THERMAL ENGINEERING - OTTO CYCLE

OTTO CYCLE

(Constant Volume Cycle)

(Nickolous Otto)

Applicable in SI Engines

PROCESSES:

(1-2): Isentropic Compression:

        During isentropic compression the volume V1 decreased upto V2 due to piston movement from BDC (Bottom Dead Center) to TDC (Top Dead Center). Therefore the pressure raised from P1 to P2. So, the temperature also increased from T1 to T2. During isentropic (S1 = S2) there is no transfer of heat. 

Q1-2 = 0

(2-3): Heat Supplied (Qs)at Constant Volume:

        During constant volume process the volume V2  equal to V3. At the end of compression, the electric spark will be ignited from spark plug and combustion takes place. During 2-3, the pressure raised from P2 to P3 and temperature increased from T2 to T3 maximum. 

Q2-3 = m.CV.dt

Q2-3 = QS = m.CV.(T3 -T2)

(3-4): Isentropic Expansion:

        During isentropic expansion the volume V3 increased to V4 due to piston movement from TDC (Top Dead Center) to BDC (Bottom Dead Center). Therefore the pressure decreased from P3 to P4. So,  the temperature also increased from T3 to T4. During isentropic (S3 = S4) there is no transfer of heat. 

Q3-4 = 0

(4-1): Heat Rejected (QR)at Constant Volume:

        During constant volume process the volume V4  equal to V1. At the end of expansion, the exhaust valve starts to open and leaving exhaust gases (heat rejected) from cylinder. During 4-1, the pressure decreased from P4 to P1 and temperature decreased from T4 to T1 minimum. 

Q4-1 = m.CV.dt

Q4-1 = QR = m.CV.(T4 -T1)

The air standard efficiency of OTTO cycle is;

The air standard efficiency of OTTO cycle is depends  on 'r' (compression ratio).

Composed by:  R.Satheesh, M.E., Asso Prof., email: rsatheeshemail@gmail.com.