Remote emissions sensing system with improved NOxdetection

• US 6,983,639 B1
• Filed: 11/13/2000
• Issued: 01/10/2006
• Est. Priority Date: 09/17/1998
• Status: Expired due to Term

• Current Assignee: Envirotest Corp. (Opus Group AB)
• Original Assignee: Environmental Systems Products Incorporated
• Inventors: Johnson, James, DiDomenico, John, Rendahl, Craig S.
• Primary Examiner(s): CYGAN, MICHAEL T
• Application Number:
  US09/709,935
• Time in Patent Office: 1,884 Days
• Field of Search: 73/233.1
• US Class Current: 73/23.31
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence
• CPC Class Codes: G01N 33/0037 NOx
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

A remote emissions sensing system is provided with NO_x detection capability. First, a reading of the ambient NO_x concentration is taken just prior to each vehicle passing through the system. This measurement accounts for any ambient NO_x concentration that may be lingering from the exhaust of a previous vehicle. Next, the system takes a blocked reading when the vehicle is located in the path of the beam. This reading accounts for any ambient or system noise that may exist. Finally, the system takes a reading of the exhaust plume as the beam passes through the plume. A processor determines the portion of the reading due to the exhaust plume by subtracting the ambient and blocked readings from the exhaust plume reading. As a result, a more accurate exhaust concentration reading is provided. Additionally, the system may process exhaust plume readings only in a predetermined wavelength band associated with the known absorption spectrum of NO_x so that data points for which there is no significant absorption of NO_x may be eliminated. Thus, any noise or other interference in the non-absorptive wavelengths are minimized. Also, changes in the intensity of the radiation are compensated by subtracting a baseline intensity from each signal.

Claims

1. A method for determining the concentration of NO_x in an exhaust plume of a vehicle passing through a beam of radiation projected along an optical path between a radiation source having an initial intensity, and a detector for measuring intensities of radiation incident upon the detector over a range of wavelengths, the method comprising:

measuring, under ambient conditions, intensities of radiation over a range of wavelengths to determine ambient NO_x concentration, wherein the range of wavelengths includes at least one absorption wavelength for NO_x;

measuring intensities of radiation, over the range of wavelengths, while the beam of radiation is passing through an exhaust plume of a vehicle after the vehicle passes through the optical path;

determining a baseline intensity by interpolating a substantially linear region over an absorption dip in an absorption curve generated from the intensities measured while the beam of radiation is passing through the exhaust plume of the vehicle;

calculating the concentration of NO_x in the exhaust plume of the vehicle, wherein calculating the concentration of NO_x includes using the baseline intensity to compensate for changes in the initial intensity; and

subtracting the ambient NO_x concentration from the concentration of NO_x in the exhaust plume of the vehicle.

2. The method of claim 1, wherein the measuring of intensities of radiation under ambient conditions occurs at predetermined intervals.

3. The method of claim 1, wherein the measuring of intensities of radiation under ambient conditions is initiated upon an occurrence of a predetermined trigger event.

4. The method of claim 1, further comprising:

taking a blocked beam reading when the vehicle is in the optical path and blocking the beam of radiation, wherein the blocked beam reading measures basline current or noise.

5. The method of claim 4, furter comprising:

substracting the blocked beam reading from the concentration of NOx in the exhaust plume.

6. The method of claim 4, wherein the blocked beam reading is taken after the measuring of intensities of radiation under ambient conditions, but before the measuring of intensities of radiation while the beam of radiation is passing through the exhaust plume of the vehicle.

7. The method of claim 4, wherein the measuring of intensities of radiation under ambient conditions occurs prior to taking the blocked beam reading.

8. The method of claim 1, wherein the range of wavelengths is selected to be substantially centered around a characteristic wavelength such that a number of data points for which there is no signficant NO_x absorption is minimized.

9. A system for determining the concentration of NO_x in an exhaust plume of a vehicle passing through a beam of radiation projected along an optical path between a radiation source having an initial intensity, and a detector for measuring intensities of radiation incident upon the detector over a range of wavelengths, the system comprising:

means for measuring, under ambient conditions, intensities of radiation over a range of wavelengths to determine ambient NO_x concentration, wherein the range of wavelengths includes at least one absorption wavelength for NO_x;

.

means for measuring intensities of radiation, over the range of wavelengths, while the beam of radiation is passing through an exhaust plume of a vehicle after the vehicle passes through the optical path;

means for determining a baseline intensity by interpolating a substantially linear region over an absorption dip in an absorption curve generated from the intensities measured while the beam of radiation is passing through the exhaust plume of the vehicle;

means for calculating the concentration of NO_x in the exhaust plume of the vehicle, wherein calculating the concentration of NO_x includes using the baseline intensity to compensate for changes in the initial intensity; and

means for subtracting the ambient NO_x concentration from the concentration of NO_x in the exhaust plume of the vehicle.

10. The system of claim 9, wherein the measuring of intensities of radiation under ambient conditions occurs at predetermined intervals.

11. The system of claim 9, wherein the measuring of intensities of radiation under ambient conditions is initiated upon an occurrence of a predetermined trigger event.

12. The system of claim 9, further comprising:

means for taking a blocked beam reading when the vehicle is in the optical path and blocking the beam of radiation, wherein the blocked beam reading measures baseline current or noise.

13. The system of claim 12, further comprising:

means for subtracting the blocked beam reading from the concentration of NO_x in the exhaust plume.

14. The system of claim 12, wherein the blocked beam reading is taken after the measuring of intensities of radiation under ambient conditions, but before the measuring of intensities of radiation while the beam of radiation is passing through the exhaust plume of the vehicle.

15. The system of claim 12, wherein the measuring of intensities of radiation under ambient conditions occurs prior to taking the blocked beam reading.

16. The system of claim 9, wherein the range of wavelengths is selected to be substantially centered around a characteristic wavelength such that a number of data points for which there is not significant NO_x absorption is minimized.