DIESEL CYCLE

Q. EXPLAIN DIESEL CYCLE WITH DIAGRAM.

ANS: DIESEL CYCLE (constant pressure cycle)

The cycle was first analyzed by Rudolf Diesel

1-2:- is-entropic compression

2-3:- heat addition at constant pressure

3:- heat supply is cut-off

3-4: is-entropic expansion

4-1:- heat rejection at constant volume

Compression ratio=v1/v2

• It is an ideal cycle. 

• It must be made clear that this does not represent what actually happens inside the cylinder of a working diesel engine. 

• It was developed to be able to model engine behavior and to analyze the effects of certain changes to the cycle without the complications of modeling an actual engine cycle.

Like an indicator diagram it is a graph of Pressure against Volume, but it makes certain assumptions:

(a) The mass of air within the cylinder remains the same: There are no inlet or exhaust valves.

(b) Fuel is not injected and burnt, but heat energy is added at constant pressure.

(c) At the end of the cycle the heat energy is rejected at constant volume.

(d) The compression and expansion of the air is adiabatic (no heat energy is added or lost) and follows the law (pv^y=c)

where c is a constant , for air Y is 1.4.

NOTE:- Thermal efficiency of diesel engine is always less then otto engine for same compression ratio.(mathematically can be shown)