Gas Power cycles Anna University Two mark question and Descriptive Problems

1.       Draw the actual PV diagram of two stroke engine

2.       What is meant by mean effective pressure?

3.       Name any four assumptions made for air standard cycle analysis

4.       Sketch the dual cycle on PV and TS coordinates

5.       Define actual and relative thermal efficiency

6.       What is an air standard cycle? Why such cycles are conceived?

7.       Define mep and stat its importance in reciprocating engines.

8.       For a given compression ratio, the air standard Diesel cycle is less efficient that air standard Otto cycle.

9.       In an engine working of an ideal Otto cycle the temperatures at the beginning at the end of compression are 27C and 327C respectively. Find the compression ratio and air standard efficiency of the engine. [ans : 5.67; 50%]

10.   Why Carnot cycle is not used practically?

       11. Draw the Pv diagram for a Dual cycle

12. How does the change in compression ratio affect air standard efficiency of an ideal cycle?

13. State thermodynamic process involved in Diesel cycle

14. Define air standard efficiency of Diesel cycle

15. In an Otto cycle pressure ratio during compression is 11. Find air standard efficiency. [ans. 49%]

Part B Questions

1.       An engine works on Otto cycle. The initial pressure and temperature of the air is 1 bar and 40C . 825kJ of heat is supplied per kg of air at the end of the compression. Find the temperature and pressure at all salient points if the compression ratio is 6. Also find the efficiency and mean effective pressure for the cycle. Assume air is used as working fluid and take all ideal conditions.  [au 14, 16]

2.       A gas turbine works on an air standard Brayton cycle. The initial condition of the air is 25C and 1 bar. The maximum pressure and temperature are limited to 3 bar and 650C. Find the following:  a) cycle efficiency b) heat supplied and rejected per kg of air  c) work output  d) exhaust temperature. [au14, 16]

3.       Derive an expression for air standard efficiency of diesel cycle. Explain why the efficiency of Otto cycle is more than that of the diesel cycle for the same compression ratio [au13, 16]

4.       In an oil engine working on Dual cycle the heat supplied at constant pressure is twice that of heat supplied at constant volume. The compression and expansion ratios are 8 and 5.3. The pressure and temperature at the beginning of cycle are 0.93 bar and 27C. Find the efficiency of the cycle and mean effective pressure. [au13,16]

[Ans. Effcy 53%; mep = 5.5 bar; r_p = 1.56]

5.       A SI engine working on an ideal Otto cycle has the compression ratio as 6. The initial pressure and temperature of air are 1 bar and 37C. The maximum pressure in the cycle is 30 bar. For unit mass flow find,

a)      p,V and T at various salient points of the heat rejected. B) the ratio of heat supplied to the heat rejected [au12 16]  [Ans : Qs /Qr  = 2.1 ; T4 = 9300K, P4 = 2.4bar]

6.       Air standard Dual cycle has a compression ratio of 18 and compression begins at 1 bar, 40C. The maximum pressure is 85 bar. The heat transferred to air at constant pressure is equal to that at constant volume. Find. A) the pressure and temperature at salient points  b) the cycle efficiency  c) mep  [au 12 , 16]

[Ans: p2 = 57 bar; T2 994K; p5 = 2 bar; T5 = 624K, effcy = 68%; mep = 5.5 bar]

7.       In an engine working on Dual cycle the temperature and pressure at the beginning of the cycle are 90c and 1 bar respectively. The compression ratio is 9. The maximum pressure is limited to 68 bar and total heat supplied per kg of air is 1750kJ. Find a) pressure and temperature at all salient points, efficiency and mep [au12, 16]

[ans; rp = 3.13; effcy = 58%;  mep = 11bar]

8.       A four stroke four cylinder petrol engine of 250mm bore and 375 m stroke works on an Otto cycle. The clearance volume is 0.01052 m3. The initial pressure and temperature are 1 bar and 47C. If the maximum pressure is limited to 25 bar, find the a) the air standard efficiency  b) mep. [au11, 16 ]

[ans: efficiency = 33%; mep = 9.9 bar]

9.       In an air standard Dual cycle the pressure and temperature at the beginning of compression are 1 bar and 57C respectively. The heat supplied in the cycle is 1250 kJ/kg, two third of this being added at constant volume and rest at constant pressure. If the compression ratio is 16, find the maximum pressure and temperature in the cycle, thermal efficiency and mep. [au 11, 16] 

 [ans: p3 = 106bar; re = 13.3; WD = 832kJ/kg; effcy = 66%; mep = 9.7 bar]

    10. A six cylinder four stroke petrol engine has a swept volume of 300 cubic cm per cylinder. A compression ratio of 10 and operates at a speed of 3500 rpm. If the engine is required to develop an output of 73.5kW at this speed find the cycle efficiency, the necessary rate of heat addition the mep, max pressure and temperature of the cycle efficiency ratio. The pressure and temperature before isentropic compression are 1 bar and 15C. [au10 16]

[Hint = W = mep*Vs*N/60*n; Ans; Qs=122kW; mep =0.7bar;]