FE TYPE PROBLEMS (56 points) PROPER STEPS NEED BE SHOWN FOR FULL CREDIT 1) Air i

Question

FE TYPE PROBLEMS (56 points) PROPER STEPS NEED BE SHOWN FOR FULL CREDIT 1) Air in an ideal Diesel cycle is compressed from 4 L to 0.25 L, and then it expands during the constant pressure heat addition process to 0.50 L. Under cold air standard conditions, the thermal efficiency of this cycle is (a) 49.0% (b) 38.6% (c) 61.4% (d) 67.0% (e) 79.5% 2) process. The temperature of helium before the expansion process is (a) 1668°C (b) 1182C (c) 1941 (d) 812°C (e) 575°C 0.25 L, and its temperature increases by an additional 800°C during the heat addition 6 Helium gas in an ideal Otto cycle is compressed from 12°C and 2 L to

Explanation / Answer

1)

n= 1- ((a^x)-1)/(x*e^(x-1) *(a-1)
n=efficiency
e=compression ratio= v1/v2
a=cut off ratio=V3/V2
x=Cp/Cv=1.4 for air

v1=4L
v2=0.25L
v3=0.5 L

e= 4/0.25=16
a= 0.5/0.25 =2

n= 1- ((2^1.4)-1)/(1.4*16^(1.4-1) *(2-1) = .6138 = 61.4%

option C is correct

2)

Follow step 1-2 of an ideal Otto cycle

It says it is an Isentropic compression, so...

T1/T2=(v2/v1)^(k-1)
therefore
T2=T1[(v1/v2)^(k-1)]

T1=285K
v1=2L
v2=.25L

T2=285*[(2/.25)^(1.667-1)]-(273K)
=868C +800C = 1668 C

Option A is correct

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