DE102008061787A1 - Method for operating petrol-internal-combustion engine for diagnosis of start of combustion process, involves evaluating electrical measured variables or actuating variable of ignition system for diagnosing starting of combustion process - Google Patents

Abstract

The method involves injecting fuel directly and/or indirectly into a combustion chamber of a cylinder, and igniting a combustion mixture present in the combustion chamber by an ignition system i.e. corona-ignition system, at predetermined ignition time points (0a-0c, 4a-4c), where the ignition system ignites the combustion mixture by producing non-thermal plasma and the ignition duration is arbitrarily adjustable. Electrical measured variables (U1, U2, U3) or actuating variable e.g. resistance, of the ignition system is evaluated for diagnosing starting of the combustion process.

Description

The The invention relates to a method for operating an Otto internal combustion engine, at the fuel directly and / or indirectly in at least one Combustion chamber of a cylinder is injected and that in the combustion chamber present combustion mixture by means of an ignition system is ignited to a predetermined ignition timing, wherein the ignition system as a corona ignition system for Igniting the combustion mixture by generating a so-called non-thermal plasma is formed and the ignition duration is arbitrarily adjustable.

Currently There are many efforts to reduce fuel consumption at partial load while maintaining extremely low pollutant emissions. Enthrottled Otto-Otto layer firing processes show thereby great potential in terms of consumption reduction. In this case, in the stratified combustion process or lean operation, the fuel injection into the cylinder just before ignition, so that at the time of ignition despite a very small amount of injected fuel an ignitable Combustion mixture forms around the spark plug.

There in an inflammation of the combustion mixture by means a conventional spark plug ignition system the Ignition by a spark that is between the electrode and the mass of the spark plug propagates the spark plug must be at very low fuel combustion mixtures at the right time and possibly with a longer ignition duration to be detonated. The ignition duration for spark plug ignition systems However, due to the energy required to generate the spark can only be influenced within narrow limits. Thus, it may be possible come to so-called misfires.

In addition to the conventional spark plug ignition systems, novel ignition systems - so-called corona ignition systems are currently being developed, in which the combustion mixture is not ignited via a spark, but by generating a so-called non-thermal plasma. In contrast to conventional ignition systems, we do not produce a conductive ion channel from the electrode to the ground, we also speak of a so-called incomplete spark breakdown. In such corona ignition systems, for example, a very high voltage is generated at the electrode in the combustion chamber via a Tesla coil, which is set in resonance via a high-frequency AC voltage, which generates an extremely high electric field in the combustion chamber. Due to the strong electric field strong electromagnetic forces act on the molecules in the combustion chamber (air-fuel mixture). With a sufficiently large field strength, electrons are ejected from the molecules at several points. Radicals form, causing a chemical chain reaction in the combustion chamber. Due to the generated so-called non-thermal plasma, which projects far into the combustion chamber, the burning time can be significantly shortened. This combustion process is thermodynamically superior to that of conventional spark plug combustion. An example of such a corona ignition system is from DE 10 2006 005 792 A1 known.

In front the background of a stable burning process, a necessary one Emission reduction and good acoustics during combustion a diagnosis of combustion is necessary. In particular, it is here a diagnosis regarding the start of combustion, misfiring, the firing rate, the combustion center of gravity or other parameters influencing the combustion process (e.g. B. cylinder internal pressure, lambda) necessary to a proper To be able to ensure operation of the internal combustion engine.

at conventional systems, the quality of combustion is over determines the combustion voltage curve and / or the spark duration. Mistakes are diagnosed by special sensors (for example, crankshaft sensors), which are the rotational irregularities evaluate the internal combustion engine. A diagnosis of the burning rate is in conventional spark plug ignition systems not possible.

Regarding the diagnostic capability of internal combustion engines with corona ignition systems is from the DE 102 39 411 B4 For the diagnosis of the flame size, it is known to evaluate a physical quantity which is dependent on the plasma in the combustion mixture and at the same time makes it possible to adjust the flame size. A detailed procedure regarding the diagnosis by means of the physical quantities is not described.

task The invention is a method for diagnosing the course of combustion an Otto internal combustion engine when using a corona ignition system, Specify in particular for the diagnosis of a combustion start.

These The object is achieved by a method according to claim 1. Advantageous developments emerge from the dependent Claims.

The method according to the invention is intended for an Otto internal combustion engine, in particular for a direct-injection Otto internal combustion engine, in which fuel is injected directly into at least one Combustion chamber of a cylinder is injected. In order to ignite the combustion mixture, an ignition system must be provided which causes the ignition of the combustion mixture depending on the determined optimum ignition timing. Since conventional spark plug ignition systems can ignite only a very small area and thus the combustion is relatively slow, the ignition system is designed as a corona ignition system for igniting the combustion mixture by generating a so-called non-thermal plasma. In this case, such a high voltage is generated to ignite the combustion mixture at the ignitor or at the electrode in the combustion chamber due to a high-frequency AC voltage, which causes an extremely high electric field in the combustion chamber. Due to the strong electric field strong electromagnetic forces act on the molecules in the combustion chamber (air-fuel mixture). At sufficiently high field strength, electrons are ejected from the molecules, ie an incomplete spark gap (corona) is generated, in which electrons are torn or knocked out of the atomic or molecular hulls. However, this does not produce a complete, conductive ion channel from the high frequency / high voltage electrode to the ground. Radicals form, causing a chemical chain reaction in the combustion chamber. With a suitable choice of frequency, the combustion process is thermodynamically much better than with a conventional spark plug.

basic idea The invention is in the use of an ignition system based on a corona discharge by measuring and analyzing the physical-electrical Effects or electrical measurements or Manipulated variables of the corona ignition system Condition and quality of burn. The evaluation of the electrical parameters, in particular taking into account a characteristic course the measurand provides insights about the condition and / or the quality of the combustion. through a predefined rule strategy is then under Taking into account the diagnostic results the corona ignition system to an optimal corona formation at an optimal ignition timing regulated.

The inventive method for operating a thus designed Otto internal combustion engine with a corona ignition system is characterized by the fact that for diagnosis of the start of combustion an electrical measurand or manipulated variable (selective or temporal course) of the corona ignition system, in particular, an ignition parameter representing the combustion process of the corona ignition system is evaluated to determine clearly to know if and when the combustion was started. This procedure or feature is necessary to be effective To ensure combustion process control.

advantageously, are used in the diagnosis of the combustion start as electrical measure of Corona ignition system on the primary side of the corona ignition system applied primary voltage and / or on the secondary side the corona ignition system adjacent secondary voltage and / or the current on the primary side and / or secondary side of the corona ignition system and / or the resistor and / or the frequency on the primary and secondary side considered, since each of these ignition parameters depending on the combustion process a characteristic Course has, by means of which, for example, can be detected or determined, when the combustion is started and how the combustion proceeds. In particular, for the diagnosis of the combustion start the electric Measured variable of the corona ignition system the at least one combustion parameter representing the ignition process of the corona ignition system are taken into account in such a way that the start of combustion depending on the entrance a predetermined expected change in the measured value the measured variable to be evaluated is detected. change For example, the value of the measured variable to be evaluated jump in a given direction can be concluded be that the combustion is started.

For example. is the characteristic course of the on the primary side of the corona ignition system applied primary voltage configured such that at a start of combustion, the primary voltage of their starting level decreases. Accordingly, the on the primary side of the corona ignition system applied primary voltage be evaluated to diagnose the combustion start such that at a drop in the primary voltage of a given Primary voltage output level (maximum voltage) - advantageously by a given voltage difference - the start of the Combustion is detected. Will within a given time interval If no drop in the primary voltage is detected, this can lead to Determining a misfire be used.

Next the diagnosis of the combustion start can be one of the electrical parameters the corona ignition system also for the diagnosis of combustion speed and / or for diagnosing the center of gravity of the combustion and / or for the diagnosis of the in-cylinder pressure and / or for the diagnosis of the air-fuel ratio be evaluated.

The Invention will now be described with reference to an embodiment explained. It shows the

1 different characteristic Pri märspannungsverläufe U1, U2 and U3 of a corona ignition system during ignition at different load points, and

2 different primary voltage curves Uch and Uza a corona ignition system with normal ignition of the combustion mixture and a misfire.

In the 1 are three different voltage applied to the primary side of a corona ignition system characteristic primary voltage waveforms U1, U2 and U3 shown that adjust due to the physico-electrical effects of combustion of the combustion mixture. For the first combustion process, the characteristic primary voltage curve U1 is from time 0a to time 4a. Similarly, for the second combustion process, the characteristic primary voltage curve U2 from time 0b to time 4b, and for the third combustion process, the characteristic primary voltage curve U3 from time 0c to time 4c. At the times 0a, 0b and 0c, the respective primary voltage U1, U2 and U3 is increased to initiate an ignition process, wherein at the times 4a, 4b, and 4c, the end of the ignition process is reached, and the respective primary voltage U1, U2 or U3 (zero) is reduced.

The different characteristic voltage curves U1, U2 and U3 are essentially different in height the generated or reached maximum voltage VL, TL and LL, the for initiating a combustion process by generating a non-thermal Plasmas around the high voltage electrode is necessary. These different ones Maximum voltages VL, TL and LL result due to the different Load ranges in which the internal combustion engine is operated. So when idling is a relatively small maximum voltage LL for generating non-thermal plasma for ignition of the combustion mixture necessary. In contrast, the maximum voltage already slightly larger at part load (see TL), and highest at full load, see VL.

Based on 2 is explained in detail using the example of the illustrated primary voltage waveform Uch the characteristic curve of a primary voltage of the corona ignition system. At the beginning, at time 0, the primary voltage Uch is increased up to the so-called corona threshold voltage Umax (time 1) during which a non-thermal plasma or a corona is formed around the region of the ignitor (high-voltage or high-frequency electrode) , In forming the desired corona size, the primary voltage Uch is stabilized at the high voltage level Umax. As a result of the formation of the corona, the current increases until the combustion of the combustion mixture starts at time 2. At the start of combustion, the current that flows through the corona increases again, and leads to a drop in the primary voltage Uch (time 2). This drop in the primary voltage Uch can now be used to diagnose the combustion start. To end the ignition process, the primary voltage Uch is reduced to zero at time 4.

In contrast to the characteristic course of the primary voltage Uch, there is also in 2 shown primary voltage waveform Uza no (spontaneous) voltage drop from the maximum voltage Umax instead. Rather, the primary voltage is actively reduced to zero only at the time 4 'to end the attempted ignition. Due to the lack of the voltage drop caused by the combustion start by a predetermined amount from the maximum voltage Umax, it can be concluded that the combustion mixture was not ignited. There is thus a misfire.

The Primary voltage Uch drops at the start of combustion with a voltage drop gradient g by an amount d (times 3). The voltage drop gradient g and the absolute voltage drop d also draw conclusions about the combustion process In particular, the voltage drop gradient g provides a statement about the rate of combustion and thus can be used to diagnose the Burning rate be used and evaluated. The evaluation of the achieved maximum voltage Umax (start time 2) and the voltage drop gradient g or the absolute voltage drop d from the high voltage level Umax provides a statement about the center of gravity of the combustion.

After all can, depending on the maximum voltage Umax the cylinder internal pressure or the density in the combustion chamber are determined and thus a diagnosis the cylinder internal pressure take place. The bigger the Maximum stress Umax is, the higher the cylinder internal pressure or the density in the combustion chamber and vice versa. Likewise behaves It is characterized by the air-fuel ratio characterizing Lambda value, so that for the diagnosis of lambda also the primary voltage Uch, in particular the maximum voltage Umax can be evaluated because a high lambda value Umax to another voltage maximum a low lambda value leads. Not shown here but also possible is a determination of the lambda value over the determination of electrical conductivity.

Instead of evaluating the primary voltage, it is also possible to use other electrical measured variables or other ones that represent the combustion process Ignition parameters of the corona ignition system are analyzed and evaluated. All diagnostic options are a prerequisite for the suitability of a corona ignition system as an ignition system in stationary and transiently operated internal combustion engines, as the diagnosis possibilities an effective combustion initiation and rapid control and influencing or correcting the combustion process can be ensured.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102006005792 A1 [0004]
• - DE 10239411 B4 [0007]

Claims (8)

Method for operating an Otto internal combustion engine, in which fuel is injected directly and / or indirectly into at least one combustion chamber of a cylinder and the present in the combustion chamber combustion mixture is ignited by an ignition system to a predetermined ignition timing, wherein the ignition system as a corona ignition system for igniting the Combustion mixture is formed by generating a so-called non-thermal plasma and the ignition duration is arbitrarily adjustable, characterized in that for diagnosing the start of the combustion (2) an electrical measured variable (U1, U2, U3, Uch, Uza) or manipulated variable of the corona Ignition system is evaluated. Method according to claim 1, characterized in that that as electrical measured variable (U1, U2, U3, Uch, Uza) of the corona ignition system, the combustion process representing firing parameter (U1, U2, U3, Uch, Uza) of Corona ignition system is evaluated. Method according to claim 1 or 2, characterized that as electrical parameter of the corona ignition system those on the primary side of the corona ignition system applied primary voltage (U1, U2, U3, Uch, Uza) and / or on the secondary side of the corona ignition system adjacent secondary voltage and / or the current on the primary side and / or Secondary side of the corona ignition system and / or the cons stood on the primary side and / or secondary side of the corona ignition system and / or the frequency on the primary side and / or secondary side of the corona ignition system be evaluated. Method according to one of the preceding claims, characterized in that for diagnosis of the start of combustion the electrical measured variable (U1, U2, U3, Uch, Uza) of the corona ignition system is evaluated such that the start combustion depending on the occurrence of an expected incoming measured variable change detected becomes. Method according to one of the preceding claims, characterized in that for diagnosis of the start of combustion those on the primary side of the corona ignition system adjacent primary voltage is evaluated such that at a drop of the primary voltage (d) of a given or reached maximum voltage (Umax) the start of combustion is detected. Method according to claim 5, characterized in that that at a drop in the primary voltage (d) of a predetermined or reached maximum voltage (Umax) by a predetermined Voltage difference the start of the combustion is detected. Method according to claim 5 or 6, characterized that in the absence of drop in the primary voltage of the predetermined or reached maximum voltage (Umax) within a misfire is detected in a predetermined time window. Method according to one of the preceding claims, characterized in that the electrical parameter (U1, U2, U3, Uch, Uza) of the corona ignition system also for Diagnosis of the burning rate and / or for the diagnosis of the center of gravity the combustion and / or diagnosis of the cylinder internal pressure and / or evaluated for the diagnosis of the air-fuel ratio becomes.