エンジンの正体｜熱を捨てなければ、エンジンは動かない

A car engine loses more than half of the heat from its fuel through the exhaust and radiator. And some of that heat is essential for the engine to function. So what does the engine convert fuel into work? This video delves into the mechanisms of how engines convert heat into work, at a university lecture level, tracing its history from Newcomen and Watt's steam engine, to Sadie Carnot's The Power of Fire (1824) and Carnot efficiency, the second law of thermodynamics, the exchange between efficiency and power (Curzon and Ahlborn, 1975), Renoir and Otto's four-stroke engine and compression ratio, knocking and octane rating/tetraethyl lead, diesel compression ignition, hybrids and lean combustion, and finally to large ship engines with thermal efficiencies exceeding 50%. ▼ Table of Contents (Chapters) 0:00 Introduction 1:29 Chapter 1: What Pushes the Piston 4:07 Chapter 2: Steam Engines and Cold Places 6:42 Chapter 3: Carnot's Upper Limit 10:19 Chapter 4: You Can't Go Back Unless You Discard It 12:45 Chapter 5: The Price of Speed 15:20 Chapter 6: Techniques for Compression 19:01 Chapter 7: Knocking 21:15 Chapter 8: Octane Rating and Lead 23:45 Chapter 9: Compressing Only Air 26:33 Chapter 10: Light Load and Thin Fuel 29:38 Chapter 11: The Bigger, the More Efficient 32:40 Conclusion ▼ What you'll learn from this video: Why engines waste most of the heat from their fuel, and why some heat must be wasted for the engine to function (Carnot efficiency and the second law of thermodynamics) How compression ratio determines thermal efficiency, and the knocking that has hindered it (the difference between premium and regular gasoline) Why diesel engines are highly efficient, and why fuel economy is poor in city driving (pumping losses) Why larger ship engines are more efficient *This video explains the mechanisms. It does not evaluate the merits or demerits of any specific car model or manufacturer. ▼ Sources (main ones) • Carnot S. Réflexions sur la puissance motrice du feu (1824) • Curzon FL, Ahlborn B. Efficiency of a Carnot engine at maximum power output. American Journal of Physics 43:22-24 (1975) • U.S. Department of Energy / EPA, fueleconomy.gov "Where the Energy Goes: Gasoline Vehicles" "Where the Energy Goes: Hybrids" • Kyoto University "Gasoline and Diesel Engines Achieve Net Maximum Thermal Efficiency of Over 50%" (2019) / Japan Science and Technology Agency "Passenger Car Engines Achieve Thermal Efficiency of Over 50%" • Wikipedia "Carnot's theorem (thermodynamics)" "Second law of thermodynamics" "Endoreversible thermodynamics" "Engine efficiency" "Thermal efficiency" "Newcomen atmospheric engine" "Watt steam engine" "Four-stroke "engine," "Lenoir cycle," "Nicolas Otto," "Engine knocking," "Octane rating," "Tetraethyllead," "Thomas Midgley Jr.," "Diesel engine," "Rudolf Diesel," "Atkinson cycle," "Lean-burn," "Toyota Dynamic Force engine," "Wärtsilä-Sulzer RTA96-C," "Formula One engines," "Adiabatic flame temperature," "Heat capacity ratio," Japanese version of "leaded gasoline," etc. (Accessed 2026-09-30) • paultan.org/Carscoops "Mercedes F1 engine 50% thermal efficiency" (2017) ▼ Credits Music: 'Origami' by Scott Buckley – released under CC-BY 4.0. www.scottbuckley.com.au Image: Sadi Carnot (Louis-Léopold Boilly, Public domain) / Newcomen's Engine, 1717 engraving (Public (Public domain) / James Watt (Thomas Lawrence, Public domain) / Boulton-Watt's Steam Engine, 1784 (Robert Henry Thurston, Public domain) / Renoir's Gas Engine (Public domain) / Nikolaus Otto (Public domain) / Thomas Midgley (Public domain) / Rudolph Diesel (Public domain) / Emma Maersk (Alf van Beem, CC0) — All from Wikimedia Commons All diagrams are newly drawn schematics for this video (the curves are calculated from the formulas mentioned in the script). — University for Adults Who Want to Learn — This is a commentary channel that delves into all kinds of topics, going deep into the field and to the cutting edge. ▶ Share what you've learned in the comments. Questions and opinions are welcome, and we'll answer each one. ▶ Subscribe to the channel and explore together next. #engine #thermodynamics #adultlearning