Mechanical Engineering - Thermodynamics - Discussion

The compression ratio is defined as the total cylinder volume when the piston is at the bottom dead center to the clearance volume.

Cutoff ratio-Say Fuel is injected into combustion chamber where only air compressed and is at high temperature. Fuel is injected for a duration of time, say T. The piston would not have reached the bottom dead centre in time T. The fuel is cut off when the volume is, say V2. The clearance volume is V1. The ratio V2/V1 is cut off ratio.

As far as the inefficiencies go the formula for for both diesel and Otto cycle have compression ratio in their formula. I don't understand how cut off ratio comes into play. If any one can find a suitable answer please post it and till that time even I am looking into this question.

What is cut off?

Cut off ratio is nothing but ratio of volume after heat addition to vol before heat addition. V3/v2 (in diesel cycle).

Why cut-off ratio of an diesel cycle is always greater than 1.0?

Because, generally the volume will obviously increase after heating. And so it is greater than 1.0.

What is meant by combustion ratio?

If cut off ratio tends to unity then the efficiency of diesel cycle approaches to otto cycle.

Diesel cycle efficiency = 1 - ((1/Y*r^ (y-1) * lim ((Ρ^y -1) / (Ρ-1))).

Ρ-> 1.

As a limit term become 0/0, so applying L hospital's law. We get any term which cancels out why in the first term. So diesel cycle efficiency exactly becomes equal to otto cycle.

Practically I don't whether it is possible or not.

I am satisfied with your explanation, Thanks @Anjani Kumar.

When cut off ratio is 1 then the efficiency of diesel cycle is maximum which is equal to the efficiency of the otto cycle. So right answer should be when cut off ratio is 1.

How the cut-off will become zero?