Problems in OTTO cycle

      The minimum pressure and temperature in an Otto cycle are 100 kPa and 27°C. The amount of heat added to the air per cycle is 1500 kJ/kg. 

    Determine the pressures and temperatures at all points of the air standard Otto cycle. Also calculate the specific work and thermal efficiency of the cycle for a compression ratio of 8 : 1.  Take for air: Cv = 0.72 kJ/kg K, and γ = 1.4.

Given:

P1  = 100 kPa = 105 N/m2 or 1 bar

T1 = 27 + 273 = 300 K

Heat added QS= 1500 kJ/kg;

r = 8 : 1 ; Cv = 0.72 kJ/kg ; γ = 1.4.

To Find:

(i) Pressure and temperature at all points

(ii) ηotto   and    (iii) Specific work

   

  Solution:

Result:

Specific work = 847 KJ/Kg

Air standard efficiency, ηotto = 56.47%

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

Problems in OTTO cycle

          In an air standard constant volume cycle, the compression ratio is 8 to 1, and the compression commences at 1 bar, 27°C. The constant volume heat addition is 800 kJ per kg of air. 
Calculate: 
                 (i)  the thermal efficiency and 
                 (ii) the indicated mean effective pressure, P_mi.

SOLUTION:

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

Problems in OTTO cycle

       An engine of 250 mm bore and 375 mm stroke works on Otto cycle. The clearance volume is 0.00263 m3.     The initial pressure and temperature are 1 bar and 50°C. If the maximum pressure is limited to 25 bar, 
     find the following:

   (i) The air standard efficiency of the cycle.

   (ii) The mean effective pressure for the cycle. Assume the ideal conditions.

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

Problems in OTTO cycle

        The ratio of compression of an engine working on the constant volume cycle is 8.6:1. At the beginning of compression the temperature is 32°C and at the end of heat supply the temperature is 1600°C. If the index of compression and expansion is 1.4, 

       find: (a) the temperature at the end of compression; 

               (b) the temperature at the end of expansion and 

               (c) the air standard efficiency of the cycle.

      Solution:

   S

 

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

THERMAL ENGINEERING - DIESEL CYCLE

DIESEL CYCLE 

(constant pressure cycle)

(Rudolf Diesel)

Applicable in CI 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 Pressure:

        During constant pressure process, from the volume V2  to V3. At the end of compression, the diesel fuel injected from fuel injector and combustion takes place. During 2-3, the pressure P2 equal to P3 and temperature increased from T2 to T3 maximum. 

Q2-3 = m.CP.dt

Q2-3 = Qs = m.CP.(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 DIESEL cycle is depends  on 'r' (compression ratio) and 'rc' (cutoff ratio).

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

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.