Mechanical Engineering - Thermodynamics - Discussion

The correct answer is: cut-off is decreased.

The Diesel cycle and Otto cycle are both idealized thermodynamic cycles used to model internal combustion engines. The main difference between them is the way heat is added to the system.

As the cut-off ratio (the ratio of the volume at the end of combustion to the volume at the beginning of combustion) in a Diesel cycle decreases, the cycle approaches the Otto cycle. This is because a smaller cut-off ratio means that the combustion process is more similar to the constant-volume heat addition process in the Otto cycle.

In contrast, a large cut-off ratio means that the combustion process is more similar to the constant-pressure heat addition process in the Diesel cycle. A cut-off ratio of zero would mean no heat addition and a constant cut-off ratio would not change the fundamental characteristics of the cycle.

If you all compare both the cycle in one PV diagram. The Otto cycle highest temp meet to diesel cycle highest temp when cut off is zero. So the given answer is right.

When cut-off is zero OR in other words cut-off ratio is one (i.e. When heat is being added at constant volume), diesel cycle approaches to Otto cycle.

The answer is right.

Because here (Cut-off) is mention so, when cut-off will be zero then the efficiency of diesel cycle approaches to the efficiency of otto.

Where CUT-OFF and CUT-OFF RATIO both are different, If cut-off ratio is unity then the efficiency of the diesel cycle will approach to efficiency of otto cycle.

By L-HOSPITAL rule, you can prove, but for cut-off ratio.

In the options, they said cutoff(vol after combustion-vol before) not cutoff ratio (vol after combustion/vol before combustion).

Therefore as cutoff reaches zero it becomes constant volume process.

If Cut off ratio equal to one.
Then efficiency diesel cycle equal to the efficiency of otto cycle.

It is ratios of two constant volume of decrease and increases the cp and CF or acrobatics process.

Answer is B.

When cutoff is decreased, diesel cycle efficiency approaches (not equal) to the otto cycle efficiency.

No,

Here the term used "approached". Not used equal to. Understand the key.

The Answer must be cut off ratio is 0.

Many guys can think, it can be 1 then also it can be right. But, when cut off ratio is 1, the cycle will be comprised of 3 processes, which is impossible. Along with that, it will reach in the limit of 0/0 form.

Here, the Correct answer must be: When cut-off ratio is 0, the diesel cycle approached to Otto cycle.

It is ratio of volume after heat addition to volume before heat addition in diesel cycle at constant pressure.

V2/V1.