# An I.C engine having 6 cylinders, works on Otto-cycle. It has a bore of 20 cm and a stroke of 40 cm. If the clearance volume is 9000 cm3, the compress

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An I.C engine having 6 cylinders, works on Otto-cycle. It has a bore of 20 cm and a stroke of 40 cm. If the clearance volume is 9000 cm3, the compression ratio is:

1. 10.03
2. 8.53
3. 9.38
4. 7.33

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Correct Answer - Option 3 : 9.38

Concept:

Compression ratio (r):

It is defined as the ratio of the sum of clearance volume and swept volume to the clearance volume.

It is given by

${\bf{r}} = \frac{{{{\bf{v}}_{\bf{c}}} + {{\bf{v}}_{\bf{s}}}}}{{{{\bf{v}}_{\bf{c}}}}} = \frac{{{{\bf{v}}_1}}}{{{{\bf{v}}_2}}}$

where

${{\bf{v}}_{\bf{s}}} = Swept ~volume= \;\frac{{\bf{\pi }}}{4}\; × \;{{\bf{d}}^2}\; × \;{\bf{l}}\times n$

Calculation:

Given:

Number of cylinder (n) = 6, bore (d) = 20 cm, stroke length (l) = 40 cm, vc = 2000 cm3, r = ?

Now, we know that

Swept volume is:

${{\bf{v}}_{\bf{s}}} = \;\frac{{\bf{\pi }}}{4}\; × \;{{\bf{d}}^2}\; × \;{\bf{l}}\times n$  =  0.7854 × 20× 40 × 6

∴ vs = 75398.22 cm3

Compression ratio is:

${\bf{r}} = \frac{{{{\bf{v}}_{\bf{c}}} + {{\bf{v}}_{\bf{s}}}}}{{{{\bf{v}}_{\bf{c}}}}}= \;\frac{{9000\; + \;75398.22}}{{9000}}$

∴ r = 9.38