1. Equivalence ratio (ϕ) is frequently more meaningful than air-fuel (AFR) ratio when comparing different fuels,
because ϕ calculates the actual ratio of air-fuel (AFR)actual over the stoichiometric ratio of air-fuel (AFR)st. Thus if
(AFR)actual is higher than (AFR)st or ϕ>1 , the mixture is fuel rich. On the contrary, if (AFR) actual is smaller than (AFR)st or
ϕ<1 , the mixture is fuel lean. This way, we can choose which fuels is more efficient by comparing the ϕ results, the
closest result to 1 (stoichiometric) is the better/more efficient.
2. The chemical structure of 3-ethyl-3-methylpentane C8H18:
3. -skipped
4. Assumption: Tref 298o K, Pref 1 atm = 101325 Pa, Tfinal 1902o K, Tavg 1100o K
a. flow rates of propane and air
100 KW = 100 KJ/s
Assume a complete combustion, the moles fractions are 16.67% for C3H8 and 83.33% for air or O2 & N2
…
b. equivalence ratio ϕ and excess air percentage
stoichiometric condition:
C3H8 + 5 (O2+3.76 N2) 3 CO2 + 4 H2O + 18.8 N2
with the help of excel, the moles are found w.r.t. the oxygen contentration of 3% in the dry-basis product:
C3H8 + 5.355 (O2+3.76 N2) 3 CO2 + 4 H2O + 20.135 N2 + 0.71 O2
ϕ=
(F
A)
(
F
A
)
st
=
(1
5.355 )
(1
5)
=0.934
%of excess air =100% ×1−ϕ
ϕ=100 % ×1−0.934
0.934 =7.098 %
c. adiabatic flame temp (Tad) by manual calculation
Result = 2280 K
