Intake Boost vs. Compressive Power Requirement
Intake Boost vs. Compressive Power Requirement
(OP)
In a compression-ignition Diesel cycle engine, what is the relationship between intake tract boost pressure and the required amount of crankshaft power to compress that amount of charge air in the cylinders?
I.E. What would the penalty be to BSFC if a turbodiesel engine operated steady-state at 15pisg instead of 5psig boost, assuming equal load, RPM, fueling, etc.
I.E. What would the penalty be to BSFC if a turbodiesel engine operated steady-state at 15pisg instead of 5psig boost, assuming equal load, RPM, fueling, etc.
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RE: Intake Boost vs. Compressive Power Requirement
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RE: Intake Boost vs. Compressive Power Requirement
Wouldn't the high(er) pressure charge air help fill the cylinders, providing more downward force on the pistons during the intake stroke? That would be something of an offset, but perhaps insignificant considering the disparity in magnitude with actual combustion chamber power stroke pressures.
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RE: Intake Boost vs. Compressive Power Requirement
RE: Intake Boost vs. Compressive Power Requirement
RE: Intake Boost vs. Compressive Power Requirement
So, the work gained during the intake stroke is about half of the work lost during the expelling stroke (due to the higher pressure on the turbine).
RE: Intake Boost vs. Compressive Power Requirement
RE: Intake Boost vs. Compressive Power Requirement
globi5 - how do you surmise TIP is double compressor boost?
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RE: Intake Boost vs. Compressive Power Requirement
More pressure resisting the compression stroke results with more pressure on the power stroke, not considering extra fuel.
More boost from a turbo (which is not the OP) requires more energy from the exhaust which results in higher exhaust manifold pressure and therefore higher piston blow down pressure.
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RE: Intake Boost vs. Compressive Power Requirement
boost pressure = double manifold pressure is rather a rule of thumb.
It's not surprising though, both the compressor as well as the turbine have an adiabatic efficiency of roughly 70%. If one multiplies them, one ends up with an overall efficieny of 50% or less.
RE: Intake Boost vs. Compressive Power Requirement
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RE: Intake Boost vs. Compressive Power Requirement
RE: Intake Boost vs. Compressive Power Requirement
Why would a given engine pumping more air without burning it require less power as the exact same engine pumping less air but burning all?
RE: Intake Boost vs. Compressive Power Requirement
RE: Intake Boost vs. Compressive Power Requirement
I agree that as a compressor's pumping performance rises, the turbine's power requirement also increases. However, I don't understand where that "rule of thumb" came about... I don't think we could double TIP in relation to boost w/o destroying the charger!
As the compressor approaches an edge of it's efficiency map, every additonal psi of boost requires an ever-increasing amount of drive pressure... is that what you were getting at?
dcasto - what turbocharger parameters did you input?
Your simulation is fairly close to an observed 50% steady-state load.
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RE: Intake Boost vs. Compressive Power Requirement
RE: Intake Boost vs. Compressive Power Requirement
- I was thinking more in terms of housing A/Rs and wheel trims...
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RE: Intake Boost vs. Compressive Power Requirement
Can you plot TIP/boost-ratio in relation to the boost pressure?
RE: Intake Boost vs. Compressive Power Requirement
RE: Intake Boost vs. Compressive Power Requirement
0-5 psig boost = 3+ psig TIP
5-10 " " = 4+ " "
10-15 " " = 5+ " "
15-20 " " = 7+ " "
20-25 " " = 9+ " "
25-30 " " = 11+ " "
30-35 " " = 13+ " "
35-40 " " = 16+ " "
40-45 " " = 20+ " "
45-50 " " = 25+ " "
More fuel, more gear or more track would likely grenade the turbo on that curve's progressive rise.
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RE: Intake Boost vs. Compressive Power Requirement
RE: Intake Boost vs. Compressive Power Requirement
'Tis the other way 'round - 1st coloumn is compressor boost range, 2nd coloumn is additional TIP required over & above 1:1 ratio.
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RE: Intake Boost vs. Compressive Power Requirement
I have some experimental data for a turbocharged non-EGR diesel engine.
At some engine conditions, intake pressure could be as much as 14 inches of mercury higher than exhaust pressure.
At "worst" engine conditions, intake pressure was 2 inches of mercury lower than exhaust pressure.
You can make the pressure ratio across the turbine very low by making turbine inlet temperature very high (provided nothing melts). If the pressure ratio across the turbine is low, then exhaust pressure is low.
j2bprometheus
RE: Intake Boost vs. Compressive Power Requirement
RE: Intake Boost vs. Compressive Power Requirement
RE: Intake Boost vs. Compressive Power Requirement