DE102008042925B3 - Cetane number determination involves injecting fuel for combustion in cylinder of internal combustion engine by using engine management system - Google Patents

Abstract

Cetane number determination involves injecting fuel for combustion in a cylinder (3) of an internal combustion engine by using engine management system. Exhaust gases are discharged through a flue gas conduit (2) from the cylinder, where concentration of an exhaust gas component is measured with a sensor (1) provided in exhaust line. The measured concentration is used as an input parameter for engine operating map deposited in the engine management system, where an output value is known as cetane number of the fuel.

Description

The The invention relates to a method for determining the cetane number CZ a fuel that is capable of combustion in the at least one Cylinder of an internal combustion engine with engine control injected is, with the exhaust gases over at least one exhaust pipe are removed from the at least one cylinder.

Such a method is used, for example, in JP 03105042 A described.

in the In the context of the present invention, the term "internal combustion engine" includes diesel engines, but also hybrid internal combustion engines. Due to the limited occurrence of mineral oil as raw material for The extraction of fuels is the use of alternative fuels and thus also the use of hybrid internal combustion engines or hybrid combustion processes increasingly as goal-oriented considered. In the context of the present invention, therefore, all Fuels with which a diesel engine can basically be operated, referred to as diesel fuels or fuels.

The Traditional diesel engine process is characterized by an air compression, an inhomogeneous mixture, a self-ignition and the Quality control.

The required auto-ignition of the fuel-air mixture sets a high degree of ignitability of the diesel fuel ahead. Is the ignitability of the used fuel too low, accumulate large quantities recycled fuel-air mixture in the cylinder at self-ignition lead to a steep rise in pressure at the beginning of combustion, or but an ignition Stay off.

The ignition of a fuel can be given by the cetane number CZ, which is related to the ignition delay time, which is a measure of the time between the beginning of the fuel injection into the cylinder d. H. the start of injection SOI and the pressure increase due to combustion of the fuel-air mixture.

The Cetane CZ of a fuel indicates how much volume percent Cetane contains a mixture of cetane and α-methylnaphthalene, the under otherwise identical conditions has the same Zündverzugszeit as the one to be tested Fuel whose cetane number is to be determined. The higher the Cetane number of a fuel is the higher its ignitability or the shorter is the ignition delay time.

The Cetane number CZ of a diesel fuel or a certain type of fuel can vary, so that when operating an internal combustion engine not from a uniform and unchanging Cetane number of the fuel used can be assumed. To lead not just impurities and manufacturing tolerances too Variations in fuel quality, especially cetane number, on the same vehicle market. The different regulatory Guide provisions worldwide diesel fuels have different cetane numbers in different countries can have.

different Cetane numbers lead to different ignition d. H. Ignition delay. To account for this, there is an on-board diagnosis of the fuel currently used to operate the internal combustion engine required, thus operating parameters of the internal combustion engine, in particular the start of injection, are adapted to the cetane number of the fuel can.

To The prior art attempts to run in the cylinder Combustion process directly or indirectly by measurement to capture knowledge about the ignitability of the currently used fuel.

So the cylinder pressure can be measured directly by means of a pressure sensor detected be the pressure curve to determine the beginning of the combustion SOC serves, which in turn together with the start of injection SOI for Determination of ignition delay d. H. the ignition delay time is used. The ignition delay determined in this way is characterized the fuel and is - much like the cetane number - a Measure of the ignitability of the fuel. The disadvantage of this method is the need to having to provide a pressure sensor which represents a comparatively expensive measuring technique.

The EP 1 775 584 A2 describes a method in which the ignition delay - as a measure of the cetane number - is determined by means of a previously metrologically detected cylinder pressure.

According to one Another approach is a knock sensor or acceleration sensor d. H. strain attached to the cylinder block of the internal combustion engine to the cylinder running combustion process indirectly metrologically too capture and determine the beginning of the combustion SOC. The indirect ones Measurement is inherently subject to major inaccuracies d. H. of lower quality as the direct measurement. It must be considered be that the indirect measurement is greatly influenced from external factors, For example, the running in other cylinders combustion processes.

Another way to capture the combustion process by measurement indirectly, is to measure the speed of the crankshaft, the acceleration of which can be concluded on the running in the cylinder combustion processes. Such a method is the subject of JP 2007321706 A , The disadvantages are those already mentioned above.

In front the background of what has been said, it is the task of the present Invention, a method according to the preamble of claim 1 d. H. of the generic type to show with the cetane number CZ of a fuel during operation of the internal combustion engine cost-effective and at the same time with a higher one Accuracy can be determined as this with the from the state the technique known method is possible.

• – die Konzentration C eines Abgasbestandteils mit einem in der mindestens einen Abgasleitung vorgesehenen Sensor meßtechnisch erfaßt wird, und
• – diese Konzentration C als Eingangsgröße für ein in der Motorsteuerung hinterlegtes Kennfeld verwendet wird, um die Cetanzahl CZ des verwendeten Kraftstoffes als Ausgangsgröße aus diesem Kennfeld auszulesen.

This object is achieved by a method for determining the cetane number CZ of a fuel which is injected for combustion in the at least one cylinder of an internal combustion engine with engine control, wherein the exhaust gases are discharged via at least one exhaust pipe from the at least one cylinder, and which is characterized that

• - The concentration C of an exhaust gas component is detected by measurement with a provided in the at least one exhaust gas sensor sensor, and
• - This concentration C is used as an input for a stored in the engine control map to read the cetane CZ of the fuel used as the output from this map.

The inventive method uses the fact that different cetane numbers CZ otherwise same boundary conditions - d. H. also assumed the same operating parameters of the internal combustion engine - to different Ignition delay lead, which the combustion process taking place in the at least one cylinder affected is, and the concentrations in the chemical implementation of the Fuel-air mixture formed combustion products in the combustion gas d. H. Vary exhaust gas.

Become in a specific operating point of the internal combustion engine, in particular at a fixed injection time, equal amounts of fuel different Fuels injected into the cylinder cause different ignition delays due to different Cetane numbers to an earlier or later Start of combustion. This results in different pressure and temperature gradients In the combustion chamber, the concentrations of the combustion products or Exhaust gas components decisive influence.

According to the invention Concentration C of at least one exhaust gas component with one in the at least an exhaust pipe provided sensor detected by measurement. These Concentration C serves as an input for a in the engine control stored map from which the cetane number CZ of the currently used Fuel read as output can be.

The Map was previously - for example, on an engine test bench - for one concrete operating state d. H. a concrete operating point of Engine created, which is considered suitable, to determine the cetane number CZ of a fuel, the internal combustion engine then in real operation to determine the cetane number at the operating point, which is the basis of the map, is or must be transferred to the in the creation of the map existing boundary conditions d. H. To realize operating parameters.

Or but there are more operating parameters of the internal combustion engine used as input variables, such that a multi-dimensional map or a set of maps stored in the engine control and used and it is not is required, the internal combustion engine to determine the cetane number into a concrete singular Operating point, namely the one that underlies the map, to convict. By this procedure can one of the implementation the method according to the invention preferably independent Operation of the internal combustion engine can be realized.

Advantageous are therefore also embodiments of the method in which at least one further operating parameter the internal combustion engine as additional Input variable for the map is used to read the cetane CZ as an output.

Advantageous are in this context, in particular embodiments of the method, in which the beginning of the injection SOI of the fuel in the at least a cylinder as additional Input variable for the map is used.

Of the Injection time has - how the cetane number or the ignitability of the fuel - relevant Influence on the burning process and the during formed the combustion of the fuel-air mixture Pollutants or exhaust gas components. In that sense, it makes sense, the Injection start to use as another input variable, if - as in this case - the exhaust gas concentrations as a benchmark for the Cetane number of the fuel used are used.

The start of injection influences the ignition delay and variations at the start of injection ie Ab Softnesses of the start of injection of a setpoint underlying the map lead to greater inaccuracies in determining the cetane number, so that it is advantageous to use the start of injection as a variable ie additional input, if not - assuming possible inaccuracies - assumed a fixed injection start should be or will.

According to the in Presented embodiment is therefore either a three-dimensional map or a Set of n maps used, n maps for n different Injection timing includes SOI, where each map shows the relationship between exhaust concentration C and cetane number for one concrete injection start and a concrete exhaust gas component reflects.

By the inventive method the problem underlying the invention is solved, namely a To show a method by which the cetane number CZ of a fuel cost-effective and at the same time with a higher one Accuracy can be determined as this with the from the state the technique known method is possible.

Has been determines the cetane number of the currently used fuel the operating parameters of the internal combustion engine, in particular the parameters fuel injection, according to a preferred embodiment of the process to the fuel used d. H. the determined Adjusted cetane number, in terms of fuel consumption and / or pollutant emission behavior to ensure optimized operation of the internal combustion engine.

Further advantageous variants of the method according to the subclaims discussed below.

Advantageous is it basically if the method in an operating point of the internal combustion engine carried out is realized in which comparatively stable boundary conditions can be and which is therefore particularly suitable for determining the cetane number.

stable Increase boundary conditions the goodness d. H. the accuracy of the procedure and are preferable to reproducible and meaningful results for the To generate cetane number. Stable boundary conditions ensure that that differences in the cetane number actually determined by different fuel qualities are conditional and not through changes in the boundary conditions d. H. be caused in the measurement conditions.

One such operating point is characterized for example by that the air path in this operating point of the internal combustion engine is little prone for unwanted Variations d. H. the intake side of the internal combustion engine or the sucked cylinder fresh charge a stable condition, in particular a reproducible composition, wherein the pressure and the temperature of the cylinder fresh charge also a crucial Meaning.

Out For this reason, to carry out the Method, for example, operating points advantageous in which no Exhaust gas recirculation takes place. Because even minor changes in the recirculated exhaust gas amount change the Composition and temperature of fresh cylinder charge, what the ignition delay noticeable affected.

Advantageous are for the reasons mentioned above in particular embodiments of the method in which the determination of the cetane number CZ in overrun the internal combustion engine performed becomes.

Of the Push operation is characterized by a largely stable air path out. There is no exhaust gas returned and in principle no fuel injected, with an optional throttle is closed, so that also scatters d. H. unwanted variations in the throttle position the result d. H. the cetane number is not participate. In overrun inaccuracies in the determination the cetane number, by varying a variety of operating parameters can be caused eliminated.

Now is according to the invention - in deviation from the usual Push operation - one predeterminable amount of fuel in the at least one cylinder of the internal combustion engine injected and burned, as the combustion gases or the concentration at least one exhaust gas constituent for determining the cetane number be used or will.

The Injection of fuel in the context of carrying out the method according to the invention leads - in the Rule - too an unintentional in overrun operation acceleration of the internal combustion engine and thus the vehicle, which is driven by the internal combustion engine becomes. This acceleration depends also from the injected fuel quantity. To carry out the Process or for generating sufficiently large amounts of exhaust gas may be required be to inject a minimum amount of fuel.

In overrun operation, therefore, embodiments of the method may be advantageous in which an acceleration of the internal combustion engine during the overrun operation as a result of the injection tion and combustion of fuel is prevented by the internal combustion engine is braked.

Advantageous are embodiments of the process in which the fuel is used to determine the cetane number CZ in the at least one cylinder of the internal combustion engine to a Time SOI is injected, to which the combustion process especially sensitive to changes reacted in the cetane number.

Becomes the fuel, for example, near top dead center (TDC) d. H. injected at high cylinder pressure and high cylinder temperature, a different cetane number is less noticeable the combustion process, as if at a later time Time is injected because the ignition delay and thus the combustion process near the top Dead center decisive determined by the high cylinder pressure and the high cylinder temperature and the influence of Cetane number decreases on the firing process.

In order to the cetane number the ignition delay and thus the burning process dominates and different cetane numbers to be felt d. H. also measurable changes in the burning process, it is advantageous if in the expansion phase, preferably more than 30 ° KW resp. 60 ° KW after OT, fuel to carry of the method is injected.

Embodiments of the method are advantageous in which the concentration C _NOX of the nitrogen oxides NO _{x present} in the exhaust gas, as concentration C of an exhaust gas constituent, is detected by measurement with a NO _x sensor.

These Process variant uses the fact that in particular the education the nitrogen oxides or the amount of formed during combustion Nitrogen oxides decisive is determined by the temperature in the cylinder, to which the cetane number is crucial Has influence. The higher the cetane number is shorter is the ignition delay and the bigger the proportion of injected fuel that is burned, what to higher To press and temperatures in the cylinder, whereby the formation of nitrogen oxides is favored.

The Nitrogen oxides are therefore the exhaust gas constituent, which is particularly sensitive on changes in the ignition delay - caused through changes in the cetane number - reacted. In this respect, the nitrogen oxide concentration in the exhaust gas is changing Cetane number one for the inventive method advantageous big Fluctuation and thus measurable Differences.

Furthermore feature Nitrogen sensors over a higher one measurement accuracy and a quick response. Optionally, to carry out this Process variant one already provided in the exhaust pipe Nitrogen oxide sensor, for example, to monitor the functionality a storage catalyst is used, what the Costs to implement the method lowers. The latter applies - regardless of the type of sensor or exhaust gas component - in principle, as far as one already existing sensor is used.

Also advantageous are embodiments of the method in which the concentration C _HC of the unburned hydrocarbons HC present in the exhaust gas, as concentration C of an exhaust gas constituent, is detected by measurement technology with an HC sensor.

These Process variant uses the fact that the concentration unburned hydrocarbons in the exhaust gas decreases the more of the injected Fuel is burned. As already related to the Formation of nitrogen oxides was previously carried out, the proportion decreases of injected fuel being burned with rising Cetane number too.

Also advantageous are embodiments of the method in which the concentration C _O2 of the oxygen O _{2 present} in the exhaust gas, as concentration C of an exhaust gas constituent, is detected by measurement with an O ₂ sensor. As the cetane number increases, more of the injected fuel is burned and a larger portion of the oxygen supplied to the cylinder is consumed. Consequently, the oxygen concentration in the exhaust gas decreases as the cetane number increases.

at the use of an oxygen sensor must be taken into account that the Sensor signal affected is due to oxidation processes, which run on the sensor itself. The oxygen concentration delivered by the sensor is therefore not proportional to the actual burned in the cylinder Fuel quantity, but rather to the total injected Fuel quantity.

At least a portion of the exhaust constituents to be oxidized, ie, carbon monoxide (CO) and unburned hydrocarbons (HC), are oxidized as the sensor passes the sensor. These oxidation processes are similar to those occurring in an oxidation catalyst reactions; also because the sensor is at least partially coated with similar or identical materials as an oxidation catalyst. However, the oxidation processes taking place at the sensor can not assume an arbitrarily large extent. If the HC concentration upstream of the sensor exceeds a certain threshold, the sensor is not in able to oxidize all unburned hydrocarbons.

Advantageous are further embodiments of the method in which the concentration C of an exhaust gas constituent by means of a sensor serving as a lambda probe by measurement detected becomes.

The Knowledge of the air ratio λ is in the frame the operation or the control of an internal combustion engine of particular Meaning, which is why engines invariably with a so-called Lambda probe are equipped and the use of this probe to carry out the method according to the invention offering.

The Air ratio λ is basically set the amount of fuel to be injected, the injection timing and / or needed to control an exhaust gas recirculation, but also for monitoring and for operating the different exhaust aftertreatment systems, used according to the prior art for the reduction of pollutants become.

Considered Need to become but again the running at the probe oxidation processes and their effect on the signal delivered by the probe. It will Referred to in connection with the oxygen sensor made statements.

The Lambda probe has a similar fast Responsiveness as the nitrogen oxide sensor discussed above. It can Response times in the range of a hundred milliseconds and less will be realized.

at Internal combustion engines in which at least one exhaust aftertreatment system is provided in the at least one exhaust pipe, embodiments are the method advantageous in which the sensor for detecting the Concentration C of an exhaust gas component upstream of the at least one exhaust aftertreatment system is arranged.

There the discharged from the cylinder and introduced into the exhaust gas exhaust gas as part of an exhaust aftertreatment its composition changes due to the conversion of exhaust components is it is advantageous to use the sensor to detect the concentration of a Exhaust component upstream to arrange this exhaust aftertreatment.

Basically the arrangement of the sensor but also downstream of the at least one exhaust aftertreatment system possible. In this process variant must but then the running in the exhaust aftertreatment system reactions, in particular also an optionally expiring recording d. H. Absorption or Release of exhaust components, be taken into account to starting from the downstream detected by sensor concentration on the concentration of the exhaust gas component upstream of the Close system to be able to which for the method according to the invention is.

There the consideration of an exhaust aftertreatment system is usually model-based, leads one Such approach, taking into account an exhaust aftertreatment must become, to a certain blur d. H. Inaccuracy in the determined exhaust gas concentrations. The order the sensor upstream the exhaust aftertreatment increased hence the accuracy of the procedure.

at Internal combustion engines in which at least one turbine in the at least an exhaust pipe is provided, embodiments of the method advantageous in which the sensor for detecting the concentration C of an exhaust gas component downstream of the at least one turbine is arranged.

In the following, the invention is based on the 1 and 2 described in more detail. Hereby shows:

1 schematically an embodiment of an internal combustion engine for carrying out the method, and

2 schematically shows the influence of the cetane number CZ and the start of injection SOI on the nitrogen oxides NO _x .

1 schematically shows an embodiment of an internal combustion engine for carrying out the method. The internal combustion engine has an intake line 4 to supply the cylinders 3 with fresh air or fresh mixture and via an exhaust pipe 2 for discharging the hot combustion gases.

The internal combustion engine is equipped with a supercharging, the turbine 5a an exhaust gas turbocharger 5 in the exhaust pipe 2 and the associated compressor 5b in the intake pipe 4 is arranged. In addition, for post-treatment of the exhaust gas two exhaust aftertreatment systems 6a . 6b downstream of the turbine 5a intended.

As 1 it can be seen, is downstream of the turbine 5a and upstream of the two exhaust aftertreatment systems 6a . 6b a sensor 1 arranged, with which the concentration C of an exhaust gas component is detected by measurement. The concentration C determined in this way is called Ein output quantity for a map stored in the engine control (not shown) used to read the cetane CZ of the fuel used as the output from this map.

2 schematically shows an example of such a map, which in the present case the influence of the cetane CZ and the injection start SOI on the nitrogen oxides NO _x represents ie the nitrogen oxide concentration C _NOx and the injection start SOI used as inputs to read the cetane number CZ as an output.

On the ordinate the nitrogen oxide concentration C _NOx is plotted in parts per million (ppm) and along the abscissa the start of injection SOI in degrees crank angle (° CA). The different cetane numbers CZ form hyperbolas, assuming the same start of injection SOI, the nitrogen oxide concentration C _NOx increases as the cetane number CZ increases.

1

sensor

2

exhaust pipe

3

cylinder

4

suction

5

turbocharger

5a

turbine

5b

compressor

6a

aftertreatment system

6b

aftertreatment system

C

concentration an exhaust gas component

C _NOX

concentration the nitrogen oxides in the exhaust gas

_HC

concentration the unburned hydrocarbons in the exhaust gas

C _O2

concentration of the oxygen in the exhaust gas

CO

Carbon monoxide

CZ

cetane

HC

unburned hydrocarbons

° CA

Degree crank angle

n

number of the maps

NO _X

Nitrogen oxides

O ₂

oxygen

OT

upper dead

SOC

beginning the combustion

SOI

beginning the injection

Claims (10)

Method for determining the cetane number CZ of a fuel which is intended for combustion in the at least one cylinder ( 3 ) of an internal combustion engine is injected with engine control, wherein the exhaust gases via at least one exhaust pipe ( 2 ) from the at least one cylinder ( 3 ) are discharged, characterized in that - the concentration C of an exhaust gas component with a in the at least one exhaust pipe ( 2 ) provided sensor ( 1 ) is detected by measurement, and - this concentration C is used as an input for a stored in the engine control map to read the cetane CZ of the fuel used as the output from this map. Method according to claim 1, characterized in that the beginning of the injection SOI of the fuel into the at least one cylinder ( 3 ) is used as an additional input for the map. Method according to claim 1 or 2, characterized the determination of the cetane number CZ is carried out in the overrun mode of the internal combustion engine. Method according to claim 3, characterized that an acceleration of the internal combustion engine during the Overrun due to injection and combustion of fuel is prevented by the internal combustion engine is braked. Method according to one of the preceding claims, characterized in that the concentration C _NOX of the nitrogen oxides NO _{x present} in the exhaust gas, as the concentration C of an exhaust gas constituent, with a NO _x sensor ( 1 ) is detected by measurement. Method according to one of claims 1 to 4, characterized in that the concentration C _HC of the unburned hydrocarbons HC located in the exhaust gas, as the concentration C of an exhaust gas constituent, with an HC sensor ( 1 ) is detected by measurement. Method according to one of claims 1 to 4, characterized in that the concentration C _O2 of the oxygen present in the exhaust gas O ₂ , as concentration C of an exhaust gas constituent, with an O ₂ sensor (1) is detected by measurement. Method according to one of the preceding claims, characterized in that the concentration C of an exhaust gas constituent by means of a sensor ( 1 ) serving lambda probe is detected by measurement. Method according to one of the preceding claims for determining the cetane number CZ of a fuel which is intended for combustion in the at least one cylinder ( 3 ) is injected an internal combustion engine, wherein the exhaust gases via at least one exhaust pipe ( 2 ) from the at least one cylinder ( 3 ) and at least one exhaust aftertreatment system ( 6a . 6b ) in the at least one Exhaust pipe ( 2 ), characterized in that the sensor ( 1 ) for detecting the concentration C of an exhaust gas constituent upstream of the at least one exhaust aftertreatment system ( 6a . 6b ) is arranged. Method according to one of the preceding claims for determining the cetane number CZ of a fuel which is intended for combustion in the at least one cylinder ( 3 ) is injected an internal combustion engine, wherein the exhaust gases via at least one exhaust pipe ( 2 ) from the at least one cylinder ( 3 ) and at least one turbine ( 5a ) in the at least one exhaust pipe ( 2 ), characterized in that the sensor ( 1 ) for detecting the concentration C of an exhaust gas component downstream of the at least one turbine ( 5a ) is arranged.