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Tuesday, April 11, 2006
HW #4 - P #9 - Thermal Efficiency of an Automobile Engine
An automobile engine consumes fuel at a rate of 28 L/h and delivers 60 kW of power to the wheels. If the fuel has a heating value of 44,000 kJ/kg and a density of 0.8 g/cm3, determine the thermal efficiency of this engine.
2 comments:
Anonymous
said...
so i am having some problems here. To determine Qh: (fuel rate * heating value = Qh). That is giving me units of (Liters per hour times kiloJoules per kiloGram). I can convert that to Btu/H. Then to find W: I take the 60 kW and convert to Btu/H.
I then divide W by Qh, and get an answer that is much greater than one. What am i missing.
2 comments:
so i am having some problems here. To determine Qh: (fuel rate * heating value = Qh). That is giving me units of (Liters per hour times kiloJoules per kiloGram). I can convert that to Btu/H. Then to find W: I take the 60 kW and convert to Btu/H.
I then divide W by Qh, and get an answer that is much greater than one. What am i missing.
Anon 6:10
Your method for calculating QH is correct. But why go to Btu/h ? All the units in this problem are SI.
Use the definition of thermal efficiency and you are done. No unit conversions required.
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