DE102019001517A1 - Method for operating an internal combustion engine of a motor vehicle, in particular a commercial vehicle - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine (10) of a motor vehicle, which has at least one combustion chamber (12), in which, within one working cycle of the internal combustion engine (10), at least one main quantity of a gaseous fuel and at least one second quantity of a liquid fuel that is smaller than the main quantity and self-igniting fuel for igniting the gaseous fuel are introduced into the combustion chamber (12), with at least a third amount of the liquid fuel being introduced into the combustion chamber (12) within the working cycle after the introduction of the main amount and the second amount in such a way that combustion the third amount is omitted in the combustion chamber (12) and the third amount is expelled unburned from the combustion chamber (12) into an exhaust tract of the internal combustion engine (10).

Description

The invention relates to a method for operating an internal combustion engine of a motor vehicle according to the preamble of patent claim 1.

One such method for operating an internal combustion engine of a motor vehicle that has at least one combustion chamber is already, for example WO 2014/089702 A1 as known. In the method, at least one main quantity of a gaseous fuel and at least one pilot quantity of a liquid and self-igniting fuel, which is smaller than the main quantity, is introduced into the combustion chamber, in particular directly, for igniting the gaseous fuel within a respective work cycle of the internal combustion engine.

The object of the present invention is to further develop a method of the type mentioned at the beginning in such a way that particularly high exhaust gas temperatures can be implemented in a particularly simple manner.

This object is achieved by a method with the features of claim 1. Advantageous refinements with expedient developments of the invention are specified in the remaining claims.

In order to further develop a method of the type specified in the preamble of claim 1 in such a way that particularly high exhaust gas temperatures can be achieved in a particularly simple manner, the invention provides that at least a third amount of the liquid fuel within the working cycle after the introduction of the main amount and the pilot amount is introduced into the combustion chamber, in particular directly, in such a way that there is no combustion of the third quantity in the combustion chamber and the third quantity is pushed unburned from the combustion chamber into an exhaust tract of the internal combustion engine. The main amount is also referred to as the first amount, with the pilot amount also being referred to as the second amount. The third amount can correspond to the second amount, be smaller than the second amount or be larger than the second amount. Because the third quantity is not burned in the combustion chamber, but is pushed out of the combustion chamber unburned and thus reaches the exhaust tract without being burned, the third quantity or the liquid fuel forming the third quantity can be stored in the exhaust tract, which is also known as the exhaust system or exhaust system ignited and subsequently burned, in particular exothermic, whereby exhaust gas flowing through the exhaust tract can be heated particularly effectively. This means that particularly high exhaust gas temperatures, also referred to as exhaust gas temperatures, can be achieved in the exhaust gas tract.

The unburned third quantity is ignited, for example, in an oxidation catalytic converter of the exhaust tract and / or in a particulate filter of the exhaust tract, designed for example as a diesel particulate filter, and subsequently burned exothermically. In this way, particularly high exhaust gas temperatures of around 600 degrees Celsius, for example, can be achieved. In this way, the particle filter can be regenerated in a particularly advantageous manner, in particular when it is loaded with particles.

A diesel fuel, for example, is used as the self-igniting liquid fuel. The third quantity is pushed out of the combustion chamber, for example, during an exhaust stroke of the internal combustion engine and thus introduced into the exhaust tract without being burned, whereby particularly high exhaust gas temperatures can be ensured. The third quantity is transported, for example, by a turbine of an exhaust gas turbocharger of the internal combustion engine arranged in the exhaust gas tract and then, for example, ignited and exothermically burned in the aforementioned oxidation catalytic converter and / or in the particle filter itself.

The method according to the invention enables particularly high exhaust gas temperatures to be achieved, the number of parts in the internal combustion engine being able to be kept particularly low. The invention is based in particular on the following findings: If, for example, a high-pressure pump with an integrated low-pressure suction pump is used, for example to transfer at least one of the fuels, in particular a liquid fuel, from a fuel tank to an injector for introducing the one fuel, in particular the liquid fuel, To convey into the combustion chamber, there is often the problem that there is no intermediate outlet between the high-pressure pump and the low-pressure suction pump, via which a metering system, also known as an HC metering system, is supplied with one fuel, in particular with the liquid fuel can. Such an HC metering system can, however, be desirable in order to introduce the uncombusted liquid fuel into the exhaust system by bypassing the combustion chamber by means of the HC metering system. In this way, unburned hydrocarbons (HC) can be introduced into the exhaust system. The unburned hydrocarbons can then be burned exothermically in the exhaust gas tract, whereby particularly high exhaust gas temperatures can be achieved. Usually the unburned hydrocarbons introduced into the exhaust gas tract by means of such an HC metering system at a pressure of five bar up to and including six bar, with such a pressure usually being available at an output of a mechanical feed pump. The burned hydrocarbons are usually introduced into the exhaust gas tract by means of the HC system, bypassing the combustion chamber, downstream of the turbine, also referred to as the exhaust gas turbine, and for example upstream of the oxidation catalytic converter and / or upstream of the particle filter.

In order to enable unburned hydrocarbons to be introduced into the exhaust gas tract, an intermediate outlet between the high pressure pump and the integrated low pressure suction pump is required, or a high pressure pump with an integrated low pressure suction pump cannot be used, but a high pressure pump and a separate low pressure pump. Suction pump can be used.

The method according to the invention now makes it possible to introduce the third amount unburned into the exhaust tract, whereby unburned hydrocarbons can be introduced into the exhaust tract without an HC metering system or an outlet between a high pressure pump and an integrated low pressure suction pump being required or provided for this. As a result, the number of parts and thus the costs and the weight of the internal combustion engine or the motor vehicle can be kept particularly low overall.

The second quantity is introduced into the combustion chamber, for example, by what is known as a pilot injection, in particular injected directly into the combustion chamber. The first quantity is introduced into the combustion chamber, for example, by what is known as a main introduction, the main introduction also being referred to as the main injection or main injection.

The third quantity is introduced into the combustion chamber, for example, by a so-called post-injection, in particular injected directly into the combustion chamber, the post-injection being carried out after the pilot injection and the main injection within the work cycle. Within the work cycle, for example, a total amount, in particular a total volume, of fuel is introduced into the combustion chamber, especially directly, with the first amount making up five percent and the second amount 90 percent of the total amount. The gaseous fuel is a so-called main fuel, which is ignited by means of the liquid, pre-burned or burned fuel, which is also referred to as an ignition source or functions as an ignition source. Since the post-injection is also carried out, the method according to the invention includes a late post-injection strategy, whereby structural requirements such as the aforementioned intermediate outlet and the additional HC metering system can be avoided.

For example, it is conceivable that the post-injection is carried out exactly once, so that, for example, the third quantity is introduced into the combustion chamber, in particular injected directly, as part of a single post-injection. It is also conceivable to carry out the post-injection multiple times or to carry out multiple or multiple late post-injections, by means of which a respective third quantity of the liquid fuel is introduced into the combustion chamber, in particular directly injected, within the work cycle after the introduction of the first quantity and the second quantity. Natural gas, for example, is used as the gaseous fuel, and particularly low-emission and efficient operation of the internal combustion engine can be achieved.

In particular, it is possible to operate the internal combustion engine by means of the method as a so-called HPDI motor, in particular as an HPDI commercial vehicle engine (HPDI - High Pressure Direct Injection). The invention is also based on the knowledge that, in particular with an HPDI engine, the smoke map is at a very low level compared to a conventional diesel engine, so that the regeneration frequency of the particle filter is lower than is usual with a modern common rail diesel engine.

For example, due to the system, the injection pressure is only 500 bar, in particular only 300 bar, the liquid fuel, for example in the form of diesel fuel, being introduced into the combustion chamber at the specified injection pressure, in particular being injected directly. This very low injection pressure results in a low jet penetration depth of the third quantity or a so-called post-injection spray, which is formed by the third quantity, in the direction of a cylinder wall delimiting the combustion chamber compared to conventional common rail diesel engines. This reduces the accompanying risk of oil washing and fuel entry into the engine oil compared to diesel engines, in which diesel fuel is injected at up to around 2500 bar.

Furthermore, it has also been shown to be advantageous if the second quantity is at least partially, in particular at least predominantly or completely, introduced into the combustion chamber before the introduction of the first quantity into the combustion chamber begins.

In a further embodiment it is provided that the introduction of the pilot quantity begins after the introduction of the main quantity or at least partially before the end of the introduction of the main quantity.

For example, the third quantity is injected directly into the combustion chamber at a pressure, the pressure being at most 500 bar, in particular at most 300 bar. The pressure with which the third quantity is blown directly into the combustion chamber is preferably in a range from 250 bar up to and including 750 bar.

Further advantages, features and details of the invention emerge from the following description of a preferred exemplary embodiment and with reference to the drawing. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the single figure can be used not only in the specified combination, but also in other combinations or on their own, without the frame to leave the invention.

The drawing shows, in the single figure, a partial schematic sectional view of an internal combustion engine which is operated according to a method according to the invention.

The single FIGURE shows a partial schematic sectional view of an internal combustion engine designed as a reciprocating piston engine 10 of a motor vehicle, which is preferably designed as a utility vehicle. The motor vehicle is by means of the internal combustion engine 10 drivable. The internal combustion engine 10 has at least one combustion chamber 12 on, which is partly through a cylinder 14th , partly through a combustion chamber roof 16 and partly by a piston 18th is limited. The cylinder 14th is through a cylinder wall 20th a housing element 22nd the internal combustion engine 10 limited so that the housing element 22nd for example a crankcase or a cylinder crankcase. The piston 18th can be moved translationally into the cylinder 14th recorded and thus translationally movable back and forth between its top dead center and its bottom dead center. In other words, it is the piston 18th relative to the cylinder wall 20th translationally movable back and forth between the top dead center and the bottom dead center. The combustion chamber roof 16 is formed, for example, by a second housing element, the housing elements being formed separately from one another and connected to one another. The second housing element is, for example, a cylinder head. The combustion chamber 12 is an injector device 24 assigned, which is also simply referred to as an injector.

The piston 18th is about a connecting rod 26th articulated with an output shaft of the internal combustion engine which is designed, for example, as a crankshaft and cannot be seen in the figure 10 coupled so that the translational movements of the piston 18th in the cylinder 14th can be converted into a rotary movement of the output shaft. A respective work cycle of the internal combustion engine 10 includes exactly two complete rotations of the output shaft and thus 720 degrees crank angle. The internal combustion engine 10 is designed as a four-stroke engine so that the respective work cycle comprises exactly four strokes. A first of the cycles is, for example, an intake cycle during which the piston is 20th moved from its top dead center to its bottom dead center. Immediately after the first cycle, there is a second cycle, the second cycle being a compression cycle. During the second stroke the piston moves 20th from its bottom dead center to its top dead center. Immediately after the second stroke, a third of the strokes follows, during which the piston moves from its top dead center to its bottom dead center. The third cycle is a power cycle during which the piston and thereby the output shaft as a result of being in the combustion chamber 12 combustion taking place are driven. The fourth stroke immediately following the third stroke is a so-called exhaust or push-out stroke, during which the piston moves from its bottom dead center to its top dead center. During the working cycle, the combustion chamber takes place 12 formed a mixture which comprises at least air and fuel. Both the air and the fuel are fed into the combustion chamber 12 introduced within the work cycle. The mixture is preferably ignited within the working cycle by self-ignition and then burned, so that the internal combustion engine 10 is preferably a compression ignition internal combustion engine.

A method for operating the internal combustion engine is described below 10 described, the method preferably during a fired operation of the internal combustion engine 10 is carried out. During the fired operation of the internal combustion engine 10 - as previously described - the air and the fuel in the combustion chamber 12 introduced, whereupon the mixture is ignited and burned. Combustion of the mixture thus takes place during the fired operation within the respective work cycle. The combustion produces exhaust gas, which is released from the combustion chamber in the course of the exhaust stroke 12 pushed out and into an exhaust tract of the internal combustion engine 10 is initiated. Of the The exhaust gas tract includes, for example, an oxidation catalytic converter through which the exhaust gas can flow and a particle filter, designed for example as a diesel particle filter, by means of which particles, in particular soot particles, can be filtered from the exhaust gas.

In the case of the method, the internal combustion engine 10 at least or precisely one main injection and at least or precisely one pilot injection carried out. As a result of the main injection or by performing the main injection, a first quantity of a gaseous fuel, for example in the form of natural gas, is injected by means of the injector device 24 directly into the combustion chamber 12 blown into the combustion chamber 12 brought in. As a result of the pilot injection or the implementation of the pilot injection, a second quantity of a liquid and self-igniting fuel is used within the respective work cycle to ignite the gaseous fuel by means of the injector device 24 directly into the combustion chamber 12 injected and thus into the combustion chamber 12 brought in. The first amount is also referred to as the main amount, the second amount also being referred to as the pilot amount. The main quantity or the gaseous fuel is ignited by means of the pilot quantity, in particular in such a way that the pilot quantity and the fuel in the combustion chamber 12 Introduced air comprising mixture is ignited by self-ignition, whereby, for example, a mixture comprising the gaseous fuel and the air is ignited.

As a result, for example, the aforementioned mixture is in total in the combustion chamber 12 ignited and burned. The pilot quantity is smaller than the main quantity. If, for example, the pilot quantity and the main quantity together form a total quantity, in particular a total volume, the pilot quantity is, for example, five percent of the total quantity, and the main quantity is, for example, 90 percent of the total quantity. It should be emphasized in particular that both the gaseous fuel and the self-igniting and liquid fuel for igniting the gaseous fuel by means of the same injector device 24 directly into the combustion chamber 12 be introduced.

In order to be able to achieve particularly high temperatures of the exhaust gas in the exhaust tract in a particularly simple manner, the method provides that at least or precisely one post-injection is carried out or several post-injections are carried out within the work cycle after the pilot injection and after the main injection. Through the respective post-injection or by carrying out the respective post-injection, a third amount of the liquid and self-igniting fuel is introduced into the combustion chamber within the working cycle after the introduction of the first quantity and after the introduction of the second quantity 12 introduced, in particular injected directly, that a combustion of the third quantity in the combustion chamber 12 is omitted and the third quantity is unburned from the combustion chamber 12 into the exhaust system of the internal combustion engine 10 is pushed out. The third quantity is also referred to as the post-injection quantity, with combustion of the post-injection quantity in the combustion chamber 12 is omitted. As a result, the post-injection quantity reaches the exhaust gas tract unburned, since the post-injection quantity is for example during the exhaust stroke by means of the piston 20th together with the exhaust gas from the combustion chamber 12 is pushed out and introduced into the exhaust system. As a result, unburned hydrocarbons (HC) formed by the third quantity are introduced into the exhaust system. The third quantity or the unburned hydrocarbons is or are transported through the exhaust tract, for example through a turbine of the exhaust gas turbocharger, whereupon the third quantity is ignited in the oxidation catalytic converter and / or in the particle filter and subsequently burns exothermically. As a result, the exhaust gas can be heated to particularly high temperatures and, for example, approximately 600 degrees Celsius, whereby the particle filter, for example, can be regenerated particularly effectively. Complex structural expenses such as an intermediate outlet between a high pressure pump and a low pressure suction pump as well as an additional HC dosing system can be avoided, so that the number of parts and thus the weight and costs of the internal combustion engine 10 can be kept particularly low. Nonetheless, unburned hydrocarbons can be introduced into the exhaust gas tract in the manner described to regenerate the particle filter.

It is provided that the post-injection by means of the injector device 24 is carried out, so that the third quantity is also carried out by means of the injector device 24 directly into the combustion chamber 12 injected and thereby into the combustion chamber 12 is introduced. This can reduce the number of parts and thus the weight and costs of the internal combustion engine 10 can be kept in a particularly small framework.

List of reference symbols

10

Internal combustion engine

12

Combustion chamber

14th

cylinder

16

Combustion chamber roof

18th

piston

20th

Cylinder wall

22nd

Housing element

24

Injector device

26th

Connecting rod

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

• WO 2014/089702 A1 [0002]

Claims (6)

Method for operating an internal combustion engine (10) of a motor vehicle, which has at least one combustion chamber (12), in which at least one main quantity of a gaseous fuel and at least one second quantity of a liquid and self-igniting fuel, which is smaller than the main quantity, for ignition within a working cycle of the internal combustion engine (10) of the gaseous fuel are introduced into the combustion chamber (12), characterized in that within the working cycle after the introduction of the main amount and the second amount at least a third amount of the liquid fuel is introduced into the combustion chamber (12) such that combustion of the third Amount in the combustion chamber (12) is omitted and the third amount is pushed unburned from the combustion chamber (12) into an exhaust tract of the internal combustion engine (10). Procedure according to Claim 1 , characterized in that the third amount is injected directly into the combustion chamber (12). Procedure according to Claim 2 , characterized in that the third quantity is injected directly into the combustion chamber (12) at a pressure, the pressure being in a range from 250 bar up to and including 750 bar. Method according to one of the preceding claims, characterized in that the main amount is blown directly into the combustion chamber (12). Method according to one of the preceding claims, characterized in that the introduction of the second amount begins after the introduction of the main amount or at least partially before the end of the introduction of the main amount. Method according to one of the preceding claims, characterized in that the second amount is at least partially, in particular at least predominantly or completely, introduced into the combustion chamber (12) before the introduction of the first amount into the combustion chamber (12) begins.

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