Are there two-stroke diesel engines?

Yes—two-stroke diesel engines exist and remain widely used, especially in large marine propulsion and in some locomotive, naval, and stationary power applications. While they largely disappeared from modern road vehicles due to emissions and efficiency rules, two-stroke diesels are still built today by major engine makers and power many of the world’s biggest ships; some are also seeing a revival in advanced opposed-piston designs and dual-fuel configurations.

What a two-stroke diesel is and how it works

A two-stroke diesel completes a power cycle in two piston strokes (one crankshaft revolution) rather than four. To make that possible, it relies on forced induction—typically a blower and/or turbocharger—to push fresh air into the cylinder and expel exhaust in a process called scavenging. Fuel is injected directly and ignites from compression heat, as in any diesel. Because the crankcase cannot be used for scavenging air (it must hold oil for lubrication), two-stroke diesels use dedicated air-handling hardware.

Common scavenging and architecture types

The following architectures describe how two-stroke diesels move air and manage valving, which is central to their operation and emissions.

• Uniflow with exhaust valves (single piston): Fresh air enters via ports in the cylinder liner; exhaust exits through poppet valves in the head. This is used by Detroit Diesel (historic), EMD locomotives, and most large marine engines (crosshead design).
• Opposed-piston uniflow (no cylinder head): Two pistons share one cylinder, with intake and exhaust ports at opposite ends. Timing overlap delivers efficient scavenging. Fairbanks Morse and modern Achates Power designs use this layout.
• Crosshead low-speed marine engines: A uniflow variant where the piston is separated from the crankcase by a crosshead, enabling precise lubrication and very long strokes. This is the standard for modern container ships and tankers.

Each architecture balances manufacturing complexity, emissions potential, and mechanical efficiency; uniflow scavenging dominates because it offers the cleanest and most efficient gas exchange in a two-stroke diesel.

Where two-stroke diesels are used today

Two-stroke diesels remain the go-to in sectors that prize either very high power density or ultra-high thermal efficiency at steady loads. Below are the most common applications and examples.

• Deep-sea shipping: Low-speed, crosshead two-strokes from MAN Energy Solutions (ME-C/ME-GI/ME-LGIM/ME-LGIA families) and WinGD (X, X-DF, methanol- and ammonia-capable variants) power most large container ships and tankers, routinely achieving ~50% or higher brake thermal efficiency.
• Locomotives: EMD’s 567/645/710 series two-strokes dominate legacy fleets. New U.S. Tier 4-compliant locomotives have moved to four-stroke designs, but EMD 710 two-strokes continue in service, in remanufacture, and in some export and marine/power roles.
• Naval and stationary power: Fairbanks Morse opposed-piston two-strokes and EMD 710s are used at sea and in power generation, valued for compactness and service familiarity.
• R&D and new concepts: Achates Power’s opposed-piston two-stroke has been demonstrated for trucks and military vehicles, aiming for high efficiency and lower emissions; large marine makers are fielding dual-fuel two-strokes (LNG, methanol today; ammonia in trials) to meet decarbonization targets.

The common thread is predictable duty cycles and operating regimes where two-stroke advantages—efficiency at scale or high specific output—outweigh their more complex air-handling and emissions control needs.

Notable historical and current models

The following names illustrate both the heritage and the modern state of two-stroke diesels across industries.

• Detroit Diesel Series 71/92/149: Iconic uniflow two-strokes that powered mid-20th-century trucks, buses, and equipment; phased out as on-road emissions rules tightened.
• EMD 567/645/710: Two-stroke uniflow locomotive engines; the 710 remains in production for non–Tier 4 U.S. uses and globally for marine and power applications.
• Fairbanks Morse 38D 8-1/8 (opposed-piston) and modern OP updates: Naval and stationary staples leveraging compact two-stroke architecture.
• MAN B&W low-speed ME-series and WinGD X/X-DF: Today’s standard-bearers for oceangoing ships, including dual-fuel versions for LNG and methanol, with ammonia-capable variants in development and early deployment.
• Wärtsilä RT-flex96C: A famous large two-stroke design (now under WinGD) known for powering ultra-large container ships.
• Napier Deltic and Junkers Jumo 205 (opposed-piston): Notable historical two-stroke diesels in military/naval and aviation contexts.

Taken together, these engines show that while two-stroke diesels vanished from passenger roads, they remain central to heavy transport and specialized power.

Why you don’t see them in modern cars

Two-stroke diesels face hurdles that don’t align with passenger-car requirements. The points below summarize the main constraints.

• Emissions control: Scavenging creates potential fuel-air “short-circuiting” and higher particulate/NOx without sophisticated hardware and calibration.
• Noise, vibration, harshness: The firing every revolution and high specific output complicate refinement to car standards.
• Cost and complexity: Blowers, turbo-compounding, and precise lubrication add hardware compared with compact four-strokes.
• Regulatory pressure: On-road standards pushed manufacturers toward cleaner, easier-to-certify four-stroke platforms.

As a result, automakers standardized on four-stroke diesels for decades, and increasingly on hybrids and electrification, leaving two-strokes to niches where their strengths shine.

Advantages and trade-offs

Two-stroke diesels persist where their benefits are decisive. Here are the main advantages commonly cited by operators and engineers.

• High power density: A power stroke every crank revolution boosts specific output.
• Excellent efficiency at large scale: Low-speed marine two-strokes achieve around or above 50% brake thermal efficiency.
• Simplified valvetrain (in some designs): Uniflow layouts can reduce valvetrain complexity versus four-strokes of similar output.
• Fuel flexibility: Modern marine two-strokes are available in dual-fuel versions (LNG, methanol; ammonia under development) to meet emissions goals.

These benefits translate to lower fuel consumption per ton-mile at sea and compact, powerful packages for locomotives and naval use.

The same designs come with engineering trade-offs that manufacturers manage through advanced systems. The list below highlights common drawbacks.

• Complex air handling: Blowers, turbochargers (often mechanically assisted), and precise control are mandatory for scavenging.
• Emissions challenges: Managing NOx and particulates requires EGR/SCR, optimized timing, and, in marine use, cylinder lubrication strategies.
• Oil consumption and maintenance: Large crosshead engines use dedicated cylinder lubrication; opposed-piston designs demand exacting timing and sealing.
• Regulatory fit: Meeting the strictest on-road standards has proven difficult without prohibitive cost.

Where duty cycles are steady and maintenance expertise is in place, these trade-offs are acceptable—and even preferable—for overall efficiency and lifecycle cost.

Summary

Two-stroke diesel engines not only exist—they are foundational to global shipping and remain important in locomotives, naval vessels, and power generation. Modern examples from MAN Energy Solutions and WinGD dominate large ships, while EMD and Fairbanks Morse two-strokes continue in rail, marine, and stationary roles. They vanished from passenger roads due to emissions, noise, and regulatory pressures, but ongoing development—including opposed-piston concepts and dual-fuel capability—keeps the two-stroke diesel relevant where its efficiency and power density matter most.

Do two-stroke diesels exist?

Yes, two-stroke diesel engines exist and are used in applications such as large marine vessels and some industrial or military machinery, though they are not common in modern cars or light-duty trucks due to emissions regulations and their inherent drawbacks in those applications. Famous examples include the Detroit Diesel two-stroke engines used in American trucks and machinery.
 
How They Work

• Two-stroke diesel engines complete the combustion cycle (intake, compression, combustion, exhaust) in just two strokes of the piston, or one crankshaft revolution. 
• Unlike four-stroke engines, they don’t need separate intake and exhaust strokes. 
• They use a combination of exhaust valves and ports covered by the piston to let in air and expel exhaust. 
• Large marine engines use their slow speed for high thermal efficiency and can burn heavy fuel oil. 

This video explains how two-stroke diesel engines work: 39sRepairman22YouTube · Jul 2, 2023
Applications

• Marine Engines: Two-stroke diesels are still widely used in large container ships and other marine applications. 
• Industrial and Military: They have historically been used in industrial machinery and military vehicles. 
• Series Hybrids: Some series hybrid automobiles can use a two-stroke diesel as an onboard generator. 
• Historical Applications: Detroit Diesel’s two-stroke engines were once prevalent in over-the-road trucks but were phased out due to emissions issues. 

Why They Are Not More Common

• Emissions: Two-stroke diesels inherently produce “dirtier” exhaust and more NOx emissions than their four-stroke counterparts, making it difficult to meet modern emissions standards. 
• Complexity of Modern Control: While advances in electronic controls helped, they weren’t enough to overcome the inherent design challenges for road vehicles. 
• Shift to Four-Stroke: Most modern diesel engines, especially for vehicles, are now four-stroke designs. 

What is the nickname for the Detroit Diesel 2-stroke?

The Screaming Jimmy
The Detroit Diesel 2-stroke engine earned the nickname “The Screaming Jimmy” due to its unique, high-pitched whine. This signature sound, caused by its high RPM and exhaust characteristics, became iconic among enthusiasts and operators alike.

What is the most powerful 2-stroke diesel engine?

Wärtsilä-Sulzer RTA96-C

RT-flex96C
Overview
Output
Power output	80,080 kW (107,390 hp)
Dimensions

Did Cummins make a 2-stroke diesel engine?

Applications. The compact 14.3L ACE produces 1,000 hp, and a peak torque of 2424 lb-ft. This four-cylinder, two-stroke, opposed-piston diesel engine is equipped with eight pistons, as well as supercharging and turbocharging capabilities that eliminate the necessity for a valve train.