DE102009028321A1 - Method for determining composition of mixture of fuels such as gasoline and ethanol, in fuel storage tank for operating Otto engine of vehicle, involves determining composition of fuel mixture from pressure and temperature of fuel mixture - Google Patents

Abstract

The method involves operating an internal combustion engine with a fuel mixture of two fuels, and determining pressure in a fuel storage tank or a container associated with the storage tank. Composition of the fuel mixture is determined from the pressure and the temperature of the fuel mixture at the fuel storage tank or the container associated with the tank. The temperature of the fuel mixture is determined by a model based on temperature of internal combustion engine, vehicle speed and/or activity of a fuel pump. An independent claim is also included for a device for determining composition of a fuel mixture in a fuel storage tank for operating an internal combustion engine.

Description

The The invention relates to a method for determining the composition a fuel mixture in a fuel tank for operating an internal combustion engine, which with a fuel mixture operated from a first and at least a second fuel is, with a pressure in the fuel tank or an associated container.

The The invention further relates to a device for determining the Composition of a fuel mixture in a fuel reservoir for operating an internal combustion engine, which with a fuel mixture operated from a first and at least a second fuel is, wherein in the fuel reservoir, a pressure gauge for determining the pressure in the fuel reservoir is provided.

State of the art

Internal combustion engines On the basis of gasoline engines are generally fueled Hydrocarbons derived from fossil fuels based on refined Operated oil. To this fuel is increasingly off renewable raw materials (plants) produced alcohol, for example Ethanol or methanol, in different mixing ratios added. In the US and in Europe is often a mix of 75-85% ethanol and 15-25% gasoline under the brand name E85 used. The internal combustion engines are designed so that with both pure gasoline and with blends all the way to E85 can be operated; this is called "flex-fuel operation". For economical operation with low pollutant emissions At the same time high engine power must be the operating parameters in flex-fuel operation to the respective existing fuel mixture be adjusted. By way of example, a stoichiometric Air / fuel ratio at 14.7 weight parts air However, if you use ethanol, you must have one Air content of 9 parts by weight of air per share of fuel mixture be set.

about the interaction of sensors will dictate the instantaneous fuel composition the injection timing and the current exhaust gas composition, ie the oxygen partial pressure in the exhaust gas, determined and to the control electronics the internal combustion engine passed on. Based on this sensor data is the combustion of the internal combustion engine, in particular over the setting of the ignition timing and the cheapest Air / fuel ratio, optimized.

From the DE 4117440 C2 a method for adaptively adjusting a fuel / air mixture for taking into account fuel properties in the operation of an internal combustion engine is known which comprises a lambda controller which outputs a control factor RF, and having an adaptation integrator which outputs a variable adaptation speed adaptation factor AF, in addition to the control factor FR affects the setting of the fuel / air mixture. It is provided that it is checked whether the lambda control deviation amplitude exceeds a first threshold, and if so, the adaptation speed is set to an increased value until a predetermined conditions is met, after which switched back to a low adaptation speed becomes.

The method makes it possible to operate internal combustion engines, which can be operated with different fuels, trouble-free. For example, when changing from a fuel gasoline to a fuel mixture of 85% ethanol and 15% gasoline, the injection time must be extended by more than 40% to obtain the same lambda values in the exhaust gas. This is due to the different air requirements for stoichiometric combustion, which is 9.0: 1 for gasoline at a ratio of 14.7: 1 and for a mixture of 85% ethanol and 15% gasoline (designation E85). After in the scriptures DE 4117440 C2 described method is carried out a corresponding adaptation intervention. Since, in the case of a fuel change, a very large correction of the injection times and thus of the adaptation intervention must be made in comparison with the compensation of aging influences or manufacturing influences, in the proposed method the adaptation speed is significantly increased in the case of a recognized fuel change.

adversely in the described methods, multiplicative errors, that is, errors that have the same effect throughout the entire load-speed range, in stationary operation of a warm internal combustion engine initially not of mixture deviations due to a change Fuel mixture ratio and thus changed Stoichiometry factor of the fuel mixture to distinguish are. It is therefore possible that the fuel adaptation Mixture error as a change in the mixing ratio interpreted and adapted accordingly. In particular, a temporary, but systematically present during fuel adaptation Mixture error, leads to a consideration in the fuel adaptation. As an improvement of the process is it is common to turn off the mixture adaptation after refueling and assume that only an adaptation of the fuel ("Ethanol adaptation") is to be made.

On the lambda setting of the warm internal combustion engine in steady state operation Initially, this misinterpretation has no negative effects, because the stoichiometric correction is correct overall. The exact knowledge of the fuel mixture ratio However, it is necessary elsewhere for more fuel properties to take into account. That's how it gets Fuel mixing ratio, for example for Zündwinkelberechnung needed to optimize the efficiency of the internal combustion engine.

to Determination of the composition of the fuel mixture can also fuel type sensors, also called "fuel composition sensors "are used. Types of fuel sensors use the different properties of alcohol and gasoline for determining the fuel composition. For example, ethanol a protic solvent containing hydrogen ions and a large, but dependent on the water content, Dielectric constant has. Gasoline is an aprotic solvent with a small dielectric constant. Based on this, there are fuel type sensors which determine the fuel composition determine the dielectric properties of the fuel mixture. Other fuel type sensors use the different electrical Conductivity or the different optical properties the fuels such as the different refractive indices.

adversely in the known fuel type sensors are the high additional Cost of these components and the associated Transmitters. The high cost of the components result, inter alia, that the fuel type sensors especially for the determination of the composition of fuel mixtures are developed and take no further functions or used for no further applications. The number of manufactured fuel type sensors is thus limited which leads to high costs.

From the Scriptures DE 10 2007 054813 The applicant is a method and an apparatus for determining the composition of a fuel mixture of a first and at least a second fuel for operating an internal combustion engine known, wherein a heating element for preheating and / or evaporation of the fuel mixture is provided and wherein fuel mixtures of different composition different specific heat capacities and / or have different heat of vaporization and / or different boiling points. It is provided that the fuel mixture is supplied to the heating element, that the heating element of the fuel mixture extracted heat energy or a dependent parameter is determined and that from the heat energy withdrawn from the heating element or the dependent thereon, the composition of the fuel mixture is determined.

Farther Systems are known for determining the fuel composition which do not use special fuel type sensors but the Evaluate the signals of existing on the engine sensors. Both in these systems and in the systems with fuel type sensors a mixture adaptation is carried out which shows systematic mixture errors Corrected, for example, by leakage air or rail pressure offset may occur.

In Systems without ethanol sensor, the determination of the Fuel mixture ratio by a fuel adaptation. When refueling, the refill is refueled after refueling temporarily set and the tank ventilation is locked so that not an undefined amount of fuel over the supply air can falsify the fuel adaptation. Subsequently can exemplify this for a stoichiometric Combustion required quantity ratio of air and Fuel, the fuel mixture ratio of ethanol and Be determined gasoline.

Especially a temporary but systematic during the Fuel adaptation present mixture deviation leads to a divergence of the adaptation values. Likewise, one may not be correct adapted fuel mixing ratio incorrectly be adapted as a mixture error in the mixture adaptation or a mixture error occurring during the fuel adaptation in the fuel adaptation mistakenly as a fuel mixing ratio be adapted. An incorrectly determined fuel mixture ratio Although in stationary operation of a warm-running internal combustion engine no effect on the air-fuel ratio lambda However, it has a distorting effect on the settings of the Motor control for ignition angle calculation, for cold start behavior and to optimize the efficiency.

It It is an object of the invention to provide a method which a reliable and cost-effective detection the composition of a fuel mixture of at least two Allows fuels or at least improved.

Disclosure of the invention

The device of the invention relating to the invention is achieved in that from the pressure and a temperature of the fuel mixture in the fuel tank or the associated Be container, the composition of the fuel mixture is determined. The vapor pressure of fuel mixtures of gasoline and ethanol depends on both their temperature and their ethanol content. Therefore, on the basis of a pressure measurement in the fuel storage tank or a container associated therewith, the proportion of ethanol in a fuel mixture can be determined, or at least additional indications for a determination based on other methods can be derived. This can also be used to derive a determination of the correct function of fuel type sensors or other methods. After a refueling, which can be detected with a level sensor in the fuel tank, on the other hand assuming a refueling with pure gasoline on the one hand and with E85 on the other hand, two estimates for the composition of the fuel tank located in the fuel mixture can be derived. These values can be made plausible by the method according to the invention. The method according to the invention is also helpful insofar as in practice there is often a mixture deviating from E85. By way of example, when the outside temperature is low, "E85" often uses a mixture with an ethanol content that is 10% to 50% lower, since otherwise the low vapor pressure of the fuel mixture can lead to malfunctions of the internal combustion engine.

Becomes the pressure in the fuel reservoir by means of a device intended for tank leak detection, the process can be realized particularly cost be because then the necessary sensors are present and the Data already forwarded to the control of the internal combustion engine. During a tank leak detection, the vent becomes the fuel tank temporarily closed and the resulting from the evaporation of the fuel pressure certainly. But it can also be provided to carry out the Process your own pressure sensor at a suitable location in the fuel system provided.

A Embodiment of the invention provides that the temperature the fuel mixture by means of a fuel temperature sensor or from a model as a function of a temperature of the internal combustion engine, a vehicle speed and / or depending an activity of a fuel pump is determined. It For this purpose, a temperature sensor in the fuel tank be provided or exemplified - often already existing - temperature sensor in the pressure line ("injection rail") the fuel supply can be used.

A change the composition of the fuel mixture in the fuel tank arises in particular in a refueling operation. thats why it is advantageous if from a determination of a fuel level A fueling is detected in the fuel tank and if from an existing in the fuel tank amount of fuel mixture and a refueling amount and an assumption a refueling with pure gasoline or with E85 two possible ones Compositions of the fuel mixture in the fuel reservoir be determined and if the two possible compositions as starting values of an ethanol adaptation method for the determination of Composition of the fuel mixture can be used. hereby is an acceleration of the ethanol adaptation achievable. At the same time, it can be assumed that in the case of refueling no Influence on a mixture adaptation is exercised by way of example To correct changes in fuel metering. When refueling thus both shares can be separated.

In An embodiment of the invention provides that the inventive method for plausibility a value determined in a control of the internal combustion engine the composition of the fuel mixture is used. hereby can be a mutual monitoring of different procedures and sensors are realized.

The The object relating to the device is solved by an evaluation device for determining the composition of the Fuel mixture from a pressure value in the fuel tank and a temperature of the fuel mixture is provided. The pressure value in the fuel tank can by means of one, in many already existing, pressure sensor determined from a tank leak detection become. The temperature can be determined by direct measurement in the fuel tank, by means of an existing sensor for measuring the temperature of the fuel in the high-pressure feed line to metering valves on cylinders the internal combustion engine or by means of a model as a function of Temperature of the internal combustion engine, a vehicle speed and / or an activity of a fuel pump become.

Advantageous the inventive method in a with gasoline or a mixture of gasoline and ethanol, preferably with a mixture of gasoline and a maximum of 85% ethanol, operable internal combustion engine can be applied, as the vapor pressure of pure gasoline and of fuel blends with an admixture of ethanol a dependency on the ethanol content having.

Especially can such mixtures by evaluation of the vapor pressure differentiated and characterized at different temperatures become.

Brief description of the drawings

The Invention will be described below with reference to one shown in the figures Embodiment explained. Show it:

1 a representation of the relationship between a vapor pressure and an ethanol content in a fuel mixture,

2 a representation of the relationship between temperature and vapor pressure for fuel mixtures with different content of ethanol.

1 shows in a first diagram 10 the relationship between the vapor pressure of a fuel mixture of gasoline and ethanol and the proportion of added ethanol. Along a percentage of ethanol scale axis 13 and a first pressure axis divided into kilopascals 11 shows a vapor pressure curve 12 at a given temperature the context. An admixture of more than 5% of ethanol in the gasoline-ethanol mixture leads to a reduction in the vapor pressure of the fuel mixture, wherein the dependency at an ethanol content to about 50% is relatively low and the vapor pressure at an ethanol content about about 75% decreases sharply.

In 2 is in a second diagram 20 the temperature-dependent vapor pressure for fuel mixtures of gasoline with different ethanol content applied. The pressure curves are on a temperature axis 28 , which is divided into degrees Celsius and along a pressure axis 21 , which is divided into kilopascals, worn away. A fifth pressure curve 26 shows the vapor pressure of regular gasoline CEC-RF-08. A first pressure curve 22 shows the vapor pressure curve for a fuel mixture with an admixture of 5% ethanol, a second pressure curve 23 for 15% ethanol admixture, a third pressure curve 24 for 50% ethanol admixture, a fourth pressure curve 25 for 85% ethanol admixture and a sixth pressure curve 27 for pure ethanol. The first, second and third pressure curves 22 . 23 and 24 show only slight differences between each other, but are of the fifth pressure curve 26 for pure gas CEC-RF-08 clearly distinguishable. Therefore, at least at a temperature above 70 ° C, a gasoline-ethanol mixture with a share between 5% and 50% can be clearly distinguished from pure regular gasoline. The fourth and sixth pressure curve 25 . 27 for an ethanol content of 85% and for pure ethanol differ from the fifth pressure curve 26 for regular gasoline and the first, second and third pressure curve 22 . 23 and 24 clearly, so that by means of the vapor pressure these fuel mixtures are well distinguishable. According to the invention can therefore be concluded from the vapor pressure in the fuel tank on the degree of admixture of ethanol to gasoline in a fuel mixture.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 4117440 C2 [0005, 0006]
• - DE 102007054813 [0011]

Claims (7)

Method for determining the composition of a fuel mixture in a fuel reservoir for operating an internal combustion engine, which is operated with a fuel mixture of a first and at least a second fuel, wherein a pressure in the fuel reservoir or a container associated therewith are determined, characterized in that the composition of the fuel mixture is determined from the pressure and a temperature of the fuel mixture in the fuel tank or the container associated therewith. Method according to claim 1, characterized in that that the pressure in the fuel tank by means of a Device for tank leak detection is determined. Method according to claim 1 or 2, characterized that the temperature of the fuel mixture by means of a fuel temperature sensor or from a model as a function of a temperature of the internal combustion engine, a vehicle speed and / or depending an activity of a fuel pump is determined. Method according to one of claims 1 to 3, characterized in that from a determination of a fuel level A fueling is detected in the fuel tank and that from an existing in the fuel tank amount of fuel mixture and a refueling amount and an assumption a refueling with pure gasoline or with E85 two possible ones Compositions of the fuel mixture are determined and that the two possible compositions as starting values of an ethanol adaptation process used to determine the composition of the fuel mixture become. Method according to one of claims 1 to 4, characterized in that the method for plausibility a value determined in a control of the internal combustion engine the composition of the fuel mixture is used. Device for determining the composition of a Fuel mixture in a fuel storage tank for operating an internal combustion engine, which with a fuel mixture operated from a first and at least a second fuel is, wherein in the fuel reservoir, a pressure gauge for determining the pressure in the fuel reservoir is provided, characterized in that an evaluation for determining the composition of the fuel mixture from a Pressure value in the fuel reservoir and a temperature of the fuel mixture is provided. Application of the method according to one of the preceding Claims in one with gasoline or a mixture of Gasoline and ethanol, preferably with a mixture of Gasoline and maximum 85% ethanol, operable internal combustion engine.

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