DE102011083458A1 - Method for introducing unburnt hydrocarbons into an exhaust gas pipe of a four-stroke-piston-combustion engine, involves introducing hydrocarbons into combustion chamber in area of ignition-upper dead center - Google Patents

Abstract

The method involves introducing hydrocarbons into the combustion chamber in the area of an ignition-upper dead center, i.e. the upper dead center of the piston in the area of ignition of a hydrocarbon or air-mixture, by an injection process. The hydrocarbons are introduced into the combustion chamber in the range of 40 degrees kilowatts before a gas exchange-upper dead center up to the gas exchange-upper dead center, i.e. the upper dead center of the piston in the area of gas exchange, by an injection process.

Description

The invention relates to a method for introducing unburned hydrocarbons into an exhaust tract of a four-stroke reciprocating internal combustion engine having the features of the preamble of patent claim 1.

In current exhaust aftertreatment systems for diesel internal combustion engines, the exhaust gas must be at least temporarily conditioned according to the respective requirements. This is necessary to ensure the correct operation of these exhaust aftertreatment systems over a longer period of time. Specifically, in the current diesel exhaust aftertreatment systems, particulate filters (DPF) and NO _x storage catalytic converter (NSC) require cyclic regeneration.

Requirement for diesel particle filter regeneration: The exhaust gas temperature upstream of the DPF must be raised to a high level (approx. 580-650 ° C for non-additive systems), as far as possible from the load point, in order to effect the thermal oxidation of the soot deposited in the DPF. As an additional condition, a high (residual) oxygen content in the exhaust gas must be ensured before the DPF, so that enough oxygen is available for this reaction. In real operation, a 15-minute DPF regeneration typically has to be performed approximately every 1200 km (depending on the driving profile). The current state of many diesel internal combustion engines is to raise the exhaust gas temperatures by internal engine settings. This is done by throttling the engine and applying multiple fuel injections in the combustion cycle. Some of these injections can also be partially applied late after the ignition TDC (up to about 180 ° CA (crankshaft) after top dead center of the piston). This late application causes an increase in the exhaust gas temperatures when opening the gas exchange outlet valve, as well as an increase in the HC / CO emissions (hydrocarbon / carbon monoxide) in the exhaust gas. The oxidation of the partially high HC / CO emissions in the catalytic converter connected downstream of the engine leads to an additional exotherm in the exhaust system. In sum, the desired regeneration temperature level before and also in the DPF is achieved due to the internal engine-elevated exhaust gas temperature level and the exotherm due to the HC / CO oxidation.

NSC (NO _x Storage Catalyst) Regeneration Requirements: In order to carry out NGC regeneration (the so-called "DeNO _x " reaction, the conversion of nitrates stored in the NSI to nitrogen), a specific lambda level in the exhaust gas must be less than or equal to zero typically about 0.92) before the NPC. The fuel components (H ₂ , CO, HC) in the exhaust gas which are not completely oxidized due to the lack of oxygen serve as reducing agents for the stored nitrates. The residual oxygen content in the exhaust gas at the NSC should be as low as possible in this operating mode because it impairs the DeNO _x reduction process. In real operation, an NSC regeneration with a duration of up to 15 seconds is required approximately every ten minutes to reduce the total stored nitrate. The current state of many diesel internal combustion engines is similar to the DPF regeneration mode is to find combustion settings for the internal combustion engine, which lead to a lambda level less than one in the exhaust system. The main measures that are common today to achieve this goal are, in turn, the strong throttling of the internal combustion engine and the application of sometimes very high post-injection quantities at injection times up to about 180 ° CA after TDC.

This results in the following disadvantages:
The operating range of the above-mentioned combustion settings is limited: Especially in low-load operating points, the high amount of fuel required for increasing the temperature and lambda reduction can no longer be introduced by post-injection without the engine output torque being increased. Thus, such combustion settings can not be displayed in low-load operating points.

High fuel consumption:

Specially DPF regeneration Combustion settings can no longer be efficiently displayed at constant speeds at low speeds due to high fuel consumption. Some of the heat generated within the engine, from the fuel supplied, is dissipated by the coolant circuit of the internal combustion engine and is no longer available in the exhaust gas. This lack of heat increases the fuel consumption in the DPF regeneration settings.

Low oxygen content in the exhaust gas:

The above fuel over-consumption results in a lower residual oxygen content in the exhaust gas at DPF regeneration settings. This lower oxygen content limits the Rußabbrandgeschwindigkeit.

High component temperatures on the exhaust side:

Since usually the majority of the temperature increase takes place inside the engine and thus usually only small exotherms in the downstream, catalytically active elements are achieved, is with high component temperatures (exhaust manifold, exhaust manifold, Exhaust gas turbocharger, etc.) to be expected in higher load operating points. This leads to increased component load and also difficulties in the representation of DPF combustion settings in these load ranges.

High oil dilution:

The introduction of post fuel injection quantities in the combustion cycle at times when the piston has already moved far away from top dead center often results in the fuel injection jets penetrating from the injector to the cylinder wall. On the relatively cold cylinder wall, unburned fuel accumulates, which in the next upward movement of the piston past the piston rings can pass into the oil space under the cylinder bore (so-called "oil dilution"). The amount of fuel thus introduced into the oil can lead to problems in the operation of the internal combustion engine (viscosity loss of the oil, exceeding the maximum oil level, etc.).

In the DE 10 2006 042 875 A1 , from which the invention proceeds, is provided with a method for injecting unburned hydrocarbons into the exhaust gas tract of an internal combustion engine, in particular for the purpose of regeneration of a particulate filter provided in the exhaust tract and / or for the purpose of desulfurization of a storage catalytic converter provided in the exhaust tract, in which by means of a In the exhaust system provided injector the unburned hydrocarbons are injected as part of an injection process, which is characterized in that the per unit time .DELTA.t injected amount .DELTA.m _{HC is} controlled in unburned hydrocarbons in the injection process, trying to solve the above problems.

Disadvantages of this known method are the additionally required hardware components in the form of an injection nozzle, piping, etc., as well as an additional control unit function.

The object of the present invention is o. G. To avoid disadvantages.

This object is solved by the features in the characterizing part of patent claim 1.

The change of the fuel injection pattern during regeneration adjustments in the form is proposed:

First:

• a.) bei DPF-Regenerationen hohe Exothermen über ein nachgeschaltenes katalytisches Element zu erreichen und
• b.) bei DeNO_x Regenerationen das Lambda im Abgas stark abzusenken.

The offset of at least one fuel injection during the charge cycle, preferably in the region shortly before the gas exchange TDC, with the aim of greatly increasing the HC / CO emissions in the exhaust gas. For example, it is possible to greatly increase the HC / CO emissions

• a.) to achieve high exotherms via a downstream catalytic element in DPF regenerations and
• b.) to greatly lower the lambda in the exhaust gas during DeNO _x regenerations.

Secondly:

During the combustion cycle, the deposition of at least one main injection and gem. Claim 2 at least one post injection placed well after the combustion TDC. (with or without one or more pre-injections) with the aim of achieving a moderate internal engine temperature increase / lambda reduction without exceeding the component temperature limits.

The inventive method thus allows the extension of the operating range of regeneration settings. The introduction of fuel in the charge cycle with open Gaswechselauslassventil is largely torque neutral. Thus, even in low-load points, the required high fuel quantities can be introduced into the combustion chamber and thus into the exhaust gas. DeNO _x and DPF regeneration settings are stable at much lower loads than before.

Furthermore, a significantly reduced additional fuel consumption results in DPF regenerations. The amount of post-injection introduced in the charge cycle takes only a rudimentary part in combustion and oxidation processes in the combustion chamber. The predominant part is transferred as HC / CO into the exhaust gas. These HC / CO emissions are highly efficiently (thermally) oxidized at the downstream catalytic elements and, as desired, directly heat the exhaust gas without giving up heat to the engine cooling circuit. The thus increased overall efficiency of the regeneration temperature attainment process, or in the DPF, results in a significant fuel economy benefit during DPF regeneration.

Furthermore, the process according to the invention leads to a higher residual oxygen content. The above-mentioned increased overall efficiency results in a lower overall fuel injection quantity with the same exhaust gas mass flow and thus in a significantly increased residual oxygen content before or in the DPF. Soot burn-off during DPF regeneration is significantly accelerated by the higher residual oxygen content.

Furthermore, the method according to the invention leads to lower component temperatures on the exhaust gas side. The introduction of high amounts of HC / CO into the exhaust gas makes it possible to achieve high exotherms of a few hundred degrees via the catalytic elements in the exhaust gas system. Thus, with the same target temperature before or in the DPF, the temperature before these elements, and thus the component temperatures, can be greatly reduced. Lower component temperatures (manifold, ATL, etc.) are realized in an advantageous manner.

Furthermore, the inventive method leads to a reduced oil dilution. By choosing the fuel injection timing in the charge cycle near / before the charge cycle OT the injection jet no longer hits the cylinder wall, but the piston and / or the piston recess. The thus reduced cylinder wall wetting leads to a greatly reduced oil dilution.

In the following the invention is explained in more detail with reference to two figures.

1 shows in a diagram an in-cylinder pressure curve and an injection curve according to the invention for an internal combustion engine.

2 shows a temperature profile for a known method and the inventive method.

1 shows in a diagram an in-cylinder pressure curve 1 and an injection process according to the invention 5 for a four-stroke reciprocating internal combustion engine. About the Y-axis is the in-cylinder pressure 1 from 0 to 40 [bar] and over the X-axis the crank angle KW [degrees] of the crankshaft from -80 ° to 640 ° is plotted.

Shortly after about 0 ° CA, in ignition TDC (top dead center) of the piston, the cylinder internal pressure 1 its maximum value of about 32 bar and falls until the change of charge OT at 360 ° KW to about exhaust manifold pressure. A valve lift curve 3 a Gaswechselauslassventils extends from about 140 ° CA to about 380 ° KW, a valve lift 4 a gas exchange inlet valve extends from about 340 ° CA to about 580 ° KW. A fuel injection process (main injection) in this embodiment is three single injection operations 2 divided in the range of the highest cylinder internal pressure.

An inventive injection process 5 lies in the range of the charge exchange OT at approx. 340 ° KW. According to the invention, it can be between 40 ° CA before the charge-exchange TDC and until the charge-exchange TDC, so that the fuel does not hit any cylinder wall, but only a piston or a piston recess. Next takes place at about 40 ° CA, in an expansion phase after the ignition TDC, an additional injection process 6 instead of.

2 shows a temperature profile for a known method (base) and the inventive method. A gas temperature of 0 to 800 ° C is plotted over a Y axis. Measuring points for the temperature are plotted over an X-axis. T21 is an intake air temperature, T31 an exhaust gas temperature after the engine, T40 an exhaust gas temperature after a turbocharger of an exhaust gas turbocharger (ATL), three further exhaust gas temperatures in a DeNO _x storage catalytic converter (NSC) and an exhaust gas temperature TvCSF after the NSC and in front of a particulate filter (DPF).

The associated temperature profile for the known method (base) is entered with diamonds in the diagram, the associated temperature profile for the inventive method (invention) is entered with rectangles in the diagram.

Based on 2 is now clearly seen that the exhaust gas temperature T31 is significantly lowered by about 200 ° C, shown by an arrow by the inventive method, but within the NSC by the above effects, however, again at the conventional level, so that in the DPF a Minimum Rußbrbrandtemperatur is ensured.

• • Bauteiltemperaturabsenkung,
• • starke Exothermenanhebung,
• • hohe Exotherme direkt im NSC Eintrittsbereich.

Thus, as detailed above, the following temperature effects are achieved by the method according to the invention:

• • component temperature reduction,
• • strong exothermic increase,
• • high exotherm directly in the NSC inlet area.

LIST OF REFERENCE NUMBERS

1

Cylinder pressure

2

Injection process

3

Valve lift curve Gas exchange outlet valve

4

Valve lift curve Gas exchange inlet valve

5

Inventive injection process

6

additional injection process

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 102006042875 A1 [0010]

Claims (2)

Method for introducing unburnt hydrocarbon into an exhaust tract of a four-stroke reciprocating piston combustion engine, in particular for regenerating a arranged in the exhaust tract particulate filter and / or for the desulfurization and / or DeNO _x ation of a arranged in the exhaust tract storage catalytic converter by means of an injection nozzle, with the hydrocarbons in a combustion chamber of the internal combustion engine can be injected, wherein the combustion chamber of a cylinder in which a reciprocating piston is arranged with a piston recess and a cylinder head is limited with gas exchange valves, characterized by the following process steps: - introducing hydrocarbons into the combustion chamber in the region of an ignition TDC (top dead center of the piston in the region of ignition of a hydrocarbon / air mixture) by at least one injection process, - introduction of hydrocarbons in the combustion chamber in the range of 40 ° CA before a change of charge TDC until the charge cycle sel-OT (top dead center of the piston in the region of a charge change) by at least one injection process. Method according to claim 1, characterized by the following method step: - Introducing hydrocarbons in the combustion chamber after the ignition TDC during an expansion phase by at least one injection process.

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