Internal Combustion Engine Deep Dive

Posted on Nov 22, 2024 in Technology

Internal Combustion Engine

1. History of the Engine

The internal combustion engine evolved from the steam engine. The key difference is that the internal combustion engine generates work from a mixture of air and fuel, while the steam engine uses steam pressure from external combustion.

Key milestones:

  • May 1876: Nikolaus Otto builds the first four-stroke engine.
  • 1878: Dugald Clerk builds the first two-stroke engine.
  • 1882: Gottlieb Daimler and Wilhelm Maybach start their company, focusing on lightweight, high-speed gasoline engines.
  • 1886: Daimler’s car reaches 11 km/h.
  • 1890: Daimler Motor Company gains renown.
  • 1892: Rudolf Diesel invents the diesel engine.
  • 1897: First diesel engine constructed.
  • 1957: Felix Wankel tests the rotary Wankel engine.

The automotive industry emerged globally with key players like Henry Ford (Ford Motor Company), Renault brothers, Adam Opel, and Giovanni Agnelli (FIAT). Ford’s Model T in 1908 revolutionized car production. General Motors’ rise marked US dominance in the industry. Post-war mergers and acquisitions shaped the modern automotive landscape. The 1980s saw the rise of Japanese manufacturers, introducing concepts like just-in-time production and Kaizen principles. Current trends focus on hybrid and electric vehicles.

2. Internal Combustion Heat Engine (Otto)

The Otto engine converts thermal energy (explosion) into mechanical energy. Combustion occurs within the engine’s chamber. Qualities of internal combustion engines:

  • Good performance (efficient energy conversion).
  • Low fuel consumption relative to power.
  • Clean exhaust gases.
  • Reliability and durability.
  • Low manufacturing and maintenance costs.

3. Classification of Internal Combustion Engines

Internal combustion engines can be classified by:

  • Combustion initiation: Otto engines, Diesel engines.
  • Cycle: Two-stroke engines, Four-stroke engines.
  • Piston movement: Reciprocating piston engines, Rotary piston engines.

Otto Engine

The conventional Otto engine is a four-stroke, spark-ignition engine. Efficiency is limited by friction and cooling losses. Efficiency depends on the compression ratio (typically 8:1 or 10:1). Higher ratios increase efficiency but require high-octane fuels. Maximum power is achieved between 5,000 and 7,000 rpm. Average efficiency is 20-25%.

Diesel Engine

The Diesel cycle differs from the Otto cycle in that combustion occurs at constant pressure rather than constant volume. Most diesel engines are four-stroke. Four phases: air intake, compression (heating air to ~440°C), fuel injection and ignition, power stroke, and exhaust. Some use auxiliary ignition systems for cold starts. Efficiency is higher than Otto engines (over 40%), achieved with a higher compression ratio (14:1). Diesel engines are heavier but more efficient and use cheaper fuel. They typically operate at lower crankshaft speeds than gasoline engines.

Four-Stroke Engine

The four-stroke engine follows the same basic steps as the two-stroke but with more parts and movements:

  1. Intake: Piston moves down, intake valve opens, air/fuel mixture enters.
  2. Compression: Piston moves up, intake valve closes, mixture compresses.
  3. Explosion: Spark plug ignites mixture, gases push piston down.
  4. Exhaust: Piston moves up, exhaust valve opens, gases exit.

The crankshaft’s rotation controls valve timing via the camshaft and timing chain/belt.

Two-Stroke Engine

The two-stroke engine completes a power stroke every two stages. Less efficient than four-stroke but produces more power for the same size. Uses sliding valves or ports instead of valves. Fuel intake and exhaust occur during a fraction of a stroke. Simpler design but less efficient.

Reciprocating Piston Engine

Converts thermal energy into mechanical energy. Key parts include the engine block, piston, connecting rod, crankshaft, and cylinder head. Operates on a four-stroke or two-stroke cycle.

Rotary Piston Engine (Wankel Engine)

Developed by Felix Wankel, it uses a triangular rotor in an oval chamber. Fuel intake, compression, ignition, and exhaust occur as the rotor rotates. Compact, lightweight, and low vibration, but has faced durability issues.

Four-Stroke Otto Engine

1. Characteristics

The four-stroke gasoline engine is an internal combustion engine that consumes a pre-prepared air-fuel mixture. Four stages: intake, compression, expansion (power), and exhaust.

Mechanical, Thermal, and Volumetric Characteristics

  • Carburetion: Air-fuel mixture is prepared outside the cylinder (carburetor or injection).
  • Compression Ratio and Power: Limited by fuel ignition temperature, affecting power output. High engine speeds are possible due to external mixture preparation.
  • Combustion: Constant volume combustion. Spark ignition causes rapid expansion of gases, generating power.
  • Ignition: Electric spark ignites the mixture.

Definitions

  • TDC (Top Dead Center): Piston’s highest position.
  • BDC (Bottom Dead Center): Piston’s lowest position.
  • Stroke: Distance between TDC and BDC.
  • Cycle: Repetitive sequence of events (Otto cycle).
  • Mixture: Air-fuel mass entering the cylinder.
  • Engine Displacement: Swept volume of the cylinder (Vu = πD²/4 * L).
  • Compression Ratio (Rc): Ratio of total volume to combustion chamber volume (Rc = (Vu + Vc) / Vc).

2. Engine Components

Fixed Components

  • Engine Block: Structural support, houses cylinders. Can be inline, V-shaped, or horizontally opposed.
  • Cylinder Head: Closes cylinders at the top, houses valves, forms combustion chamber.
  • Cylinder Head Gasket: Seals the block and head.
  • Rocker Cover: Protects moving parts at the top.
  • Oil Pan (Crankcase): Protects moving parts at the bottom, contains oil.
  • Intake Manifold: Delivers air/fuel mixture to cylinders.
  • Exhaust Manifold: Carries exhaust gases out.

Moving Components

  • Piston: Moves within the cylinder, receives combustion force.
  • Piston Rings: Seal, lubricate, and transfer heat between piston and cylinder.
  • Connecting Rod: Connects piston to crankshaft.
  • Crankshaft: Converts reciprocating motion to rotary motion.
  • Flywheel: Stores kinetic energy, regulates crankshaft rotation.

Valve Train (Distribution)

  • Valves: Control gas flow.
  • Valve Springs: Keep valves closed.
  • Valve Guides: Guide valve movement.
  • Camshaft: Controls valve timing.
  • Pushrods/Tappets/Rocker Arms: Transmit camshaft motion to valves.
  • Timing Chain/Belt: Connects crankshaft to camshaft.

Auxiliary Systems

  • Oil Circuit: Lubricates and cools moving parts.
  • Cooling Circuit: Maintains engine temperature.
  • Power Circuit: Prepares and delivers air/fuel mixture (varies for gasoline and diesel engines).

3. Theoretical Otto Cycle

Four stages:

  1. Intake (0-1): Piston moves down, intake valve open, cylinder fills.
  2. Compression (1-2): Both valves closed, piston moves up, mixture compresses.
  3. Combustion (2-3): Spark ignites mixture, pressure increases.
  4. Power (3-4): Both valves closed, piston moves down, work is produced.
  5. Exhaust Valve Opens (4-1): Pressure drops.
  6. Exhaust (1-0): Piston moves up, exhaust valve open, gases exit.

4. Practical Otto Cycle

The practical cycle differs from the theoretical cycle in valve timing. Valve opening and closing are offset from TDC and BDC to improve cylinder filling and emptying, increasing power and efficiency. Valve Overlap: Intake and exhaust valves are open simultaneously for a short period, aiding in gas exchange.

Four-Stroke Diesel Engine

1. Characteristics

The diesel engine relies on self-ignition (compression ignition). Fuel ignites when it contacts hot, compressed air. Ignition Delay: Time between fuel injection and ignition. Two types of combustion chambers: direct injection and indirect injection.

2. Engine Components

Similar to Otto engine, but with key differences in the fuel system:

  • Fuel Tank
  • Fuel Pump
  • Fuel Filter
  • Injection Pump: Delivers fuel to injectors at high pressure.
  • Injectors: Spray fuel into combustion chambers.

3. Supercharging

Turbochargers are commonly used to increase power and efficiency. They compress intake air using exhaust gas energy.

4. Theoretical Diesel Cycle

Similar to the theoretical Otto cycle, but with combustion at constant pressure rather than constant volume.

5. Practical Diesel Cycle

Similar to the practical Otto cycle, with differences in valve timing and injection timing.

Engine Characteristics

1. Engine Performance

Engine converts chemical energy (fuel) into mechanical energy (work). Energy losses occur due to heat, friction, and incomplete combustion. Efficiency: Percentage of fuel energy converted into useful work.

2. Types of Efficiency

  • Thermal Efficiency: Percentage of fuel energy converted into crankshaft work.
  • Mechanical Efficiency: Percentage of piston work transmitted to the crankshaft (affected by friction and auxiliary systems).
  • Effective Efficiency: Overall efficiency considering all losses.
  • Volumetric Efficiency: Ratio of actual air intake to theoretical air intake at BDC.

3. Main Engine Characteristics

  • Torque: Rotational force. Higher torque means stronger acceleration and ability to move heavier loads.
  • Power: Work done per unit time. Higher power means higher top speed.
  • Specific Fuel Consumption: Amount of fuel consumed per unit of power produced. Lower specific fuel consumption means better efficiency.