Method to determine the composition of a fuel mixture

is * <p £ v

^ D. 0 (12) Patent Specification do) SE 533 595 C2

Sweden (21) Patent application number: 0801177-7 (45) Patent granted: 2010-11 -02 (41) Application generally available: 2008-11-24 (22) Patent application submitted: 2008-05-21 (24) Maturity date: 2008- 05-21 (51) International class:

F02D 41/00 (2006.01)

F02D 19/08 (2006.01)

F02D 45/00 (2006.01) (83) Deposit of microorganism: - (30) Priority information: 2007-05-23 DE 10 07 023 899.3

<td>(73) Patent holders: (72) Inventor:</td><td>Robert Bosch GmbH, Postfach 30 02 20, 70442 Stuttgart DE Alexander Schenck To Schweinsberg, Schwieberdingen DE Corren Heimgaertner, Stuttgart DE Klaus Ries-Mueller, Bad Rappenau DE</td>

<td>(74) Agents:</td><td>Albihns.Zacco AB, Box 5581, 114 85 Stockholm SE</td>

<td>(54) Name:</td><td>Method for determining the composition of a fuel mixture</td>

<td>(56) Publications cited: (47) Summary:</td><td>US 20020083927 Al The invention relates to a method for determining the composition of a fuel mixture of a first and at least a second fuel for operating an internal combustion engine with at least one combustion chamber, the first and second fuels having different boiling points and / or different evaporation enthalpies. In this case, it is assumed that the composition of the fuel mixture is determined from the pressure in the combustion chamber and / or a parameter associated with the pressure and / or the time course of the pressure and / or the time course of a parameter associated with the pressure during and / or after a fuel injection during a compression injection. of the fuel-air mixture.</td>

Advantageously in the method according to the invention, hereby the fuel mixture ratio can be determined already during a first start-up process after a refueling, which has been adjusted through the refueling process.

<img file="SE533595C2_D0001.tif" />

533 595

Summary

The invention relates to a method for determining the composition of a fuel mixture of a first and at least a second fuel for operating a first combustion engine with at least one combustion chamber, the first and second fuels having different boiling points and / or different vaporization enthalpies. In this case, it is assumed that the composition of the fuel mixture is determined from the pressure in the combustion chamber and / or a parameter associated with the pressure and / or the temporal course of the pressure and / or the temporal course of a parameter associated with the pressure during and / or after a fuel injection. compression phase of the fuel-air mixture.

Advantageously in the method according to the invention, hereby the fuel mixture ratio can be determined already during a first start-up process after a refueling, which has been adjusted through the refueling process.

533 595

The prior art

The invention relates to a method for determining the composition of a fuel mixture of a first and at least a second fuel for operating an internal combustion engine with at least one combustion chamber, the first and second fuels having different boiling points and / or different evaporation enthalpies.

Combustion engines based on Otto engines are generally fueled with fossil fuel hydrocarbons based on refined crude oil. To this fuel is added increasing ethanol in various mixing ratios derived from regrowing raw materials (plants). In the US and Europe, a mixture of 75-85% ethanol and 15-25% gasoline is often used under the brand name E85. The internal combustion engines are so designed that they can be operated with clean gasoline as well as with mixtures up to E85; this is referred to as Flex-Fuel operation. For economical operation with low emissions of harmful substances at the same time as high engine performance, the operating parameters of the Flex-Fuel operation must be adapted to the respective fuel mixture present. For example, a stoichiometric fuel-air ratio is present at 14.7 parts by volume of air per share of gasoline, however, when using ethanol, an air proportion of 9 parts by volume must be adjusted. Minor and / or slow changes in ethanol content can be recognized and taken into account by the combustion engine's motor control by means of a lambda probe and / or a knock sensor. However, for example, after a refueling, rapid changes can also occur, with a considerable deviation of the composition of the fuel mixture. Operating the combustion engine with 100% gasoline and refueling with the E85 in the near-empty tank can lead to ignition problems and combustion disturbances, which can also increase exhaust emissions. According to the prior art, such rapid changes in the composition of the fuel can be recognized by an ethanol sensor. However, this design part raises the costs of the internal combustion engine.

From DE 4117440 C2, a method is known for the adaptive adjustment of a fuel / air mixture to take into account fuel properties in the operation of an internal combustion engine, which has a lambda regulator which outputs a control factor

533 595

RF and the display integration integrator, which outputs an adaptation factor AF with variable adaptation speed, which, in addition to the control factor FR, influences the setting of the fuel / air mixture. In this case, it is assumed that the deviation amplitude of the lambd a control exceeds a first threshold value and if this is the case, the rate of adaptation is set as long as an increased value until a set condition is met, after which it is fed back at a lower rate of adaptation.

The process enables interference-free drive engines that can be operated with different fuels. Thus, for example, the injection time of a change from a gasoline fuel to a fuel mixture of 85% ethanol and 15% gasoline must be extended by more than 20% to obtain the same lambda value in the exhaust gas. According to the procedure described in DE 4117440 C2, a corresponding adaptation intervention is also carried out. Since a very strong correction of the injection time and thus the adaptation intervention must be undertaken in the event of a fuel change, compared with the equalization of aging or manufacturing influence, the rate of adaptation of the proposed process is significantly increased in the case of a recognized fuel change.

On the basis of the set adaptation value, the fuel mixture ratio can be determined. Despite the increased rate of adaptation, the process needs a sufficiently long turn-in time. If a strong change in the fuel mixture ratio is caused by a refueling process, this can lead to starting difficulties and combustion interruptions, which in turn leads to increased exhaust emissions.

It is the object of the invention to provide a process which allows for rapid and cost-effective recognition of the composition of a fuel mixture of fuels having different boiling points and / or evaporative antipyres.

Advantages of the invention

The object of the invention is solved in that the composition of the fuel mixture is determined from the pressure in the combustion chamber and / or a parameter associated with this pressure and / or the temporal progression of the pressure in the combustion chamber and / or the temporal course of a correlation with this pressure and / or the parameters / after a fuel injection during the compression phase of the fuel-air mixture.

During or after a fuel injection, there is at least a partial evaporation of fuel components in the combustion chamber. This, on the one hand, leads to a volume increase of the now gaseous fuel. On the other hand, the evaporation of fuel parts due to the energy required for this causes a cooling of the air contained in the combustion chamber and thus a reduction in volume. In this way, the decrease in volume due to cooling is the dominant effect. Depending on the crank angle determined by the combustion chamber volume, cooling causes a reduction in the pressure in the combustion chamber.

How strongly the air is cooled through the evaporation, that is, how strongly the pressure change occurs, depends on the properties of the fuel, especially from the evaporation enthalpy and the boiling point and the cooking process respectively. Today, ordinary fuels differ significantly. Thus, ethanol has a fixed boiling point of 78 ° C, while gasoline shows a boiling range of 25 ° C to 215 ° C. Evaporation enthalpy at ethanol is at 904 kJ / kg, while that for gasoline is in the range of 380 kJ / kg to 500 kJ / kg.

Therefore, upon knowing the pressure or pressure in the combustion chamber after a fuel injection, conclusions about the fuel or fuel mixture ratio can be drawn.

The differences in the fuels can be determined on the basis of parameters dependent on the pressure in the combustion chamber or their time course. In addition, it may be assumed that the composition of the fuel mixture is determined from the torque of the combustion engine and / or the temporal course of the torque of the combustion engine and / or from the combustion engine's speed and / or the temporal course of the combustion engine.

A sufficiently rapid determination of the composition of the fuel mixture on the basis of the pressure, the pressure course or a parameter dependent thereon is achievable by determining the composition of the fuel mixture from the signal from a fuel chamber pressure sensor and / or from the signal from a torque sensor.

533 595 and / or from the signal from a knock sensor and / or from the speed signal. In particular, the evaluation of the speed signal shows several advantages, since no further sensors are necessary for this, and correction and the adjustment procedure for accuracy improvement of the signal are already standard in the engine control system. Consequently, the new application is feasible through a pure software extension. But also combustion chamber pressure sensors and torque sensors, which for other uses offer a further added benefit, are increasing incrementally in modern internal combustion engines, so that no significant additional costs are caused by the further evaluation of sensor signals for determining the fuel mixture ratio. The insertion of a knock sensor is only possible if it comes to a combustion after injection, as here the combustion sound is evaluated accordingly.

A change in fuel composition is only to be expected when a refueling process has taken place. In particular, at a first start of the internal combustion engine after a refueling operation, a rapid recognition of the fuel composition is necessary to carry out an adjustment of the fuel measurement to the fuel and to avoid starting difficulties and combustion interruptions until the fuel adaptation of the lambda control has reached a corresponding adjustment. Therefore, it may be assumed that the determination of the composition of the fuel mixture is carried out after an identified refueling process and / or at the start of the combustion engine.

In order to carry out an evaluation of the pressure or pressure process in a compression phase, in which there is a greatest possible difference between the various fuels, it may be assumed that the fuel injection is divided into several injection pulses to determine the composition of the fuel mixture.

A very large pressure difference between different fuels occurs if the injection into the combustion chamber takes place in already compressed air. Thus, for example, the fuel injection at a layered injection can occur shortly before the upper turning point. Here, the compressed air already has a temperature of about 100 ° C, whereby large parts of the fuel are evaporated, leading to a significant change in pressure.

533 595

According to an alternative embodiment of the invention, it may be provided that a pilot injection occurs during the compression phase and that the composition of the fuel mixture is determined during and / or after the pilot injection and / or during and / or after the main injection. As a pilot injection, a defined minimum amount of fuel may be envisaged, which is supplied in a compression phase in which a clear pressure change is to be expected.

According to a further alternative embodiment of the invention, it may be provided that the fuel-air mixture resulting from the pilot injection is ignited and that the composition of the fuel mixture is determined from the pressure process during combustion. In doing so, the fact that the pressure flow of different fuels clearly differs after ignition is utilized. The execution variants can be combined with an earlier evaluation of the pressure course during or after the pilot injection to increase the evaluation reliability of the procedure.

According to a particularly preferred design variant of the invention, it may be provided that a pressure and / or pressure process and / or a parameter related to the pressure is determined in a known fuel mixture and used as a reference quantity in determining the composition of an unknown fuel mixture. By this adaptation of the pressure process in the fuel chamber (the fuel chamber pressure process) and the signal derived therefrom, it is possible to eliminate interference and engine tolerances.

In this case, it may be provided that the composition of the fuel mixture is determined by means of the signal of a lambda probe arranged in an exhaust channel of the combustion engine and / or over a fuel adaptation to adjust the amount of fuel dosed to the combustion engine. Fuel adaptation by means of the lambda control circuit is for the most part predicted for Flex-Fuel internal combustion engines and enables the precise determination of the fuel mixture ratio, however on a longer time scale. The pressure or pressure process can thus be determined for the mixture ratio determined over the fuel adaptation and deposited as a reference.

533 595

A precise determination of the fuel mixture ratio can be obtained by determining and storing and storing a pressure and / or pressure process and / or a pressure related parameter and / or a pressure related parameter with known fuel composition and / or defined operating states of the internal combustion engine. for determining the composition of the fuel mixture, the associated measured value or values ​​are compared with the stored value or the stored values.

A careful comparison of the measured values ​​with the stored values ​​can be obtained when the pressure and / or the pressure course and / or a pressure related parameter and / or a process of a pressure related parameter depending on the crank angle and / or the speed and / or the engine temperature and / or fuel composition and / or the amount of injection are determined and stored. The pressure or pressure is strongly dependent on the mentioned parameters. Thus, the comparison between the previously determined reference values ​​and the values ​​measured for determining the fuel mixture ratio is accurately possible, the more accurate the conditions for determining the reference values ​​are in accordance with those when determining the fuel mixture ratio on the basis of the pressure or pressure gradient.

It is envisaged that the recognition of the composition of the fuel mixture during a first start-up of the internal combustion engine takes place after a refueling and that correction of the amount of fuel supplied to the internal-combustion engine takes place during the first start-up process, thus starting difficulties can be safely avoided after a refueling process, even after a strong change in fuel.

According to a preferred embodiment of the invention, it may be provided that recognition of the composition of the fuel mixture takes place during an engine braking phase of the internal combustion engine. During the engine braking phase, no ignition of the air / fuel mixture occurs. Thereby, there are constant conditions in the combustion chamber without an energy introduction through combustion. The temperature change in the combustion chamber by evaporation of the fuel and the resulting pressure change is not superimposed from the additional input energy from the combustion of the fuel at the current or a previous operation 533 595, which allows a very accurate evaluation of the pressure flow and a corresponding adaptation of the pressure adaptation to the pressure adjustment.

The process is particularly advantageous for determining the composition of a gasoline / ethanol fuel mixture and / or for separating diesel and biodiesel and / or for separating winter fuel and summer fuel and / or for determining the water content of ethanol and / or for the recognition of a field refueling.

Brief description of the drawings

The invention is further explained in the following with the aid of the embodiment shown in the figure. It shows:

Fig. 1 in a graphical illustration illustrates the process of pressure in a combustion chamber of an internal combustion engine when injecting gasoline as compared to injecting an ethanol gasoline mixture.

Embodiments of the invention

Fig. 1 shows in a graphical illustration of the pressure process in a combustion chamber of an internal combustion engine when injecting gasoline as compared to injecting an ethanol gasoline mixture.

On an abscissa 10 the angle of rotation of the internal combustion engine is shown. An ordinate 11 shows the pressure in the combustion engine's combustion chamber. A first pressure process 12 shows the pressure in the combustion chamber when injecting an ethanol-gasoline mixture, here in a mixing ratio of 85% ethanol and 15% gasoline, depending on the crank angle. A fuel mixture of this composition is also referred to as E85. A second pressure process 13 shows the pressure in the combustion chamber during gasoline injection. A third pressure course 14 corresponds to the pressure in the combustion chamber without fuel injection. The curves extend congruently in the illustrated embodiment to a region 15.1, the region 15, on the other hand, enters a clear pressure difference between the first printing process 12 and the second printing process 13 and the third printing process 14. The pressure difference between the first printing process 12 and the second printing process 13 lies in the the example in an order of about 3 bar.

Gasoline and ethanol differ markedly in their cooking behaviors and in their vaporizing antipyres. Thus, ethanol has a solid boiling point of about 78 ° C, while gasoline has a boiling range from 25 ° C to 215 ° C. The evaporation enthalpy of ethanol amounts to about 904 kJ / kg, that of gasoline is in a range of 380 kJ / kg to 500 kJ / kg. Because of these differences, there is a changing compression process.

After a fuel injection, a partial evaporation of fuel parts in the combustion chamber. This, on the one hand, leads to a volume increase through the now gaseous fuel, on the other hand to a volume reduction by cooling the air contained in the combustion chamber. Thereby, the other effect, ie the cooling through the evaporation, is the dominant one. Here, the various evaporation antipers show considerable differences between gasoline and ethanol.

In the embodiment, the injection takes place in the form of a layered injection. In this case, the injection point is injected shortly before the upper turning point (OT) into the warm, already compressed air. In this phase, the air in the combustion chamber has a temperature of typically about 100 ° C, whereby a large portion of the fuel injected can be vaporized. This leads to a marked cooling of the compressed air and thus to a pressure drop in comparison with the third pressure process 14 without fuel injection. The pressure difference between the first pressure course 12 after injection of E85 and the second pressure course 13 after injection of pure gasoline amounts to about 3 bar in the embodiment. Further mixing ratios between the two fuels gasoline and ethanol produce pressure between them. The pressure process in the combustion chamber after fuel injection gives a direct reference to the fuel mixture ratio, the fuel mixture ratio can then be determined over the pressure process.

The pressure process in the combustion chamber can already be determined during an initial start-up process after a refueling process and compared with stored reference values.

533 595

Thus, the fuel mixture ratio can be determined even before a first combustion with a changed mixture ratio and, for example, the amount of fuel supplied to the combustion engine is corrected corresponding to the fuel composition.

The pressure flow can be determined directly by a correspondingly predicted pressure sensor. However, this can also be evaluated with parameters correlating with the pressure. In this way, a torque signal or a speed signal can be evaluated.

The process may be for direct fuel injection or for suction pipe injection systems. In this way, the direct fuel injection offers the advantage that multiple injection can be foreseen. In this way, for example, defined minimum amounts of fuel can be supplied to the combustion chamber in the form of a pilot injection and the pressure process is correspondingly evaluated. Furthermore, it is conceivable that these smallest amounts are ignited and further conclusions about the fuel composition are drawn from the pressure process after ignition.

In order to as far as possible eliminate the interference effect and engine tolerances, it is advantageous to carry out an adaptation of the pressure process in the combustion chamber and the signal derived therefrom at known fuel mixture ratio. In order to determine the fuel mixture ratio as a reference value, a lambda probe can be provided which smoothes fuel fluctuations over a known fuel adaptation. Throughout this fuel adaptation, the fuel mixture ratio is known, however, with a necessary turn-in time. When the fuel mixture ratio is so determined, the combustion chamber pressure process can be stored under defined, reproducible operating conditions, for example engine start, idling or rolling of the internal combustion engine. These combustion chamber pressure processes stored for different fuel mixture ratios can be compared with the measured pressure process after a refueling process and from this the fuel mixture ratio can be derived.

533 595