Simplified method for measuring concentration of various exhaust gas mixture components utilizing dissimilar sensors

Abstract

A simplified method for measuring a first property and a second property of an exhaust gas mixture utilizing sensors manufactured for the purpose of measuring a first property, but having a cross-sensitivity to a second property of the exhaust gas mixture. Sensor response characteristics to the first property and the second property are accounted for and used in conjunction with a direct differential measurement between sensors to quantify the concentrations of a first and a second property.

Description

STATEMENT REGARDING FEDERALLY SPONSERD RESEARCH

(Not Applicable)

BACKROUND OF THE INVENTION

Current ceramic NO_x sensors exhibit cross-sensitivities to NH₃. This cross-sensitivity reduces the accuracy of the reported NO_x concentration from a sensor if NH₃ is also present in the exhaust gas mixture. These NO_x sensors have a cross-sensitivity to NH₃ greater than 0 but less or equal to 1. For example, a NO_x sensor with a low cross-sensitivity to NH₃ would have a cross-sensitivity value closer to 0, while a NO_x sensor with a higher cross-sensitivity to NH₃ would have a value closer to 1. A cross-sensitivity value of “a” means that 1 ppm of NH₃ appears as “a” ppm of NO_x (0<a≦1). The disclosed invention covers a simplified method for measuring concentrations NO_x and NH₃ in an exhaust gas mixture using NO sensors of different NH₃ cross-sensitivities. Previous inventions required the use of more than one type of sensor (i.e. NO_x and NH₃ sensors), or other catalytic components. One example of recent prior art (U.S. Pat. No. 7,810,313) simplifies the approach by using at least two sensors in a system, but still requires complex algorithms and a decoupling observer module in order to quantify the relative concentrations of NO_x and NH₃ in an exhaust gas mixture. The complexity of the above methods is unnecessary and can be reduced further in the non-obvious method of the disclosed invention.

BRIEF SUMMARY OF THE INVENTION

The disclosed invention covers a simplified method for measuring concentrations NO_x and NH₃ in an exhaust gas mixture using NO_x sensors of substantially different NH₃ cross-sensitivities.

BRIEF DESCRIPTION OF THE DRAWING

(Not Applicable)

DETAILED DESCRIPTION OF THE INVENTION

Two NO_x sensors having different, but known, cross-sensitivities to NH₃ are used to determine both NO_x and NH₃ concentrations using the following method: A difference in signals from a first NO_x sensor (NO_x1) with a known cross-sensitivity to NH₃ (a₁) and a second NO_x sensor (N_O2), with a different known cross-sensitivity to NH₃ (a₂), is determined (NO_x1-NO_x2). The resulting value can divided by the difference in the respective NH₃ cross-sensitivities of a₁ and a₂ resulting in an accurate NH₃ measurement. The formula is:

NH₃=(NO_x1−NO_x2)/(a₁−a₂)

The value for NO_x concentration can then be determined by multiplying a₁ by NH₃ and subtracting the result from NO_x1. Two variations of the formula are:

NO_x=NO_x1−a₁×NH₃

or

NO_x=NO_x2−a₂×NH₃

This process is substantially different from the methods using a decoupling observer module in that the math above can be performed largely, or in whole, as the function of an analog circuit and does not require complex algorithms or processing hardware to achieve a result.

Claims

1. A method for simultaneously measuring a plurality of properties associated with an exhaust gas mixture, said method comprising: combining a plurality of sensors wherein each sensor among said plurality of sensors exhibits known sensitivities to a first property and exhibits known, but measurably different, cross-sensitivities to a second property in an exhaust gas mixture; wherein said plurality of sensors provide differential signals indicative of an amount of said first property and said second property in said exhaust gas mixture; directly reading, between two of said sensors, a differential value.

2. The method of claim 1, wherein said plurality of sensors comprises at least two NOx sensors, of measurably different cross-sensitivities to NH3, for detecting. said first property, wherein said first property comprises a concentration of NOx; said second property comprises a concentration of NH3 in said exhaust gas mixture.

3. A method for simultaneously measuring both the NOx and NH3 quantities in an exhaust gas mixture comprising; a first NOx sensor exhibiting a first known cross-sensitivity to NH3; a second NOx sensor with a second known cross-sensitivity to NH3; said first known cross-sensitivity being measurably different from said second known cross-sensitivity; directly measuring a differential between said first NOx sensor and said second NOx sensor a difference indicative of the quantities of NOx and NH3 in said exhaust gas mixture.

4. The method of claim 1 wherein said first property comprises NOx and said second property comprises NH3.

5. The method of claim 2 further comprising: configuring at least one of said NOx sensors to comprise a zirconia-based multilayer sensing element.

6. The method of claim 1 wherein at least one of said sensors among said plurality of sensors comprises an electrically-based sensor.