Introduction to Heat Engines

• Heat Engines convert heat energy to mechanical work.

• Fuel combustion provides heat energy.

Classification of Heat Engines

• Internal Combustion Engines (IC Engines): Combustion occurs inside the engine cylinder (e.g., Diesel, Petrol, Gas engines).

• External Combustion Engines (EC Engines): Combustion occurs outside the working cylinder (e.g., Steam Engines, Steam turbines).

Classification of IC Engines

1. Cycle of Operation:

   • Two Stroke Cycle Engines

   • Four Stroke Cycle Engines

2. Thermodynamic Cycle:

   • Otto Cycle (constant volume combustion)

   • Diesel Cycle (constant pressure combustion)

   • Semi Diesel (Dual combustion)

3. Fuel Type:

   • Petrol Engines

   • Diesel Engines

   • Gas Engines

4. Ignition Method:

   • Spark Ignition (SI)

   • Compression Ignition (CI)

5. Cooling System:

   • Air-cooled

   • Water-cooled

6. Valve Location:

   • L Head, T Head, I Head, F Head engines.

Key Terminology in IC Engines

1. Bore: Diameter of the cylinder.

2. Top Dead Center (TDC): Maximum height of the piston.

3. Bottom Dead Center (BDC): Lowest position of the piston.

4. Stroke: Distance between TDC and BDC.

5. Compression Ratio (r): $r = \frac{V<em>{max}}{V</em>{clear}}$.

6. Cylinder Volume (V): $V = V<em>s + V</em>c$, where $Vs$ is swept volume and $Vc$ is clearance volume.

7. Swept Volume (V_s): Volume displaced by piston movement.

8. Clearance Volume (V_c): Volume when piston is at TDC.

Main Components of IC Engine

• Cylinder Block: Main structure, houses cylinders and other components.

• Cylinder Head: Attached to the cylinder block, contains water jackets for cooling.

• Cylinder Liners: Sleeves inside the cylinder for wear resistance (wet and dry types).

• Crankcase: Houses crankshaft, may be integral with the block.

• Oil Pan: Contains lubricating oil.

• Piston: Moves to compress and transmit forces.

• Piston Rings: Seals for high-pressure gases (compression rings and oil rings).

• Connecting Rod: Connects piston to crankshaft, transmits force.

• Crankshaft: Converts reciprocating motion to rotary motion.

• Camshaft: Controls valve operation through cams.

Fuel Types in Engines

• Petrol Engines: Two-stroke and Four-stroke classifications.

• Diesel Engines: Similar structure to petrol, but uses diesel for fuel injection.

Comparisons

• SI Engines vs. CI Engines:

  • SI: Uses petrol, lower pressure/temperature, has spark plugs.

  • CI: Uses diesel, higher pressure/temperature, has fuel injectors.

• Four-Stroke vs. Two-Stroke Engines:

  • Two-Stroke: One power stroke per revolution, simpler design.

  • Four-Stroke: One power stroke per two revolutions, more complex but efficient.