The Main Types of Internal Combustion Engines

The main types of internal combustion (IC) engines are spark-ignition (gasoline) and compression-ignition (diesel), each commonly built as four-stroke or two-stroke designs; additional major forms include rotary (Wankel) engines and continuous-combustion gas turbines/jet engines. These categories are further distinguished by ignition method, thermodynamic cycle, mechanical architecture, fuel, and air handling, which together determine performance, efficiency, and applications from cars and trucks to ships and aircraft.

How engineers classify internal combustion engines

Engineers group IC engines along several axes: how the fuel-air mixture ignites, how the cycle is completed (number of strokes), the machine’s mechanical architecture (reciprocating pistons, rotary, turbine), the fuel and mixture preparation method, and how the engine breathes and is cooled. Understanding these dimensions clarifies why different types dominate different uses.

By ignition method (primary typology)

Ignition method is the most fundamental distinction because it drives fuel choice, compression ratios, combustion temperatures, emissions, and efficiency.

• Spark-ignition (SI, typically gasoline): A spark plug ignites a premixed air–fuel charge. Common in passenger cars, motorcycles, small equipment. Modern SI includes port fuel injection (PFI), gasoline direct injection (GDI), and stratified/ultra-lean systems with prechamber ignition.
• Compression-ignition (CI, diesel): Air is compressed to high temperature; fuel is injected and auto-ignites. Favored for heavy-duty vehicles, marine propulsion, and generators due to high thermal efficiency and torque.
• Dual-fuel and pilot-ignited: Predominantly gaseous fuel (e.g., natural gas) is ignited by a small diesel pilot, combining cleaner combustion with diesel-like reliability; common in large stationary and marine engines.
• Low-temperature auto-ignition modes: HCCI/SPCCI, PCCI, and RCCI blend SI and CI traits by promoting auto-ignition of a premixed or partially premixed charge for lower NOx and particulate emissions and higher efficiency; used selectively in production (e.g., Mazda Skyactiv-X SPCCI) and research/limited commercial engines.

These ignition modes set the combustion regime, which shapes engine hardware (compression ratio, injection system) and downstream components like aftertreatment.

By thermodynamic cycle and number of strokes

The stroke arrangement determines how the engine completes intake, compression, combustion, and exhaust, affecting size, power density, and emissions.

• Four-stroke cycle: Separate strokes for intake, compression, power, and exhaust. Dominant in road vehicles and most industrial engines for cleaner combustion and better control.
• Two-stroke cycle: Completes a power event every crank revolution using port timing or valves; high power density and simplicity but historically higher emissions. Still prevalent in small engines, some motorcycles, outboards, drones, and very large marine diesels (crosshead two-strokes).
• Atkinson/Miller variants: Valve timing or boosting strategies alter the effective compression/expansion ratio to improve efficiency; widely used in modern hybrids and turbocharged engines.

While four-stroke designs dominate for emissions and efficiency, two-strokes excel where compactness and specific power are paramount, and Miller/Atkinson strategies optimize efficiency in many contemporary engines.

By mechanical architecture

Mechanical layout influences smoothness, size, reliability, and application domain.

• Reciprocating piston engines: The most common type. Cylinders can be inline, V, flat/boxer, radial, or opposed-piston (two pistons per cylinder without a cylinder head). Configurations scale from single-cylinder tools to massive multi-cylinder powerplants.
• Rotary (Wankel) engines: A triangular rotor orbits in an epitrochoid housing, delivering smooth power with high power density and few moving parts; trade-offs include sealing challenges and emissions. Seeing niche revivals (e.g., range extenders, UAVs).
• Gas turbines and jet engines: Continuous-combustion internal combustion machines using compressor, combustor, and turbine stages. Turbofans, turbojets, turboprops dominate aviation; industrial gas turbines serve power generation. They differ from reciprocating engines but are still internal combustion devices.

Each architecture targets different performance envelopes: pistons for versatility and efficiency, Wankels for compact smooth output, and turbines for high power-to-weight and continuous operation.

By fuel and mixture preparation

Fuel type and how it blends with air affect energy density, combustion speed, emissions, and aftertreatment needs.

• Gasoline (SI, PFI/GDI): Fast-burning, supports high RPM; GDI enables stratification and higher compression but can raise particulates, requiring gasoline particulate filters.
• Diesel (CI): High cetane and lubricity for compression ignition and injector durability; requires aftertreatment (DPF, SCR) to control particulates and NOx.
• Natural gas, CNG/LNG, LPG: Used in SI or dual-fuel CI; lower CO2 per unit energy and low particulates; common in buses, fleets, and stationary power.
• Biofuels and e-fuels: Ethanol/E85 in SI; biodiesel/FAME and HVO/renewable diesel in CI; synthetic drop-in fuels are emerging to decarbonize existing fleets.
• Hydrogen ICE: Burns H2 in modified SI or CI-like concepts (often with prechambers); near-zero CO2 at the tailpipe with attention to NOx and backfire control; under active development in heavy-duty and motorsport.
• Mixture strategies: Homogeneous (PFI), direct injection (GDI/DI diesel), stratified charge, and prechamber ignition for ultra-lean burn.

Fuel and preparation strategy are tightly coupled to ignition mode and dictate hardware such as injectors, pumps, and catalytic systems.

By aspiration and air handling

Air management determines charge density and efficiency across operating conditions.

• Naturally aspirated: Simpler, linear response, and often favored for durability and cost.
• Turbocharged: Exhaust-driven compressors increase power and efficiency; intercooling reduces charge temperature. Now ubiquitous across SI and CI engines.
• Supercharged: Mechanically driven compressors give immediate boost; used where transient response is critical or in combination with turbos.
• Turbo-compounded and e-boosted systems: Recover exhaust energy via a power turbine or use electric assist on compressors to widen efficient operating range.

Modern engines frequently combine boosting with variable valve timing/lift and exhaust gas recirculation (EGR) to optimize efficiency and emissions.

By cooling method and cylinder layout

Thermal management and geometry influence reliability, packaging, and application fit.

• Cooling: Air-cooled for simplicity and weight savings (small engines, some aircraft); liquid-cooled for precise temperature control and tighter emissions.
• Layouts: Inline (I), V, flat/boxer, radial (aircraft heritage), and opposed-piston (high efficiency, compact height). Cylinder count ranges from single to 20+ in large industrial and marine engines.

Cooling and geometry choices align engines with their operating environment—harsh duty cycles, ambient conditions, and space constraints.

Where each type is used

Applications reflect the strengths of each engine type in power density, efficiency, and operating profile.

• Passenger cars and light trucks: Four-stroke SI with turbocharging; some diesels; hybrids favor Atkinson-like cycles.
• Heavy-duty trucks and buses: Four-stroke CI diesels; growing use of natural gas and hydrogen ICE pilots.
• Motorcycles and small equipment: SI four-stroke and some two-stroke for simplicity and power density.
• Marine: Very large two-stroke CI diesels for main propulsion; four-stroke CI for auxiliaries; LNG dual-fuel on newer vessels.
• Aviation: Piston aircraft use air-cooled SI (and some CI) opposed engines; helicopters and airplanes rely heavily on gas turbines (turboshafts, turboprops, turbofans).
• Stationary power and CHP: Large CI diesels and SI natural gas engines; industrial gas turbines for higher outputs and continuous duty.

The fit between engine type and use case is driven by duty cycle, fuel availability, emissions rules, and total cost of ownership.

Emerging trends and industry direction

IC engines are evolving alongside electrification and climate policies. Advances include variable compression ratio systems, prechamber lean-burn SI (as used in high-efficiency and racing engines), refined aftertreatment, friction reduction, and widespread turbo-Miller strategies. Novel architectures like opposed-piston two-strokes are reappearing for efficiency gains. Fuel innovation spans renewable diesels, synthetic gasoline/jet fuels, and hydrogen ICE for heavy-duty and off-highway use. Even as many markets adopt electrified powertrains, IC engines remain essential in heavy transport, aviation, marine, and backup power, with decarbonization focused on efficiency and low-carbon fuels.

Bottom line

The core types of internal combustion engines are spark-ignition and compression-ignition designs, built as four-stroke or two-stroke, with notable alternatives like rotary (Wankel) and gas turbines/jet engines. Their practical diversity—spanning fuel type, architecture, and air handling—allows IC engines to serve everything from lawn equipment to container ships and airliners.

Summary

Internal combustion engines are chiefly categorized as spark-ignition (gasoline) and compression-ignition (diesel), implemented as four-stroke or two-stroke cycles. Additional major forms include rotary Wankel engines and continuous-combustion gas turbines and jet engines. These types further vary by fuel and mixture preparation, boosting, cooling, and layout, aligning performance and efficiency with specific applications across road, marine, aviation, and stationary power.

What is the most common combustion engine?

Four-stroke engines
Four-stroke engines are the most common internal combustion engine design for motorized land transport, being used in automobiles, trucks, diesel trains, light aircraft and motorcycles. The major alternative design is the two-stroke cycle.

What are the types of internal combustion engines?

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.

What are the two types of combustion engines and how does it work?

In external combustion engines, fuel combustion occurs in a combustion chamber located outside of the rest of the engine. In internal combustion engines, combustion takes place inside the engine. In modern motor vehicles, fuel and air are drawn into each of the engine’s cylinders and burned.

What is the 3 type of engine?

ATC Blog ● Engine Type #1: Gas Engines . The traditional engine type that still lives under the hood of countless vehicles on the road today is the internal combustion gasoline engine .Engine Type #2: Hybrid and Electric Engines .Engine Type #3: Diesel Engines .