Chapter: Mechanical and Electrical : Thermal Engineering : Gas Power Cycles

Solved Problems: Gas Power Cycles

Mechanical and Electrical - Thermal Engineering - Gas Power Cycles

SOLVED PROBLEMS

1. In an Otto cycle air at 1bar and 290K is compressed isentropic ally until the pressure is 15bar The heat is added at constant volume until the pressure rises to 40bar. Calculate the air standard efficiency and mean effective pressure for the cycle. Take Cv=0.717 KJ/Kg K and Runiv = 8.314KJ/Kg K.

Given Data:

Pressure (P1) = 1bar = 100KN/m2

Temperature(T1) = 290K

Pressure (P2) = 15bar = 1500KN/m2

Pressure (P3) = 40bar = 4000KN/m2

Cv = 0.717 KJ/KgK

Runiv = 8.314 KJ/Kg K

To Find:

i) Air Standard Efficien cy (ηotto) ii) Mean Effective Press ure (Pm)

Solution:

Here it is g Runiv = 8.314 KJ/Kg K

We know

2. Estimate the lose in air st andard efficiency for the diesel engine for the c ompression ratio 14 and the cutoff change s from 6% to 13% of the stroke.

=55.93%

Lose in air standard efficiency = (ηdiesel CASE(i) ) - (ηdiesel CASE(i) )

= 0.6043-0.5593

= 0.0449

= 4.49%

3. The compression ratio o f an air standard dual cycle is 12 and the maximum pressure on the cycle is limited to 70bar. Th e pressure and temperature of the cycle at the b eginning of compression process are 1bar a nd 300K. Calculate the thermal efficiency and M ean Effective Pressure. Assume cylinder bore = 250mm, Stroke length = 300mm, Cp=1.005K J/Kg K, Cv=0.718KJ/Kg K.

Given data:

Assume Qs1 = Qs2

Compression ratio (r) = 12

Maximum pressure (P3) = (P4) = 7000 KN/m2

Temperature (T1) = 300 K

Diameter (d) = 0.25m

Stroke length (l) = 0.3m

To find:

Dual cycle efficiency (ηdual)

Mean Effective Pressure (P m)

Solution:

By Process 1-2:

= 832.58/0.0147

Pm = 56535 KN/m2

4.A diesel engine operating an air standard diesel cycle has 20cm bore and 30cmstroke.the clearance volu me is 420cm3.if the fuel is injected at 5% of the stroke,find the air standard efficiency.

Given Data:-

Bore diameter (d) =20cm=0.2mk

Stroke, (l) =30cm=0.3m

Clearance volume, (v2 ) =420cm3=420/1003= m3