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Solved Problems: Gas Power Cycles

Mechanical and Electrical - Thermal Engineering - Gas Power Cycles




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 otto) ii) Mean Effective Press ure (Pm)




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.




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 dual)

Mean Effective Pressure (P m)




By Process 1-2:



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=420/1003m3


To Find:-


Air standard efficiency, (diesel) Solution:-

Compression ratio,

r = v1/v2

= (vc+vs)/vc


We know that,


Stroke vo lume,    vs=area*length

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