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DIFFERENCE BETWEEN S.I AND C.I ENGINES

Criteria S.I. Engine (Petrol or Spark Ignition Engine) C.I. Engine (Diesel or Compression Ignition Engine) Working Cycle Works on Otto Cycle or Constant Volume Cycle. Works on Diesel Cycle. Mixture During Suction Stroke Takes a mixture of air and petrol during the suction stroke. Takes only air during the suction stroke. Fuel Used Uses petrol as fuel. Uses diesel as fuel. Compression Ratio Has a compression ratio that varies from 6 to 10. Has a compression ratio that varies from 16 to 20. Engine Weight and Cost S.I. engines are lighter and cheaper. C.I. engines are heavier and costlier. Initial Cost Initial cost is lower compared to C.I. engines. Initial cost is high due to high compression ratio. Starting Starting is easy. Starting is difficult, especially in cold conditions. ...

RELATIONSHIPS BETWEEN Cp and Cv

Relationship Between  Specific Heat Cp and Specific Volume Cv

Let us m kg of mass( gas) in a enclosed
Container and is being heated at constant pressure.

Let  
T1=  initial temperature of gas
T2 = Final temperature of gas
V1= Intial Volume of gas
V2= Final volume of gas
CP=  Specific heat at Constant pressure 
CV= Specific heat at Constant temp.
P  = Absolute  Constant pressure 
U = Internal energy 



we know that heat suplied to the gas at Constant pressure. 
 
                Q = m Cp (T2−T1)       ------(1)

we also khow that a Part of this heat is utilised in doing external work, while the remaining Part of heat is used in increasing the internal energy of ges
                       Q= W + dU               -------(2)

Now heat utilised for external work.
                      W = P(V2 - V1)       -------(3)

Change in internal energy
 
                   dU = mCv (T2 - T1)    -------(4)


*Putting the Value of Q in equation (2)
            
Q = P ( V2 - V1) + mCv ( T2 - T1).   -----(5)


using Charactersticgas equation.

              PV1 =  mRT1 ( For Intial condition
              PV2 =  mRT2 ( For Final condition 
P ( V2 - V1) = mR ( T2 - T1 ).     

Putting the value P ( V2 - V1) in eq (5)

Q = mR (T2 - T1) + mCv ( T2 - T1) ----(6)

Now we have the value of Q as eq (6)

put the value of Q in eq (1)

mCp( T2 -T1) = mR(T2 -T1)+ mCv (T2-T1)

mCp( T2 -T1) = m(T2 -T1) ( R + Cv )

Note :-  m(T2 -T1)  is same both side thats why they are cut

                 Cp = R + Cv

                 Cp - Cv = R
OR
                R= Cp-Cv











u = m³/ kg 

P= N/m²

Ru-8314 J/kg-mol/k


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DIFFERENCE BETWEEN S.I AND C.I ENGINES

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