How to Identify Different Types of External Combustion Engines

This article explains the working of various types of engines used in different applications. There are two main types of engines: external combustion and internal combustion. The steam engine is an example of an external combustion engine that converts heat from a heat source into mechanical work using the Rankine cycle.

Meanwhile, internal combustion engines like the Stirling engine utilize fuel within a combustion chamber to produce energy through the expansion and contraction of gasses in a cylinder. These engines are crucial in various industrial applications, from transportation and marine propulsion. To electricity generation and power generation. Where they efficiently convert fuel into power by harnessing temperature and pressure variations. They often incorporate intricate designs involving pistons, heat exchangers, and precise mechanical systems to generate heat and drive mechanical processes.

What Is an External Combustion Engine?

The steam engine, developed by inventors like Thomas Savery, Thomas Newcomen, and James Watt, fundamentally transforms chemical energy from combustible fuel into mechanical energy to perform work. It’s categorized into two types: the external combustion engine that utilizes an external heat source like burning coal to heat a working fluid such as water, causing it to reach temperatures where it expands and powers the expansion. This energy is then harnessed to set a machine or a vehicle in motion.

How External Combustion Engines Work

The external combustion engine functions by employing an external heat source to ignite a burning fluid such as coal within a boiler. This source heats water from a reservoir, which is then circulated via a feed pump to produce steam. The resulting steam powers the engine cylinder where a piston creates reciprocator motion converted into rotatory motion by a crankshaft. This rotational force is captured by a flywheel to generate power, ultimately propelling a vehicle’s tires and facilitating their movement. The Stirling engine and steam engine exemplify such external combustion engines, utilizing pressure and temperature changes to operate, distinguishing them from the prevalent internal combustion engines.

Types of External Combustion Engines

The external combustion engine has the following major two types:

Steam Engine

The steam engine, invented in the 18th century, revolutionized transportation with its diverse uses in locomotives and external combustion engines. It harnesses thermal energy from burning products like coal or wood, initiating a phase change in water to produce steam, the working medium for generating mechanical work. These steam engines laid the groundwork for modern-day power plants, from coal-fired to nuclear, employing steam turbines within the Rankine cycle to convert thermal energy into rotational energy.

The steam engine operates via a reciprocating motion of the piston within the cylinder, linked to a crankshaft and connecting rod to transform it into rotational motion. This transformed energy propels locomotives or supports the steering systems in vehicles. The EC engine relies on steam as the working media, utilizing. The ideal thermodynamic cycle known as the Rankine cycle to convert thermal energy into mechanical work. It’s a historical cornerstone that paved the way for the efficient utilization of steam as a driver for numerous engines in various applications.

Stirling Engine

In external combustion engines, fuel is burned outside the cylinder to produce energy. The sealed system uses an inert working fluid like helium or hydrogen moving between hot and cold chambers. These engines, though on a small scale, offer advantages in residential settings and CHP applications, leveraging various heat sources like solar energy or biological materials. They excel in quiet operation, quick starts even in cold weather, and their flexibility to utilize diverse energy inputs like nuclear, geothermal, or biological sources. However, challenges persist, including high capital costs. Technical barriers, and ensuring durability while reducing emissions and maintenance needs.

Steam Turbines

The Liddell Power Station in New South Wales, Australia, stands as a testament to the durability and longevity of steam turbine generator technology. For over four decades, this station has generated up to 2,000 Megawatts of electricity, showcasing its large capacity and energy potential. Its application diversity across particular scenarios highlights the relevance of such external combustion engines in our energy system. In various cases, this variant of technology continues to prove its worth. Serving as a crucial component in powering regions and industries.

Advantages of External Combustion Engines

  • Various types of fuels possess different capabilities to generate power. Choosing the right fuel can lead to higher thermal efficiency and the ability to transform a large amount of energy into useful work for high-power applications.
  • Engines with simple designs and fewer moving parts not only boast high durability but also require less maintenance. Additionally, they tend to operate with low noise, making them safer for various settings.
  • Prioritizing low emission rates is crucial for a suitable and sustainable environment. Fuels that enable low emissions play a significant role in cleaner energy generation processes.

Disadvantages of External Combustion Engines

  • IC engines are essential for heavy duty applications despite working fluid leakage issues and higher initial costs. 
  • Though they may suffer from lubrication oil consumption and slower response times during acceleration and deceleration. Their low-power aspects are compensated by their reliability.
  • In IC engines, working fluid leakage issues and lubrication oil consumption can lead to higher initial costs and slower response times during acceleration and deceleration in heavy applications.
  •  However, their low-power concerns are balanced by their indispensable role.
  • Despite facing working fluid leakage issues and higher initial costs.
  •  IC engines excel in heavy duty applications, providing reliability despite low-power. Along with slower response times during acceleration and deceleration, necessitating more lubrication oil consumption.

Environmental Impact and Efficiency of External Combustion Engine Uses

External combustion engines, such as steam engines, operate by utilizing thermal energy from renewable or non-conventional fuels. They efficiently convert this energy into mechanical work for power generation, often achieving efficiencies close to or exceeding 50%. However, their environmental impact is significant due to the necessity of large amounts of water and steam, leading to management issues and contributing to carbon emissions. These engines are generally larger and bulkier than their internal combustion counterparts, necessitating increased resource usage and construction.

The choice between external and internal combustion engines depends on various factors. While external combustion engines offer benefits like adaptability, their drawbacks necessitate thoughtful management to mitigate potential environmental issues. Despite their efficiency in converting thermal energy into work, their reliance on fossil fuels and substantial water usage poses challenges in power plant operations, demanding careful consideration and management to lessen their environmental footprint.

In summary, external combustion engines, through mechanisms like steam turbines, achieve efficient power generation. However, their reliance on non-renewable fuels and substantial water requirements present environmental challenges. Managing these concerns in power plants is crucial to reduce their environmental impact. Balancing the benefits and drawbacks of these engines is essential. As their larger size and increased resource usage highlight the need for thoughtful environmental management in utilizing their benefits for power generation.

Applications of External Combustion Engines

In the realm of propulsion and experimental systems, rocket engines stand as the pinnacle of innovation. These powerful mechanisms find specific applications in various domains, from spacecraft to aircraft and even boats and ships. Their unparalleled propulsion efficiency is vital for achieving fuel efficiency and controlling emissions in marine transportation, contributing to research and conservation efforts.

When it comes to electricity generation, renewable energy sources play a crucial role. Technologies like solar, biomass, and geothermal power. Make energy more accessible and commonly produce power for houses, offices, and other buildings. Moreover, harnessing waste heat from power plants enhances fuel efficiency and supports the supply of easily accessible electricity.

In the domain of transportation, optimizing emissions control and fuel efficiency is key, especially in vehicles, such as buses and trains. Where traditional internal combustion (IC) engines have been famous. In agriculture, these engines power essential machinery like threshing machines and irrigation pumps. Contributing to fuel efficiency and emissions control while supporting vital farming processes.

External Combustion Engine VS Internal Combustion Engine

The engines utilizing large size cylinders tend to have a high weight and demand more installation space. This setup makes the initial start of these engines difficult and the process of getting them running consumes more time. While they burn fuel inside, their thermal efficiency falls within the range of 15% to 25%. Despite their high capital cost, these engines exhibit low thermal efficiency due to their design, leading to high costs in the long run.

Conversely, engines with small sizes require low installation space and are light, making them easy to start. They kick into action swiftly and efficiently, starting very quickly. These engines, burning fuel outside, boast a thermal efficiency ranging between 35% to 45%. Their low capital cost is a significant advantage, along with their high thermal efficiency. Making them the most efficient engine despite the high costs of their fuel.


In conclusion, the diverse realm of external combustion engines, exemplified by mechanisms like steam turbines and Stirling engines, showcases remarkable efficiency in power generation. However, their reliance on non-renewable fuels and substantial water usage poses significant environmental challenges, necessitating careful management in power plant operations to reduce their impact. Balancing these engines’ advantages and drawbacks is crucial, particularly considering their larger size. Increased resource usage, and the need for thoughtful environmental strategies to harness their benefits effectively for power generation across various applications.


What is the working principle of an external combustion engine?

An external combustion engine is a heat engine where an (internal) working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine produces motion and usable work.

What are the different types of combustion engines?

Combustion engines are of two general types: Internal combustion engine. External combustion engine.

 Where is EC engine used?

An external combustion engine is unique from other EHEs because it requires a fuel to undergo combustion to create the heat that is used for work. External combustion engines are no longer used in transportation. As mobile designs are not efficient enough, but they continue to be used in power plants.

What vehicles use external combustion engines?

A steam car is a car (automobile) propelled by a steam engine. A steam engine is an external combustion engine (ECE). Whereas the gasoline and diesel engines that eventually became standard are internal combustion engines (ICE).