IC vs EC Engine: Key Differences Explained

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internal combustion
external combustion
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An engine is a device that converts chemical energy into thermal energy (heat) and then uses this energy to perform mechanical work. There are two main types of heat engines: IC (Internal Combustion) engines and EC (External Combustion) engines.

Both IC and EC engines follow the fundamental principles of heat engines, which are described by the laws of thermodynamics. They are essential devices for various applications, including transportation, power generation, and industrial machinery.

IC and EC engines differ significantly in their combustion processes, working principles, efficiency, and applications.

IC (Internal Combustion) Engine Working Principle

The IC engine operates by converting the chemical energy stored in a fuel into mechanical work. A typical four-stroke IC engine (gasoline or diesel) consists of four phases: intake, compression, power, and exhaust.

Figure 1 depicts a typical IC engine. In this type of engine, fuel combustion occurs in a confined space known as the combustion chamber.

IC Engine IC Engine

  • Intake Stroke: Air (in SI engines) or a mixture of air and fuel (in CI engines) is drawn into the engine’s combustion chamber as the piston moves downward.
  • Compression Stroke: The piston moves upward, compressing the air or air-fuel mixture to a high pressure.
  • Power Stroke: A spark (in SI engines) or high compression (in CI engines) ignites the fuel, causing a rapid expansion of gases. This expansion forces the piston downward, creating mechanical work.
  • Exhaust Stroke: The spent gases are expelled from the cylinder as the piston moves upward again.

This continuous cycle of intake, compression, power, and exhaust strokes produces the engine’s rotational motion, which is used to drive vehicles or power machinery.

Types and Examples of IC Engines

Following are the types and examples of internal Combustion engines:

  • Spark Ignition (SI) Engines:
    • Characteristics: Ignition by spark plug, low compression ratio, smooth operation, used with gasoline or natural gas.
    • Example: Gasoline engines used in most passenger cars.
  • Compression Ignition (CI) Engines:
    • Characteristics: Ignition by compression, high compression ratio, more fuel-efficient, run on diesel fuel.
    • Example: Diesel engines found in trucks, buses, and some passenger vehicles.
  • Rotary Engines:
    • Characteristics: Uses rotary design with no pistons, compact and lightweight, smooth high-speed operation.
    • Example: Wankel engine, used in Mazda sports cars.
  • 2-Stroke Engine:
    • Characteristics: Simple design, few moving parts, less fuel-efficient, more polluting compared to 4-stroke engines.
    • Example: Older small engines used in mopeds and chainsaws.

EC (External Combustion) Engine Working Principle

An EC engine operates by using an external heat source to generate steam or heat a working fluid. This fluid then expands and performs mechanical work. For example, in a steam engine, water is heated externally to produce steam, which is directed into a piston or turbine. The steam’s expansion against the piston or blades drives them, creating mechanical motion.

EC Engine EC Engine

Figure 2 depicts a typical EC engine. It uses a working fluid (liquid, gas, or both). In this type of engine, the working fluid is heated by fuel burned outside of the engine.

Types and Examples of EC Engines

Following are the types and examples of External Combustion engines:

  • Steam engines
  • Stirling engines
  • Gas turbines or Brayton Cycle Engines
  • External Combustion Rocket Engines
  • External Combustion Stirling Engines (Thermal engines)

Difference between IC Engine and EC Engine

Let’s compare IC vs. EC engines with respect to various parameters and highlight the differences between them in a tabular form.

SpecificationsIC EngineEC Engine
Full formInternal combustion engineExternal combustion engine
Combustion locationOccurs internally in the combustion chamber of the engineOccurs externally, and heat is transferred to the working fluid
TypesSI (Spark Ignition) and CI (Compression Ignition) enginesSteam engines, Stirling engines, some Brayton engines
Heat sourceFuel-air mixture combustionExternal heat source (e.g., furnace) is required to heat a working fluid (e.g., steam, water)
Fuel TypeTypically uses gasoline, diesel, natural gas, or other liquid/gaseous fuelsCan use a wide range of heat sources, including solid fuels, gas, and concentrated solar energy
IgnitionSI engines use spark plugs; CI engines rely on compression for spontaneous ignitionCombustion is initiated externally; no spark plugs or compression ignition needed within the engine
EfficiencyGenerally higher thermal efficiencyOften lower thermal efficiency compared to modern IC engines
Environmental ImpactProduces tailpipe emissions (CO2, NOx, etc.) and may contribute to air pollutionMore environmentally friendly due to reduced emissions, depending on the heat source
Noise levelCan be noisyGenerally quieter operation
SizeSmallLarge
AdvantagesSimple in design, less in weight, high overall efficiency, portable, lower costHigh starting torque, cheap fuels including solid fuels
DisadvantagesVibration issue, inability to use a wide variety of fuelsLess suitable for transport vehicles due to heavy weight, high initial cost, and difficulty transporting fluid
ExamplesDiesel engine, Petrol engine, Gas engineSteam Engine, Steam turbine
ApplicationsWidely used in automobiles, motorcycles, and small enginesLess common in modern applications; used in steam locomotives, ships, and some power plants

Conclusion

The primary difference between IC and EC engines lies in their combustion processes and where they generate mechanical work. IC engines combust fuel and air internally, within the engine’s combustion chamber. EC engines generate heat externally and transfer it to a working fluid like water or steam. IC engines are versatile and commonly used in vehicles and machinery, whereas EC engines are less common in modern applications as they have lower thermal efficiency.

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