Internal Combustion Engines and Refrigeration Systems Explained

Engine Performance and Mechanics

Key performance metrics include power (measured in CV), torque (starting, acceleration, and nominal), and fuel efficiency. Compression ignition engines can operate on 2-stroke or 4-stroke cycles. They differ from spark-ignition engines by replacing spark plugs with fuel injectors.

Diesel Engine Characteristics

Diesel engines share similar parameters with gasoline engines but feature higher compression ratios and lower immediate power. Benefits include:

• Increased thermal efficiency
• Lower fuel consumption
• Cheaper fuel
• Reduced pollution
• Greater durability

Drawbacks include heavier vehicle weight, increased vibration, higher noise levels, and greater manufacturing costs.

The 4-Stroke Cycle

• Admission: Piston moves from TDC to BDC; the cylinder fills with air as the crankshaft rotates 180 degrees. The intake valve closes at BDC.
• Compression: Valves remain closed as the piston moves from BDC to TDC, increasing temperature and pressure. Fuel is injected near TDC and ignites.
• Expansion: The third stroke; valves remain closed as the piston moves from TDC to BDC, performing useful work.
• Exhaust: The fourth stroke; the exhaust valve opens as the piston moves from BDC to TDC, expelling gases.

Stirling Engines

The Stirling engine is an external combustion machine using two spaces at different temperatures separated by a regenerator. The cycle consists of:

• 1-2: Expansion of hot gas absorbing heat (Q).
• 3-4: Compression of gas in the cold space, releasing heat (Q2).
• 2-3, 4-1: Isochoric transformation as gas flows through the regenerator.

These engines can utilize any heat source, offer low pollution, and do not require waste heat conversion.

Fuel Properties

Fuel is a substance that reacts with oxygen to release heat. Key properties include:

• Calorific Value: Total heat evolved.
• Volatility: Tendency to evaporate (Gasoline is more volatile than diesel).
• Flammability: Tendency to ignite under pressure or temperature (Diesel is less flammable).
• Auto-ignition Temperature: Minimum temperature required for spontaneous combustion in air.
• Octane Number: Measures detonation resistance (0 for heptane, 100 for isooctane).
• Cetane Number: Measures self-ignition tendency (Diesel is typically 40-50).

Refrigeration Systems

The most common cooling machines use a compression cycle consisting of four basic elements:

1. Compressor: Provides energy and compresses the refrigerant fluid.
2. Condenser: Liquefies the gas through cooling and releases heat (Q1).
3. Expansion System: Regulates pressure before reaching the evaporator.
4. Evaporator: Completes the cooling cycle.