Differences Between Internal Combustion Engines and External Combustion Engines

[AdalynnAnn]

The following are the differences between internal combustion engines and external combustion engines: 1. Different fuels: The biggest difference between internal combustion engines and external combustion engines lies in where the fuel is burned. In internal combustion engines, the fuel burns inside the engine, while in external combustion engines, the fuel burns outside. Steam engines, for example, use boilers to generate steam, which is then directed into cylinders to perform work. Since the combustion process occurs outside the cylinders, they are called external combustion engines. There are many types of internal combustion engines, with gasoline engines and diesel engines being typical examples. 2. Ignition methods: Internal combustion engines can be either compression ignition or spark ignition. For instance, gasoline engines are spark ignition, while diesel engines are compression ignition. External combustion engines can only be spark ignition.

[JohnFitz]

The most significant difference between internal combustion engines and external combustion engines lies in the location of fuel combustion. Internal combustion engines, like the ones in our cars, burn gasoline directly inside the cylinders. This energy directly drives the pistons, making them highly efficient, typically achieving 30%-40% efficiency. However, external combustion engines, such as old-fashioned steam engines, burn fuel outside the boiler to produce steam, which then drives mechanical devices. This design results in a significant amount of heat being wasted, with efficiency usually below 20%. Due to this difference, most cars and motorcycles now use internal combustion engines, as direct drive is more fuel-efficient. External combustion engines are more commonly used in special scenarios, such as steam turbines in nuclear power plants or solar power plants, where external heat sources can be utilized without being limited by fuel types.

[DeBrody]

If you care about the environment, internal combustion engines and external combustion engines are also quite different. Internal combustion engines burn gasoline or diesel directly, emitting exhaust gases that contain pollutants such as carbon monoxide and nitrogen oxides, which are one of the main causes of urban smog. On the other hand, external combustion engines also burn fuel, but because they can utilize various external heat sources—such as nuclear energy, geothermal, or solar energy—they can achieve cleaner operation. I recall that some polar research stations use external combustion engines, which produce almost zero emissions when powered by geothermal energy. However, the heat transfer process in external combustion engines is longer and much less efficient, often requiring complex heat exchange systems. Therefore, from a resource utilization perspective, internal combustion engines are suitable for scenarios that prioritize efficiency, while external combustion engines are better suited for special energy environments.

[Morgan]

From the perspective of operation, the characteristic of internal combustion engines lies in their quick response. When you press the accelerator, gasoline explodes directly in the cylinders to generate propulsion, delivering power almost instantaneously. This makes them well-suited for vehicles requiring frequent speed changes. In contrast, external combustion engines like steam engines must first heat water to produce steam before transmitting power, resulting in a noticeable lag. In the past, operating old steam trains required pre-pressurizing the steam. This fundamental difference determines their applications: internal combustion engines dominate the transportation sector, while external combustion engines are still found in large-scale power plants, such as the boiler systems of thermal power stations, where slow heating enables stable output of massive electrical energy. Additionally, external combustion engines have relatively simpler structures with lower maintenance thresholds, making them favored by factories in the 19th century.