Method for sensing a stoichiometric air / fuel ratio

Abstract

A method for determining the stoichiometric air / fuel ratio (SAFR) of fuel blends comprising mixtures of gasoline, methanol and ethanol, the method comprising the following steps: - Measuring a conductivity of a fuel mixture, wherein measuring the conductivity comprises using a first electrode defining a cathode and a second electrode defining an anode, wherein the first electrode surrounds the second electrode such that the fuel mixture can flow between the first electrode and the second electrode, - Determining a capacity of the fuel mixture, - Determining a permittivity of the fuel mixture, - Measuring the temperature of the fuel mixture, and - Determining the SAFR of the fuel mixture based on the determined permittivity and temperature of the fuel mixture, wherein the determination of the conductivity of the fuel mixture by the capacitor formed by the two electrodes and the capacitance of the capacitor formed by the two electrodes is carried out by means of two different operating modes using two different oscillators.

Description

Technical area

[0001] The present invention relates to a method for sensing a stoichiometric air / fuel ratio (SAFR) for measuring the permittivity, conductivity and temperature of a given fuel mixture and for outputting the SAFR. background

[0002] The use of alcohols as an alternative fuel is increasing. One of the biggest challenges with using alcohols as fuel is the difference in the stoichiometric air-to-fuel ratio (SAFR) of gasoline compared to that of alcohols. These different SAFRs mean that the fuel pump and fuel injectors must deliver a different volume of fuel depending on the alcohol concentration in the fuel. This challenge is further exacerbated by the fact that different types of alcohols have different SAFRs.

[0003] A conventional flex-fuel sensor is capable of determining the concentration of ethanol in a given fuel, or alternatively, the concentration of methanol in a given fuel. The disadvantage of this technology is that the sensor cannot measure both simultaneously. Each sensor must be calibrated for either ethanol or methanol, and the sensor will be inaccurate if the other alcohol is present in the fuel. This limitation on measurement flexibility is likely to pose problems for a market where both alternative fuels are offered.

[0004] An alternative conventional solution uses a wide-range oxygen sensor, also known as a lambda sensor. This method uses an oxygen sensor in the exhaust line to measure the amount of oxygen remaining after combustion. The air / fuel ratio is then adjusted accordingly. This is a feedback method and can only make adjustments after combustion has already occurred. A refueling event can cause a large shift in the alcohol content, which can take the lambda sensor several minutes to detect. This delay leads to increased emissions and a loss of vehicle power while the system "learns" the properties of the new fuel.

[0005] A conventional near-infrared sensor can eliminate the concentration of gasoline, methanol, and ethanol blends with good accuracy. However, the near-infrared sensor is expensive, and the sensor can be affected by environmental influences and durability limitations.

[0006] Thus, there is a need to provide a sensor system for measuring the permittivity, conductivity, and temperature of a given fuel and outputting the SAFR for output to the engine control module.

[0007] Further prior art includes US 2014 / 0 116 117 A1, US 7 983 864 B2, US 2010 / 0 007 360 A1 and the internet publication entitled “Flex Fuel Sensors” (CVEL: Flex Fuel Sensors. URL: http: / / www.cvel.clemson.edu / auto / sensors / flex-fuel-sensor.html, archived in http: / / www.archive.org on April 6, 2012 [accessed June 15, 2021]). Summary

[0008] An object of the present invention is to meet the need identified above. In accordance with the principles of one embodiment, the solution is achieved by a method that determines the stoichiometric air / fuel ratio (SAFR) of fuel mixtures. The system includes a first electrode defining a cathode and a second electrode defining an anode, the first electrode surrounding the second electrode such that a fuel mixture can flow between the first electrode and the second electrode. The electrodes are configured and arranged to provide data for determining a conductivity and permittivity (i.e., dielectric conductivity) of the fuel mixture. A temperature sensor is configured and arranged to measure a temperature of the fuel mixture.A processor is configured and arranged to determine the SAFR of the fuel mixture based on the measured temperature and permittivity of the fuel mixture.

[0009] According to the invention, a conductivity of the fuel mixture is detected, a capacitance of the fuel mixture is determined, a permittivity of the fuel mixture is determined, and a temperature of the fuel mixture is measured. Based on the determined permittivity and temperature of the fuel mixture, the SAFR of the fuel mixture is determined, which can be transmitted to an engine control module. The determination of the conductivity of the fuel mixture by the capacitor formed by the two electrodes and the capacitance of the capacitor formed by the two electrodes is carried out using two different operating modes, using two different oscillators.

[0010] Other objects, features and characteristics of the present invention, as well as the methods of operation and functions of the respective elements of the structure, the combination of parts and the economy of manufacture, will be better understood by considering the following detailed description and the appended claims with reference to the accompanying drawings, all of which items form a part of this description. Short description of the drawings

[0011] The invention will be more fully understood from the following detailed description of the preferred embodiments thereof taken in conjunction with the accompanying drawings, wherein like reference numerals indicate like elements, and wherein: Fig. 1 is a curve showing the relationship of SAFR to fuel permittivity. Fig. Figure 2 is a table showing the permittivity and SAFR of different fuel blends. Fig. 3 is a schematic view of a measuring cell and its electrical equivalent in accordance with an embodiment. Fig. 4 is a flow diagram of a measuring principle, which is carried out with the help of the measuring cell and with the help of the processor from Fig. 3 has been achieved. Fig. Figure 5 is a curve showing dielectric values ​​as a function of the SAFR value for a first test sample. Fig. Figure 6 is a curve showing dielectric values ​​as a function of SAFR for a second test sample. Detailed description of an exemplary embodiment

[0012] In accordance with the embodiment discussed below, it has been determined that the stoichiometric air / fuel ratio (SAFR) of a given fuel can be related to its dielectric properties, regardless of the type of alcohol used. The relationship of the dielectric properties with respect to the SAFR is shown in Fig. 1. In the diagram, the permittivity increases with increasing concentration of alcohol in the fuel along the X-axis, while the SAFR decreases. The table of Fig. Figure 2 shows the permittivity and SAFR for different fuel blends.

[0013] With reference to Fig. 3 has a measuring cell generally designated by reference numeral 10, which is provided in accordance with an embodiment, the data of the Fig. 1 and Fig. 2. The measuring cell 10 has a first sensor electrode 12, which is a cathode, and a second sensor electrode 14, which is an anode. The electrodes define a capacitor. The electrical equivalent of the measuring cell 10 is also shown in Fig. 3, where the capacitor C is connected in parallel with a resistor R. The first electrode 12 surrounds the second electrode 14. A fuel mixture 16 flows between the electrodes 12 and 14 so that the electrodes can provide data for determining the conductivity and permittivity of the fuel mixture 16. The capacitor C essentially functions in two different modes of operation (using two different oscillators, for example) so that the permittivity and conductivity measurements can be performed. Since the permittivity of each fuel varies as a function of temperature, the temperature of the fuel must also be known for an accurate determination of the SAFR, as explained below. Thus, the cell 10 includes a temperature sensor 18, such as a thermistor.A processor 19 is associated with the measuring cell 10 and is configured and arranged to perform desired calculations and output desired results. The measuring cell 10 and the processor 19 define a sensor system 36 of the embodiment. It is preferred that the processor be part of the cell 10.

[0014] The measuring cell 10 may be of the type described in U.S. Patent No. 6,842,017 B2, the contents of which patent document are hereby incorporated by reference into the present specification. The conventional sensor measures the permittivity, conductivity, and temperature of a given fuel and outputs the ethanol or methanol concentration.

[0015] Fig. Figure 4 is a flow chart of the measuring principle in accordance with an embodiment, using the measuring cell 10 of Fig. 3. In step 20, a capacitance value of the fuel mixture 16 is measured. In step 22, the conductivity of the fuel mixture 16 is measured, and in step 24, the permittivity of the fuel 16 is calculated using the processor 19 based on the measured capacitance and conductivity. The temperature of the fuel 16 is measured in step 26 using the temperature sensor 18. Based on the measured temperature and permittivity, the air / fuel ratio of the fuel 16 is interpolated using the processor 19 in step 28. Fault detection is performed in steps 30 and 32, with the fuel SAFR and temperature being output from the processor 19 to an engine control module (ECM) 34 ( Fig. 3).

[0016] Thus, instead of outputting a conventional ethanol or methanol concentration of fuel 16, measuring cell 10 and processor 19 determine the permittivity, conductivity, and temperature of a given fuel, with the processor outputting the SAFR value. The software in processor 19 is designed to measure blends of gasoline, methanol, and ethanol. The aforementioned conventional sensor is limited to blends of gasoline and methanol or gasoline and ethanol, since the addition of alcohol results in errors when using conventional software.

[0017] Test measurements confirmed that a relationship exists between the dielectric value of a fuel and the air / fuel ratio of that fuel. Furthermore, the dielectric value can be mapped to the air / fuel ratio with a high degree of accuracy, which is required for stoichiometric combustion of this fuel in an internal combustion engine, regardless of the actual composition of that fuel. The curves in Fig. 5 and Fig. 6, which refer to two different test samples, show the relationship between permittivity and SAFR over the temperature range from -40°C to +125°C. Each set of data markers represents a fuel blend over the temperature range, with the SAFR value along the x-axis and the permittivity along the y-axis.

[0018] Thus, measuring the dielectric value of a fuel flowing through the sensor cell 10 can determine the SAFR value, which is useful for an internal combustion engine with regard to fuel injection and cold-start strategies. The SAFR value can then be "transmitted" to the engine control module 34 for adjustment of the SAFR value prior to combustion to minimize emissions and maximize performance. This transmission / control scheme addresses the disadvantages of the aforementioned conventional oxygen sensor or near-infrared sensor. The transmission solution improves engine combustion performance, reduces emissions, and avoids mechanical problems such as engine knock and misfire, which can occur with a conventional oxygen (lambda) sensor.

[0019] The foregoing preferred embodiments have been shown and described for the purpose of illustrating the structural and functional principles of the present invention, as well as methods of practicing the embodiments, and may be modified without departing from such principles. Thus, this invention includes all modifications encompassed within the spirit of the following claims.

Claims

[1] A method for determining the stoichiometric air / fuel ratio (SAFR) of fuel blends comprising mixtures of gasoline, methanol and ethanol, the method comprising the following steps: - Measuring a conductivity of a fuel mixture, wherein measuring the conductivity comprises using a first electrode defining a cathode and a second electrode defining an anode, wherein the first electrode surrounds the second electrode such that the fuel mixture can flow between the first electrode and the second electrode, - Determining a capacity of the fuel mixture, - Determining a permittivity of the fuel mixture, - Measuring the temperature of the fuel mixture, and - Determining the SAFR of the fuel mixture based on the determined permittivity and temperature of the fuel mixture, wherein the determination of the conductivity of the fuel mixture by the capacitor formed by the two electrodes and the capacitance of the capacitor formed by the two electrodes is carried out by means of two different operating modes using two different oscillators. [2] The method of claim 1, wherein the step of determining the permittivity comprises using the determined capacitance and the measured conductivity of the fuel mixture. [3] Method according to one of the preceding claims, further comprising the following steps: - supplying the determined SAFR of the fuel mixture to an engine control module of an internal combustion engine, and - Adjusting the SAFR before combustion.

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