The fossil-fuel revolution: Key terms, quiz and sources

Understanding Energy / Module 5: The fossil-fuel revolution Wrap-up

The fossil-fuel revolution: review

Key terms

Primary energy: Energy in the form first taken from nature, such as coal, crude oil, gas, uranium, wind or sunlight, before conversion.
Energy transition: A shift, usually over decades, in the mix of energy sources or prime movers that a society relies on.
Power density: The rate of energy flow per unit of land area, in watts per square metre; high for mines and wells, low for forests.
Coke: A hard, porous, nearly pure carbon fuel made by baking coal without air, used to smelt iron in blast furnaces.
Coking coal: A grade of coal that softens and re-solidifies into strong coke when heated, traded separately from thermal coal.
Blast furnace: A tall furnace in which coke and a hot air blast reduce iron ore to liquid pig iron.
Atmospheric engine: Newcomen's steam engine, in which condensing steam creates a vacuum and air pressure drives the piston.
Separate condenser: Watt's improvement that condensed steam outside the working cylinder, so the cylinder stayed hot.
Prime mover: A machine that converts energy into mechanical work, such as a water wheel, steam engine, turbine or internal combustion engine.
Four-stroke engine: An internal combustion engine cycle of intake, compression, power and exhaust, introduced by Otto in 1876.
Compression ignition: Igniting fuel by the heat of highly compressed air, the principle of the diesel engine.
Mass-to-power ratio: The weight of an engine per unit of its power, in grams per watt; its fall made cars and aircraft possible.
Steam turbine: A rotary engine in which steam spins bladed rotors, invented by Parsons in 1884 and used in most thermal power plants.
Alternating current: Electric current that reverses direction many times a second, allowing transformers to change voltage for long-distance transmission.
Saltation: Smil's term for the leap in technical invention between 1867 and 1914.
Energy servants: The number of adult human labourers whose work would equal a person's share of useful energy use.
Exajoule (EJ): 10^18 joules; world primary energy use in 2024 was about 592 EJ.

Try it in the table

Open the 'Coal and peat' tile and find the energy content per kilogram for different coal ranks. Compare the best and worst with the 15-18 MJ/kg of dry wood used in Part 1.
On the 'Coking coal' tile, compare its price with 'Thermal coal'. Using Part 2, explain why steelmakers pay a premium for coal that forms strong coke.
Open 'Steam turbines and thermal power plants' and check the efficiency range it gives. How many kilograms of coal would a plant at that efficiency burn to deliver 1 kWh (3.6 MJ)?
Go to 'Internal combustion engines and gensets' and compare the efficiency of gasoline and diesel engines with the 0.5% of Newcomen's engine. By what factor has the best prime mover improved?
Open 'Electric motors and drives' and look at what share of electricity motors use. Relate it to the shift from line shafts to unit drives described in Part 3.
On the 'Crude oil' tile, find current world consumption in barrels per day and convert it to EJ a year (one barrel is about 6.1 GJ). Does it match the 199 EJ from the Energy Institute?

Final quiz

In what year did coal's energy contribution overtake wood's in the United States?

1884; abundant forests kept wood dominant through most of the 19th century.

Who first smelted iron with coke, and where?

Darby, in 1709, though coke took decades to displace charcoal.

Roughly how efficient was Newcomen's atmospheric engine?

Most of the heat was wasted reheating the cylinder; it paid only at mines where coal was nearly free.

Around when did oil overtake coal in world primary energy, by Smil's count?

About 1964, a century after Drake's well, after decades of steady growth in vehicle use.

What finally made alternating current the standard for grids?

High-voltage transmission cuts losses; Tesla and Westinghouse's AC systems won after Niagara in 1895.

Why did falling engine mass per watt matter so much?

From about 150 g/W for steam to about 1 g/W for 1940s aero engines, each step opened new uses.

Which fuel was the largest single source of world primary energy in 2024?

Oil, at about 199 EJ or 34%, ahead of coal (about 165 EJ) and gas (about 149 EJ).

What distinguishes the transition away from fossil fuels from earlier energy transitions?

Wood and coal use kept growing even as newer fuels took share; decarbonisation needs absolute decline.

Next module: Oil, gas and coal: how they form, are found, moved and priced →

Sources for this module

Smil, Energy and Civilization: A History (2017) · via Smil Mastery Course, M5 'Coal and the great transition', 'Coke, iron and the steam engine', 'Oil and the internal combustion engine', 'Electricity: the new quality of energy', 'Fossil-fuelled civilization'
Smil, Energy Transitions: History, Requirements, Prospects (2010; 2nd ed. 2017) · via Smil Mastery Course, M5 'Coal and the great transition'
Smil, Energy in World History (1994) · via Smil Mastery Course, M5 'Coal and the great transition'
Smil, Energies: An Illustrated Guide to the Biosphere and Civilization (1999) · via Smil Mastery Course, M5 'Coke, iron and the steam engine'
Smil, Still the Iron Age: Iron and Steel in the Modern World (2016) · via Smil Mastery Course, M5 'Coke, iron and the steam engine'
Smil, Two Prime Movers of Globalization: The History and Impact of Diesel Engines and Gas Turbines (2010) · via Smil Mastery Course, M5 'Coke, iron and the steam engine', 'Oil and the internal combustion engine'
Smil, Oil: A Beginner's Guide (2008) · via Smil Mastery Course, M5 'Oil and the internal combustion engine'
Smil, Creating the Twentieth Century: Technical Innovations of 1867-1914 (2005) · via Smil Mastery Course, M5 'Oil and the internal combustion engine', 'Electricity: the new quality of energy', 'The great saltation of 1867–1914'
Smil, Numbers Don't Lie: 71 Stories to Help Us Understand the Modern World (2020) · via Smil Mastery Course, M5 'Electricity: the new quality of energy', 'The great saltation of 1867–1914'
Smil, Transforming the Twentieth Century: Technical Innovations and Their Consequences (2006) · via Smil Mastery Course, M5 'Transforming the 20th century'
Smil, Grand Transitions: How the Modern World Was Made (2021) · via Smil Mastery Course, M5 'Transforming the 20th century', 'Fossil-fuelled civilization'
Smil, How the World Really Works (2022) · via Smil Mastery Course, M5 'Fossil-fuelled civilization'
Smil, Energy in Nature and Society: General Energetics of Complex Systems (2008) · via Smil Mastery Course, M5 'Fossil-fuelled civilization'
Energy Institute (2025). Statistical Review of World Energy 2025, 74th edition (2024 data). London: Energy Institute. web ↗ · web
Energy Institute (2026). Statistical Review of World Energy 2026, 75th edition, summary version (2025 data). web ↗ · web