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Homework Help: I.C. Engine Question. Solve for: Mean Effective Pressure & Volumetric Efficiency

  1. Jun 23, 2012 #1


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    Hello all. I am new to the forums. I am having trouble solving a couple of questions. Maybe some of you can help me out. Thanks in advance!

    1. The problem statement, all variables and given/known data

    Number of cylinders 4
    Stroke cycle 4
    running at 4400 rpm
    Volume compression ratio 7.6:1
    Cylinder diameter 78 mm
    Stroke 105 mm
    Brake Power 38 KW
    Indicated Power 47.5 KW
    Air consumption 21 kg/kg fuel
    Fuel consumption 13.6 kg/l
    Each kg of fuel releases 41800 kg of energy
    Given R = 0.287 kJ/kgK

    a. Mechanical efficiency
    b. The mean effective pressure
    c. The volumetric efficiency (refer to 101.3 kpa and 0 C)
    d. Brake thermal efficiency

    3. The attempt at a solution

    I think I solved for both parts a and d. I'll show them below.
    I am however having a very hard time with parts b and c. Any help would be great.

    a. Mechanical efficiency = (Brake Power / Indicated Power) x 100
    = (38000 w / 47500 w) x 100
    = 80 %

    d. Brake thermal efficiency
    Brake Thermal Efficiency = 3600 x Brake Power / Fuel consumption x calorific value
    = 3600 x 38 KW / 13.6 kg/l x 41800 kg of energy
    = 136800 / 568480
    = 0.24 or 24%
  2. jcsd
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