I.C Engines

Heat Engine

• Heat engine is a system which converts heat energy into mechanical work
• Heat Engines are classified on the basis of
• Combustion
• Internal Combustion (IC) Engines
• External Combustion Engines (EC) Engines
• Motion
• Reciprocating
• Rotary
• 

IC and EC Engines

• 
• I.C Engines
• Combustion takes place inside the plant
• All processes take place inside the plant
• Examples: Spark Ignition (SI), Compression Ignition(CI) Engines
• E.C Engines
• Combustion takes place outside the plant
• All processes except Expansion take place outside the plant
• Examples: Steam Engines, Steam Turbines

IC and EC engine Differences

Components of an IC Engine

• 
• Piston
• Piston Rings
• Cylinder Block
• Combustion chamber
• Cylinder Head
• Intake and Exhaust valves
• Cam and Camshaft
• Gudgeon Pin
• Crankshaft
• Connecting Rod

Material Selection

Thermodynamics of IC engine

• Top Dead Center (TDC) - The position where the Piston is farthest from the Crankshaft
• Bottom Dead Center (BDC) - The position where the Piston is nearest from the Crankshaft
• The length covered by the Piston from BDC to TDC is known as Stroke length or Stroke
• The diameter of the cylinder block is given by Bore
• The volume covered by the piston covered in a stroke is given by Swept Volume
• Clearance volume is provided as to not let the piston hit the Cylinder head
• Optimal Clearance is important because
• Higher clearance results in Power Loss
• Lower Clearance results in Knocking
• 

Compression and Clearance Ratio

• Volume Ratio - Ratio of larger volume to smaller volume in any process in a cycle
• Volume Ratio for Compression - Compression Ratio
• Volume Ratio for Expansion - Expansion Ratio
• Clearance Ratio (c) - Ratio of Clearance Volume to Swept Volume
• 

List of Processes of an Air Standard Cycle

• Heat Addition
• If Volume is Constant then Otto Cycle
• If Pressure is Constant then Diesel Cycle
• If Constant Pressure and Constant Volume Processes are used then Semi - Diesel or Dual Cycle
• Expansion
• Isentropic
• Heat Rejection
• IsoChoric
• Compression
• Isentropic

Not Possible Cases

• Heat Addition
• Adiabatic
• Isothermal - Change in Temperature exists during Heat addition and Rejection
• Polytropic - Final Volume is less than Clearance Volume which is not permitted
• Heat Rejection
• Isobaric - Gas can't flow with no pressure difference
• Adiabatic
• Isothermal
• Polytropic

Otto Cycle

• 
• Used in SI Engines
• Compression Ratio = 6-10

Diesel Cycle

• Used in CI Engines
• Compression Ratio = 16 - 20
• Has higher Efficiency as Compression Ratio is higher

Dual Cycle

Mean Effective Pressure

• MEP is an imaginary Pressure value which gives the same work done in a cycle under the same Swept Volume
• MEP is an indicator of the Capacity of an engine and is used for comparison of various other cycles and engines.
• 
• 

Comparison of Cycle Efficiencies