EXTERNAL COMBUSTION ENGINE

An external combustion engine (ECE) is a type of heat engine where the combustion process takes place outside the engine walls directly or via a heat exchanger. The heat generated by the combustion of a fuel source is transferred to the working fluid, which expands in the engine chamber and exerts pressure to push the piston inside the cylinder back and forth to do mechanical work.

There are several types of external combustion engine and they are as follows; stirling engine, Eriksson engine, steam engine, closed cycle gas turbine, rankine cycle engine, organic rankine cycle engine, kalian cycle engine, thermo-acoustic engine etc.

The stirling engine is a closed cycle regenerative engine that uses a working fluid such as helium or hydrogen to convert heat energy into mechanical work.

The steam engine is a type of heat engine that uses the thermal energy generated from the combustion from various types of fuels (e.g. coal, wood etc.) to generate steam thus converting the thermal energy in the steam to push the piston inside the cylinder to and fro to do mechanical work.

The ericsson engine is a type of heat engine that uses a regenerator to store heat energy. It operates on a closed cycle regenerative thermodynamic cycle similar to the stiriling engine. The engine uses a displacer to move the working fluid between the hot and cold heat exchanger generating power through a piston and cylinder arrangement.

The closed cycle gas turbine is a turbine that uses a gas (e.g. nitrogen, helium, argon etc.) as the working fluid in a closed energy cycle.  In the closed cycle gas turbine, the working fluid is compressed by a compressor which then flows into a heating chamber. In the heating chamber the compressed air or gas is heated with the help of heat supplied from an external source before it is passed over the turbine blades. When these hot and compressed gas flow over the turbine blades they expands and rotate the turbine blades to do mechanical work.

The rankine cycle engine is a type of vapor power cycle engine that generates power by converting the energy of a high pressure vapor into mechanical work. The engine uses a boiler to generate high pressure steam which expands through a turbine or piston to produce power.

The organic rankine cycle (ORC) engine is a type of engine that uses an organic working fluid to generate power from low-temperature heat sources. The engine operates on a similar principle to the rankine cycle engine, but uses an organic fluid with a lower boiling point to enable efficient energy conversion at lower temperature.

The kalina cycle engine is a type of heat engine that uses a mixture of ammonia and water as the working fluid to generate power. The engine operates on a similar principle to the rankine cycle engine but uses the unique properties of the ammonia- water mixture to achieve higher efficiency and flexibility.

The thermo-acoustic engine is a type of engine that uses sound waves to convert heat energy into mechanical work. The engine uses a temperature gradient to generate acoustic waves which are then converted into mechanical energy using a transducer.

The advantages of external combustion engines are as follows: external combustion engines can use a wide range of heat sources including fossil fuels, biomass, solar energy and waste heat. External combustion engines can achieve high efficiency especially when used in combined heat and power plant (CHP) applications. External combustion engines can produce low emissions especially when using clean heat sources like solar or biomass. External combustion engines can have a long life span with some steam turbines operating for decades.

The disadvantages of external combustion engines are as follows: external combustion engines can be complex systems that require precise engineering and maintenance. External combustion engines can be more expensive than internal combustion engines, especially for small scale applications. External combustion engines can be large and heavy requiring significant space and infrastructure. External combustion engines can require significant time to start up and reach operating temperature.

External combustion engines finds widespread use in the following areas of industry: external combustion engines are widely used in power generation applications, such as solar power plants, biomass power plants and waste heat recovery systems. External combustion engines are used in various industrial processes such as pumping, compressing and material processing. External combustion engines such as steam turbines are used in marine propulsion applications, including naval vessels and commercial ships. External combustion engines are used in combined heat and power applications to provide both heat and electricity for buildings and industries.

The future of external combustion engines depends on the energy trends and development of the following technologies: external combustion engines such as stirling engines could play a vital role in solar power generation especially in concentrated solar power systems (CSP). External combustion engines could be used to receive waste heat from industrial processes reducing energy consumption and emissions. External combustion engines could be used to generate electricity from biomass providing a renewable and sustainable energy source. The development of advanced materials such as high temperature ceramics could enable the creation of more efficient and compact external combustion engine.

 

SOURCES:

• Internal and external combustion engines by Carl Sommer.
• External combustion engine: Types and parts by Nicholas Amendolare and Dina El Chammas Gass.
• Steam engines principles and applications by R. Keith Mobley.
• Stirling engines by Graham Walker.
• Thermodynamics: An interactive introduction by Schroeder, Daniel V. Shroeder.