Question

The conditions at the beginning of compression in an Otto engine operating on hot-air standard with k=1.35 and 101.325 kPa, 0.05m3 and 32C. The clearance is 8% and 15kJ are added per cycle. Determine the mean effective pressure.

Answer 1

Answer:

$P_m=181.42 KPa$

Explanation:

$P_1=101.325 KPa,V_1=0.05m^3,T_1=32C$,K=1.35

Clearance is 8%.

Heat added=15 KJ

We know that compression ratio $r=1+\dfrac{1}{C}$

$r=1+\dfrac{1}{0.08}$  

r=13.5

$r=\dfrac{V_1}{V_2}$

$13.5=\dfrac{0.05}{V_2}$

$V_2=3.7\times 10^{-3}$

We know that efficiency of otto cycle

$\eta =1-\dfrac{1}{r^{k-1}}$

$\eta =1-\dfrac{1}{13.5^{1.35-1}}$

$\eta =0.56$

$\eta =\dfrac{W}{Q}$

W is the work out put and Q is the heat addition.

$0.56 =\dfrac{W}{15}$

W=8.4 KJ

We know that Work =Mean effective pressure x swept volume.

Here swept volume $V_s=V_1-V_2$

$V_s=0.05-3.7\times 10^{-3}$

$V_s=0.0463 m^3$

Noe by putting the values

Work =Mean effective pressure x swept volume.

$8.4=P_m\times 0.0463$

$P_m=181.42 KPa$