ANNA UNIVERSITY, CHENNAI
DEPARTMENT :MECHANICAL ENGINEERING
REGULATION 2013
SUBJECT CODE/NAME: ME6404 - THERMAL ENGINEERING
This post covers the first two units of question bank ( 2 marks
and 16 marks) of the subject Thermal Engineering which are
repeated questions asking from Anna university.
PART-A
1. Mention the
assumptions made on the air standard cycle analysis. [May/June-2009]
2. In an Otto cycle,
pressure ratio during compression is 11. Calculate the air standard efficiency.
[May/June-2009]
3. Enumerate the
factors which shall be considered while selecting a boiler? [Nov/Dec-2009]
4. What is steam trap?
[Nov/Dec-2009]
5. What is the effect
of compression ratio on efficiency of Otto cycle? [April/May-2010]
6. Define Mean
Effective Pressure (MEP). [April/May-2010], [May/June-2012], [Nov/Dec-2013]
7. In What respects
the working processes in an actual engine differ from a theoretical cycle.
[Nov/Dec-2010]
8. What are quality
governed engines? [Nov/Dec-2010]
9. What are the
differences between actual and ideal cycle? [May/June-2012]
10. Explain the term
Knocking. [Nov/Dec-2012]
11. What is meant by
lean and rich mixture? [Nov/Dec-2012]
12. Mention the ranges
of compression ratio for SI and CI engines. [May/June-2013]
13. What is relative
efficiency? [May/June-2013]
14. For a given
compression ratio the Otto cycle is more efficient than Diesel cycle. Justify?
[Nov/Dec-2013]
15. What is an air
standard efficiency? [May/June-2014]
16. Define (a)
Compression ratio (b) cut off ratio. [May/June-2014]
17. Define the terms
actual thermal efficiency and relative efficiency. [Nov/Dec-2012]
18. What is an
air-standard cycle? Why such cycles are conceived? [Nov/Dec-2012]
PART-B
1. Fuel supplied to an
SI engine has a calorific value 42,000KJ/Kg. The pressure in the cylinder at
30% and 70% of the compression stroke are 1.3bar and 2.6bar respectively.
Assuming that the compression follows the law pV1.3=Constant. Find
the compression ratio, if the relative efficiency of the engine compared with
the air-standard efficiency is 50%. Calculate the fuel consumption in Kg/KW-hr.
(12) [May/June-2009]
2. A gas engine working
on the Otto cycle has a cylinder of diameter 0.2m and stroke 0.25m. The
clearance volume is 1570cc. Find the air standard efficiency. Assume cp=1.004KJ/Kg-K
and cv=0.717KJ/Kg-K for air. (4) [May/June-2009]
3. A diesel engine has
a compression ratio of 20 and cut-off takes place at 5% of the stroke. Find the
air standard efficiency. Assume y=1.4. (6) [May/June-2009]
4. In an engine
working on the diesel cycle the ratios of the weights of air and fuel supplied
is 50:1. The temperature of air at the beginning of the compression is 333K and
the compression ratio used is 14:1. What is the ideal efficiency of the engine
calorific value of fuel used is 4200KJ/Kg. Assume cp=1.004KJ/Kg-K
and cv=0.717KJ/Kg-K for air. (10) [May/June-2009]
5. Derive an
expression for the air standard efficiency and MEP of a Diesel cycle. (16)
[April/May-2010]
6. The compression
ratio of an air standard Dual cycle is 12 and the maximum pressure in the cycle
is limited to 70bar. The pressure and temperature of the cycle at the beginning
of compression process are 1bar and 300K. Calculate the thermal efficiency and
mean effective pressure. Assume Cylinder bore=250mm, stroke length=300mm, cp=1.005KJ/Kg-K,
cv=0.718KJ/Kg-K. (16) [April/May-2010]
7. An engine with
200mm cylinder diameter and 300mm stroke works on theoretical Diesel cycle. The
initial pressure and temperature of air used are 1bar and 270C. The
cut-off is 8% of the stroke. Determine the
i.
Pressure and temperature
at all salient points.
ii.
Theoretical air
standard efficiency.
iii.
Mean effective
pressure.
iv.
Power of the
engine if the working cycles per minute are 380.
Assume that compression ratio is 15 and
working fluid is air.
Consider all conditions to be ideal. (16)
[Nov/Dec-2010]
8. Air enters the
compressor of a gas turbine plant operating on Brayton cycle at 101.325KPa, 270C.
The pressure ratio in the cycle is 6. Calculate the maximum temperature in the
cycle and cycle efficiency. Assume WT=2.5WC, where WT
and WC are the turbine and the compressor work respectively. Take
γ=1.4 (8) [Nov/Dec-2010]
9. An engine working
on Otto-cycle in which the salient points are 1, 2, 3 and 4 has upper and lower
temperature limits T3 and T1. If the maximum work per Kg
of air is to be done, then show that the intermediate temperature is given by If an engine works on Otto-cycle between temperature limits
1430K and 300K, find the maximum theoritical power developed by the engine
assuming the circulation of air per minute is 0.4Kg. (8) [Nov/Dec-2010]
10. A diesel engine has
a compression ratio of 14 to 1 and fuel is cut off at 0.08 of stroke. Calculate
the mass of fuel used per KW hour, if the calorific value is 42000KJ/Kg and the
relative efficiency is 0.54. (10) [May/June-2012]
11. Show that the
efficiency of the Otto cycle is greater than diesel cycle for the same
compression ratio. (6) [May/June-2012]
12. 1 kg of air is
taken through a diesel cycle. Initially the air is at 150C and 1bar.
The compression ratio is 15 and the heat added is 1850KJ. Calculate the ideal
cycle efficiency and the mean effective pressure. (10) [May/June-2012]
13. Compare the actual
and ideal PV diagram of a four and two stroke engine. (6) [May/June-2012]
24. The following data
were given for an oil engine working with Otto cycle.
Brake power = 14.7KW
Suction Pressure = 0.9bar
Mechanical Efficiency = 80%
Ratio of compression = 5
Index of compression curve = 1.35
Index of expansion curve = 1.3
Maximum explosion pressure = 24bar
Engine speed = 1000r.p.m
Ratio of stroke: bore =
1.5
Find the dia and stroke
of piston. (16) [Nov/Dec-2012]
15. Explain the method
of air cooling in IC engines. (8) [Nov/Dec-2012]
16. Explain any one
type of lubrication method for IC engines. (8) [Nov/Dec-2012]
17. State the four
processes that constitute the Ericsson cycle and show the cycle on the T-s and
p-v diagrams. (6) [May/June-2013]
18. A gas turbine works
on an air standard Brayton cycle. The initial condition of the air is 250C
and 1bar. The maximum pressure and temperature are limited to 3bar and 6500C.
Determine the cycle efficiency and work output, heat supplied and heat rejected
per Kg of air. (10) [May/June-2013]
19. With suitable
sketches, explain the differences between the actual and theoretical p-v
diagrams of a four stroke Otto cycle engine. (6) [May/June-2013]
20. An air standard
dual cycle has a compression ratio of 16. The compression begins at 1bar and 500C.
The maximum pressure is 70bar. The heat transferred to air at constant pressure
is equal to that at constant volume. Estimate the pressure and temperature at the
cardinal points of the cycle and the cycle efficiency. (10) [May/June-2013]
21. An air standard
dual cycle has a compression ratio of 18, and the compression begins at 1bar,
400C. The maximum pressure is 85bar. The heat transferred to air at
constant pressure is equal to that at constant volume. Estimate:
i.
The pressure and
temperature at the cardinal points of the cycle.
ii.
The cycle
efficiency and
iii.
The mean
effective pressure of the cycle. (16) [Nov/Dec-2012]
22. An air standard
Diesel cycle has a compression ratio of 18. The pressure at the beginning of
compression stroke is 1bar and the temperature is 300C. The heat
supplied is 1800KJ/Kg. Determine:
i.
The efficiency (4)
ii.
Pressure and
temperature at salient points (4)
iii.
Heat rejected (4)
iv.
Mean Effective
Pressure. Assume the CP, CV, R, γ suitably (4) [Nov/Dec-2013]
23. An air-standard
Diesel cycle has compression ratio of 8 and the heat transferred to the working
fluid is 1800KJ/Kg. The pressure and temperature at the beginning of the
compression Stroke are 1bar and 300K respectively. Calculate (i) the pressure
and temperature at each point of cycle, (ii) the air-standard efficiency and
(iii) the mean effective pressure assume the values of CP and R as
1.005 and 0.287. (16) [May/June-2014]
24. An Otto cycle has a
compression ratio of 7. The initial pressure and temperature at the beginning
of compression stroke is 1bar and 400C. The heat supplied is
2510KJ/Kg. Find
i.
The maximum
temperature and pressure (4)
ii.
Workdone per of
air (4)
iii.
The cycle
efficiency (4)
iv.
Mean Effective
Pressure. Take CV=0.713KJ/Kg-K and R=287J/Kg-K (4) [Nov/Dec-2013]
25. Derive an
expression for air-standard efficiency of dual-combustion cycle. (16)
[May/June-2014]
26. A spark ignition
engine working on ideal Otto cycle has the compression ratio 6. The initial
pressure and temperature of air are 1bar and 370C. The maximum
pressure in the cycle is 30bar. For unit mass flow, calculate
i.
p, V and T at
various salient points of the cycle and
ii.
The ratio of
heat supplied to the heat rejected. Assume γ=1.4 and R=8.314KJ/KmolK. (16)
[Nov/Dec-2012]
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