INTERNAL COMBUSTION ENGINE

 #Part-1Analysis of Gas Power Cycles Used in IC engines

➢ An important application of thermodynamics is the analysis of power cycles through which the energy absorbed as heat can be continuously converted into mechanical work.

➢ A thermodynamic analysis of the heat engine cycles provides valuable information regarding the design of new cycles or for improving the existing cycles.

Assumptions

➢ The working substance consists of a fixed mass of air and behaves as a perfect gas.

➢ There is no change in the chemical equilibrium of the working fluid and also composition.

➢ The specific heats Cp and Cv of air do not vary with temperature

 

Otto Cycle

 Otto cycle consists following processes.

➢ Isentropic Compression[1-2]

➢ Constant volume heat addition[2-3]

➢ Isentropic Expansion[3-4]

➢ Constant volume heat rejection[4-1]

 

Swept Volume

 

Vs = V1 – V2 

 

Clearance Volume

 

Vc = V2

 

Efficiency of Otto Cycle 

 ➢ As we know efficiency is given by :

           
➢ By solving this we get :

        
➢ Compression ratio r :

         

➢ So efficiency :

         

Effect of compression ratio on Efficiency of Otto Cycle

➢ So efficiency :

 

                          

Diesel Cycle



Diesel Cycle consists following processes.

➢ Isentropic Compression[1-2]

➢ Constant pressure heat addition[2-3]

➢ Isentropic Expansion[3-4]

➢ Constant volume heat rejection[4-1]

 

Swept Volume

         Vs = V1 – V2 

Clearance Volume

         Vc = V2 

Some Important Terms:

Cut off Ratio

          

Expansion Ratio

        

Efficiency of Diesel Cycle

➢ Efficiency is given by

        

Dual Cycle


➢ In dual cycle heat addition takes place by 2 process.

➢ Cycle is shown in figure.

Pressure Ratio

            

Cut off Ratio

           

Efficiency of Dual Cycle

➢ Efficiency is given by :

               

Comparison of Otto, Diesel and Dual Cycles

Case 1: Same Compression Ratio and Heat Addition:

Otto cycle has the highest work output and efficiency. Diesel cycle has the least efficiency and Dual cycle having the efficiency between the two.

Case 2: Same Compression Ratio and Heat Rejection:

Otto cycle has the highest efficiency. Diesel cycle has the least efficiency and Dual cycle having the efficiency between the two.

Case 3: Same Peak Pressure, Peak Temperature and Heat Rejection:

The Diesel cycle efficiency is greater than the Otto cycle efficiency and Dual cycle having the efficiency between the two.

Case 4: Same Maximum Pressure and Heat Input:

The Diesel cycle efficiency is greater than the Otto cycle efficiency and Dual cycle having the efficiency between the two.

Case 5: Same Maximum Pressure and Work Output:

The Diesel cycle efficiency is greater than the Otto cycle efficiency and Dual cycle having the efficiency between the two.

Some Questions from these topics:

1.For the same compression ratio:
(A) Otto cycle is more efficient than the Diesel cycle
(B) Diesel cycle is more efficient than the Otto cycle
(C) Both Otto and Diesel cycles are equally efficient
(D) None of these

2.Compression ratio of IC engines is:
(A) The ratio of volumes of air in cylinder before compression stroke and after compression stroke
(B) Volume displaced by piston per stroke and clearance volume in cylinder
(C) Ratio of pressure after compression and before compression
(D) Swept volume / cylinder volume

3.For the same maximum pressure and peak temperature, which cycle will be most efficient
(A) Otto cycle
(B) Diesel cycle
(C) Both Otto and Diesel cycles are equally efficient
(D) Dual cycle

4.Air standard efficiency of a diesel cycle is dependent upon
A. Ratio of specific heats
B. Cut off ratio
C. Adiabatic compression ratio
(A) Only A
(B) Only B
(C) A, B and C
(D) Only C

5.For a 4-stroke diesel engine, the compression ratio is 21 : 1 and the cut off ratio is 2 : 1. What is its expansion ratio?
(A) 7 : 1
(B) 10.5 : 1
(C) 12 : 1
(D) 19 : 1

6.For an engine operating on air standard Otto cycle, the clearance volume is 10% of the swept volume. The specific heat ratio of air is 1.4. The air standard cycle efficiency is
(A) 38.3%
(B) 39.8%
(C) 60.2%
(D) 61.7%
 

Comparison of Otto, Diesel and Dual Cycles

Case 1: Same Compression Ratio and Heat Rejection:

Otto cycle has the highest work output and efficiency. Diesel cycle has the least efficiency and Dual cycle having the efficiency between the two.

Case 2: Same Peak Pressure, Peak Temperature and Heat Rejection:

The Diesel cycle efficiency is greater than the Otto cycle efficiency and Dual cycle having the efficiency between the two.

 

Internal Combustion Engine and Its Type:


➢ An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the engine itself.

➢ In 1872, American George Brayton invented the first commercial liquid-fueled internal combustion engine. In 1876, Nicolaus Otto, working with Gottlieb Daimler and Wilhelm Maybach, patented the compressed charge, four-stroke cycle engine.

➢ It is used mainly in all type of automobiles.

Internal Combustion Engine and Its Type:

According to working cycle completion IC engines are classified as :

1. Two Stroke IC Engine

2. Four Stroke IC Engine

According to fuel ignition mechanism IC engines are classified as :

1. Spark Ignition Engine

2. Compression Ignition Engine

Four Stroke IC Engine:

➢ A four-stroke cycle engine is an internal combustion engine that utilizes four distinct piston strokes (intake, compression, power, and exhaust) to complete one operating cycle.

Construction

                       

➢ There is two valves in this type of engine.

➢ Gas movement takes place through valves called inlet and exhaust valve.

Working of Four Stroke IC Engine:

Some Questions from these topics:

1.Which of the engine has a spark plug used for igniting the fuel?
(A) Petrol
(B) Diesel
(C) Gas
(D) Steam

2.In an IC engine, the connecting rod connects which of the following pair of parts?
(A) Piston and crankshaft
(B) Cylinder and crankshaft
(C) Cylinder and piston
(D) None of these


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