FR2928736A3 - Fuel's ethanol rate determining method for e.g. petrol engine, in flex-fuel vehicle, involves deducing ethanol rate of injected fuel from octane number, based on model or map providing correspondence between octane number and ethanol rate - Google Patents

Abstract

The method involves deducing an octane number of injected fuel from an intermediate spark advance based on a model or a map providing correspondence between the advance and the octane number. An ethanol rate of the injected fuel is deduced from the octane number, based on the model or map providing correspondence between the octane number and the ethanol rate. The limit spark advance (AL1) of reference fuel e.g. E0-E30 fuel, is determined.

Description

Method for estimating the ethanol content in a fuel

The invention is in the field of spark-ignition engines (spark ignition engine, or combustion engine). The invention relates more precisely to the estimation of the ethanol content in the fuel injected into a spark ignition engine. 10 As anti-pollution standards become more and more severe, it is important for car manufacturers to be well versed in controlling the injection of fuel into their engines, in order to limit pollutant emissions. One of the important parameters for fuel injection in spark ignition engines is the nature of the fuel. Especially for gasoline engines, the emergence of flex-fuel combustion systems using a mixture of gasoline and ethanol greatly complicates the basic settings defined during the engine calibration. Flex-fuel vehicles (or VCL variable fuel vehicles) are therefore vehicles comprising such combustion systems. VCL fuel-efficient vehicles are able to automatically adapt their operation for any mixture of gasoline and pure ethanol in proportions between 0% and 100% by volume of ethanol. The concentration of ethanol in the fuel varies in significant proportions depending on the regulations in force depending on the country.

The concentration of ethanol in the fuel conditions the self-ignition properties of the fuel, that is, the autoignition time and therefore the knocking resistance of the engine. This delay is important because it conditions the phasing of the combustion in the thermodynamic cycle, compared to a given ignition advance setpoint, poorly phased combustion leading to an increase in pollutant emissions, an increase in fuel consumption and a decrease in performance. A high concentration of ethanol also makes the cold start conditions more severe. It is therefore very important to take into precise account the nature of the fuel present in the tank for adjusting the engines. Currently, this concentration of ethanol in the fuel is taken into account during the development of the engine. The engine settings are optimally set for a given fuel. If in the principle two fuels are compatible with a given combustion system, it involves in practice a modification of the engine settings when changing fuel. Indeed, in operation, if the vehicle 25 is used with a fuel other than that for which the engine settings were made (for example by the concentration of ethanol, density, octane or lower calorific value). PCI) the engine no longer works with its optimum settings. It is therefore necessary to know the fuel or mixture of fuels in use, so that the computer adapts its control strategy.

To determine the nature of the fuel contained in the tank, it is known to use sensors to determine the amount of gasoline of a fuel in a supply circuit of a motor vehicle.

Thus for example the international application WO 02/093150 describes a fuel level sensor using a single capacitor operated in two different modes to determine the conductivity and permittivity of a fuel mixture, in order to obtain data relating to the composition of a fuel mixture. Such a sensor is particularly adapted to be implemented in a fuel system of a motor vehicle. The main problem of using a sensor in the fuel circuit is its cost because such a solution requires the implementation of a specific sensor. However, the Applicant surprisingly discovered that it was possible to know the fuel (or fuel mixture) in use without the need to implement in the fuel system, a specific sensor. More particularly, the Applicant has discovered that it is possible to determine, for a given operating point of the engine, the octane number of the fuel injected on the basis of the ignition advance limit of the mixture, and of the difference between the ignition limit advance of a first gasoline-rich reference fuel and the optimum ignition advance of a second ethanol-rich fuel.

Fuel rich in gasoline, in the sense of the present invention, means a fuel comprising more than 50% gasoline. In Europe, as a fuel rich in gasoline, a fuel comprising more than 70% gasoline is generally used. By fuel rich in ethanol is meant in the sense of the present invention, a fuel comprising more than 50% ethanol. In Europe, a fuel with more than 70% ethanol is generally used as fuel rich in ethanol. In advance of the ignition limit, the meaning of the present invention is understood to mean the highest ignition advance possible for suppressing knock, for a given operating point of the engine and in the case of a fuel rich in gasoline. For the purposes of the present invention, chattering is understood to mean an abnormal combustion process characterized by premature self-ignition of the air-fuel mixture, which is caused by an excess of ignition advance. For operating points of the engine where the engine torque is very high, this excess ignition advance generates very high pressure and temperature in the engine cylinder. The rise in pressure and temperature becomes so great that the fuel, wedged against the walls of the cylinder, self-ignites in several places. The resulting micro-explosions produce vibrations in the acoustic range of the order of 5000 and 10000 Hertz, which are manifested by a metallic noise and a specific signature that an accelerometer placed on the motor makes it possible to record. By high engine torque is meant, in the sense of the present invention, a torque for which we can observe a pinging phenomenon. This value (threshold) of torque is variable according to the motors and can therefore be fixed at the time of the development of the engine. Optimum ignition advance means, in the sense of the present invention, the ignition advance for which the efficiency of the engine is highest, for a given operating point of the engine and a fuel rich in ethanol . Since ethanol has a very high octane number which provides high knock resistance, a fuel rich in ethanol will therefore have a high knock resistance. For such a fuel, the ignition advance is not degraded by the appearance of a knock, even for operating points of the engine where the engine torque is high.

The subject of the present invention is therefore a method for determining the ethanol content in a fuel injected into a spark ignition engine which comprises an engine control computer, characterized in that it comprises the following steps: • deduction of the octane number of said fuel injected from an intermediate feed, based on a model or a map giving the correspondence between said intermediate advance and the octane number of the fuel; • deduction of the ethanol content of the fuel injected from its octane number, based on a model or mapping giving the correspondence between the octane number and the ethanol content. Advantageously, the method according to the invention comprises an additional step for determining the intermediate advance at which the engine has rattling for said injected fuel. This step consists of a scan by the calculator of the ignition advance between an ignition limit advance for a first reference fuel and an optimum ignition efficiency of a second reference fuel, in order to find the intermediate lead at which rattling begins to appear. This step can be carried out intermittently, for example with a timer or with a counter, etc. Advantageously, the method of the invention may also comprise an additional step of determination by said computer, for a point of operation of the engine where it produces a high engine torque, of a limit lead to ignition to suppress rattling for a first reference fuel rich in gasoline. Advantageously, the method of the invention may also comprise an additional step of determination by said computer, for an operating point of the engine where it produces a high engine torque, of an optimal ignition advance allowing obtain the optimum yield for a second reference fuel rich in ethanol. Thus, during the acceleration phases of the vehicle, which require a high engine torque, the engine is relatively loaded (high air and fuel flow rates), which is favorable to the occurrence of knocking. In general, the ignition timing is relatively small to avoid this phenomenon with fuel rich in gasoline. However, in the method of the invention, the computer takes advantage of the acceleration phases of the vehicle during which the engine produces a high torque 10 to achieve a scanning advance ignition between the limit advance to the ignition of the first reference fuel (rich in gasoline) previously determined, and the optimum advance ignition of the second reference fuel (rich in ethanol), also previously determined. In particular, it will be possible to take advantage of the so-called takeoff phases, that is to say from the moment when, as the speed is no longer zero or low, the transmissions start transmitting torque to the wheels for initiate a movement of the vehicle. According to an advantageous and nonlimiting embodiment of the method of the invention, the advance limit on ignition of the first reference fuel and the optimum ignition advance of the second reference fuel 25 are determined on the basis of ignition advance maps for each of the fuels, for said engine operating point (with high engine torque). According to a first advantageous characteristic of this embodiment, the first reference fuel contains 100% to 70% of gasoline and 0 to 30% of ethanol, namely a fuel chosen from EO fuels (containing 100% of gasoline). gasoline) at E30 (containing 70% gasoline and 30% ethanol). As an example of reference fuel rich in gasoline usable in the process of the invention, the fuels designated by the abbreviations EO (containing 100% gasoline) and E26 (containing 26% ethanol and 74%) are recommended. gasoline). According to a second advantageous characteristic of this embodiment, the second reference fuel contains 100% to 70% ethanol and 0 to 30% gasoline, namely a fuel selected from fuels E100 to E70. As an example of a reference fuel rich in ethanol that can be used in the process of the invention, the fuels designated by the abbreviations E85 (containing 85% of ethanol and 15% of gasoline) and E100 (containing 100%) are recommended. ethanol). In the case of fuels rich in ethanol, the engine computer seeks to determine the ignition advance of better engine performance by a high engine torque because the ignition advance is not degraded by the appearance a clatter. In the case of petrol-rich fuels, the engine computer seeks to determine the ignition timing at the limit of occurrence of knock. Other features and advantages of the invention will appear on reading the following description of a preferred embodiment of the method of the invention with reference to the appended figures, in which: FIG. the ignition advance AL1 of a first reference fuel rich in gasoline; FIG. 2 is an optimal advance map A01 at the ignition of a second reference fuel rich in ethanol; FIG. 3 schematically illustrates the scanning by the engine computer between the ignition limit advance AL1 and the optimum ignition advance A01; FIG. 4 is a map showing the correspondence between the octane number of the injected fuel and the intermediate advance AI at which the knock for said fuel appears; and FIG. 5 is a table integrated in the engine computer giving the correspondence between the octane number of a gasoline-ethanol mixture and the ethanol content of this mixture. FIG. 1 shows a first mapping (mapping No. 1) giving, for an operating point of the engine (engine speed, engine torque) where it produces a high torque, the advance limit at ignition AL1 allowing to suppress rattling for a gasoline-rich reference fuel (first reference fuel). FIG. 2 shows a second mapping (mapping No. 2) giving, for an operating point of the engine (engine speed, engine torque) where it produces a high torque, the optimum ignition advance A01 allowing obtain the optimum yield for a reference fuel rich in ethanol (second reference fuel).

Mappings 1 and 2 are both integrated in the calculator. FIG. 3 schematically illustrates the scanning carried out by the ignition advance calculator between the ignition timing advance AL1 of the first reference fuel and the optimum ignition advance A01 of the second reference fuel, to determine at which intermediate advance AI the engine is rattling for the injected fuel (mixture given gasoline-ethanol).

FIG. 4 shows a map showing the correspondence between the octane number I0 of the injected fuel and the intermediate advance AI at which the knock for said fuel appears. This correspondence is expressed by a coefficient which is designated by the symbol cc. The octane number IO of the injected fuel is determined using the following equation (1), from the octane number I01 of the first reference fuel rich in gasoline, of the coefficient,, the intermediate feedrate AI and the ignition advance limit AL1:

(1) IO = I01 + a * (AI-AL1)

The coefficient a, which is determined by focusing, is a variable coefficient, depending on the operating point of the engine, and more particularly the engine speed, and to a lesser extent the load. FIG. 5 shows a table integrated in the engine computer giving the correspondence between the octane number IO of a gasoline / ethanol mixture and the ethanol content of this mixture. This table makes it possible to determine the ethanol content of the fuel injected from the octane number IO of the fuel injected established from the map shown in FIG. 4.

We will now detail a preferred embodiment of the method according to the invention with reference to Figures 1 to 5 attached. This process essentially comprises four steps which take place as follows for an operating point of the engine (engine speed, engine torque) where it produces a high torque: Step 1: the computer determines the limit feedrate AL1 ignition to suppress the pinging for a gasoline-rich reference fuel from the mapping shown in Figure 1, and the optimal ignition advance AO1 to obtain the optimum efficiency for a rich reference fuel in ethanol from the map shown in Figure 2; Step 2: The computer progressively increases the ignition advance from the limit advance AL1 to the optimum advance AO1 until it finds and stops at the intermediate advance AI at which the pinging (the pinging being detected using one or more accelerometers placed on the motor); Step 3: from the intermediate feedrate AI found in step 2 and the ignition advance lead AL1 determined in step 1, and knowing the octane number IO1 of the reference fuel. rich in gasoline, the computer determines the octane number IO of the fuel injected using relation (1) described above and on the basis of the mapping illustrated in Figure 4 giving the coefficient a; Step 4: the calculator determines the ethanol content of the fuel injected, from the octane number I0 of the injected fuel determined in step 3 and from the table illustrated in FIG. 5 giving the relationship between the rate of ethanol of a gasoline / ethanol mixture and the octane number of this mixture.

Claims (7)

1. A method for determining the ethanol content in a fuel injected into a spark ignition engine which comprises an engine control computer, characterized in that it comprises the following steps: • deduction of the octane number of said fuel injected from an intermediate advance (AI), based on a model or mapping giving the correspondence between said intermediate advance (AI) and the octane number of the fuel; • deduction of the ethanol content in said fuel injected from its octane number, based on a model or mapping giving the correspondence between the octane number and the ethanol content. 2. Method according to claim 1, characterized in that it comprises the following additional step: scanning by the computer of the ignition advance between an ignition limit advance (AL1) for a first fuel reference numeral and optimum ignition advance (AO1) of best efficiency of a second reference fuel, to determine at which intermediate feedrate (AI) the engine is rattling for said injected fuel; 3. Method according to claim 1 or 2, characterized in that it comprises the following additional step: determination by said computer, for an operating point of the engine where it produces a high engine torque, an ignition timing advance (AL1) for suppressing pinging for a first gasoline-rich reference fuel. 4. Method according to any one of the preceding claims, characterized in that it comprises the following additional step: determination by said computer, for an operating point of the engine where it produces a high engine torque, a optimum advance (A01) at ignition to obtain the optimum efficiency for a second reference fuel rich in ethanol. 5. Method according to any one of claims 2 to 4, characterized in that the ignition limit advance (AL1) of the first reference fuel and the optimal ignition advance (A01) of the second fuel of reference are determined on the basis of ignition advance mappings for each of the fuels. 6. Method according to any one of claims 2 to 5, characterized in that the first reference fuel contains 100% to 70% gasoline and 0 to 30% pure ethanol. 7. Method according to any one of claims 2 to 6, characterized in that the second reference fuel contains 100% to 70% ethanol and 0 to 30% gasoline.