HiMSEN: Hyundai Medium-Speed Marine Engines

HiMSEN (Hi-touch Marine and Stationary ENgine) is the in-house four-stroke medium-speed engine brand of HHI-EMD (Hyundai Heavy Industries Engine & Machinery Division), launched in March 2001. The family spans bore sizes from 170 mm to 460 mm and delivers outputs from roughly 575 kW to 26 MW, serving both marine auxiliary generating sets and propulsion duties on smaller and specialist vessels. Cumulative production passed 10,000 units in 2016 and 15,000 units on 29 January 2024, with engines operating in more than 60 countries. The programme has expanded from the original diesel-only H21/32 and H25/33 to dual-fuel methanol variants in commercial service and ammonia-capable engines that completed seven-class type approval in late 2025. Estimate genset output using the auxiliary medium-speed genset calculator and compare thermal efficiency with the SFOC-to-efficiency calculator.

Why HHI developed its own medium-speed engine

Korean shipbuilding in the 1990s had a structural problem: Korean yards built the hulls, but the medium-speed auxiliary engines running inside them came entirely from Europe. Wartsila (Finland), MAN B&W subsidiary Holeby (Denmark), and MaK (Germany) supplied virtually every auxiliary genset on Korean-built ships. Every engine purchase transferred foreign currency out of Korea, extended supply chains beyond Korean control, and left Korean yards dependent on the production schedules of foreign suppliers who had their own order books to manage.

HHI’s engine and machinery division already licensed MAN B&W slow-speed two-stroke designs for main propulsion and Holeby designs for auxiliary engines, so it had engine-building infrastructure but no proprietary medium-speed product. The distinction matters because a licensee pays royalties per cylinder to the design owner and cannot change the design without the design owner’s permission. Developing an in-house engine would eliminate royalty outflows on that product, give HHI engineering control over upgrades and fuel variants, and let HHI price the engine competitively in export markets without the constraint of a licence agreement.

The R&D programme started in 1993 and ran for eight years. HHI drew on knowledge accumulated from licence-building Holeby engines and from its own engine test facilities at Ulsan. The test engine passed its first successful run in July 2000. HiMSEN launched commercially in March 2001 with two simultaneous products: the H21/32 for small genset duty and the H25/33 for larger gensets and smaller propulsion applications.

The strategic calculation proved correct on two dimensions. First, by 2011 HHI had stopped producing licensed four-stroke auxiliary engines altogether, replacing that entire line with HiMSEN. Second, the export market opened: an engine that doesn’t carry a third-party royalty can be priced more aggressively in competitive bids. Today HiMSEN competes directly against Wartsila’s 32 and 34DF families, MAN’s L32/40 and L48/60 lines, and Caterpillar-MaK in the auxiliary and medium-propulsion segments.

Naming convention and engine identification

HiMSEN’s model numbers encode the engine’s core geometry in a compact string. The letter H signals the HiMSEN brand, the two digits before the slash give bore diameter in centimetres, and the two digits after give stroke in centimetres. So H21/32 has a 210 mm bore and a 320 mm stroke; H32/40 has a 320 mm bore and a 400 mm stroke.

Suffixes extend the code to identify configuration and fuel type:

• No suffix: base diesel-only in-line configuration
• V: V-cylinder arrangement (two banks at an angle), used to increase cylinder count and output within a shorter block length
• C: a bore variant designation used on some recent models (H22C, H32C)
• DF: dual-fuel operation on natural gas (LNG) and diesel
• LM: liquid methanol dual-fuel (high-pressure methanol injection)
• LA: liquid ammonia dual-fuel (high-pressure ammonia injection)
• P: propulsion-rated variant with CPP (controllable pitch propeller) optimization

An engine called 9H35DF means nine cylinders, H35/40 bore-stroke geometry, dual-fuel gas. The cylinder count prefix scales the same block design across a wide power band: a six-cylinder and a nine-cylinder H35DF share virtually all their major components but deliver roughly 3,060 kW and 4,590 kW respectively at 720 rpm, depending on the specific mark.

The HiMSEN engine families

The table below summarizes the current and recent HiMSEN line-up from the official HD Hyundai Engine & Machinery product pages and published project guides. Power figures are indicative rated outputs; actual values depend on cylinder count, speed, and layout point.

The H17/28 sits at the smallest end and is used on smaller vessels and stationary power applications. The H21/32 is by far the highest-volume model, carried on virtually every HHI-built ship as an auxiliary engine. The H46/60 at 460 mm bore is HiMSEN’s largest current diesel design, with V-configuration variants reaching 26 MW, putting it in direct competition with Wartsila 46F and MAN L48/60.

H21/32: the volume engine

The H21/32 is the engine that built HiMSEN’s unit count. Its 210 mm bore and 320 mm stroke give a stroke-to-bore ratio of 1.52, relatively long-stroke for a medium-speed engine, which keeps mean piston speed at a moderate level and supports lower SFOC at rated load. The engine runs in-line configurations of five, six, seven, eight, and nine cylinders at speeds of 720, 750, 900, and 1,000 rpm, covering an output band of roughly 1,000 kW to 1,800 kW per engine.

On an HHI-built very large crude carrier or container ship, the electrical plant typically carries three or four H21/32 auxiliary gensets. HHI’s practice of specifying its own engines on its own hulls is the primary reason for HiMSEN’s exceptional unit volumes: every ship HHI builds is a captive order for multiple H21/32 units. Since HHI has for several decades been among the three largest shipbuilders in the world by tonnage, the captive demand alone would have made HiMSEN a major producer even before export sales were counted.

The H21C is a later variant with a slightly revised block designation used on some newer production runs.

H25/33: inline and V for larger gensets

The H25/33 at 250 mm bore enters territory where the choice between in-line and V-cylinder configurations becomes commercially important. An in-line nine-cylinder H25/33 delivers roughly 2,700 kW. A V-configuration (H25/33V) stacks two cylinder banks to offer twelve, fourteen, sixteen, or eighteen cylinders in a shorter overall length, reaching up to 6,400 kW. That range covers large naval vessel gensets, ferry electrical plants, and some propulsion-rated installations on smaller ships.

The H25/33 was the second of the two launch models in 2001 and immediately received type approvals from seven class societies: ABS, Bureau Veritas, DNV, ClassNK, Korean Register, Lloyd’s Register, and RINA. Seven-class approval is now standard for each new HiMSEN variant as it reaches type-approval testing.

H32/40: the propulsion and large-genset workhorse

At 320 mm bore and 400 mm stroke, the H32/40 bridges the gap between the H25/33 genset range and the larger propulsion engines. The in-line variant covers 3,000 kW to 4,500 kW; the V-configuration (H32/40V) extends the ceiling to around 10,000 kW. That upper end is relevant to OSV propulsion, ferry propulsion, and the electrical plants of large cruise ships.

The H32/40 and H32/40V appear frequently in offshore vessel applications, including offshore support vessels, platform supply vessels, and anchor handling tugs, where the combination of medium bore, moderate speed (720 to 750 rpm), and diesel-cycle reliability matches the duty cycle well. Eneti Inc. specified HiMSEN engines for its wind turbine installation vessels (WTIV), with each vessel carrying four units of 9H32/40 and two units of the smaller 7H21C, the engines powering both vessel propulsion and crane operations.

H35/40 and H35DF: the dual-fuel step

The H35/40 at 350 mm bore is the platform on which HHI built HiMSEN’s dual-fuel capability. The H35DF uses the same bore-stroke geometry but adds a gas-admission system that allows the engine to run on natural gas (from an LNG fuel system) with a small pilot diesel injection for ignition. In gas mode the H35DF operates on the Otto cycle; in diesel mode it falls back to conventional compression ignition.

The H35DF(V)P project guide (2023 edition) covers the propulsion-rated variant optimized for CPP installations. At 720 rpm, an in-line six-cylinder 6H35DF produces 3,060 kW and a nine-cylinder 9H35DF delivers 4,590 kW. V-configuration variants extend the output further. The engine uses an enhanced Miller cycle with optimized turbocharging to achieve lower SFOC and reduced NOx in both fuel modes.

The IMO Tier III NOx limit (MARPOL Annex VI Regulation 13) applies to vessels built after 2016 operating in Emission Control Areas. HHI-EMD meets this on H35DF installations primarily through the gas-mode combustion itself, which produces substantially lower NOx than diesel combustion, plus SCR for diesel-mode operation in Tier III zones.

H46/60: the large-propulsion engine

The H46/60 at 460 mm bore and 600 mm stroke is HiMSEN’s largest current production engine. At 514 rpm, the specific output per cylinder is approximately 1,080 kW in standard diesel variants. V-configurations using sixteen to twenty cylinders reach outputs between 15.6 MW and 26 MW, covering propulsion requirements for cruise vessels, large ferries, large OSV, and the upper end of specialist vessels.

At this bore size, HiMSEN competes with Wartsila 46F and MAN L48/60, both established large-bore four-stroke families with decades of service history. HiMSEN’s competitive position here is weaker than in the smaller genset segment because the alternatives have longer operational track records in the largest cruise and ferry applications, and because classification societies and owners are more conservative about large bore marine engines where failure consequences are severe.

Engine architecture

Trunk piston, four-stroke cycle

All HiMSEN engines are trunk piston four-stroke designs. The piston extends below the combustion chamber and connects directly to the connecting rod via a wrist pin, with no separate crosshead. This is the standard configuration for medium-speed four-stroke marine engines and contrasts with the crosshead arrangement used in the slow-speed two-stroke engines HHI-EMD also builds under licence.

The four-stroke cycle on the HiMSEN completes intake, compression, combustion, and exhaust over two crankshaft revolutions. This gives a power stroke on every other downstroke per cylinder, which is the reason a four-stroke at the same speed and bore produces roughly half the specific power of a two-stroke: you get one power stroke per two revolutions rather than one per revolution. However, the four-stroke compensates with lower exhaust temperatures, more room for valve and injection system engineering, and better part-load SFOC on the small-to-medium bore sizes most relevant to auxiliary genset duty.

High stroke-to-bore ratio and combustion pressures

The H21/32 has a stroke-to-bore ratio of 1.52, which is towards the long-stroke end for medium-speed engines. Long-stroke geometry reduces mean piston speed at the same engine rpm, which lowers cylinder wear rates and supports lower fuel consumption. HiMSEN engines are designed with maximum combustion pressures up to 200 bar and fuel injection pressures up to 2,000 bar (on common-rail variants), both high values for medium-speed engines and consistent with the push for lower SFOC and cleaner combustion.

The published compression ratio for the H21/32 is approximately 17:1. Combined with the high injection pressure and Miller-cycle timing on many variants, this supports NOx reduction at source, which reduces the size and cost of downstream aftertreatment systems.

Common rail fuel injection

Modern HiMSEN models use electronically controlled common rail injection. The high-pressure rail (typically 1,500 to 2,000 bar depending on model and mark) supplies fuel to each injector on demand. Electronic control allows variable injection timing, multiple injection pulses per combustion event, and precise cylinder-by-cylinder balancing. The practical effect on an auxiliary genset is more consistent power across varying load levels, which matters because a ship’s electrical load swings continuously as equipment cycles on and off.

Earlier HiMSEN models used camshaft-driven injection; the shift to common rail on newer marks is consistent with the progression seen across the industry as manufacturers sought lower NOx and SFOC.

Four-valve cylinder heads

HiMSEN uses four valves per cylinder: two intake and two exhaust. Four-valve heads give better breathing efficiency than two-valve arrangements, allowing higher volumetric efficiency at the same bore and enabling higher peak power densities. The four-valve layout also allows a central injector position, which improves fuel spray distribution across the combustion chamber.

Turbocharging

Single-stage turbocharging is standard across most HiMSEN bore sizes. V-configuration variants typically carry one turbocharger per cylinder bank. On the H35DF and other larger models, the turbocharger is matched to the Miller cycle timing: intake valve closing is advanced relative to bottom dead centre, which reduces the effective compression ratio and the in-cylinder temperature, cutting NOx formation without penalty to power output because the turbocharger makes up for the lost charge mass.

Electronic engine management

HiMSEN’s engine management system handles fuel injection timing, cylinder load balancing, speed governing, fault diagnostics, and alarm output to the ship’s integrated alarm management system. The system communicates with the vessel’s automation network via industry-standard protocols. For genset duty, tight speed governing is critical: the alternator frequency must stay within narrow limits (typically ±2.5% under sudden load changes) or the ship’s electrical network trips.

Genset and propulsion applications

Marine auxiliary gensets: the primary market

The largest share of HiMSEN production by unit count is auxiliary generating sets on commercial ships. An auxiliary genset pairs a HiMSEN engine with a marine alternator, usually through a flexible coupling, and runs at constant speed to generate the ship’s electrical power. The H21/32 dominates this segment, and its genset duty largely determines HiMSEN’s aggregate unit volumes.

A typical large tanker or bulk carrier carries three H21/32-driven gensets, each rated at 1,500 to 1,800 kW, sized so the vessel can run on two sets in normal service and maintain propulsion and essential loads on one set in an emergency. The constant-speed duty cycle suits the H21/32’s mechanical design and is far less demanding on engine wear than a propulsion duty cycle, which is part of why the engine has accumulated 15,000 total units across the fleet with strong reliability records.

For medium-sized gensets on larger vessels, including cruise ships, vehicle carriers, and LNG carriers, the H25/33 in in-line and V configurations covers the 2,000 to 6,400 kW range. Read the full field context in marine auxiliary engines and generators.

Propulsion on specialist and smaller vessels

HiMSEN enters the propulsion market on vessel types where a medium-speed four-stroke makes more sense than a low-speed two-stroke. The key candidates are:

Offshore supply vessels and OSVs: DP vessels running diesel-electric or diesel-mechanical propulsion with variable loads are a natural fit for H32/40 and H35 engines. Variable speed operation and the need for full electrical load on station make medium-speed engines with good part-load SFOC preferable to large two-strokes.

Ferries: Short, frequent voyages with many manoeuvers and high hotel loads suit the medium-speed four-stroke. HiMSEN H35 and H46/60 variants appear in European and Asian ferry propulsion plants.

Wind turbine installation vessels: Eneti’s WTIVs specified 4 units of 9H32/40 for vessel propulsion and crane power, plus 2 units of 7H21C as hotel/auxiliary sets per vessel, an arrangement where HiMSEN units do dual duty across a diesel-electric plant.

Smaller container feeders and general cargo: Vessels below roughly 5,000 DWT where a two-stroke would be oversized and a high-speed engine undersized can use H32/40 or H35/40 in direct-drive or geared-drive configurations.

On propulsion duty, HiMSEN engines typically connect to the propeller shaft through a reduction gearbox, since medium-speed engines run too fast for direct-drive on propellers of practical size. Controllable pitch propellers (CPP) are common in ferry and OSV applications, allowing speed control without changing engine rpm, which keeps the engine on its efficiency curve.

IMO Tier III compliance options

MARPOL Annex VI Regulation 13 sets three tiers of NOx limits for marine diesel engines above 130 kW. Tier I applies to engines built before 2011, Tier II to those built between 2011 and 2015, and Tier III to engines built from 2016 onwards and operating in designated Emission Control Areas (ECAs). Tier III limits are roughly 80% stricter than Tier II for the speed class most HiMSEN engines fall into (below 2,000 rpm).

HHI-EMD offers three technical paths to Tier III on applicable HiMSEN models:

Selective catalytic reduction (SCR): Urea is injected into the exhaust upstream of a catalyst bed, converting NOx to nitrogen and water. SCR can achieve 90%+ NOx reduction and is the most proven Tier III technology across the medium-speed sector. The Eneti WTIV engines (7H21C units) were ordered with SCR as the Tier III compliance method.

Exhaust gas recirculation (EGR): A fraction of exhaust gas is recirculated back to the intake, diluting the charge oxygen and reducing peak combustion temperature, which cuts NOx formation at source. EGR avoids the need for a urea consumable and associated storage, which is an advantage on vessels with limited tank space or infrequent port calls where urea supply may be inconvenient.

Charge Air Moisturiser (ChAM): This is HHI-EMD’s proprietary water-injection system, which injects fine water droplets into the charge air to lower combustion temperature and reduce NOx. It is specific to HiMSEN and uses the ship’s freshwater system. ChAM is simpler than SCR in terms of consumables but the NOx reduction is typically less than SCR’s 90% ceiling.

In gas mode, the H35DF and other dual-fuel variants achieve Tier III NOx levels without aftertreatment, because premixed gas combustion at Otto-cycle conditions produces far less NOx than diesel-cycle direct injection at the same power output. This is one of the reasons dual-fuel operation became commercially attractive in ECAs from 2016 onwards: LNG or methanol as the main fuel delivers Tier III compliance without the capital cost of an SCR system.

Dual-fuel and alternative-fuel development

H35DF: gas-diesel dual fuel

The H35DF was HiMSEN’s first dual-fuel engine. It burns natural gas supplied from an LNG fuel system in gas mode, with pilot diesel injection to initiate combustion, and can switch to full diesel operation without stopping the engine. The H35DF(V) in V-configuration extends the power envelope into ranges useful for ferry and larger OSV propulsion.

Gas-mode operation reduces SFOC on an energy basis versus diesel and cuts CO2 per unit output (since natural gas has a lower carbon-to-hydrogen ratio than fuel oil). In Emission Control Areas, gas-mode operation meets IMO Tier III NOx limits and eliminates SOx emissions entirely. Outside ECAs, dual-fuel engines still run on LNG where it is available and cheaper than fuel oil, with diesel as the fallback when LNG bunkering is not accessible.

H32DF-LM: methanol dual fuel for Maersk

HHI-EMD completed the Factory Acceptance Test of the H32DF-LM methanol dual-fuel HiMSEN engine in December 2022, with Maersk as the shipowner present at the Ulsan test facility. The engine is rated at approximately 5,400 bhp in genset configuration and operates on high-pressure direct-injection methanol with a pilot diesel ignition charge. This mirrors the diesel-cycle combustion approach rather than Otto-cycle premix, which allows methanol operation at the same compression ratio and injection timing as diesel and avoids the methane-slip characteristic of gas-mode four-stroke operation.

The first vessel to carry a commercial methanol HiMSEN engine was the 2,100 TEU container ship built by Hyundai Mipo Dockyard for Maersk, the world’s first methanol-fuelled container ship. The H32DF-LM delivers a genset function on that vessel rather than direct propulsion, supplying electric power for a diesel-electric drive system.

HD Hyundai subsequently signed a deal for 16 sets of methanol-fuelled HiMSEN engines, reflecting order book depth as the methanol-powered container ship sector expanded. Maersk’s methanol feeder programme alone accounts for multiple sets. Methanol HiMSEN engines also passed ethanol full-load testing, since ethanol and methanol have similar combustion characteristics at high injection pressure.

H22CDF-LM: small-bore methanol dual fuel

The H22CDF-LM (220 mm bore, methanol dual-fuel) completed its Type Approval Test on 19 to 22 March 2024. Seven class societies signed off: ABS, Bureau Veritas, DNV, ClassNK, Korean Register, Lloyd’s Register, and RINA. Rated at 1,440 kW to 2,160 kW depending on cylinder count, the H22CDF-LM targets container feeders, tankers, and bulk carriers as a methanol-capable auxiliary genset, extending methanol HiMSEN availability down the vessel-size scale. HD Hyundai described the H22CDF-LM as the world’s first methanol engine in this bore class to achieve seven-class approval simultaneously. In 2024 the methanol HiMSEN engine was named one of Korea’s Top 10 Mechanical Technologies, recognition from the Korean engineering community for the combustion and materials engineering required to handle methanol’s corrosive properties at high injection pressure.

H22CDF-LA and H32CDF-LA: ammonia dual fuel

Ammonia carries no carbon, so its combustion produces no CO2, making it one of the most discussed alternative fuels for the IMO’s 2050 decarbonization target. It also produces no SOx. The challenge is that ammonia combustion produces elevated NOx compared to diesel and has a slow flame speed that demands specialized combustion engineering.

HHI-EMD developed the H22CDF-LA as the world’s first high-pressure direct-injection ammonia dual-fuel engine in the small-bore class. The engine uses liquid ammonia injection (not premix) and a pilot diesel charge for ignition, the same approach as the methanol LM variants. HHI-EMD was preparing to launch the H22CDF-LA commercially from mid-2024 after completing initial engine testing.

The H32CDF-LA extended this technology to a larger bore. Based on the H32C diesel platform with a 320 mm bore, the H32CDF-LA produces a maximum output of 5.4 MW. It completed a type approval test campaign at Ulsan from 29 September to 2 October 2025, attended by representatives of seven class societies: ABS, Bureau Veritas, ClassNK, DNV, Korean Register, Lloyd’s Register, and RINA. Lloyd’s Register issued the first type approval. The H32CDF-LA is the world’s first marine engine above 5 MW to hold ammonia dual-fuel type approval from all seven major class societies simultaneously. HHI-EMD noted that the H32CDF-LA reduces NOx and addresses ammonia slip through aftertreatment, but the specific NOx reduction pathway is subject to ongoing regulatory interpretation as the IMO develops its NOx framework for ammonia-fuelled engines.

The ammonia as marine fuel article covers the wider safety, bunkering, and regulatory context for ammonia propulsion.

Production scale and the HD Hyundai context

Cumulative milestones and production rates

HiMSEN production milestones as reported by HD Hyundai Heavy Industries Engine & Machinery:

• March 2001: Commercial launch with H21/32 and H25/33
• 2002: Type approvals from seven major class societies
• July 2000: First successful engine test run (pre-launch development)
• 2011: HHI stops producing licensed four-stroke auxiliary engines; HiMSEN replaces the entire line
• 2016: Cumulative production reaches 10,000 units
• 29 January 2024: Cumulative production reaches 15,000 units

The 15,000-unit milestone was marked with a ceremony at the Ulsan facility. Production went from 10,000 to 15,000 units in eight years, implying an average of roughly 625 units per year over that period, though actual annual rates vary with the shipbuilding cycle.

The H21/32 accounts for the largest share of that cumulative count because it is specified on virtually every HHI-built commercial ship as an auxiliary engine and is also exported widely. Larger engines (H32/40, H35, H46/60) add fewer units annually but represent more production value per engine.

HD Hyundai corporate context

HiMSEN was developed inside Hyundai Heavy Industries and has moved with that company through subsequent restructurings. The parent group reorganized in 2017 into HD Korea Shipbuilding & Offshore Engineering (KSOE) as the intermediate holding for the shipbuilding and engine operations. The engine division operates as HD Hyundai Heavy Industries Engine & Machinery and maintains the Ulsan site, which houses both the low-speed two-stroke assembly halls (for licence-built MAN B&W and WinGD engines) and the HiMSEN four-stroke production and test facilities.

The co-location matters commercially. An engine that ships a few metres across a yard to a hull being assembled carries no freight cost and no transit time. For HHI’s own ship orders, specifying HiMSEN as the auxiliary engine is a straightforward decision: comparable or better reliability than European alternatives, Korean pricing, and integration within the same corporate supply chain. That captive demand floor is structurally unavailable to European competitors bidding for the same slots.

The division’s claim to be the world’s largest medium-speed marine engine maker by unit count rests primarily on the H21/32 volume. Whether that claim holds by installed kilowatts rather than units depends on how V-configuration Wartsila and MAN B&W large-bore output is counted across their respective licensee networks.

Export reach

HiMSEN engines operate in more than 60 countries. Export customers include Chinese shipbuilders (a significant volume), European yards building OSVs and ferries, and specialist builders of research vessels, naval auxiliary ships, and offshore units. The 60-country figure counts end-user and flag-state geography rather than shipyard geography: a HiMSEN engine built at Ulsan, assembled into a ship at a Chinese yard, and operated by a Greek owner under a Maltese flag counts against three geographies but one export transaction.

Competition and commercial position

HiMSEN’s direct competitors in the marine medium-speed segment are:

Wartsila: The W32, W34DF, W31, W46F, and W50DF families cover comparable bore ranges. Wartsila has deeper penetration in cruise ships and is the dominant supplier in the high-power medium-speed segment above 10 MW. HiMSEN’s pricing is generally competitive with Wartsila’s equivalent bore classes, and Korean yards prefer HiMSEN for in-house commercial vessel gensets.

MAN Energy Solutions: The L21/31, L32/40, L32/44CR, and L48/60 families from MAN (the Holeby heritage line plus the Bergen acquisition) compete directly. MAN’s Holeby L23/30H has a long installed base in the auxiliary genset segment that HiMSEN has targeted. MAN’s larger engines (L48/60 and above) have the same market overlap as H46/60.

Caterpillar-MaK: The M-series (M43C, M46DF, M20C) targets similar offshore and ferry applications in the medium and large bore range.

Daihatsu and Yanmar: Japanese small-bore medium-speed engines compete in the H17/28 and H21/32 equivalent classes for smaller vessels.

HiMSEN’s competitive advantage concentrates in three areas: captive demand from HHI’s own yards, pricing in export markets where there is no royalty burden, and the dual-fuel and alternative-fuel roadmap that lets owners specify a methanol or ammonia engine from a single Korean supplier. The weakness is in applications where Wartsila or MAN has very long installed base track records with specific vessel classes, particularly large cruise ships and high-power ferries, where owner engineering departments are conservative about changing engine suppliers.

The marine engine makers article covers the wider competitive structure of the four-stroke medium-speed sector.

HiMSEN in the alternative-fuel transition

The series of dual-fuel and alternative-fuel developments described above reflects a deliberate positioning strategy. HHI-EMD has sequenced: diesel only (2001), LNG/diesel dual-fuel (H35DF), methanol/diesel (H32DF-LM in 2022, H22CDF-LM with class in 2024), and ammonia/diesel (H22CDF-LA from 2024, H32CDF-LA with seven-class approval in 2025). Each step shares the trunk-piston four-stroke platform; only the fuel admission and safety systems change substantially.

The methanol variants address the growing order book for methanol-fuelled container ships, where large operators including Maersk have committed to ordering methanol-capable newbuilds. The H32DF-LM and H22CDF-LM position HiMSEN as a supplier into that segment, particularly for genset duty on diesel-electric methanol vessels and for propulsion on smaller methanol-fuelled feeders.

The ammonia variants address a longer time horizon. Ammonia-fuelled vessels are not in large-scale commercial service as of 2025, but class societies, shipowners, and flag states are building the regulatory framework. Having a type-approved ammonia engine is a prerequisite for any owner who wants to order an ammonia-fuelled vessel, so the H32CDF-LA’s seven-class approval positions HHI-EMD for orders once the commercial and bunkering infrastructure matures.

The methanol as marine fuel and ammonia as marine fuel articles give the wider regulatory and bunkering context for each of these fuels.

Limitations

The following caveats apply when using HiMSEN technical data from any source, including this article:

Performance data is mark-specific. HiMSEN engine marks change over the product life. An H21/32 built in 2005 has a different SFOC, NOx profile, and injection system from one built in 2023. Always refer to the project guide for the specific mark and model being evaluated.

Dual-fuel SFOC figures depend on gas fraction. In gas mode, published SFOC values assume a specific gas-to-pilot-diesel ratio. Real-world operation varies with load, gas quality, and engine condition. CO2 reduction from dual-fuel operation depends on the well-to-wake carbon intensity of the gas supply, which varies by source.

Alternative-fuel type approvals do not equal commercial orders. The H32CDF-LA received type approval in 2025, but type approval is a regulatory certificate confirming the engine can meet class requirements, not evidence of volume production or commercial availability. Actual vessel orders using ammonia HiMSEN engines had not been publicly announced as of the date of this article.

Market share figures are builder claims. HHI-EMD’s descriptions of HiMSEN as the world’s largest medium-speed marine engine brand by unit count are corporate claims, not third-party-verified market data. The claim is plausible given the H21/32’s volumes on HHI-built hulls, but direct comparison against Wartsila or MAN unit counts is not supported by publicly audited data.

Bore and stroke figures across publications vary slightly. Some sources list the H25/33 with a 330 mm stroke; others round to 330 mm or list 325 mm. Use the manufacturer’s project guide for a specific engine as the authoritative reference.

Four-stroke medium-speed engines are not suitable for all vessel types. The choice between a slow-speed two-stroke main engine and a four-stroke medium-speed alternative depends on vessel size, propeller design, power requirement, and space constraints. HiMSEN’s propulsion models are best suited to vessels below roughly 15,000 DWT or specialist applications (OSV, ferry, cruise) where diesel-electric or geared-drive arrangements are preferred. Very large ships almost universally use slow-speed two-stroke main engines because of the direct-drive efficiency advantage. See medium-speed four-stroke marine engines for the selection criteria.

See also

• HHI-EMD (Hyundai Heavy Industries Engine & Machinery Division)
• Medium-Speed Four-Stroke Marine Engines
• Marine Auxiliary Engines and Generators
• Trunk Piston Engine Architecture
• Four-Stroke Marine Diesel Engine Fundamentals
• Methanol as Marine Fuel
• Ammonia as Marine Fuel
• Marine Engine Makers
• Wartsila 32 Medium-Speed Engine
• MAN L32/44CR Medium-Speed Engine

Related calculators:

• Auxiliary Medium-Speed Genset Calculator
• SFOC to Thermal Efficiency Calculator
• HiMSEN H21/32 Reference
• HiMSEN H25/33 Reference