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  • Engine emissions: from ppm to g/bhp-hr

    I need some help converting engine emissions taken with a portable analyzer. The engine is a CAT 3516 and I might be able to find all the needed data. I need to know the formula to convert from ppm to grams/bhp-hr to see if I have enough information.

    Thanks in advance for any help

  • #2
    Re: Engine emissions: from ppm to g/bhp-hr

    Originally posted by TurboDog View Post
    I need some help converting engine emissions taken with a portable analyzer. The engine is a CAT 3516 and I might be able to find all the needed data. I need to know the formula to convert from ppm to grams/bhp-hr to see if I have enough information.

    Thanks in advance for any help
    Ppm will be micromoles of the pollutant of interest to moles of total exhaust.
    You will need the molar mass of the pollutant (derive from formula and periodic table) and a measure of moles of exhaust per brake hp hour. This will vary with the operating point of the engine.

    From volume, temperature amd pressure of exhaust, calculate total moles (per brake hp hour) then multiply by ppm and molar mass to get grams of pollutant.

    Comment


    • #3
      Re: Engine emissions: from ppm to g/bhp-hr

      Thanks for that information...but I don't have enough information yet about the exhaust volume.

      How do I use the following data about the emissions I looked up?
      NO = 30.0061 g/mol
      NO2 = 46.0056 g/mol
      CO = 28.0101 g/mol

      I'm not sure how to relate the exhaust volume to moles.

      Comment


      • #4
        Re: Engine emissions: from ppm to g/bhp-hr

        Originally posted by TurboDog View Post
        Thanks for that information...but I don't have enough information yet about the exhaust volume.

        How do I use the following data about the emissions I looked up?
        NO = 30.0061 g/mol
        NO2 = 46.0056 g/mol
        CO = 28.0101 g/mol

        I'm not sure how to relate the exhaust volume to moles.
        At a given power level, you will have a certain volume of exhaust per hour. That volume will depend on temperature and pressure. You can solve ideal gas law for n, number of moles, PV = nRT.

        Alternatively, it can be calculated from intake air, fuel flow, and the combustion equation for the fuel (some of the O2 will be consumed, burning the fuel, and converted to CO2 and H20, so moles of exhaust will be different than moles of intake air.

        You will need the gross exhaust in moles per hour at a given power level. Then for each pollutant, multiply that gross value by the ppm of the pollutant to get moles of each pollutant per hour, then by the molar mass you looked up to get grams/hour. You are doing all this at a known power level in hp

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        • #5
          Re: Engine emissions: from ppm to g/bhp-hr

          Thanks again for the help...

          I found the following information about the exhaust:
          19048.7 cfm flow
          921.9 degF temperature
          .067 bar max backpressure

          So when I put that into the ideal gas law posted I get 588.885 moles. Now, since the exhaust volume is in cubic feet per minute, is the answer 588.885 moles/minute? So to convert to hours can I just multiply by 60?

          Comment


          • #6
            Re: Engine emissions: from ppm to g/bhp-hr

            Originally posted by Turbo Dog View Post
            Thanks again for the help...

            I found the following information about the exhaust:
            19048.7 cfm flow
            921.9 degF temperature
            .067 bar max backpressure

            So when I put that into the ideal gas law posted I get 588.885 moles. Now, since the exhaust volume is in cubic feet per minute, is the answer 588.885 moles/minute? So to convert to hours can I just multiply by 60?
            I don't know. I have never used the Ideal Gas Law with "english" units. It is possible to find a value for the gas constant, with english units but I think you would get pound-moles if you did. ("Real" moles are gram-moles). What units and what value for the gas constant did you use?

            The exhaust flow seems unbelievable high, also did you convert temperature and pressure to absolute? What is the displacement of the engine, and RPM?

            I frankly don't believe the exhaust volume, but it is 539.4 m/min. At that temperature and pressure (767.54 K, 108 kPa), molar volume is 59.1 L/mol or 59.1 m/kmol. If it is correct, that 9.127 kmol/min or 547.7 kmol/h.

            Comment


            • #7
              Re: Engine emissions: from ppm to g/bhp-hr

              I used this website for the ideal gas law calculation:
              www dot chemicool.com/idealgas dot html
              I don't know what they used for the constant.

              The exhaust flow is for a CAT 3516 running at 1800 rpm with a displacement of 4764.73 cubic inches. It is a 16 cylinder engine with a 6.69" bore and a 8.46" stroke (and that's small in my world of 18" bore and 18"stroke engines). I didn't do any conversion to the temperature or pressure, I just used them as they were listed on the spec sheet. So is my 588 moles wrong?

              Comment


              • #8
                Re: Engine emissions: from ppm to g/bhp-hr

                Originally posted by Turbo Dog View Post
                I used this website for the ideal gas law calculation:
                www dot chemicool.com/idealgas dot html
                I don't know what they used for the constant.

                The exhaust flow is for a CAT 3516 running at 1800 rpm with a displacement of 4764.73 cubic inches. It is a 16 cylinder engine with a 6.69" bore and a 8.46" stroke (and that's small in my world of 18" bore and 18"stroke engines). I didn't do any conversion to the temperature or pressure, I just used them as they were listed on the spec sheet. So is my 588 moles wrong?
                Your 588 moles is wrong. I think you used the back pressure which is a gauge pressure vs atmospheric. You have to use absolute pressure, so add atmospheric, 1.013 bar, total 1.08 bar. With that, I got 9129 mol/min using your mixed units and website, vs 9.127 kmol/min by converting everything to metric (essential the same). So it apparently handles all the different units OK.

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                • #9
                  Re: Engine emissions: from ppm to g/bhp-hr

                  Yes, that backpressure was guage pressure

                  Thanks for all the help

                  Comment


                  • #10
                    Re: Engine emissions: from ppm to g/bhp-hr

                    If you need to know the answer just email me the nox ppm and O2 % and I will reply to you in grams// bhp-hr marty@martysengine.com I have done this many times.

                    Comment

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