Engineering Homework Help

An automotive SI engine is fueled with liquid octane at the rate of 0.0006 kg/sec.
Both air and fuel enter the engine at 25⁰C and 1 atm. The exhaust gases leave the engine
at 900K and 1 atm. Steady-state operation at equivalence ratio 0.833 results with 88% of the
fuel carbon to form carbon dioxide and the remaining 12% forming carbon monoxide.
Measurements show that the heat loss from the engine is equal to 80% of the theoretical engine
work. Using this information calculate the following:

(a) The air to fuel ratio in [kg air/kg fuel],

(b) The combustion products composition in [ppm],

(c) The theoretical engine power output in [kW],

(d) The specific fuel consumption in [g/kW hr].

Please note:

(1) the molar formation enthalpies of CO2, CO, H2O, and octane are as follows; h
0
f,CO2 = -393.51
MJ/kmol, h
0
f,CO = -107.55 MJ/kmol, h0
f,H2O = -241.82 MJ/kmol, and h0
f,fuel = -224.01 MJ/kmol.

(2) the molar sensible enthalpies for the combustion products at 900K are as follows: ΔhCO2(900K) =
28.03 MJ/kmol, ΔhH2O(900K) = 21.94 MJ/kmol, ΔhCO(900K) = 18.40 MJ/kmol, ΔhO2 (900K) = 19.24
MJ/kmol, and ΔhN2 (900K) = 18.22 MJ/kmol