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C4815 Pages: 2

a) List 2 major advantages and disadvantages of four stroke engine over two stroke
(4) engines.
b) The percentage by composition of a sample of liquid fuel by weight is C=84.8% (6) and
Ho= 15.2%. Calculate:
i)The weight of air needed for the combustion of 1 kg of fuel. ii)The volumetric
composition of the products of combustion if 15% excess air is used.
a) Describe Retardation test and its application (4) b) Derive an expression for the
efficiency of the air standard Diesel cycle in terms of (6) the cycle compression ratio and
cut-off ratio.
PART ^
Answer any four full questions, each carries 10 marks
a) What is meant by pre-ignition? Does pre-ignition occur in CI engines? Justify (3) your
answer.
b) Name the stages of combustion in ௨0.1. engine and explain with the aid of a (7) pressure
— crank angle diagram.
a) List any 2 methods for reducing NOx emission and discuss their basic principle
(5) b) Name the factors affecting detonation in 5.1. engine and discuss their
effect. (5)
a) Explain octane rating and cetane rating? (4) b) In an ideal gas turbine plant, air enters
the compressor at 1.03 bar and 35°C. the (6) pressure ratio is 6. The temperature at the
turbine inlet is 1200°C. Mass flow rate of air is 10 kg/s. Determine:
i) Power required to run the compressor ii)Turbine power output iii)
Net power output of plant iv)Thermal efficiency
For air, take: Cp = 1.005 kJ/kg.K and ratio of specific heats as 1.4.
a) Write short notes on alternative fuels and bio-fuels. (5) b) With the aid of a diagram,
explain the working of an annular combustion for gas (5) turbines.
Air is drawn in a gas turbine unit at 15°C and 1.01 bar and pressure ratio is 7:1. (10) The
compressor is driven by high pressure (HP) turbine and low pressure (LP) turbine drives
a separate power shaft. The isentropic efficiencies of compressor, and the HP and LP
turbine are 0.82,0.85 and 0.85 respectively. If the maximum cycle temperature is 610°C,
calculate:
i)The pressure and temperature of gases entering the turbine
ii) The net power developed by the turbine iii) The work
ratio
iv)The thermal efficiency of the unit
a Derive an expression for the optimum cooling pressure for minimum compressor (4)
work for a two-stage compression with perfect intercooling
b) Explain any three methods to improve the efficiency of gas turbine. (6)

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