For comparison of Diesel- and Otto-engine cycles:
(a) Show that the thermal efficiency of the air-standard Diesel cycle can be expressed as

where r is the compression ratio and rc is the cutoff ratio, defined as r_c = V_A/V_D. (See Fig. 8.10.)

(b) Show that for the same compression ratio the thermal efficiency of the air-standard Otto engine is greater than the thermal efficiency of the air-standard Diesel cycle.

(c) If γ = 1.4, how does the thermal efficiency of an air-standard Otto cycle with a compression ratio of 8 compare with the thermal efficiency of an air-standard
Diesel cycle with the same compression ratio and a cutoff ratio of 2? How is the comparison changed if the cutoff ratio is 3?

Fig. 8.10

Transcribed Image Text:

- 1 y(r. - 1) n = 1-