System and method for determining whether an engine is on or off based on a pressure of exhaust gas produced by the engine

1. A system comprising:

a pressure sensor configured to measure pressure in an exhaust gas supply line that supplies exhaust gas from an engine to an emissions measurement system, the emissions measurement system including a dilution tunnel, a sample probe, and a sample collector, wherein the exhaust gas is diluted with a dilution gas in the dilution tunnel, and the sample probe supplies a portion of the diluted exhaust gas to the sample collector; and

an engine state module configured to determine whether the engine is on or off based on at least one of:

a frequency of pulsations in the exhaust gas supply line pressure; and

a magnitude of the pulsations in the exhaust gas supply line pressure.

2. The system of claim 1 wherein the engine state module is configured to determine that the engine is on when the frequency of the pulsations in the exhaust gas supply line pressure is greater than or equal to a predetermined frequency.

3. The system of claim 1 wherein the engine state module is configured to determine that the engine is on when the magnitude of the pulsations in the exhaust gas supply line pressure is greater than or equal to a predetermined value.

4. The system of claim 3 wherein the engine state module is configured to determine the magnitude of the pulsations in the exhaust gas supply line pressure based on a difference between a maximum value of one of the pulsations and a minimum value of one of the same pulsation or one of the pulsations immediately before or after the same pulsation.

5. The system of claim 1 wherein the engine state module is configured to determine whether the engine is on or off based on both the frequency of the pulsations in the exhaust gas supply line pressure and the magnitude of the pulsations in the exhaust gas supply line pressure.

6. The system of claim 5 wherein the engine state module is configured to:

identify N of the pulsations that have a frequency which is greater than or equal to a predetermined frequency; and

determine whether the engine is on or off based on the magnitudes of the N pulsations, wherein N is an integer.

7. The system of claim 6 wherein the engine state module is configured to determine that the engine is on when an average value of the magnitudes of the N pulsations is greater than or equal to a predetermined value, wherein N is greater than one.

8. The system of claim 1 wherein the pressure sensor is configured to measure the exhaust gas supply line pressure at a frequency that is greater than or equal to 1 kilohertz.

9. The system of claim 1 further comprising:

an emissions concentration sensor configured to measure a concentration of an emission in the exhaust gas; and

an emissions mass module configured to determine a mass of the emission in the exhaust gas based on the measured emission concentration and whether the engine is on or off.

10. The system of claim 1 further comprising a valve control module configured to control a valve to regulate flow of the diluted exhaust gas from the dilution tunnel to the sample collector based on whether the engine is on or off.

11. A method comprising:

measuring pressure in an exhaust gas supply line that supplies exhaust gas from an engine to an emissions measurement system, the emissions measurement system including a dilution tunnel, a sample probe, and a sample collector, wherein the exhaust gas is diluted with a dilution gas in the dilution tunnel, and the sample probe supplies a portion of the diluted exhaust gas to the sample collector; and

determining whether the engine is on or off based on at least one of:

a frequency of pulsations in the exhaust gas supply line pressure; and

a magnitude of the pulsations in the exhaust gas supply line pressure.

12. The method of claim 11 further comprising determining that the engine is on when the frequency of the pulsations in the exhaust gas supply line pressure is greater than or equal to a predetermined frequency.

13. The method of claim 11 further comprising determining that the engine is on when the magnitude of the pulsations in the exhaust gas supply line pressure is greater than or equal to a predetermined value.

14. The method of claim 13 further comprising determining the magnitude of the pulsations in the exhaust gas supply line pressure based on a difference between a maximum value of one of the pulsations and a minimum value of one of the same pulsation or one of the pulsations immediately before or after the same pulsation.

15. The method of claim 11 further comprising determining whether the engine is on or off based on both the frequency of the pulsations in the exhaust gas supply line pressure and the magnitude of the pulsations in the exhaust gas supply line pressure.

16. The method of claim 15 further comprising:

identifying N of the pulsations that have a frequency which is greater than or equal to a predetermined frequency; and

determining whether the engine is on or off based on the magnitudes of the N pulsations, wherein N is an integer.

17. The method of claim 16 further comprising determining that the engine is on when an average value of the magnitudes of the N pulsations is greater than or equal to a predetermined value, wherein N is greater than one.

18. The method of claim 11 further comprising measuring the exhaust gas supply line pressure at a frequency that is greater than or equal to 1 kilohertz.

19. The method of claim 11 further comprising:

measuring a concentration of an emission in the exhaust gas; and

determining a mass of the emission in the exhaust gas based on the measured emission concentration and whether the engine is on or off.

20. The method of claim 11 further comprising controlling a valve to regulate flow of the diluted exhaust gas from the dilution tunnel to the sample collector based on whether the engine is on or off.