Short answers, pulled from the story.
The first modern internal combustion engine, the Otto engine, was designed in 1876 by the German engineer Nicolaus Otto. That year Otto was working with Gottlieb Daimler and Wilhelm Maybach when he patented the compressed charge, four-cycle engine.
An internal combustion engine is a heat engine in which a fuel burns with an oxidizer, usually air, inside a combustion chamber that is part of the working fluid flow circuit. The high-temperature, high-pressure gases from combustion press directly on engine parts such as pistons, turbine blades, a rotor, or a nozzle, turning chemical energy into kinetic energy.
A four-stroke engine makes two piston strokes per crankshaft revolution and dedicates separate strokes to intake, compression, power and exhaust. A two-stroke engine completes a full cycle every single crankshaft revolution, combining intake and exhaust through a process called scavenging.
Most internal combustion engines retain an average efficiency of about 18 to 20%, even with turbochargers and stock efficiency aids. The Wartsila-Sulzer RTA96-C marine diesel exceeds 50% thermal efficiency, and the latest Formula One engines have passed 50% as well.
Internal combustion engines produce air pollution from incomplete combustion of carbonaceous fuel, including carbon dioxide, water, and soot known as particulate matter. They also release nitrogen oxides, sulfur, carbon monoxide, uncombusted hydrocarbons, and hazardous pollutants such as benzene and 1,3-butadiene, and inhaled particulate matter is linked to asthma, lung cancer, cardiovascular issues, and premature death.
Internal combustion engines are typically powered by hydrocarbon fuels like natural gas, gasoline, diesel fuel, or ethanol. Renewable fuels such as biodiesel and bioethanol can be used, and as early as 1900 Rudolf Diesel ran his engines on peanut oil.
In an internal combustion engine the fuel burns inside a chamber that is part of the working fluid circuit, so combustion products mix with the working fluid. In an external combustion engine, such as a steam or Stirling engine, energy reaches a working fluid like air, hot water, or boiler-heated liquid sodium that is never mixed with or contaminated by combustion products.