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HW7b_09 Solution

# HW7b_09 Solution - ME 18b HW 7 Due Tuesday June 2...

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1 ME 18b, HW 7 Due Tuesday June 2, 2009 (accepted until 4 pm) Note: This homework is due on a Tuesday not a Thursday TAs for HW #7: Dan Alvarez, Sunday 8-10 pm, SFL 229; Mary Dorman, Monday 7-9 pm, SFL 331 Number of classes attended: ______ Hours spent on homework: _______ 1. Fuels and Combustion Processes A sample of pine park has the following ultimate analysis on a dry basis, percent by mass: 5.6% H, 53.4% C, 0.1% S, 0.1% N, 37.9% O and 2.9% ash. This bark will be used as a fuel by burning it with 100% theoretical air in a furnace. Determine the air-fuel ratio on a mass basis. Solution: Converting the Bark Analysis from a mass basis to a molar basis: Substance S H 2 C O 2 N 2 c/M 0.1/32 5.6/2 53.4/12 37.9/32 0.1/28 kmol/100 kg fuel 0.003 2.80 4.45 1.184 0.004 Product SO 2 H 2 O CO 2 O 2 required 0.003 1.40 4.45 -- -- Combustion requires: 0.003 + 1.40 + 4.45 = 5.853 kmol O 2 . The bark has 1.184 kmol O 2 so the net required from the air is: 4.669 kmol O 2 per 100 kg of bark. AF = 4.669(4.76)(28.97)/100 = 6.44 kg air/kg bark

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2 2. Enthalpy of Combustion: On many weekends Ashley Force Hood drives her car for just 4.5 seconds. In her car, the engine turns at 8000 rpm and has a displacement of 500 in 3 and a compression ratio of 7.5. Because she likes a lot of power, she has a supercharger on the engine that raises the intake pressure on the cylinders to 5 atm.
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