BENG2 THERMODYNAMICS (THER
205)
TUTORIAL EXAMPLES in IC ENGINES 2
(For all questions assume
induction conditions are SSL: 15ºC ; 101.325 kPa)
1.
IMEP relates to the Indicated Work of an IC engine,
and BMEP relates to the Brake Power of an IC engine, where:
Show that BMEP µ
Torque.
2.
Find the relationship between the Brake Thermal Efficiency of an
IC engine and its Brake Specific Fuel Consumption.
3.
A 3-cylinder
DI, water-cooled 2-stroke diesel engine with two horizontally opposed pistons
per cylinder has a bore of 82.6 mm and each piston has a stroke of 102 mm. The
engine was tested on a dynamometer with a brake arm of 0.381 m. The following
results were recorded during a variable speed test at a fixed throttle setting:
|
Speed (RPM) |
Brake Load (N) |
Fuel Flow (kg/min) |
|
1000 |
60.78 |
0.146 |
|
1100 |
61.46 |
0.157 |
|
1200 |
62.14 |
0.172 |
|
1300 |
62.14 |
0.185 |
|
1400 |
62.14 |
0.201 |
|
1500 |
62.14 |
0.216 |
|
1600 |
61.6 |
0.229 |
|
1700 |
60.9 |
0.241 |
|
1800 |
59.65 |
0.252 |
Plot curves of Torque, Brake Power; and BSFC against
RPM.
Convert the Torque curve to a BMEP curve by calculation of the appropriate scale factor.
4.
A 2-cylinder,
4-stroke gas engine has a bore of 380 mm and a stroke of 585 mm. At 240 RPM the
torque developed is 5.16 kNm. Calculate (a) the Brake Power and (b) the BMEP
[129.7 kW, 489 kPa]
5.
A 4-cylinder 4-stroke
petrol engine with a bore of 57 mm and stroke of 90 mm is tested at 2800 RPM
using a brake of torque arm 0.356 m. The brake load is 155N, and fuel
consumption 6.74 litres/h. A Morse test gives brake load readings of 111,
106.5, 104.2 and 111N respectively. Calculate the Torque; BMEP; Mechanical
efficiency; Brake Thermal efficiency; BSFC and IMEP of the Engine. The fuel has
a Relative Density of 0.735 and a Lower Calorific Value of 44.2 MJ/kg.
[55.18 Nm, 754.8 kPa, 0.828, 0.266, 0.306 kg/kWh, 911.6 kPa]