Maximum efficiencies of engines and turbines, 1700-2000

A major theme in human energy history is the development of new machines to replace and enhance the work of people and draft animals. Two of the most important such developments were combustion engines and turbines. In a combustion engine, a fuel such as gasoline is burned and converted into work that propels, moves, or powers whatever the engine is attached to. In a combustion turbine, also called a gas turbine, a fuel such as natural gas is burned to spin a rotary device. (Turbine stems from the Latin turbo meaning “spinning top”).

The purpose of an engine or turbine is to perform useful tasks, such as moving an automobile or spinning a generator to produce electricity. But combustion always produces some waste heat, so engineers and scientists have continuously sought to improve the efficiency of engines and turbines. Efficiency in this case refers to the ratio of the quantity of fuel burned to the amount of useful work performed.1


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Thomas Newcomen (1712) introduced a steam engine to pump water out of coal mines in England with an efficiency of just 0.5%. James Watt’s (1879) famous improvement of the steam engine boosted efficiency to 2 to 3%, still extremely inefficient, but far better than all previous versions. Watt and business partner Matthew Boulton translate these improvements into a successful business. By the early 20th century, the efficiencies of steam engines in locomotives, ships, and factories reached 25%.

Karl Benz (1886) manufactured the first internal combustion engine (ICE) motor vehicle powered by gasoline. It operated with an efficiency of less than 5%, but rapid improvements boosted the efficiency of the gasoline ICE to about 30% by the 1950s. The diesel ICE exhibited the same rapid improvement in efficiency. Note that the diesel engine is significantly more efficient than the gasoline engine due to its use of a more energy-dense fuel and to the characteristics of the engine itself.

The introduction of the gas turbine in the 1930s revolutionized air transport (people and freight) because it delivered more power per unit mass compared to the ICE. Steady advances lead to efficiencies exceeding 40% by the end of the 20th century. The gas turbine was also extensively deployed in electricity generation. Modern combined cycle power plants anchored by the gas turbine have efficiencies that exceed 60%.

This visualization demonstrates two important trends. The first is that the efficiency of a specific type of engine or turbine increased over time due to technological improvements, economies of scale, learning by doing, and improved operation. Second, the maximum efficiency of engines and turbines generally increased over time. For example, the maximum efficiency of the diesel engine is nearly twice that of the steam engine.

Historic improvements in efficiency had profound impacts on society and the environment. Less fuel required to perform a specific task translated into lower monetary costs of goods and services for both producers and consumers. Historically, most of the fuels burned in engines and turbines (wood, fossil fuels) have significant lifecycle environmental and human health impacts. An improvement in efficiency translates to less land disturbed, less water used, and fewer air pollutants released to perform a specific task. That is one reason why end-use energy efficiency (households, offices, factories) is an essential ingredient to a clean energy transition.

1 Most of the data here is from: Smil, Vaclav, “Energy and Civilization: A History,” The MIT Press, 2018.

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