Stoichiometric air to fuel ratio sensor system

Abstract

A sensor system (36) determines the Stoichiometric Air to Fuel Ratio (SAFR) of fuel mixtures. The system includes a first electrode (12) and a second electrode (14), with the first electrode surrounding the second electrode so that a fuel mixture can flow between the first electrode and the second electrode. The electrodes are constructed and arranged to provide data for determining a conductivity and permittivity of the fuel mixture. A temperature sensor (18) is constructed and arranged to measure a temperature of the fuel mixture. A processor (19) is constructed and arranged to determine the SAFR of the fuel mixture based on the measured temperature and permittivity of the fuel mixture.

Claims

1. A sensor system for determining Stoichiometric Air to Fuel Ratio (SAFR) of fuel mixtures, the system comprising: a first electrode, a second electrode, with the first electrode surrounding the second electrode so that a fuel mixture can flow between the first electrode and the second electrode, the electrodes being constructed and arranged to provide data for determining a conductivity and permittivity of the fuel mixture, a temperature sensor constructed and arranged to measure a temperature of the fuel mixture, and a processor constructed and arranged to determine the SAFR of the fuel mixture based on the measured temperature and permittivity of the fuel mixture, wherein the fuel mixture comprises blends of gasoline, methanol and ethanol, and wherein the sensor system is in combination with an engine control module of an internal combustion engine, wherein the SAFR is fed from the processor forward to the engine control module so as to adjust the SAFR prior to combustion.

2. The system of claim 1, wherein the first electrode defines a cathode and the second electrode defines an anode.

3. A method of determining the Stoichiometric Air to Fuel Ratio (SAFR) of fuel mixtures, the method comprising the steps of: measuring a conductivity of a fuel mixture, determining a permittivity of the fuel mixture, measuring the temperature of the fuel mixture, based on the determined permittivity and temperature of the fuel mixture, determining the SAFR of the fuel mixture, feeding the determined SAFR of the fuel mixture forward to an engine control module of an internal combustion engine, and adjusting the SAFR prior to combustion, wherein the fuel mixture comprises blends of gasoline, methanol and ethanol.

4. The method of claim 3, wherein the step of measuring conductivity comprises using a first electrode and a second electrode, with the first electrode surrounding the second electrode so that the fuel mixture can flow between the first electrode.

5. The method of claim 4, wherein the first electrode defines a cathode and the second electrode defines an anode, the method including determining a capacitance of the fuel mixture.

6. The method of claim 5, wherein the step of calculating permittivity includes using the determined capacitance and the measured conductivity of the fuel mixture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which:

(2) FIG. 1 is a graph showing the correlation of SAFR to permittivity of fuel.

(3) FIG. 2 is a table showing the permittivity and SAFR of various fuel blends.

(4) FIG. 3 is a schematic view of a measurement cell and its electrical equivalent in accordance with an embodiment.

(5) FIG. 4 is a flow diagram of a measurement principle obtained by the measurement cell and processor of FIG. 3.

(6) FIG. 5 is graph showing SAFR vs. dielectric value for a first test sample.

(7) FIG. 6 is graph showing SAFR vs. dielectric value for a second test sample.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

(8) In accordance with the embodiment discussed below, it has been determined that the Stoichiometric Air to Fuel Ratio (SAFR) of a given fuel can be correlated to its dielectric properties, independent of the type of alcohol being used. The correlation of dielectric properties to SAFR is shown in FIG. 1. As shown, as the concentration of alcohol in the fuel increases along the X axis the permittivity increases, and the SAFR decreases. The table of FIG. 2 shows the permittivity and SAFR of various fuel blends.

(9) With reference to FIG. 3, a measurement cell, generally indicated at 10, provided in accordance with an embodiment, obtained the data of FIGS. 1 and 2. The measurement cell 10 has a first sensor electrode 12 that is a cathode, and a second sensor electrode 14 that is an anode. The electrodes define a capacitor. The electrical equivalence of the measurement cell 10 is also shown in FIG. 3, where the capacitor C is 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 effectively operates in two different modes (using two different oscillators for example) so that the permittivity and conductivity measurements can be made. Since the permittivity of each fuel varies as a function of temperature, the temperature of the fuel must also be known to accurately determine 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 measurement cell 10 and is constructed and arranged to perform desired calculations and to output desired results. The measurement cell 10 and processor 19 define a sensor system 36 of the embodiment. It can be appreciated that the processor can be part of the cell 10.

(10) The measurement cell 10 can be of the type described in U.S. Pat. No. 6,842,017 B2, the content of which is hereby incorporated by reference into this specification. This conventional sensor measures the permittivity, conductivity, and temperature of a given fuel and outputs the ethanol or methanol concentration.

(11) FIG. 4 is a flow diagram of the measurement principle in accordance with an embodiment, using the measurement cell 10 of FIG. 3. In step 20, a capacitance of the fuel mixture 16 is measured. In step 22, the conductivity of the fuel mixture 16 is measured and in step 24, based on the measured capacitance and conductivity, the permittivity of the fuel 16 is calculated by processor 19. The temperature of the fuel 16 is measured by the temperature sensor 18 in step 26. Based on the measured temperature and permittivity, the air-to-fuel ratio of the fuel 16 is interpolated by the processor 19 in step 28. Error detection is performed in step 30 and in step 32, the fuel SAFR and temperature are outputted from the processor 19 to an engine control module (ECM) 34 (FIG. 3).

(12) Thus, instead of outputting the conventional ethanol or methanol concentration of the fuel 16, the measurement cell 10 and processor 19 determine the permittivity, conductivity, and temperature of a given fuel and the processor outputs the SAFR. The software in processor 19 is configured to measure blends of gasoline, methanol and ethanol. The conventional sensor noted above is restricted to blends of gasoline and methanol or gasoline and ethanol since the addition of alcohol causes errors with the conventional software.

(13) Testing confirmed that there is a correlation between the dielectric value of a fuel and the air-to-fuel ratio of that fuel. Furthermore, the dielectric value can be mapped with a high degree of accuracy to the air-to-fuel ratio required for a stoichiometric burn of that fuel in an internal combustion engine, regardless of the actual composition of that fuel. The graphs in FIGS. 5 and 6, regarding two different test samples, show the relationship of permittivity and SAFR over the temperature range of 40 C. to 125 C. Each set of data marks represents one fuel blend over the temperature range, with SAFR shown along the X axis and permittivity shown along the Y axis.

(14) Thus, measuring the dielectric of a fuel flowing through the measurement cell 10, the SAFR can be determined which is useful for fuel injection and cold start strategies for a combustion engine. The SAFR value can then be fed forward to the engine control module 34 to adjust the SAFR prior to combustion, in order to minimize emissions and maximize performance. This feed-forward control scheme addresses the shortcomings of the conventional Lambda sensor or near infrared sensor mentioned above. The feed-forward approach will improve engine combustion efficiency, reduce pollutant emissions, and prevent mechanical issues such as engine knocking and backfire which may occur with a conventional oxygen (Lambda) sensor.

(15) The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the spirit of the following claims.