Laser system for cross-road measurement of motor vehicle exhaust gases

• US 5,877,862 A
• Filed: 08/26/1997
• Issued: 03/02/1999
• Est. Priority Date: 08/26/1997
• Status: Expired due to Term

• Current Assignee: Aerodyne Corporation
• Original Assignee: Aerodyne Corporation
• Inventors: Nelson, David D., McManus, J. Barry, Zahniser, Mark, Kolb, Charles E.
• Primary Examiner(s): KIM, ROBERT H
• Application Number:
  US08/918,472
• Time in Patent Office: 553 Days
• Field of Search: 356/436-440, 356/320, 356/326, 250/338.5, 250/339.13, 250/343, 250/345
• US Class Current: 356/436
• CPC Class Codes: G01N 2021/3513 Open path with an instrumental source
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/39 using tunable lasers

Abstract

A cross-road motor vehicle exhaust gas analyzer uses tunable infrared laser differential absorption spectroscopy incorporating photon infrared detection to determine the absolute fractional absorption of a laser by the gaseous medium. Spectroscopic constants of the gaseous species of interest are applied to the absolute fractional absorption to calculate the pertinent absolute column densities. In addition to a laser that sweeps across one or more absorption line of an component of interest, the system of the invention includes a laser source tunable over an absorption line of a reference species; the calculated column density of the reference species is used to normalize the concentration of the component of interest to the fuel consumption rate of the motor vehicle.

Claims

1. A system for monitoring a component in the exhaust gas of a moving vehicle, said system comprising:

A. a first laser, tunable over a first frequency range encompassing an absorption line of CO₂ ;

B. a second laser, tunable over a second frequency range encompassing an absorption line of the monitored component;

C. means for sweeping the frequencies of the first and second lasers over said first and second ranges, respectively;

D. means for projecting a first beam from the first laser sweeping over the first range and a second beam from the second laser sweeping over the second range along substantially the same path through said exhaust gas;

E. means for detecting the intensities of said beams after passage through the exhaust gas;

F. means for processing the detected intensities to provide a measure of the concentrations of CO₂ and of said component along the path, the means for processing being configured to sample the detected intensities over time so as to generate respective absorption curves of CO₂ and of the monitored component; and

G. means for comparing the concentrations of the component and of CO₂ to determine the rate of emission of the component by the vehicle.

2. The system defined in claim 1 wherein the means for detecting the intensities is a single detector for detecting the intensities of beams from both of said lasers, the means for projecting beams being configured to alternately project the beams from the first and second lasers through said exhaust gas.

3. The system defined in claim 2, further including a retroreflector, the means for projecting beams along substantially the same path including a beamsplitter, the retroreflector and means for projecting beams being configured so that beams from said lasers are overlapped at the beamsplitter and projected through said exhaust gas to the retroreflector and returned by the retroreflector through said exhaust gas along a return route parallel to and nearly coincident with the path.

4. The system defined in claim 3 further including a telescope configured to direct the beam returned by the retroreflector into the means for detecting.

5. The system defined in claim 1 further including a retroreflector, the retroreflector and the means for projecting beams along substantially the same path being configured so that the beams from the lasers are projected through said exhaust gas to the retroreflector and returned by the retroreflector through said exhaust gas.

6. The system defined in claim 1 further including the following:

A. means for measuring the background of concentrations of CO₂ and of said component along the path in the absence of a said exhaust gas;

B. means for determining the ratios of the concentrations of each of CO₂ and said component in said exhaust gas to the respective background concentrations, thereby to provide normalized concentrations of CO₂ and of said component; and

C. means for comparing the normalized concentrations of CO₂ and said component to ascertain the rate of emission of said component by said vehicle.

7. The system defined in claim 1 wherein the means for detecting the intensities comprises a photovoltaic detector.

8. The system defined in claim 1 wherein the means for sweeping the frequencies of the first and second lasers turns off the first and second lasers after each respective frequency sweep.

9. The system defined in claim 1 wherein the means for processing the detected intensities uses spectroscopic constants in providing a measure of the concentrations of CO₂ and of said component along the path.

10. A system for monitoring one or more components of interest in the exhaust gas of a moving vehicle, said system comprising:

A. a source of coherent radiation, tunable over a first range encompassing a first frequency corresponding to an absorption line of a reference species, and tunable over a second range encompassing a second frequency corresponding to an absorption line of a component of interest;

B. means for causing the radiation from each of the ranges to sweep over its respective range;

C. means for projecting a first beam of radiation sweeping over the first range and a second beam of radiation sweeping over the second range over substantially the same path through said exhaust gas;

D. means for detecting the intensities of the first and second beams after projection through the exhaust gas;

E. means for processing the detected intensities to generate respective measures of the concentrations of the reference species and of the component of interest, the means for processing being configured to sample the detected intensities over time so as to generate respective absorption curves of the reference species and of the monitored component; and

F. means for comparing the concentrations of the reference species and of the component of interest to determine the rate of emission of the component of interest by the vehicle.

11. The system defined in claim 10 wherein the source of coherent radiation tunable over the first and second ranges comprises one laser, alternately tunable to the first and second frequencies.

12. The system defined in claim 10 wherein the source of coherent radiation tunable over the first and second ranges comprises a first laser tunable to the first range and a second, distinct laser tunable to the second range.

13. The system defined in claim 10 wherein the source of coherent radiation is tunable over a third frequency range encompassing an absorption line of a second component of interest, for monitoring the second component of interest.

14. The system defined in claim 13 wherein the source of coherent radiation is tunable over at least one additional frequency range, the at least one additional frequency range encompassing an absorption line of an additional component of interest, for monitoring the additional component of interest.

15. The system defined in claim 10 wherein the reference species is water vapor.

16. The system defined in claim 10 wherein the reference species is carbon dioxide.

17. The system defined in claim 10 wherein the component of interest is carbon monoxide.

18. The system defined in claim 10 wherein the component of interest is nitric oxide.

19. The system defined in claim 10 wherein the component of interest is a volatile organic compound.

20. The system defined in claim 10 wherein the component of interest is formaldehyde.

21. The system defined in claim 10 wherein the means for causing the radiation from each of the ranges to sweep over its respective range causes each beam to sweep over its respective range for a duration on the order of 250 μ

s.

22. The system defined in claim 10 wherein the means for detecting is a single detector, the means for projecting first and second beams being configured to alternately project the first and second beams.

23. The system defined in claim 22 wherein the means for projecting beams along substantially the same path includes a beamsplitter.

24. The system defined in claim 10 further including a retroreflector, the retroreflector and the means for projecting beams along substantially the same path being configured so that the beams from the lasers are projected through said exhaust gas to the retroreflector and returned by the retroreflector through said exhaust gas.

25. The system defined in claim 24 further comprising means for directing light returned by the retroreflector into the detecting means.

26. The system defined in claim 25 wherein the means for directing light comprises a telescope apparatus.

27. The system defined in claim 10 wherein the means for projecting beams along substantially the same path includes a beamsplitter.

28. The system defined in claim 27 further comprising a retroreflector for returning the beam after passage through the exhaust gas along a return route parallel to and nearly coincident with the path.

29. The system defined in claim 28 further comprising means for directing light returned by the retroreflector into the detecting means.

30. The system defined in claim 13 wherein the source of coherent radiation comprises a laser alternately tunable over the third frequency range and over at least one of the first range and the second range.

31. The system defined in claim 1 wherein the means for sweeping the frequencies of the first and second lasers over said first and second ranges causes each of the first beam and the second beam to sweep over its respective range for a duration on the order of 250 μ

s.

32. The system defined in claim 1 wherein the means for processing the detected intensities calculates the absolute column densities of the reference species and of the component of interest.

33. The system defined in claim 10 wherein the means for detecting the intensities comprises a photovoltaic detector.

34. The system defined in claim 10 further comprising means for turning off each of the first and second beams after its respective frequency sweep.

35. The system defined in claim 10 wherein the means for processing the detected intensities uses spectroscopic constants in providing a measure of the concentrations of reference species and of the component of interest.

36. The system defined in claim 10 wherein the means for processing the detected intensities calculates the absolute column densities of the reference species and of the component of interest.

37. The system defined in claim 10 wherein the component of interest is nitrous oxide.

38. A method of monitoring one or more components in the exhaust gas of a moving vehicle, the method comprising the steps of:

A. providing a first beam of coherent radiation having a frequency which sweeps over a first frequency range encompassing an absorption line of a reference species;

B. providing a second beam of coherent radiation having a frequency which sweeps over a second frequency range encompassing an absorption line of a component of interest;

C. causing the first and second beams to pass through the exhaust gas over substantially the same path while they are sweeping;

D. detecting and processing the intensities of the first and second beams, after they have passed through the exhaust gas, by sampling the detected intensities over time so as to generate respective absorption curves of the reference species and of the monitored component, to generate respective measures of the concentrations of the reference species and of the component of interest; and

E. comparing the concentrations of the reference species and of the component of interest to determine the rate of emission of the component by the vehicle.

39. The method of claim 38 wherein the first and second beams of coherent radiation are produced by a single laser, alternately tunable to the first and second frequencies.

40. The method of claim 38 the first and second beams of coherent radiation are produced by two distinct lasers.

41. The method defined in claim 38 further comprising the step of providing a third beam of coherent radiation having a frequency which sweeps over a third frequency range encompassing an absorption line of a second component of interest, for monitoring the second component of interest.

42. The method defined in claim 41 further comprising the step of providing an additional beam of coherent radiation having a frequency which sweeps over an additional frequency range encompassing an absorption line of an additional component of interest, for monitoring the additional component of interest.

43. The method defined in claim 33 wherein the reference species is water vapor.

44. The method defined in claim 38 wherein the reference species is carbon dioxide.

45. The method defined in claim 38 wherein the component of interest is carbon monoxide.

46. The method defined in claim 38 wherein the component of interest is nitric oxide.

47. The method defined in claim 38 wherein the component of interest is a volatile organic compound.

48. The method defined in claim 38 wherein the component of interest is formaldehyde.

49. The method defined in claim 41 wherein the first, second and third beams of coherent radiation are produced by a single laser, alternately tunable to the first, second and third frequencies.

50. The method defined in claim 38 wherein the step of detecting the intensity of the beams is performed a single detector, the step of causing the first and second beams to pass through the exhaust gas comprising alternately projecting the first and second beams through said exhaust gas.

51. The method defined in claim 38 further comprising the step of reflecting the beams after they have passed through the exhaust gas so that they are returned through said exhaust gas.

52. The method defined in claim 41 wherein the third beam is produced by a laser, the laser also producing at least one of the first and second beams.

53. The method defined in claim 41 wherein the third beam is produced by a laser, neither of the first and second beams being produced by the laser.

54. The method defined in claim 42 wherein the additional beam is produced by a laser, the laser also producing the third beam.

55. The method defined in claim 38 wherein the component of interest is nitrogen dioxide.

56. The method defined in claim 38 wherein the first and second beams of coherent radiation sweep over their respective frequency ranges for a duration on the order of 250 μ

s.

57. The method defined in claim 38 wherein the step of detecting the intensities of the first and second beams is performed by a photovoltaic detector.

58. The method defined in claim 38 further comprising the steps of:

A. turning off each of the first and second beams after its respective frequency sweep; and

B. measuring radiation while the first and second beams are turned off.

59. The method defined in claim 38 wherein the step of processing the intensities of the first and second beams includes using spectroscopic constants in generating respective measures of the concentrations of the reference species and of the component of interest.

60. The method defined in claim 38 wherein the step of processing the intensities of the first and second beams includes calculating the absolute column densities of the reference species and of the component of interest.

61. The method defined in claim 38 wherein the component of interest is nitrous oxide.

62. The method of claim 38 wherein the step of causing the first and second beams to pass through the exhaust gas over substantially the same path comprises alternately projecting the first and second beams through said exhaust gas, the step of detecting the intensities of the first and second beams being done by a single detector.

63. The method of claim 38 further comprising the steps of:

A. measuring the background of concentrations of CO₂ and of said component along the path in the absence of a said exhaust gas;

B. determining the ratios of the concentrations of each of CO₂ and said component in said exhaust gas to the respective background concentration, thereby to provide normalized concentrations of CO₂ and of said component; and

C. comparing the normalized concentrations of CO₂ and said component to ascertain the rate of emission of said component by said vehicle.