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• Exhaust Air Flow Rate Calculation

Discussion in 'Calculations' started by ruzfactor, Jul 2, 2011.

1. ruzfactorMember

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Hi

I need help on how to calculate the exhaust air flow rate of an engine of a gasoline/diesel car at cruise condition. Actually, I need to calculate the exhaust air flow rate for Hydrogen ICE car because I need to circulate the exhaust air for another purpose. What assumptions should I make? Where to start from?

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3. PlamenMember

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Well, that is a good one.
i really doubt you can calculate this but for beginning you could start from law of conservation of mass
http://www.grc.nasa.gov/WWW/k-12/airplane/mass.html
or
http://en.wikipedia.org/wiki/Fluid_dynamics

4. ruzfactorMember

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Is there any general data regarding the bsfc and bmep of a hydrogen fueled engine at say 2500 rpm?? I 'm stuck in the calculation just because of some data I need.

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Isn't it the number of compression cycles per minute x displacement of the engine? Example: for @2000 rpm, compression cycles = 1000 (for a four-stroke engine) x 5.0 liter (displacement of a popular V-8) = 5,000 liters/min. = 176.6 cu. ft./min

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This comment assumes operation at wide open throttle and 100% volumetric efficiency. The exhaust system has to be designed to handle these conditions at peak volumetric efficiency, where peak torque is produced, as well as a reduced volumetric efficiency at engine speeds up to max operating speed (red line).

At cruise conditions, the amount of power required may only be a few percent of the maximum power available, just enough to overcome rolling resistance, mechanical losses, and aerodynamic drag. So you need to know the rolling resistance of your tires, brakes, bearings and such, how much power is lost in spinning the transmission and differential, the frontal area of the vehicle, the drag coefficient of the vehicle, the vehicle velocity and the air density. Then you need to have the fuel consumption map for your engine that includes power at the low level that will correspond to cruise power. So this is a bit involved.

A first approximation can be developed if you know the miles per gallon the vehicle gets when driving at the desired conditions using gasoline. Using the lower heating values, calculate how much hydrogen will provide the same amount of energy. Figure out how much air is required to get stoichiometric combustion of that hydrogen consumption and add 5%. The exhaust gas constituents will primarily be water vapor and nitrogen, in the proportions derived from your combustion equation, plus the 5% excess air.

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7. ruzfactorMember

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Please check the link..there is a calculation for exhaust mass flow rate ... i have some doubts over the parameters assumed for the calculation...if i convert it to volume flow rate it becomes very large...

http://postimage.org/image/2s5suut44/

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four stroke engine
b=bore, s=stroke; n=rpm, z-= num of cyl; p= turbo pressure
Volume= phi/4 x b sqare x s x n/2 x z x 2.5= m3/sec ( b and s in mtr; s in rev/sec) + fuel consumption ( + a fraction of lube oil)
This is what is combusted, so also what gets in the exhaust. It has not the accuracy
under laboratory conditions, but pretty close I believe.

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