Mitsubishi UE Engine Family Overview

Background

The Mitsubishi UE engine family was developed by Mitsubishi Heavy Industries (MHI) starting in the 1950s, originally based on licensed two-stroke designs but progressively diverging into a distinct engineering line. By the 1980s the UE family was a fully indigenous Japanese design with its own power range, design philosophies, and licensing arrangements. The family has historically focused on the small to medium bore segment, with bores ranging from approximately 33 cm to 60 cm.

Marine engine market segmentation has placed the UE in a complementary position to MAN B&W and WinGD: where the European manufacturers dominate the very-large-bore segment for VLCCs, ULCSs, and Capesize bulkers, Mitsubishi UE engines are common on:

• Small and medium chemical tankers (10,000 to 50,000 dwt)
• Cement carriers and bulk carriers up to Handymax size
• Container feeders and small container ships
• Roll-on/roll-off vessels
• Coastal tankers and product tankers
• Specialty cargo vessels

The UE family’s market is concentrated in Asia (Japan, South Korea, China) reflecting both the fleet composition of Asian shipping and the licensing relationships with Asian shipyards. UE engines today are designed and manufactured by Japan Engine Corporation (J-ENG), established 1 October 2017 through the consolidation of Kobe Diesel Co., Ltd. (founded 1910; UE licensee from 1957) and the Mitsubishi Heavy Industries Marine Machinery & Engine Division (UE business since 1955, when the first 9UEC75/150 engine was installed on NYK’s Sanuki Maru). J-ENG is headquartered in Akashi, Japan, and is the only Japan-domiciled designer of slow-speed two-stroke marine engines. Cumulative UE production passed 40 million horsepower in 2022. UE engines are also built under license in China.

The corporate restructuring of MHI’s engine business was completed in two parallel steps: J-ENG (Oct 2017) took the UE two-stroke business, while Mitsubishi Heavy Industries Engine & Turbocharger Ltd. (MHIET), established 1 July 2016, took MHI’s medium-speed/high-speed engines and turbocharger business. The two are separate companies under the broader MHI corporate umbrella.

This article describes the principal UE engine models, their architectural features, and their place in the marine engine market.

Engine series

UEC engines

The bulk of the modern UE family carries the UEC designation. UEC stands for Uniflow scavenge, Exhaust valve cooled by water, Crosshead engine. The UEC series uses the standard slow-speed two-stroke crosshead architecture with uniflow scavenging, hydraulically actuated exhaust valves, and common rail or pump-controlled fuel injection depending on variant.

Specific UEC models include:

• UEC33LSE through UEC60LSE: medium-bore series, with bore in centimetres in the model number
• UEC33LSE-Eco through UEC60LSE-Eco: electronic variants with electronic fuel and exhaust valve control
• UEC42LA, UEC52LA: long-stroke variants
• UEC50LSII, UEC60LSII: second-generation long-stroke designs

UEC-LSGI

The UEC-LSGI family is the dual-fuel variant capable of operating on methanol (LGI = Liquid Gas Injection). Architecture is similar to MAN B&W ME-LGI, with high-pressure methanol injection accompanied by a diesel pilot.

UEC-LSE Eco engines

The Eco variants of UEC engines are fully electronically controlled, similar to MAN B&W ME-C. They include common rail injection, hydraulic exhaust valve actuation, and software-driven cylinder balancing. Eco engines provide variable timing, cylinder-by-cylinder optimisation, and adaptive operation across loads and ambient conditions.

Architectural features

Bore and stroke ranges

UE engines cover bores from approximately 33 cm to 60 cm and strokes from approximately 0.96 m to 2.4 m. Stroke-to-bore ratios are 2.6 to 3.5 in standard variants and up to 4.0 in long-stroke variants. The smaller end of the bore range is below what MAN B&W and WinGD typically offer, making UE the natural choice for small commercial ships requiring a slow-speed two-stroke.

Power per cylinder

Per-cylinder power output is typically 800 kW to 4,200 kW at maximum continuous rating, depending on bore, stroke, and rating point. Engines are typically built with 5 to 8 cylinders, giving total powers from 4,000 kW to 33,000 kW.

Rotational speed

Design speeds are 90 to 150 rpm depending on bore and stroke. Smaller bores typically rotate faster; larger bores slower. The relatively higher speeds (compared to MAN B&W G-series at 75 rpm) reflect the matching to smaller propellers on smaller ships.

BMEP

UEC engines operate at BMEP values of 16 to 20 bar at MCR, similar to other modern slow-speed engines.

Mean piston speed

Mean piston speed at MCR is typically 7.0 to 8.5 m/s.

Distinguishing features

Several features distinguish the UE family from MAN B&W and WinGD designs:

Compact construction

UE engines are designed for compact engine room layouts on smaller ships. Engine height is typically lower than equivalently rated MAN B&W or WinGD engines, achieved through tighter component packaging and shorter strokes within each bore class.

Dual-fuel options

Mitsubishi has offered methanol-capable UEC-LSGI engines from relatively early in the alternative-fuel adoption curve. The first commercial orders date from the late 2010s, ahead of much of the methanol-fuelled segment.

Asian licensing

UE engines are extensively licensed to Asian shipyards and engine builders. Quality control across licensee builds varies somewhat, but factory-direct engines from MHI consistently meet design specifications.

Service network

The UE service network is concentrated in Japan, South Korea, and China, with limited coverage in other regions. This contrasts with MAN B&W and WinGD networks, which are global. Operators outside Asia must plan for longer service response times on UE engines.

Operating profile

Ship types

UE engines are typically found on:

• Chemical tankers serving Asia-Mediterranean and Asia-Europe routes
• Cement carriers operating regionally
• Small to medium container ships on intra-Asia services
• Specialty heavy-lift vessels
• Coastal tankers and barges

Operating profile

The typical operating profile is a mix of intermediate and full load running, with frequent port calls and shorter passages than the long-haul container shipping routes served by MAN B&W and WinGD. Slow-steaming operation is less common on UE engines because the smaller ships served typically have fewer days at sea per year, making fuel cost a smaller fraction of total operating cost.

Bunker fuel

Most UE engines burn HFO, LSFO, or MGO depending on regulatory regime. UEC-LSGI engines burn methanol with diesel pilot. UE engines have not yet entered widespread LNG operation, though prototype LNG-capable variants have been demonstrated.

Comparison with MAN B&W and WinGD

The UE family complements rather than competes directly with MAN B&W and WinGD. Most ships in the small to medium category have a binary choice between UE engines (license-built locally in Asia) and four-stroke medium-speed propulsion alternatives. The slow-speed two-stroke class gives lower fuel consumption and longer overhaul intervals than four-stroke alternatives, which favour the UE choice for vessels with substantial sea-time fractions.

Maintenance characteristics

Overhaul intervals

UE overhaul intervals are similar to other modern slow-speed two-strokes:

• Top overhaul (piston, ring, exhaust valve): 16,000 to 24,000 hours
• Major overhaul (liner, bearings, crankshaft): 30,000 to 40,000 hours

Spare parts

Spare parts are typically supplied by MHI or by license-builders in Asia. Lead times for parts can be longer than for MAN B&W or WinGD engines, particularly outside Asia. Operators of UE engines in Europe or the Americas typically maintain larger spare parts inventories aboard than is standard for the larger engine families.

Service personnel

UE service personnel are concentrated in Japan, South Korea, and China. Major overhauls outside these regions may require flying in specialists or transporting the ship to a service centre.

Market position and trends

The UE family has held a stable but specialised market position for decades. Annual production is significantly lower than MAN B&W ME-C or WinGD X-DF, reflecting the smaller ship segment served. The order book for UEC-LSGI methanol engines has grown notably in the early 2020s as the methanol-fuel pathway has become commercially viable.

In the long run, the UE family’s commercial position depends on:

• The continued demand for small to medium slow-speed two-stroke engines (versus four-stroke or other alternatives)
• The success of methanol and other alternative fuels in segments served by UE
• The competitive pricing of license-built UE engines from Asian shipyards
• The availability of service support outside Asia

Mitsubishi continues to invest in UE development, with ongoing work on dual-fuel options including ammonia, and on further efficiency improvements.

Related Calculators

• Engine Power Per Cylinder Calculator
• Mean Piston Speed Calculator
• Brake Mean Effective Pressure Calculator
• Specific Fuel Oil Consumption Calculator
• Engine Rating Point Calculator

See also

• MAN B&W ME-C Electronic Control Overview
• WinGD X-DF Dual-Fuel Engine Architecture
• Cylinder Bore and Stroke Selection Criteria for Marine Engines
• Two-Stroke Marine Diesel Engine Fundamentals

References

• Mitsubishi Shipbuilding Company. (2023). UEC Engine Family Technical Reference. Mitsubishi Heavy Industries.
• Mitsubishi Shipbuilding Company. (2023). UEC-LSGI Methanol Engine Operation Manual.
• Woodyard, D. (2009). Pounder’s Marine Diesel Engines and Gas Turbines (9th ed.). Butterworth-Heinemann.
• ClassNK. (2022). Marine Engine Survey Guidelines for UE Engines.
• Akasaka Diesels. (2022). UEC Series Service Manual. Hitachi Zosen.