Difference Between Internal and External Combustion Engine.

Understanding the difference between internal and external combustion engines can unlock insights into how vehicles and machinery are powered. For car mechanics, drivers, and enthusiasts alike, this distinction is more than technical—it’s a key to grasping engine performance and efficiency.

Internal combustion engines (ICE) burn fuel directly inside the engine, making them highly efficient for modern vehicles. This engine type powers most of the cars on the road today. On the other hand, external combustion engines burn fuel outside the engine, a system seen more in historical or specialized machinery.

In this article, we will explore how these two engines work, where they are used, and why the internal combustion engine dominates the automotive industry. Let’s dive into the details!

Internal Combustion Engine:

An internal combustion engine is a type of engine where fuel is burned inside the engine itself, creating the power needed to move a vehicle. This process takes place in the engine’s cylinders, where fuel and air are ignited, producing energy that drives the pistons and, ultimately, the car. Internal combustion engines are the most common type of engine in cars today.

Example 1: A typical gasoline-powered car engine uses an internal combustion engine, burning fuel directly inside the engine to create movement.

Example 2: Diesel engines, found in many trucks and buses, are another type of internal combustion engine, known for their efficiency.

Example 3: Motorcycles also rely on internal combustion engines, making them fast and powerful for their size.

External Combustion Engine:

An external combustion engine is a type of engine where the fuel is burned outside of the engine, in a separate chamber. This heat is then transferred into the engine to create the power needed to operate machinery or vehicles. External combustion engines were more common in early industrial machines and steam engines.

Example 1: Steam engines, used in old locomotives, burn coal outside the engine to produce steam that powers the train.

Example 2: Some power plants use external combustion engines by heating water in a boiler to create steam, which then powers turbines.

Example 3: Early agricultural machinery, like steam-powered tractors, used external combustion engines for farming tasks before internal combustion engines took over.

Differences between Internal and External Combustion Engines:

Feature	Internal Combustion Engine (ICE)	External Combustion Engine (ECE)
Combustion Location	Combustion occurs inside the engine cylinder.	Combustion takes place outside the engine.
Heat Transfer	Heat is directly used for power generation.	Heat is transferred to a working fluid (e.g., steam).
Fuel Source	Uses gasoline, diesel, or other liquid fuels.	Can use solid, liquid, or gaseous fuels, including coal and biomass.
Efficiency	Generally more efficient due to direct energy conversion.	Less efficient because of heat transfer losses.
Size and Weight	Compact and lightweight for most applications.	Larger and heavier due to external components like boilers.
Application	Common in automobiles, motorcycles, and airplanes.	Used in steam engines, power plants, and ships.
Energy Conversion	Converts chemical energy directly into mechanical energy.	Converts thermal energy into mechanical energy indirectly.
Cooling Requirement	Requires water or air cooling to manage internal heat.	Heat is dissipated externally, often with less need for cooling systems.
Startup Time	Starts quickly, usually within seconds.	Takes longer to start due to the need for external heating.
Maintenance	Typically requires more frequent maintenance.	Lower maintenance due to simpler moving parts but may require maintenance for external components like boilers.

Thermal Efficiency Differences Between Internal and External Combustion Engines:

Internal Combustion Engine (ICE):

• The thermal efficiency of ICEs is generally higher, typically ranging from 35% to 45% for modern engines. This means that 35-45% of the fuel’s energy is converted into mechanical energy to move the vehicle, while the rest is lost as heat.
• The direct combustion inside the engine allows for more efficient energy conversion, with less energy wasted during the transfer of heat. Advances like turbocharging and fuel injection help improve this efficiency.

External Combustion Engine (ECE):

• The thermal efficiency of ECEs, such as steam engines, is lower, usually around 15% to 25%. A significant amount of energy is lost in the process of transferring heat from the external combustion source to the working fluid (e.g., steam).
• Since combustion occurs outside the engine, the heat must be transferred through various components, leading to greater heat loss before it can be used to do mechanical work.

Heat Loss: External combustion engines typically lose more heat in transferring energy from the combustion source to the working fluid, lowering efficiency.

Energy Losses: In internal combustion engines, friction, exhaust gases, and cooling systems contribute to energy losses, affecting overall efficiency.

Fuel Efficiency Differences Between Internal and External Combustion Engines:

Internal Combustion Engine (ICE):

• Fuel efficiency is higher in internal combustion engines because the combustion of fuel takes place directly inside the engine’s cylinders, generating power more effectively.
• Modern ICEs use gasoline, diesel, or biofuels, and technological improvements like fuel injection, turbocharging, and hybrid systems further enhance fuel efficiency.
• Since ICEs convert a higher percentage of fuel energy into mechanical work (typically 35% to 45% efficiency), they require less fuel to generate the same amount of power compared to external combustion engines.

External Combustion Engine (ECE):

• Fuel efficiency is lower in external combustion engines, like steam engines, because the combustion occurs outside the engine, and much of the heat energy is lost before it reaches the working fluid (such as steam).
• ECEs can use a wide variety of fuels, including coal, biomass, wood, and industrial waste heat, but the energy conversion process is less direct, leading to lower overall fuel efficiency.
• Due to the higher heat losses during the transfer of energy from the combustion chamber to the working fluid, ECEs consume more fuel to produce the same power output as an ICE.

How Engine Cooling Affects Efficiency

Engine cooling plays a critical role in determining an engine’s overall efficiency. It helps manage the heat generated during fuel combustion, ensuring the engine operates within a safe temperature range. However, cooling systems can also impact the efficiency of the engine in both positive and negative ways.

Internal Combustion Engines (ICEs):

Heat Management: In an ICE, fuel burns inside the cylinders, generating high temperatures. A cooling system (air or liquid-based) removes excess heat to prevent the engine from overheating, which could damage components like pistons and valves.

Efficiency Impact: While cooling prevents engine damage, it also removes some useful heat that could otherwise be used to generate more mechanical energy. This loss of heat lowers the engine’s overall thermal efficiency.

Optimizing Cooling: Advances in cooling technology, such as turbocharging and heat recovery systems, aim to capture and reuse some of the heat that would otherwise be lost, helping improve fuel and thermal efficiency.

External Combustion Engines (ECEs):

Heat Transfer Losses: In an ECE, like a steam engine, combustion occurs outside the engine, and heat is transferred to a working fluid. The cooling process is generally slower, and more energy is lost during the transfer of heat from the fuel source to the engine.

Efficiency Impact: Since more heat is lost before it can be converted into mechanical work, cooling in ECEs contributes to their lower overall efficiency. The slow and inefficient heat transfer further reduces the potential power output.

In conclusion, the Difference between Internal and External Combustion Engine lies in where fuel combustion takes place. For mechanics, drivers, and car owners, understanding this difference helps in better diagnosing engine issues. Whether for learning or teaching, knowing these distinctions can solve common engine problems efficiently, enhancing mechanical knowledge for all learners.

What is the main difference between internal and external combustion engines?

The main difference is where fuel combustion happens. Internal combustion engines burn fuel inside the engine, while external combustion engines burn fuel outside.

Which engine type is more common in cars?

Internal combustion engines are more common in cars. Most vehicles today run on internal combustion engines for efficiency.

Why are internal combustion engines preferred in vehicles?

They are smaller, more efficient, and can be built lighter than external combustion engines, making them ideal for cars.

Can external combustion engines be used in cars?

Yes, but they are not common in cars. External combustion engines are more often used in large applications like steam engines.

Which engine is more fuel-efficient?

Internal combustion engines are typically more fuel-efficient for vehicles, as they are designed for fast, direct combustion of fuel.

What fuels are used in internal and external combustion engines?

Internal combustion engines use gasoline or diesel. External combustion engines can use a variety of fuels, like coal or biomass.

Which engine type is easier to maintain?

Internal combustion engines are easier to maintain due to their compact size and widespread use, with more available parts and expertise.

What vehicles use external combustion engines?

External combustion engines are usually found in steam-powered vehicles, trains, or industrial machinery, not in modern cars.

Are external combustion engines more environmentally friendly?

They can be, depending on the fuel used. However, internal combustion engines dominate due to efficiency and convenience.

Which engine produces more power?

Internal combustion engines produce more power per weight, making them better suited for cars and other vehicles where performance matters.