the cylinder 1 with expansion in the first step. Ideally, the relaxation takes place with adiabatic throttling, so that the cylinder charge can maintain the increased temperature level from the first step. For the discharge and expansion of the compressed, warmed-up cylinder charge, the intake side 5 is controlled open at the start of the intake stroke of the four-stroke cycle - in particular within the framework of normal valve timing - (in the context of the transition from the exhaust stroke to the intake stroke), so that the compressed, warmed-up charge (via an intake valve 9) first escapes into the intake or intake tract 5 (diabatic throttled), Fig. Ic.

For the third step that follows according to the method, in which heated and expanded cylinder charge is mixed with fresh charge and then fed back to cylinder 1 - 1d - and is compressed again in the compression stroke, the intake stroke with the subsequent compression stroke continues to be used below, especially within the framework of normal gas exchange control times. With the duration of the intake stroke increasing negative pressure as a result of the intake stroke of the piston 3 (in the direction of BDC) - with continued open control of the inlet 5 - the warmed charge that escaped into the intake tract 5 in the second step is mixed with fresh charge from the intake tract 5 in the cylinder 1 sucked back and subsequently in Compression cycle compressed again (second compression).

As can be seen, normal intake valve control times can be provided for the second and third step, so that variable valve control for the intake side 5 is not required at low cost. Furthermore, it is particularly advantageous for the compression stroke to be available for the compression in the third step over its entire interval duration for a maximized charge temperature increase.

As in 1 illustrated, the method provides for the working cycle - before the first compression - to be completed without combustion, for example as part of starting or external starting of the internal combustion engine. Executed without combustion, the outlet control times for the first compression can be adjusted here, for example, by 30°-40° [°NW] in the direction of early to very early. In this way, a significant preheating of the cylinder charge can be achieved over several iterations, for example 10 to 15 iterations. By mixing the heated charge with fresh charge, the temperature level at bottom dead center can be increased by a maximum of 500 K (without combustion), for example.

2 illustrates - in the context of a starting process without combustion - an example of an end temperature of the cylinder charge that can be achieved with the method as a function of the advancement of the exhaust control curve (in [°NW]; AÖ corresponds to "exhaust opens").

It should therefore be noted that with the proposed method a significantly improved cold start capability can be achieved, together with the avoidance of white smoke. In addition, engines with a lower compression ratio are also advantageously possible.

Finally, it should be noted that in the course of the invention, a variant was also developed which provides for the inlet valve to be opened twice per working cycle. In this variant, the heated charge can flow back in front of the intake valve through additional opening in the compression stroke, so that the basic temperature level in front of the cylinder increases. However, since the compression temperature is reduced with this solution, it only makes sense to use it if fuel is injected at most in every second working cycle, e.g. as part of cylinder deactivation mode. However, such a solution is obviously expensive and also complex, while the solution according to the invention has the great advantage of being able to use the compression phase in full for compression, in particular in each working cycle.

reference list

1

cylinder

3

cylinder piston

5

admission tract

7

exhaust tract

9

intake valve

11

outlet valve

Claims (10)

Method for execution with a piston internal combustion engine as part of a four-stroke cycle with the stroke sequence working stroke, exhaust stroke, intake stroke and compression stroke, the piston internal combustion engine comprising at least one cylinder (1) with an intake tract (5) and an exhaust tract (7) and a cylinder piston (3); where within the four-stroke cycle: - In a first step, a cylinder charge is compressed and heated for the first time before the compression stroke; - is discharged in a second step in the first step compressed, heated cylinder charge with expansion from the cylinder (1); - In a third step, in the second step, heated and expanded cylinder charge mixed with fresh charge is subsequently returned to the cylinder (1) and compressed again in the compression stroke; whereby - the method is repeated over a first number of iterations, wherein a respective power stroke of the four-stroke cycle is completed without combustion; and - The cylinder charge compressed in the third step and mixed with fresh charge is charge air. procedure after claim 1 , characterized in that - the heated cylinder charge is discharged from the cylinder (1) in the second step under adiabatically throttled expansion. Method according to one of the preceding claims, characterized in that - the method is carried out outside of a hot operation or internal combustion operation of the piston internal combustion engine; and - the method is carried out as part of a cold start or a tow-start of the piston internal combustion engine; or - the method is carried out with internal combustion operation of the piston internal combustion engine. Method according to one of the preceding claims, characterized in that - the compression in the first step is effected by means of the exhaust stroke; and or - The compression is brought about in the first step by means of an advance of an exhaust timing and/or an early exhaust closing during the exhaust stroke. Method according to one of the preceding claims, characterized in that - the second step takes place with the transition from the exhaust stroke to the intake stroke and/or at the beginning of the intake stroke. Method according to one of the preceding claims, characterized in that - in the second step, compressed, heated cylinder charge is discharged into the intake tract (5) with expansion; and - in the third step, heated and expanded cylinder charge mixed with fresh charge is fed back to the cylinder (1) from the intake tract (5). A method as claimed in any one of the preceding claims, characterized in that - the method is repeated over a second number of iterations, completing a respective power stroke of the four-stroke cycle with combustion; and/or within the scope of the second number of iterations, an advancement of the exhaust control time and/or an early exhaust closing is reduced with an increasing number of iterations. procedure after claim 1 and 7 , characterized in that - the method is first repeated over the number of first iterations without combustion and then over the number of second iterations with combustion each in the power stroke of the four-stroke cycle. Method according to one of the preceding claims, characterized in that - an exhaust cam with a phase adjuster is assigned to the exhaust tract (7) for adjusting the control time. Piston internal combustion engine set up to carry out the method according to one of the preceding claims.

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