Hall Ticket No:
Question Paper Code: A3314
VARDHAMAN COLLEGE OF ENGINEERING
(AUTONOMOUS) B. Tech IV Semester Regular/Supplementary Examinations, May 2018
(Regulations: VCE-R15) THERMAL ENGINEERING-I
(Mechanical Engineering) Date: 15 May, 2018 FN
Time: 3 hours
Max Marks: 75
Answer ONE question from each Unit
All Questions Carry Equal Marks
Unit I
1.
List seven differences between SI engines and CI engines.
9M
Define the following terminology as related to internal combustion engines:
i. Bore
ii. Stroke
iii. Clearance volume
iv. Displacement volume
v. Top dead centre
vi. Bottom dead centre
6M
2.
Discuss the reasons that are responsible for deviation of actual fuel air cycles from ideal thermodynamic air standard cycles.
8M
List out advantages and disadvantages of a two-stroke cycle engine over a four-stroke cycle engine.
7M
Unit II
3.
What is meant by abnormal combustion? Explain the phenomenon of knock in SI engines.
8M
What are homogenous and heterogeneous mixtures? In which engines these mixtures are used? Explain.
7M
4.
Bring out clearly the process of combustion in CI engines and also explain the various stages of combustion.
7M
Explain with figures the various types of combustion chambers used in CI engines.
8M
Unit III
5.
Explain Morse test used to determine friction power of IC engine.
5M
A six cylinder, gasoline engine operates on the four stroke cycle. The bore of each cylinder is 80mm and the stroke is 100mm. The clearance volume in each cylinder is 70cc. At a speed of 4000rpm the fuel consumption is 20kg/h. The torque developed is 150 N-m. Calculate:
i. The brake power
ii. The brake mean effective pressure
iii. Brake thermal efficiency if the calorific value of the fuel is 43000kJ/kg
iv. The relative efficiency if the ideal cycle for the engine is Otto cycle
10M
6.
Write short notes on positive displacement machines.
5M
A gasoline engine working on four- stroke develops a brake power of 20.9kW. A Morse test was conducted on this engine and the brake power obtained when each cylinder was made inoperative by short circuiting the spark plug are 14.9, 14.3, 14.8 and 14.5 respectively. The test was conducted at constant speed. Find the indicated power, mechanical efficiency and brake mean effective pressure when all the cylinders are firing. The bore of the engine is 75mm and the stroke is 90mm. The engine is running at 3000rpm.
10M
Cont…2
2
Unit IV
7.
What are the advantages of multistage compression over a single stage compression for the same pressure ratio? Why inter-cooling is necessary in multi-stage compression?
6M
A single cylinder, single acting air compressor delivers 10kg of air per minute from 1 bar and 270C to 6 bar. The compression follows the law pv1.25= C. Determine:
i. Work required to compress and deliver 1kg of air
ii. Actual power required to run the compressor if the mechanical efficiency is 80%
iii. Heat lost through the cylinder walls per minute
iv. Isothermal efficiency
9M
8.
What is the benefit of using after cooler with an air compressor when air under pressure has to be stored over long periods?
8M
A single stage single acting air compressor of 30cm bore and 40cm stroke is running at a speed of 100RPM. It takes in air at 1 bar and 200C and compresses it to a pressure of 5bar. Find the power required to drive it when compression is:
i. isothermal
ii. PV1.2 C
iii. Adiabatic
Also find the isothermal efficiencies for the cases and (iii). Neglect clearance.
7M
Unit V
9.
With line diagram explain the essential parts of a centrifugal compressor. Also draw the pressure and velocity variations, and explain briefly.
8M
A centrifugal compressor running at 60000rpm having an impeller diameter tip diameter of 101cm has the following test data:
Mass flow rate=25kg/s
Static pressure ratio=2.12
Pressure at inlet 100kPa
Temperature=280C
Mechanical efficiency= 0.97
Find:
i. Slip coefficient
ii. Temperature of air at exit
iii. Power input
iv. Power coefficient
7M
10.
What are the advantages and disadvantages of an axial flow compressor?
6M
An air compressor has eight stages of equal pressure ratio 1.35. The flow rate through the compressor and its overall efficiency are 50kg/s and 82% respectively. If the condition of air at entry are 1 bar and 400C determine:
i. The state of air at the compressor exit
ii. Polytropic efficiency
iii. Efficiency of each stage
iv. Power required to drive the compressor assuming overall efficiency of the drive as 90%
9M