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What could cause these differences in torque, power and BSFC?

  1. Feb 27, 2014 #1
    Ive been doing some engine testing at university and have created some torque, power ad BSFC curves. The engine used is a JCB 4.4l twin turbo diesel engine. I then compared to my results to the manufacturers graphs and got these. I need some ideas on what could cause the difference in torque, BSFC? What could cause the peak torque to be higher and the torque band narrower and the BSFC to be higher? I believe that the engine used in the uni test cell is a development version of the dieselmax and the one in the manufacturer specifications was the production model what could they have changed to cause the difference. Also the engine in the test cell is relatively green (not run in very much) which would surely mean the torque and BSFC would be lower which is contrary to the results. Maybe there is some calibration errors in the equipment? Some ideas that i could look into would be great if you have any. Thanks :)

    Heres the graphs
  2. jcsd
  3. Feb 28, 2014 #2


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    Interesting graphs.
    Probable possible causes that could happen:
    -Cold start?
    -Fuel temperature? Air temperature, pressure?
    -Flywheel (is it the same?)
    -What overall setup are you using? Engine+gearbox in neutral or bare engine?
  4. Mar 1, 2014 #3
    No expert.
    The torque spike in the mid-rev range means it could be cold start(also the fact that your bsfc is higher suggests cold start).So,the engine pumps in more fuel than air at the lower rev-range(more smoke hence).During cold start,the torque curve initially drops at the lower rev-range because of incomplete combustion(yellow flame). Once the engine hits a certain rev range,the torque curve should climb up back to the full load curve.But,your experimental graph is weird.It goes above the full load curve. Maybe your dyno has a defect??
  5. Mar 3, 2014 #4


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    Gold Member

    Would resonance in the intake/exhaust give that type of torque curve with a peak at which it is tuned?
    No expert either.
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