BENG1 INTRODUCTION to
THERMO-FLUIDS (THER 103)
TUTORIAL EXAMPLES in NFEE APPLICATIONS
(SSL conditions are 101.325 kPa, and 15°C)
1.
The bore of a gas engine is 350 mm, the
stroke is 405 mm and the combustion chamber volume is 6.2 x 10-3 m3. When the piston is at top dead centre, the
gas pressure is 1.92MPa, and the temperature is 1100°C. The gas then expands according to the law pV1.35
= constant as the piston moves to bottom dead centre. Determine the work transfer during the
expansion, the average force on the piston during the stroke, and the heat
transfer which occurs during the expansion, stating its direction. For the expanding gases use CV = 710
J/kgK and R = 290 J/kgK. [17.04
kJ; 42.07 kN; +2.44 kJ]
2. A petrol engine has a volume
compression ratio of 8.5, and induces air into the cylinder at 25°C and 98 kPa. If the stroke volume
of one cylinder is 0.5 litre, find the gross work required to compress the air
adiabatically from BDC to TDC, and the temperature at the end of the
compression process. [188.0 J;
701.4 K]
3. A
diesel engine has a volume compression ratio of 22. If it is operating under
the same conditions as the engine in Q.2 and has the same stroke volume,
find the temperature at the end of the compression stroke. [1026.1 K]
Why does this temperature have to be so much higher than for the petrol engine?
4. A
compressor induces air at SSL conditions and compresses it to 900 kPa before
forcing it out of the cylinder into a reservoir. If the cylinder volume at BDC
is 1.2 litres, the clearance volume is negligible, and the compression process
follows the law pV1.2 = constant, find:
a)
the
work required to compress the air;
b)
the
work required to deliver the air;
c)
the
temperature of the delivered air. [266.9 J; 1750
J; 414.5 K]
5. Repeat
Q.4
using isothermal compression of the air.
Why is the total work less than for polytropic compression?
[ 265.6 J;
121.6 J; 288 K]