ICEs

Note: ICEs in this article refers to internal combustion engines. In other contexts ICE can denote organizations such as Immigrations and Customs Enforcement.

Internal combustion engines convert chemical energy stored in fuels into mechanical work by combusting fuel with air inside cylinders. The expanding gases push pistons, turning a crankshaft to produce motion. ICEs include reciprocating piston engines and rotary designs, and power most cars, trucks, ships, and generators.

The modern ICE developed in the late 19th century with the four-stroke Otto cycle and the diesel engine. Through the 20th century, improvements in materials, ignition, and fuel delivery boosted power, efficiency, and durability, enabling widespread use in transportation and industry.

Operation varies by type. Spark-ignition engines mix air and fuel and ignite with a spark; compression-ignition engines rely on high compression to ignite injected fuel. Two-stroke and four-stroke cycles differ in the number of piston events per power cycle. Modern designs use direct injection, turbocharging, and variable valve timing to improve efficiency.

Core components include the cylinder block, pistons, crankshaft, valvetrain, fuel system, ignition, lubrication, and cooling. Emissions controls—catalytic converters, exhaust gas recirculation, and sensors—address environmental concerns.

Efficiency and emissions depend on design and operating conditions. Typical automotive thermal efficiencies fall around 25–40%. Techniques such as turbocharging, direct injection, variable valve timing, and hybridization improve economy, while cleaner fuels and advanced catalysts reduce pollutants.

Although ICEs remain central to many applications, trends toward electrification and sustainable fuels influence the future. They are likely to persist in heavy-duty and high-energy-demand roles, even as lighter vehicles transition to alternative propulsion.