The most common combustion engine: the four-stroke, spark‑ignition piston engine

The most common combustion engine in use today is the four-stroke, spark‑ignition (Otto‑cycle) piston engine—typically fueled by gasoline and found in the majority of passenger cars and many motorcycles and small machines worldwide; in heavy-duty transport and some passenger vehicles, the four-stroke diesel (compression‑ignition) engine is also widespread. In everyday language, when people say “combustion engine,” they almost always mean these internal combustion piston engines, which have dominated road transport for over a century and still account for most engines in service as of 2025, despite rapid growth in electric vehicles.

What it is and how it works

The four-stroke spark‑ignition engine is a reciprocating internal combustion engine that converts chemical energy in fuel into mechanical work through a repeating sequence of piston movements. Each full cycle of the engine consists of four distinct strokes of the piston and two revolutions of the crankshaft.

• Intake: The intake valve opens and the piston moves down, drawing in a fuel–air mixture.
• Compression: Both valves close and the piston moves up, compressing the mixture.
• Power (combustion): A spark plug ignites the compressed mixture, the rapid combustion increases pressure, and the expanding gases push the piston down, producing work.
• Exhaust: The exhaust valve opens and the piston moves up, expelling combustion gases.

Together, these strokes transform fuel into rotational power at the crankshaft, which is then transmitted to wheels, propellers, or generators. The cycle’s simplicity, controllability, and compatibility with liquid fuels underpin its ubiquity.

Why this engine became the most common

Several engineering, economic, and infrastructure factors propelled the four-stroke piston engine—especially the gasoline, spark‑ignition variant—to global dominance in road transport and beyond.

• Manufacturing maturity: Decades of refinement enabled reliable mass production at low cost with a worldwide supplier base.
• Energy-dense fuels: Gasoline and diesel store high energy per kilogram and liter, enabling long range and quick refueling.
• Scalability: Designs scale efficiently from single‑cylinder lawn equipment to high‑power multi‑cylinder automotive and industrial engines.
• Power density: High power in compact packages suits vehicles where space and weight matter.
• Established infrastructure: Global networks for fuel distribution, service, and parts reduce ownership barriers.
• Control and drivability: Spark timing, mixture control, turbocharging, and variable valve systems provide smooth, responsive performance.

In combination, these advantages locked in a strong ecosystem around four-stroke piston engines, making them the default choice for most on-road applications for decades.

Common variants and where you’ll find them

While the spark‑ignition four‑stroke gasoline engine is the most common overall, several closely related combustion engines are prevalent in specific niches and duty cycles.

• Spark‑ignition gasoline, four‑stroke: Dominant in passenger cars, many motorcycles, light utility vehicles, and small generators.
• Compression‑ignition diesel, four‑stroke: Common in heavy‑duty trucks, buses, marine vessels, agricultural and construction equipment, and stationary power due to superior fuel efficiency and torque.
• Two‑stroke small engines (gasoline): Used in some handheld tools (e.g., chainsaws) and small outboards; lighter and simpler but typically higher emissions without modern aftertreatment.
• Gas turbines (jet engines): The standard for aircraft propulsion and some power generation; not typical for road vehicles due to efficiency and cost profiles at small scales.

Across markets, the four‑stroke piston architecture dominates road transport, with diesel favored for heavy loads and gasoline for light-duty vehicles, while specialized engines serve niche requirements.

Efficiency, emissions, and today’s trends

Modern four-stroke engines are far more efficient and cleaner than earlier generations, driven by stringent regulations and technological progress.

• Efficiency: Contemporary gasoline engines achieve peak brake thermal efficiencies around 35–41% using direct injection, turbocharging, high compression ratios, and Atkinson/Miller cycles (often in hybrids). Modern light-duty diesels can reach ~40–45%, while state‑of‑the‑art heavy‑duty diesels approach ~50% under optimal conditions.
• Emissions control: Three‑way catalysts (gasoline), particulate filters and NOx aftertreatment (diesel), precise fuel/air control, and advanced combustion strategies dramatically cut pollutants.
• Regulation: New and upcoming standards (e.g., U.S. EPA light‑ and heavy‑duty rules for late‑2020s, Europe’s Euro 7 phase‑in) continue to tighten pollutant limits, pushing further efficiency and aftertreatment improvements.
• Market shift: Electric vehicles are growing rapidly—global EVs accounted for roughly one in five new cars in 2024—but the in‑use fleet remains predominantly internal combustion, and hybrids extend the relevance of efficient four-stroke engines.

The trajectory is toward cleaner, more efficient combustion in the near term, alongside accelerating electrification that gradually reduces the share of combustion-only powertrains in new sales.

Outlook

The four-stroke spark‑ignition piston engine will remain common in the global fleet for years due to existing vehicles, cost considerations, and regional infrastructure realities. Hybrids, improved combustion processes, and increasingly capable aftertreatment will sustain its role, especially where charging access is limited. Over the long run, policy, battery progress, and total cost of ownership trends are expected to shift most light-duty markets toward electrification, with combustion engines persisting in heavy-duty, remote, or specialized applications—and potentially using low‑carbon fuels where viable.

Summary

The most common combustion engine is the four‑stroke, spark‑ignition (Otto‑cycle) piston engine, ubiquitous in passenger vehicles worldwide, with four‑stroke diesels prevalent in heavy‑duty roles. Its dominance stems from manufacturability, energy‑dense fuels, power density, and global infrastructure, and it continues to evolve with higher efficiency and cleaner emissions even as electrification expands.

What is the most common engine?

The four-cylinder inline (or straight) engine is the most common type of engine, especially in cars, due to its compact size, good balance of power and fuel economy, and lower manufacturing costs. This simple layout has cylinders arranged side-by-side in a single row, making it a practical and widely used choice for everyday vehicles.
 
Key characteristics of the inline engine:

• Simple & Compact: The cylinders are in a straight line, which makes the engine design straightforward and easier to fit into smaller vehicles. 
• Fuel-Efficient: Inline-four engines are a popular option for commuters because they offer a good blend of fuel economy and adequate power. 
• Cost-Effective: The simple configuration leads to lower manufacturing and repair costs compared to more complex engine designs. 
• Versatile: Inline engines are used in everything from small cars and motorcycles to larger vehicles and machinery. 

Other important factors:

• Engine Size: While the inline configuration is common, the number of cylinders also plays a role, with the four-cylinder (inline-four) being the majority of engines on the road today. 
• Broader Applications: While inline-fours are most common in cars, other types of engines like V8s and six-cylinder engines are used in larger vehicles and high-performance cars. 

What is the most common V8 engine?

The most popular V8 engine is the Chevrolet Small Block V8, particularly the later LS series. Introduced in 1955, the Chevrolet Small Block has sold over 108 million units, and the modern LS engines are celebrated for their lightweight aluminum construction, modular design, ease of maintenance, and excellent power potential, making them a favorite for engine swaps and hot-rodding.
 
This video explains why the Chevrolet Small Block V8 is considered the most prolific engine ever produced: 54sRare CarsYouTube · Sep 6, 2025
Why the Chevrolet Small Block V8 is so popular:

• Massive Sales & Ubiquity: The original Small Block V8, launched in 1955, is the most sold V8 engine in history. 
• LS Series Success: The later LS engines are incredibly popular due to their: 
  • Simplicity and Modularity: The design focuses on simplicity, with interchangeable parts, leading to ease of maintenance. 
  • Lightweight Aluminum Construction: The aluminum block and heads significantly reduce weight compared to previous generations. 
  • High Parts Availability: The extensive use of LS engines means parts are readily available. 
  • Modifiability: Even entry-level LS engines can handle significant power increases with minimal modifications, making them a darling for engine swaps. 
• Versatility: The LS platform is used in a wide range of vehicles, from performance cars like the Corvette to work trucks and even specialized supercars. 
• Community Support: A vast community surrounds the LS engines, including a dedicated festival, with many mechanics and enthusiasts preferring them for home builds and engine swaps. 

What’s better, inline 4 or V6?

Neither an inline-4 nor a V6 is inherently “better”; the best choice depends on your priorities. An inline-4 is generally more fuel-efficient, lighter, and cheaper to produce, making it ideal for smaller cars and daily driving, while a V6 offers more power, smoother performance, and greater capability for heavy loads, though at the cost of higher fuel consumption and manufacturing price. Modern turbocharged inline-4 engines can offer impressive power, but V6s still hold an edge in overall performance and luxury.
 
Choose an Inline-4 if you prioritize:

• Fuel Efficiency: Four-cylinder engines are typically more fuel-efficient, leading to lower running costs. 
• Cost: Inline-4 engines are generally less expensive to manufacture and purchase. 
• Compactness: Their smaller size and lighter weight are beneficial for fitting into tight engine bays, common in front-wheel-drive cars. 
• Simple Maintenance: With fewer moving parts, maintenance and repairs can be more straightforward. 

Choose a V6 if you prioritize:

• Power & Acceleration: V6 engines, with their larger displacement and more cylinders, produce more horsepower and torque for faster acceleration. 
• Smoother & Quieter Operation: V6s tend to be smoother and quieter, contributing to a more refined driving experience, especially in larger or luxury vehicles. 
• Towing & Hauling: Their greater power makes them better suited for towing heavy loads and for use in larger vehicles like SUVs and trucks. 
• Performance: For driving enthusiasts, a V6 engine provides a more powerful and responsive feel. 

Key Considerations:

• Modern Technology: Opens in new tabTurbocharging has significantly boosted the power output of modern inline-4 engines, narrowing the performance gap with naturally aspirated V6s. 
• Vehicle Size: Opens in new tabThe ideal engine choice often depends on the vehicle’s size and weight. Smaller cars are often well-suited for inline-4s, while larger vehicles benefit from the power of a V6. 
• Cost vs. Performance: Opens in new tabA V6 will generally increase the purchase price and running costs but delivers a higher level of performance and refinement. 

Is a 3 or 4-cylinder engine better?

3-cylinder engines are often considered “better” than 4-cylinder engines, especially in compact and urban cars, due to their energy efficiency, lower cost and higher torque at low revs. However, they lose out in terms of smoothness and performance at high revs, where 4-cylinder engines still have an advantage.