Question

If a diesel engine has a compression ratio of 24 and the cut-off takes place at 5% of stroke, the air standard efficiency will be ___________

(a) 60.66%

(b) 64.50%

(c) 66.60%

(d) 65.40%

I had been asked this question in an interview for job.

This key question is from Working Principles of I.C Engine topic in chapter Internal Combustion Engine of Farm Machinery

Answer 1

Correct option is (c) 66.60%

For explanation: Here, r = V1/V2 = 24

V1 = 24 V2

V3 = V2 + 0.05 (V1-V2)

V3 = V2 + 0.05(24 V2-V2)

V3/V2 = 2.15

Efficiency: 1 – (1/r)^γ-1 * [rc^γ – 1] / r [rc – 1]

= 1 – (1/24)^1.4-1 [2.15^1.4 – 1] / 1.4 [2.15-1]

= 66.60%.