We were
discussing Otto cycle, an ideal cycle for internal
combustion spark ignition reciprocating engines or simply petrol engines and
also Diesel
cycle, the ideal cycle for the operation of internal combustion compression
ignition reciprocating engines
in our previous posts. We have also discussed the derivation of efficiency of Otto cycle and efficiency of Diesel cycle.

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Today we
will see here few more very important terms i.e. volumetric compression ratio,
Expansion Ratio, Cut-off ratio and simultaneously we will also see here the
efficiency of Diesel cycle in terms of these ratios with the help of this post.

First we will have to see brief introduction and background to remind the concept of
Diesel cycle. Diesel cycle is one type of air standard cycle which is
designated as the ideal cycle for the operation of internal compression
ignition reciprocating engines.

Let us see
an overview of Diesel cycle with the help of PV diagram and TS diagram as
displayed here in following figure. As we can see in below figure, there will
be two isentropic or adiabatic processes, one constant pressure and one constant
volume process.

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**Let
us understand now the term volumetric compression ratio, ****Expansion
Ratio and Cut-off ratio**

Volumetric
compression ratio will be defined as the maximum volume to minimum volume and
it will be indicated by r

_{v}.
r

_{v}= V_{1}/V_{2}
Now we
must have to understand here that why we are focusing here to understand the
volumetric compression ratio and why we are giving stress to determine the
result or formula to calculate the efficiency of the Diesel cycle in term of
volumetric compression ratio.

As we know
very well that Diesel cycle is one theoretical cycle or ideal cycle for
internal compression ignition reciprocating engines or simply Diesel engines. Space is
one very important design criteria for any automobile and automobile designer. Designer will have to
surely consider this design criteria i.e. space restriction.

We will
have to design our engine with considering the space permitted for respective
automobile as we may not design one engine which accommodate large area as it
will not be in favour of the user of automobile and therefore there will be one
maximum volume and one minimum volume and we will have to design our engine
with considering the maximum and minimum volume.

Now we will write here the expression of efficiency of the Diesel cycle in terms of above
mentioned ratios. As we have discussed in our recent post, efficiency
of diesel cycle will
be determined with the help of following formula.

Do you
have any suggestions? Please write in comment box.

We will
see another topic in our next post in the category of thermal engineering.

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**Reference:**

Engineering
thermodynamics by P. K. Nag

Engineering
thermodynamics by Prof S. K. Som

Image
courtesy: Google

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