JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III Year II Semester IC ENGINES AND GAS TURBINES Previous Question Paper (August/September - 2024 - R16)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
PART - A
What is the main reason for the development of two stroke engines and what are the two main types of two stroke engines?
Answer
The primary motivation for developing two-stroke engines is to achieve a higher power-to-weight ratio compared to four-stroke engines by completing the power cycle in only two strokes of the piston (one revolution of the crankshaft). This results in more frequent power strokes per unit time.
The two main types are:
- Crankcase-scavenged engines (typically small spark-ignition engines).
- Blower-scavenged engines (typically large compression-ignition diesel engines).
Explain how cetane number of any particular fuel is measured?
Answer
The cetane number is a measure of the ignition quality of diesel fuel. It is measured using a standard CFR (Cooperative Fuel Research) engine by comparing the ignition delay of the test fuel against a reference mixture of two primary reference fuels:
- n-cetane (hexadecane, C16H34), which has a high ignition quality (assigned a value of 100).
- Heptamethylnonane (HMN), which has a poor ignition quality (assigned a value of 15).
The cetane number is defined as the percentage by volume of n-cetane in the mixture that produces the same ignition delay as the test fuel under identical operating conditions.
What are the functional requirements of an injection system?
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What is the effect of various engine variables on SI engine knock?
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What is the importance of specific fuel consumption?
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What is the effect of the following factors on the performance of an SI engine: (i) Compression ratio (ii) air-fuel ratio (iii) Spark timing?
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List the advantages of gas turbine over reciprocating IC engines.
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Explain various methods of improving the specific work output and thermal efficiency of gas turbine cycle.
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What is meant by Athodyd?
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What is the essential difference between rocket propulsion and turbojet propulsion?
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PART - B
Draw the ideal and actual indicator diagrams of a two-stroke SI engine. How are they different from that of a four-stroke cycle engine?
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How are SI and CI engine fuels rated?
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Sketch and discuss the hypothetical and actual valve timing diagrams for (i) four-stroke diesel engine, (ii) four stroke petrol engine. Give approximate valve timing values.
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Discuss the significance of distillation curves? Discuss the important qualities of an SI and CI engine fuel.
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The venturi of a simple carburetor has a throat diameter of 20 mm and the coefficient of flow is 0.8. The fuel orifice has a diameter of 1.14 mm and the coefficient of fuel flow is 0.65. The gasoline surface is 5 mm below the throat, calculate: i) The air-fuel ratio for a pressure drop of 0.08 bar when the nozzle tip is neglected. ii) The air-fuel ratio when the nozzle tip is taken into account iii) The minimum velocity of air or critical air velocity required to start the fuel flow when the nozzle tip is provided. Assume the density of air and fuel as 1.20 and 750 kg/m³ respectively
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What are the effects of bad design combustion chambers?
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How is the solid injection further classified? With a neat sketch, explain the various components of a fuel feed system of a CI engine?
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Compare the knocking phenomena in SI and CI engines. Explain clearly that the factors which tend to prevent knock in SI engines, in fact promote knock in CI engines.
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List and explain various methods for finding frictional power of an engine.
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Explain briefly the homogeneous charge combustion ignition. Give a brief account for the technology behind the Gasoline Direct Injection (GDI) engine.
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A four-stroke cycle gasoline engine has six single-acting cylinders of 8 cm bore and 10 cm stroke. The engine is coupled to a brake having a torque radius of 40 cm. At 3200 rpm, with all cylinders operating the net brake load is 350 N. When each cylinder in turn is rendered inoperative, the average net brake load produced at the same speed by the remaining 5 cylinders is 250 N. Estimate the indicated mean effective pressure of the engine. With all cylinders operating the fuel consumption is 0.33 kg/min; calorific value of fuel is 43 MJ/kg; the cooling water flow rate and temperature rise is 70 kg/min and 100C respectively. On test, the engine is enclosed in a thermally and acoustically insulated box through which the output drive, water, fuel, air and exhaust connections pass. Ventilating air blown up through the box at the rate of 15 kg/min enters at 170C and leaves at 620C. Draw up a heat balance of the engine stating the items as a percentage of the heat input.
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Draw the schematic diagram of gas turbine cycle with a regenerator and derive the equation for thermal efficiency.
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A gas turbine has temperature limits of 1300 K and 300 K. Compression and expansions are isentropic. Calculate i) The pressure ratio which gives the maximum net work output, ii) The maximum network output, iii) The maximum thermal efficiency at maximum work output, iv) The work ratio at maximum work output, and v) The Carnot efficiency for the same temperature limits.
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In a closed cycle gas turbine, temperature limits are 300 K and 1000 K. The pressure ratio is such that the work done per kg of air is maximum. The adiabatic efficiencies of compressor and turbine are 0.85 and 0.9 respectively. Given Cp = 1.005 kJ/kg K, γ = 1.35. Calculate: (i) Pressure ratio, and (ii) Thermal efficiency.
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A gas turbine plant works between the temperature limits of 300 K and 1000 K. The pressure limits are 5bar and 1bar. The isentropic efficiencies of the compressor and turbine are 0.80 and 0.85 respectively. Calculate actual thermal efficiency power available if fuel consumption is 0.5 kg/s. γ=1.4, CV of the fuel = 42000kJ/kg.
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Derive the efficiency expression of turbo jet cycle with the help of P-v and T-s diagrams.
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Discuss about different types of gas turbine combustion chambers with relative merits and demerits.
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A simple turbine jet unit was tested when stationary and the ambient conditions were 1 bar and 150C. The pressure ratio for the compressor was 4:1. A fuel consumption of 0.37 kg/s was obtained for an air flow of 23 kg/s. Calculate the thrust produced if the exhaust gases from the turbine were expanded to atmospheric pressure in a convergent nozzle. Assume the following data: Isentropic efficiency of compressor 80%, Isentropic efficiency of turbine 85%, Efficiency of nozzle 93%, Transmission efficiency 98%, Calorific value of fuel 42000 kJ/kg. Assume working fluid to be air throughout.
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