Question

How do internal and external combustion engines differ?

Short answer

Internal combustion engines burn fuel inside the engine, while external combustion engines burn fuel outside the engine and use the heat produced to drive a working fluid.

Step-by-step solution

Define Internal Combustion Engine

An internal combustion engine is one where the combustion of fuel occurs within the engine itself. The fuel burns in a confined space, usually a cylinder, which causes expansion and translates to mechanical work.

Define External Combustion Engine

An external combustion engine is one where the combustion of fuel occurs outside the engine. The produced heat is then used to create steam or another working fluid, which then drives a mechanical system.

Analyze the Fuel Combustion Location

In internal combustion engines, the fuel burns inside the engine, leading to direct mechanical action. In external combustion engines, fuel burns outside the engine, and the resulting heat drives another medium.

Discuss Energy Conversion

For internal combustion engines, the thermal energy from burning fuel is converted directly to mechanical energy inside the engine. In external combustion engines, thermal energy is first converted to a working fluid and then to mechanical energy.

Efficiency and Application

Internal combustion engines are typically more compact and efficient for mobile applications, such as cars and trucks. External combustion engines tend to be used in stationary applications, like power plants, where fuel efficiency and emission control are more manageable.

Key concepts

internal combustion engine

An internal combustion engine (ICE) is a type of engine where the combustion of fuel happens inside the engine itself. The fuel burns in a confined space, usually a cylinder.
This combustion process generates high-pressure gases, leading to the expansion of gases. This expansion translates directly into mechanical work by pushing a piston inside the cylinder.
Internal combustion engines are commonly found in vehicles like cars, motorcycles, and airplanes because of their compact size and efficiency.

• Key Feature: Fuel burns inside the engine's cylinders.
• Result: Direct mechanical action and high efficiency.

external combustion engine

An external combustion engine (ECE) operates differently. Here, the combustion of fuel takes place outside the engine. The produced heat is used to convert water into steam or another working fluid.
This fluid then drives the mechanical system, such as pistons or turbines, to produce work.
A classic example of an external combustion engine is a steam engine, often found in old trains and some power plants.

• Key Feature: Fuel burns outside the engine.
• Result: The generated heat drives another fluid to produce mechanical work.

energy conversion

Energy conversion in these engines involves changing thermal energy into mechanical energy. For internal combustion engines, the process is straightforward: thermal energy from burning fuel is converted directly inside the engine into mechanical energy.
In other words, the combustion of the fuel directly moves the piston, producing mechanical work.
For external combustion engines, the conversion involves an intermediary step. The thermal energy from burning fuel heats a working fluid such as steam.
This heated fluid then does the mechanical work. Although this process may seem more complex, it allows for better control over the combustion process and emissions.

• Internal Combustion Engines: Direct conversion of thermal energy to mechanical energy.
• External Combustion Engines: Indirect conversion through a working fluid.

efficiency

The efficiency of an engine refers to how well it converts fuel energy into useful mechanical work. Internal combustion engines generally have higher efficiency for mobile applications due to their direct energy conversion and compact design.
Advances in technology have led to fuel-efficient internal combustion engines found in modern cars and trucks. On the other hand, external combustion engines usually have lower thermal efficiency because of the intermediary steps involved.
However, they offer more flexibility in the types of fuels they can use and are easier to manage in terms of emissions.

• Internal Combustion Engines: High efficiency and good for mobile applications.
• External Combustion Engines: Lower thermal efficiency but better emission control.

applications of combustion engines

Both internal and external combustion engines have specific applications based on their unique characteristics. Internal combustion engines are popularly used in vehicles, aircraft, and small machines because of their compact size and efficiency.
They are ideal for mobile applications where space and weight are critical factors. External combustion engines, however, find their niche in power generation and industrial applications.
Their ability to use various fuels and manage large-scale emissions make them suitable for power plants and large industrial machines.

• Internal Combustion Engines: Vehicles, aircraft, small machines.
• External Combustion Engines: Power plants, industrial machines.