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Along with gasoline or diesel, they can also utilize renewable or alternative fuels (e.g., natural gas, propane, biodiesel, or ethanol).  They can also be combined with hybrid electric powertrains to increase fuel economy or plug-in hybrid electric systems to extend the range of hybrid electric vehicles.

HOW DOES AN INTERNAL COMBUSTION ENGINE WORK?

Combustion, also known as burning, is the basic chemical process of releasing energy from a fuel and air mixture.  In an internal combustion engine (ICE), the ignition and combustion of the fuel occurs within the engine itself. The engine then partially converts the energy from the combustion to work. The engine consists of a fixed cylinder and a moving piston. The expanding combustion gases push the piston, which in turn rotates the crankshaft. Ultimately, through a system of gears in the powertrain, this motion drives the vehicle’s wheels.

There are two kinds of internal combustion engines currently in production: the spark ignition gasoline engine and the compression ignition diesel engine. Most of these are four-stroke cycle engines, meaning four piston strokes are needed to complete a cycle. The cycle includes four distinct processes: intake, compression, combustion and power stroke, and exhaust.

Spark ignition gasoline and compression ignition diesel engines differ in how they supply and ignite the fuel.  In a spark ignition engine, the fuel is mixed with air and then inducted into the cylinder during the intake process. After the piston compresses the fuel-air mixture, the spark ignites it, causing combustion. The expansion of the combustion gases pushes the piston during the power stroke.
How Gasoline Engines Can Survive in an Electric Car Future

Combustion engines won't completely disappear any time soon, if ever. Certain transportation tasks or operating environments simply don't lend themselves to battery- or hydrogen-powered electric propulsion. A century and a half of research and development has greatly increased the efficiency of combustion engines, and engineers have loads of additional tricks up their sleeves that promise to extract even more work from a molecule of fuel while producing even fewer harmful emissions. Here are but a few we're keeping our eyes on, listed in order of complexity and cost to implement. 

A 98-Octane Fuel Standard

Simply being able to design an engine to run 15:1 or higher compression greatly improves its thermodynamic efficiency and power density, permitting further engine downsizing. That requires higher-octane fuel, and a research-octane number (RON) of 98 represents a sweet spot, above which producing/refining the fuel consumes more energy, decreasing the well-to-wheels energy/CO2 benefit. 

Smart Cylinder Deactivation

Engines are sized for worst-case scenarios like quarter-mile acceleration or towing heavy trailers up Davis Dam. Cylinder deactivation improves efficiency during less extreme driving situations by making a few cylinders work Davis Dam hard while the others do nothing. Dynamic Fuel Management can shut off any or all cylinders in GM's 5.3- and 6.2-liter V-8s to boost EPA fuel economy by up nearly 12 percent. Tula Technologies and Eaton now propose similar systems for long-haul diesel engines, where a smaller fuel efficiency payoff (1.5-4.0 percent) pays huge NOx dividends by maintaining exhaust temperatures needed to keep catalysts lit.

An engine's power is limited by the amount of air it can ingest, which is why crankshaft-powered superchargers and exhaust-powered turbochargers were developed more than a century ago.