8 fig 25 exercise 27 1 atm the volumetric ow rate of

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Unformatted text preview: ective pressures as T2 ¼ T1  ðgÀ1Þ=g P2 P1 where K P g¼ i¼1 K P i ¼1 mi cp;i : mi cv;i 2.2 Measurements of exhaust gases from a methane-air combustion system show 3% of oxygen by volume (dry base) in the exhaust. Assuming complete combustion, determine the excess percentage of air, equivalence ratio, and fuel/air ratio. 2.3 There has been a lot of interest about replacing gasoline with ethanol, but is this really a good idea? We’re going to compare a blend of ethanol (70% ethanol and 30% gasoline by volume) to gasoline. Calculate the lower heating value (LHV) of a 70% ethanol/30% isooctane mixture in terms of kJ/mol of fuel. Assume complete combustion. How does this compare to the tabulated value for gasoline (isooctane)? Assuming a 20% thermal efficiency, if you need to get 100 kW of power from an engine, how much of each fuel (in mol/ s) do you need? If you have a stoichiometric mixture of the ethanol/gasoline blend and air in your 100 kW engine, how much CO2 are you emitting in g/s? How does this compare to the same engine running a stoichiometric mixture of 100% gasoline and air? 2.4 Gasoline is assumed to have a chemical composition of C8.26 H15.5. (a) Determine the mole fractions of CO2 and O2 in the exhaust for an engine with normalized air/fuel ratio l ¼ 1.2 with the assumption of complete combustion. (b) The enthalpy of formation of C8.26 H15.5 is À250 MJ/kmol. Determine the LHV of gasoline in terms of MJ/kg. The molecular mass of C8.26 H15.5 is 114.62 kg/kmol. (c) Using an average cp for the products at 1,200 K, estimate the adiabatic flame temperature at constant pressure of 1 atm for the lean (l ¼ 1.2) mixture. 2.5 A mixture of methane gas and air at 25 C and 1 atm is burned in a water heater at 150% theoretical air. The mass flow rate of methane is 1.15 kg/h. The exhaust gas temperature was measured to be 500 C and approximately Exercises 45 Q Additional propane Q 3-way catalyst heater Station 1 T1 = 500K Station 2 T2 T0 φ = 0.8 Fig. 2.5 Exercise 2.7 1 atm. The volumetric flow rate of cold water (at 22 C) to the heater is 4 L/min....
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This document was uploaded on 01/20/2014.

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