Internal combustion engines provide outstanding drivability and durability, with more than 250 million highway transportation vehicles in the United States relying on them. 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. In a diesel engine, only air is inducted into the engine and then compressed. Diesel and gasoline engines then spray the fuel into the hot compressed air at a suitable, measured rate, causing it to ignite.
IMPROVING COMBUSTION ENGINES
Over the last 30 years, research and development has helped manufacturers reduce ICE emissions of criteria pollutants, such as nitrogen oxides (NOx) and particulate matter (PM) by more than 99% to comply with EPA emissions standards. Research has also led to improvements in ICE performance (horsepower and 0-60 mph acceleration time) and efficiency, helping manufacturers maintain or increase fuel economy.
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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.