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Thread: volumetric efficiency of 4 cylinder 4 stroke engine calculation advice

  1. #1 volumetric efficiency of 4 cylinder 4 stroke engine calculation advice 
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    I have been asked to calculate the following problem and I am struggling with calculating the volumetric efficiency part c. So far I have calculated:

    A 4 cylinder 4 stroke engine of 78mm bore and 105mm stroke develops an indicated power of 47.5kW at 4400rpm. The air/fuel ratio is 21kg air/kg fuel, the fuel consumption is 13.6 kg/h and the calorific value is 41.8Mj/kg. Calculate:

    a. mean effective pressure:

    Using IP= 100 rho LAN (For kW)

    gives : rho = IP/100LAN

    = 47.5/ 100 * (PI*{0.078^2/4}* 0.105 * 73.3/2 = 47.5/1.838 = 25.84 bar

    b. Indicated thermal efficiency

    Using eta Ith = IP/FP where FP = Mf x cv

    eta Ith= IP/mf * cv

    eta Ith= 47.5 * 10^3/ 0.037*41800 = 0.3071 = 30.7%

    c. Volumetric efficiency given inlet conditions 1 bar and 15 deg C. R=287 J/kgK.

    I have found out that volumetric efficiency is the ratio of actual air mass drawn into the engine during one cycle to that of atmospheric conditions.

    eta volumetric = actual mass of air/ rho(atmosheric conditions) * displacement

    or


    eta volumetric = rev per cycle * steady air flow in / rho(atmosheric conditions) * displacement * engine speed

    I am struggling to find the actual mass of air drawn in or steady air flow in any help will be greatly appreciated.

    Thanks James
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  2. #2  
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    Can you post the problem?
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  3. #3  
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    Hi Jilan the problem is:

    A 4 cylinder 4 stroke engine of 78mm bore and 105mm stroke develops an indicated power of 47.5kW at 4400rpm. The air/fuel ratio is 21kg air/kg fuel, the fuel consumption is 13.6 kg/h and the calorific value is 41.8Mj/kg. Calculate the Volumetric efficiency given inlet conditions of 1 bar and 15 deg C. R=287 J/kgK.

    Thanks for your help
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  4. #4  
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    Good, do you have any equations that might help us?
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  5. #5  
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    I have found out that volumetric efficiency is the ratio of actual air mass drawn into the engine during one cycle to that of atmospheric conditions.

    eta volumetric = actual mass of air/ rho(atmosheric conditions) * displacement

    or


    eta volumetric = rev per cycle * steady air flow in / rho(atmosheric conditions) * displacement * engine speed
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  6. #6  
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    So we are comparing the amount of air used with the amount of air drawn into the engine. We are doing to need to convert the volume of air to a mass. Can you calculate the density of air so we can do that?
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  7. #7  
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    Hi Jilan, It's just clicked how to do it using the ideal gas equation I can calculate the density then convert all units to si form then plug the figures in to the above equation! ! Can't believe I have overlooked that thanks for the light bulb moment I needed.

    Regards James
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  8. #8  
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    PV=nRT rears its pretty head again.
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