Mechanical Engineering - Thermodynamics - Discussion

As an diesel cycle the cut off ration is the ratio between V3/V2.
V3 - Fuel Injection Into the Cylinder Stop While Power Stroke.
V2 - Fuel Injection Into the Cylinder Start While Power Stroke.

Those V3 & V2 are Smaller than The V1(Cylinder Volume).

If cut off ratio tend to 1, then find the limiting value of diesel cycle efficiency as cut off ratio tend to 1, it will be equal to otto cycle efficiency. Also for those who are considering the cut off ratio zero, right answer, if cutt off ratio is zero means the volume of flue gases after combustion is zero, how can it be possible that flue gases will have zero volume.

Correct answer is b.

Becomes its clearly mentioned APPROACHES not When EQUAL. We can't say when cutt of ratio is zero its totally useles the question is telling you when n of diesel Engine APPROACHES. This means you have to decrease cutt of i.e. Rc !

Then it vill approach towards otto, it does not tell you when efficency of diesel eng is equal to that of otto. Even if it had mebtioned we still can't put RC (CUTT OFF) equal to zero.

Hence answer is B.

The Efficiency of diesel I think much greater then petrol so here we can say choose the value of cut off high as it decreases the efficiency of diesel which approaches to petrol. Am I right?

The efficiency will be lower if cutoff ratio is higher because the piston has already moved far down while the heat is still being added.

When the cutoff ratio ρ=1 then the efficiency of 'DUAL' cycle becomes efficiency of the Otto cycle.

And when ρ=0 then the efficiency of 'diesel' cycle becomes efficiency of the Otto cycle by L hospital's rule.

The question should be a Dual cycle, not the diesel cycle.

Because in the dual cycle there are two heat addition one at constant volume and other at constant pressure known as cut off and when this cutoff is made zero the cycle becomes Otto cycle.

Answer is C.

Because of the value of the cut-off ratio is ZERO put the value in equation of diesel cycle then both are equal.

The answer is right.

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

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

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

Correct, Thanks @Madan.