Tanta University
Faculty of Engineering
Forth Year Mech. Sheet No. 1
Fuel system
1. A race car burns Nitromethane (Nitromethane is an organic compound with
the chemical formula CH3NO2) with air at an equivalence ratio of 1.25.
Except for unburned fuel, all nitrogen ends up as N 2. Write the balanced
chemical equation.
Calculate:
a) Percent stoichiometric air. [%]
b) Air-fuel ratio
2. Isooctane (C8H18) is burned with air in an engine at an equivalence ratio of
0.8333. Assuming complete combustion, write the balanced chemical
reaction equation.
Calculate:
a) Air-fuel ratio.
b) How much excess air is used. [%]
c) AKI and FS of this fuel.
3. Methanol is burned in an engine with air at an equivalence ratio of .
Exhaust pressure and inlet pressure are 101 kPa. Write the balanced chemical
equation for this reaction.
Calculate:
a) Air-fuel ratio.
b) Dew point temperature of the exhaust if the inlet air is dry. [0C]
c) Dew point temperature of the exhaust if the inlet air has a relative humidity
of 40% at 25°C. [0C]
d) AKI of methanol.
4. A fuel mixture consists of 20% isooctane, 20% triptane, 20% isodecane, and
40% toluene by moles. Write the chemical reaction formula for the
stoichiometric combustion of one mole of this fuel.
Calculate:
a) Air-fuel ratio.
b) Research octane number. [RON]
5. Repeat problem (4) with mass fractions instead of mole fractions.
6. Propane (C3H8) at 25oc, 1 atm enters a combustion chamber operating at
steady state and burned completely with theoretical amount of air entering at
1 Dr. Eng. Medhat A. Mohammed Elkelawy
Tanta University
Faculty of Engineering
Forth Year Mech. Sheet No. 1
Fuel system
the same conditions. If the product exits at 25 oc, 1 atm .Determine the
amount of heat transfer from the combustion chamber in Kj/Kmol.
7. Hydrogen is used as a fuel in an experimental engine and is burned with
stoichiometric oxygen. Reactants enter at a temperature of 25°C and
complete combustion occurs at constant pressure. Write the balanced
chemical reaction equation.
Calculate:
c) Fuel-air (fuel-oxygen) ratio.
d) Equivalence ratio.
e) Theoretical maximum temperature from this combustion. (use enthalpy
values from a thermodynamics textbook) [K]
f) Dew point temperature of exhaust if exhaust pressure is 101 kPa. [ 0C]
8. Compute the indicated power generated at WOT by a three-liter, four-
cylinder, four stroke cycle SI engine operating at 4800 RPM using either
gasoline or methanol. For each case, the intake manifold is heated such that
all fuel is evaporated before the intake ports, and the air-fuel mixture enters
the cylinders at 60°C and 100 kPa. Compression ratio r c = 8.5, fuel
equivalence ratio = 1, combustion efficiency c = 98%, and volumetric
efficiency v = 100%. Calculate the indicated specific fuel consumption
[SFCindicated] for each fuel. [gm/kW-hr]
[Take LHV of ethyl alcohol = 24370 kj/kg]
9. A four-cylinder SI engine with a compression ratio rc = 10 operates on an air-
standard Otto cycle at 3000 RPM using ethyl alcohol as fuel. Conditions in
the cylinders at the start of the compression stroke are 60°C and 101 kPa.
Combustion efficiency c = 97%. Write the balanced stoichiometric chemical
equation for this fuel.
Calculate:
a) A/F if the engine operates at an equivalence ratio = 1.10.
b) Peak temperature in cycle. [0C]
c) Peak pressure in cycle. [kPa]
10.Tim's Buick 1993 has a six-cylinder, four-stroke cycle SI engine with
multipoint port fuel injectors operating on an Otto cycle at WOT. The fuel
injectors are set to deliver an A/F such that gasoline would burn at
stoichiometric conditions. (approximate gasoline using isooctane properties)
2 Dr. Eng. Medhat A. Mohammed Elkelawy
Tanta University
Faculty of Engineering
Forth Year Mech. Sheet No. 1
Fuel system
Calculate:
a) Equivalence ratio of air-gasoline mixture.
b) Equivalence ratio if gasoline is replaced with ethanol without readjusting
the A/F delivered by the fuel injectors.
c) Increase or decrease in brake power using alcohol instead of gasoline under
these conditions, with the same air flow rate and same thermal efficiency.
Assume ethanol would burn under these conditions with the same
combustion efficiency. [%]
11.A six-liter, eight-cylinder, and four-stroke cycle SI race car engine operates
at 6000 RPM using stoicl1iometric Nitromethane as fuel (Nitromethane is an
organic compound with the chemical formula CH3NO2). Combustion
efficiency is 99%, and the fuel input rate is 0.198 kg/sec.
Calculate:
a) Volumetric efficiency of the engine. [%]
b) Flow rate of air into the engine. [kg/sec]
c) Heat generated in each cylinder per cycle. [kJ]
d) How much chemical energy there is in unburned fuel in the exhaust.[kW]
[Hint: LHV of Nitromethane = 11300 kj/kg]
DESIGN PROBLEMS
An automobile will use hydrogen as fuel. Design a fuel tank (i.e., a fuel storage
system for the vehicle) and a method to deliver the fuel from the tank to the engine.
3 Dr. Eng. Medhat A. Mohammed Elkelawy
