DE102012207904A1 - Method for suppressing pre-ignition occurring before ignition timing in combustion chamber of engine, involves detecting occurrence or increased risk of pre-ignition and injecting water with modified injection characteristic - Google Patents

Abstract

The method involves detecting (100) occurrence of pre-ignition or an increased risk of pre-ignition. The water is injected with a modified injection characteristic at predetermined time in response to detection. The water injection quantity is increased after detection process. The nitric oxide formation is reduced by knock suppression. An independent claim is included for an engine control apparatus for internal combustion engine with water injection.

Description

It is known to inject water in an internal combustion engine in order to suppress knocking combustion and thus to increase the efficiency or the power. For this purpose, the water is injected with an injector into the intake manifold or directly to the combustion chamber or fed to the internal combustion engine engine together with the fuel. The water is usually taken from a tank and the amount of water is metered with a pulse valve.

An exemplary internal combustion engine with water injection is in the document DE 10 2011 015 628 A1 described.

In gasoline engines, especially in supercharged high-power gasoline engines, irregular combustion events may occur that are prior to the actual ignition timing set by the ignition system. Such a combustion event is also referred to as pre-ignition. In such Vorentflammungen very high pressure amplitudes can be achieved, which can lead to component damage to the engine damage.

Pre-ignition occurs preferably at high engine load and low or medium speeds. A pre-ignition is characterized by an early combustion which starts before the ignition timing set by the ignition and generates a high peak pressure. Due to the early combustion condition, the efficiency is worse than ignition caused by combustion and the associated loss of torque leads to a brief decrease in engine speed.

It is from the publication DE 10 2006 015 662 A1 known to perform by means of a sensor detection of Vorentflammungen and perform a shutdown of the affected cylinder depending on the detection.

From the publication DE 10 2009 008 248 B4 It is known to produce a fuel-rich fuel-air mixture in the combustion chamber to prevent Vorentflammungen by changing the injected fuel mass. Similarly, in the document DE 10 2008 038 102 B4 to prevent a pre-ignition an additional amount of fuel injected. The amount of fuel is increased so that the combustion chamber temperature is lowered. Analog is in the publication WO 2010/1 24699 A1 injected an amount of fuel causing a rich air ratio after detecting an irregular combustion.

Furthermore, it is from the document DE 10 2010 004 091 A1 It is known to determine a measure of the amount of pre-ignition and to make a multiple injection of fuel depending on the degree of pre-ignition.

It is an object of the invention to provide a further method for suppressing pre-ignition occurring before a predetermined ignition time and a correspondingly operating engine control unit.

The object is solved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

In the method according to the invention for suppressing pre-ignition occurring in a combustion chamber of an internal combustion engine before a predetermined ignition time, the occurrence of pre-ignition is first detected, for example by detecting the occurrence of one or a certain number of pre-ignition events. Alternatively, it can also be recognized that there is an increased risk for this, without actually having such combustion events occurred; for example, by determining that inferior fuel is present or the combustion chamber has heavy deposits. Both factors increase the likelihood of pre-ignition.

The engine is preferably a gasoline engine. In addition, a charge, in particular by means of exhaust gas turbocharger, is preferably provided.

The invention is based on the finding that by means of water injection, the Vorentflammungsneigung, especially in highly charged gasoline engines can be reduced. By injecting water, for example, glowing particles can be extinguished, so that combustion before ignition of the ignition is prevented.

Upon detection of pre-ignition (or a hazard), an injection of water will be triggered. It can also be provided that, in the event that water has already been injected beforehand (for example for knock reduction or reduction of the NOx emission), the detection of pre-ignition (or a risk thereof) injects the water with a modified injection characteristic which is suitable is to suppress pre-ignition. The change of the injection characteristic may mean, for example, that the water injection amount per cycle (ie per cycle) is increased, the water injection earlier during the work cycle or that an additional amount of water is injected to suppress pre-ignition. For example, it may be provided that in one or more pre-ignition cycles, the amount of water injection in the affected cylinder (s) is increased immediately after the event to prevent further pre-ignition cycles.

Preferably, the water is injected with an injector directly into the combustion chamber.

The water injection should start in the working cycle so early before the between the compression and working stroke top dead center (TDC) that a pre-ignition, which occurs before the ignition, is prevented by the introduction of water before their emergence. In particular, water injection should begin before ignition.

The water injection or the modified water injection characteristic triggered as a function of the recognition should, for example, be such that from a point in time which is in the range from 180 ° CA to 90 ° CA before the top dead center (ignition TDC) between compression and power stroke, Water is injected. For example, in an injection interval with an injection start ≤ 180 ° CA before the ignition TDC (ie earliest injection start 180 ° CA before ignition TDC) and an injection end ≥ 60 ° CA before the ignition TDC (ie latest injection end 60 ° CA before ignition -OT) continuously injected with water; this may be an early, first injection of a total of two or more injections per cycle.

As stated above, pre-ignition generally results in torque loss and a brief decrease in engine speed. This negative speed gradient can be diagnosed with the crank angle sensor and the associated working cycle identified as a pre-ignition cycle. Alternatively or additionally, for example, a structure-borne noise signal of a knock sensor and / or a pressure signal of a pressure sensor can be evaluated in order to detect pre-ignition.

It can be provided that, depending on the recognition, switching to engine operation with multiple water injection per working cycle, whereby for example a simple water injection or no water injection at all was present before. In multiple water injection, at least two water injection quantities are injected in at least two separate injection intervals. An early first water injection quantity serves to suppress pre-ignition, and a second water injection quantity injected thereafter during the same cycle is used, for example, for suppressing knocking or for reducing the NOx emission by cooling the cylinder charge. The injection of the first injection quantity takes place in the compression stroke; for example, it starts at the beginning of the compression stroke or later during the compression stroke. The beginning of the injection of the first injection quantity is for example in the range of 180 ° CA to 90 ° CA before ignition TDC. The end of the injection of the first injection quantity is, for example, in the range of 170 ° CA to 60 ° CA before ignition TDC.

In an engine controller for an internal combustion engine with water injection according to the invention, the engine controller is adapted to detect the occurrence of pre-ignition or an increased risk thereof. Depending on this, the engine controller may initiate the injection of water (if no water has been previously injected) or initiate the injection of water with modified injection characteristics (if water has already been injected before).

The above statements on the method according to the invention also apply correspondingly to the device according to the invention; advantageous embodiments of the device according to the invention correspond to the described advantageous embodiments of the method according to the invention.

The invention will be described below with reference to the accompanying drawings with reference to an embodiment. In these show:

1 An embodiment of the inventive method for suppressing occurring before a predetermined ignition irregular combustion; and

2 an exemplary dual water injection.

In 1 an embodiment of the inventive method for suppressing occurring before a predetermined ignition irregular combustion is shown in simplified form. The method described below is performed for each cylinder of the internal combustion engine. The following describes the method for a cylinder.

At the start of the process, there is already a single water injection per working cycle to avoid knocking combustion.

According to process step 100 pre-ignition events are detected. For this purpose, for example, a structure-borne noise signal of a knock sensor and / or a pressure signal of a pressure sensor are evaluated. Alternatively or additionally, the signal of the crank angle sensor can be evaluated and a working cycle can be recognized as a pre-ignition working cycle when the speed gradient reaches or falls below a certain negative threshold.

If a pre-ignition has been detected, a count is incremented by a certain amount (for example, by the value 32). In a work cycle without such an event, the counter reading is preferably decremented by a specific value (for example, by the value 1). It is also conceivable that the count can also be incremented by other events, for example, in a strong knock event without Vorentflammung.

If the counter reading has reached or exceeds a certain threshold value c _TH (for example c _TH = 140) (see query 110 ) is switched to a multi-water injection mode (see step 120 ). If a certain number of times has already been switched to multiple water injection, there is also a limitation of the torque (see step 120 ). The multiple water injection is performed, for example, for 3-5 cycles. If pre-ignition events continue after multiple water injection (see Poll 130 ), a cylinder deactivation takes place (see step 140 ), in particular a suppression of the injection for the affected cylinder.

Moreover, it is conceivable that one or more further measures for the suppression of pre-ignition may be taken before, after or simultaneously with the switching to the dual-water injection, for example, a multiple fuel injection may be performed.

In a simple embodiment, it would also be contemplated to switch to a multiple water injection mode of operation immediately upon detection of a single pre-ignition cycle (or a prescribed number of pre-ignition cycles) without reaching or exceeding a particular threshold value, c _TH, for a count.

In 2 is an embodiment of the in step 120 performed multiple water injection (here dual injection) shown. 2 shows the course of the injected amount of water m per unit time (Y-axis) on the angular position (X-axis) of the crankshaft. Furthermore, an exemplary profile V of the cylinder pressure p is displayed at a pre-ignition. The angular position of the crankshaft is given in ° CA (degree crankshaft).

How out 2 it can be seen in a pre-ignition long before the ignition ZZP to a massive increase in the cylinder pressure p due to the pre-ignition; For example, the cylinder filling is ignited by a glowing particle. The ignition ZZP is for example at a maximum of 5 ° before the ignition TDC.

According to 2 a late water injection quantity _{m2 is} injected during the interval from B _m2 to E _m2 , for example in the interval from approx. 25 ° KW to approx. 8 ° KW. This late water injection quantity m2 is used for knock suppression and is carried out, for example, during each working cycle without detection of pre-ignition.

Upon meeting the switching condition in step 110 (or in the case of using a simple switching condition upon detection of a single pre-ignition cycle) is switched to a multiple injection (in particular dual injection) mode wherein, in addition to a late water injection amount m2, an early water injection amount m1 during the interval of B _m1 to E _{m1 is} injected, for example, to extinguish glowing particles and to prevent the initiation of combustion before the ignition ZZP by such particles. It is also possible that after the switchover and the late water injection amount m2 is varied, for example, is reduced or, for example, takes place at an earlier or later date.

The injection of the early injection mass m1 occurs early during the compression stroke, for example at the beginning of the compression stroke or later during the compression stroke, and in particular sufficiently early before the ignition timing ZZP, for example, to extinguish glowing particles and to prevent the initiation of combustion by such particles.

In the example in 2 For example, the early injection amount m1 is injected in the interval from about -110 ° CA to about -85 ° CA.

Deposits and poor fuel quality increase the pre-ignition tendency. Therefore, the water injection to avoid pre-ignition is preferably activated (for example, the injection of the amount of water m1 in 2 ), if such a condition is detected.

Preferably, in the above-described mode of operation with multiple water injection in the case of a recognized Pre-ignition critical state switched (for example, starting from a mode of operation with single-water injection), which is associated with an increased risk of the occurrence of Vorentflammung. So it is switched without detected Vorentflammungsereignis in the operating mode with multiple water injection, z. B. low-octane low-grade fuel or a combustion chamber with heavy deposits.

The detection of low fuel quality low octane number can be done for example by evaluating the signals of the knock control. If the fuel quality is poor, the knock control reduces the firing angle of all cylinders more than it does with good fuel quality with a high octane rating. The ignition angle difference leads to an adaptation of the basic ignition angle map. Based on the adaptation angle, the fuel quality can be detected. The normal control amplitude of the knock control is, for example, a maximum of 2.5 ° CA, with larger control values, the ignition angle map is adapted. At z. B. 8 ° KW control amplitude can be closed, for example, the presence of a poorer fuel quality with RON 87.

The detection of a combustion chamber with heavy deposits can, for example, take place in the following way: During long engine operation with low partial load, in particular with bad fuel, the engine tends to Brennraumverkokung (formation of deposits in the combustion chamber). The deposits lead to a good smoothness at low part load. By evaluating the signal of the speed sensor, the presence of an unusually low rotational irregularity can be detected, which is due to heavy deposits in the combustion chamber.

In general, it can be provided that the injected amount of water is pre-controlled by a multi-dimensional map, z. B. engine load and speed dependent, depending on the temperature and humidity of the intake air, the engine temperature, the exhaust gas temperature and / or other parameters.

The metered quantity can be corrected individually for each cylinder by the knock control. For example, only so much water should be injected that the knock control does not reduce the firing angle.

In the case of water injection, different effects can be sought depending on the instantaneous state: z. B. cooling the cylinder charge to lower the NOx emission, or the suppression of Vorentflammungen or knocking by cooling the combustion chamber walls. In addition, depending on recognized pre-ignition, the amount of water can additionally be influenced by existing exhaust-gas temperature sensors or exhaust-gas temperature models in order to comply with the limit values required for component protection.

Also, the injection interval (when and how long is injected per cycle) and the injection scheme (single, double or triple injection) for the water injection can be varied depending on the parameters. For example, depending on the situation, a multiple injection, an early or a late injection is chosen to achieve an optimal effect over the entire operating range of the engine. As described above, immediately after pre-ignition, the injection strategy may be adjusted to prevent further pre-ignition.

Furthermore, it is conceivable to influence the effect of the water injection with the injection pressure. To suppress the tendency to knock and Vorentflammungsneigung can be achieved with a high pressure wall wetting for cooling the combustion chamber walls, whereas with a lower pressure and larger drops preferably the mixture is cooled in order to reduce the formation of nitrogen oxides.

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 102011015628 A1 [0002]
• DE 102006015662 A1 [0005]
• DE 102009008248 B4 [0006]
• DE 102008038102 B4 [0006]
• WO 2010/124699 A1 [0006]
• DE 102010004091 A1 [0007]

Claims (9)

Method for suppressing pre-ignition occurring in front of an ignition point in a combustion chamber of an internal combustion engine, comprising the steps: - detecting the occurrence of pre-ignition or an increased risk thereof; and Depending on this, injection of water (m1) or injection of water (m1) with modified injection characteristics. The method of claim 1, wherein the water injection before the ignition (ZZP) and in particular from a time ranging from about 180 ° CA to about 90 ° CA before the located between compression and power stroke top dead center (ignition TDC) lies, begins. Method according to one of the preceding claims, wherein depending on the detection of the injected water amount is increased. Method according to one of the preceding claims, wherein depending on the detection on a multi-injection engine operation per cycle is switched, wherein a first injected water injection quantity (m1) for suppressing pre-ignition and a temporally thereafter injected second water injection amount (m2) during the same cycle become. Method according to claim 4, wherein the first injection quantity (m1) serves for suppressing pre-ignition and the second injection quantity (m2) serves for knock suppression and / or reduction of nitrogen oxide formation. Method according to one of claims 4-5, wherein the injection of the first injection quantity (m1) takes place in the compression stroke. A method according to claim 6, wherein - the start (B _m1 ) of the injection of the first injection quantity (m1) in the range of about 180 ° CA to about 90 ° CA before the top dead center between compression and power stroke (ignition TDC) is, and - the end (E _m1 ) of the injection of the first injection quantity (m1) in the range of about 170 ° CA to about 60 ° CA before the ignition TDC is. Method according to one of the preceding claims, wherein when the injection characteristic is changed, the water injection takes place at an earlier time than before. Engine control unit for an internal combustion engine with water injection, wherein the engine control unit is set up, - to detect the occurrence of pre-ignition or an increased risk, and To initiate the injection of water (m1) or to initiate the injection of water (m1) with modified injection characteristics.

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