HiMSEN: Hyundai Medium-Speed Marine Engines

HiMSEN (Hi-touch Marine & Stationary ENgine) is the four-stroke medium-speed engine family designed and built by HD Hyundai Heavy Industries’ Engine & Machinery Division (HHI-EMD) and headquartered at Ulsan, Korea. HHI’s 2026 HiMSEN program lists diesel, LNG dual-fuel, spark-ignition gas, methanol and ammonia engines from the 170 mm bore H17/28 to the 540 mm bore H54DF, with single-engine outputs from 575 kW to 22,500 kW in the program tables. The first engine ran in July 2000, production began in August 2000, and HHI counted its 15,000th HiMSEN on 29 January 2024. Propulsion ratings carry a P in the model name. Any HiMSEN designation, including V, propulsion and fuel suffixes, can be decoded character by character with the marine engine model decoder, and the HiMSEN section of the decoder reference sets the grammar beside the other makers'.

How HHI-EMD designates a HiMSEN engine

A HiMSEN model number gives the cylinder count, then H, then the bore and stroke in centimeters, then letters for configuration, application and fuel. The key on page 11 of HHI’s 2026 program reads 18 H 32 / 40 _ V P - LM: 18 cylinders, HiMSEN, 32 cm bore, 40 cm stroke, a type position left blank for a plain diesel, vee, propulsion, liquid methanol.

The V comes after the bore and stroke (16H32/40V), never before it as in MAN’s 12V32/44CR. On the newer types the stroke disappears from the name: the H21C has a 330 mm stroke, but nothing in 7H21C says so.

Real designations from HHI’s program and news releases decode like this:

• 6H21/32: 6 cylinders, in-line, 210 mm bore, 320 mm stroke, diesel generator rating.
• 9H32/40P: 9 cylinders, in-line, 320 by 400 mm, propulsion rating.
• 12H32/40VP: 12 cylinders, vee, 320 by 400 mm, propulsion.
• 7H21C: 7 cylinders, Clean platform, 210 by 330 mm. Eneti specified two per wind turbine installation vessel in 2022.
• 6H22CDFP-LM: 6 cylinders, 220 mm bore Clean dual-fuel platform, propulsion rating, liquid methanol.
• 9H32CDF-LA: 9 cylinders, 320 mm bore Clean dual-fuel platform, liquid ammonia.
• 12H54DFV TSTC: 12 cylinders, 540 mm bore, dual fuel, vee, with two-stage turbocharging (TSTC, a separate token in HHI’s tables).

Older and informal forms

HHI’s 2010 catalog used a different key: 6 H 21 / 32 (M), (P), (S), where the bracketed letter gave the application: marine generator set, propulsion or stationary generator set. Nameplates and technical files from that era therefore carry strings such as 6H21/32P or 9H25/33(M). The M is ambiguous today because the 2026 program has a separate six-cylinder model called the H21M. Two H17/28 sub-variants, the H17/28E and H17/28U, appear in the 2026 program as six-cylinder planning products; HHI doesn’t expand the letters.

Engineers also write the brand in front, as in “HiMSEN H21/32” or “HiMSEN Diesel Engine H21/32”. The brand words carry no engineering information, and the decoder strips them before parsing.

HiMSEN engine program by bore and stroke

The table below lists every model in HHI’s 2026 program, with its highest standard rating per cylinder. Three models, the H21/32V and the gas engines H17/24G and H35/40GV, appear only in the 2010 catalog and are marked legacy. The engine output column is HHI’s quoted power range for each model across all its cylinder counts and speeds, so it isn’t the rating column multiplied out: the higher ratings apply only at the top speeds and, for the H17/28, H21/32 and H25/33, only to some cylinder counts.

Several designations that circulate in databases and older references don’t appear in either HHI program: H22/26, H27/38, H35/40 as a diesel, H46DF and H46/60DF. A diesel engine of 350 by 400 mm has not been offered; that geometry belongs to the H35DF and the H35G gas engines. Treat any of these strings on a document as a transcription error and confirm against the engine’s EIAPP certificate.

H17/28: the smallest generator engine

The H17/28 is a generator engine only in the 2026 program, with no propulsion rating. Its standard rating is 120 kW per cylinder at 1,000 rpm (115 at 900), and the higher power rating of 125 kW per cylinder applies to six to eight cylinders. That gives 575 kW for a five-cylinder set at 900 rpm and 1,000 kW for eight cylinders. The 6H17/28E (660 kW) and 6H17/28U (805 kW) are fixed six-cylinder ratings listed beside it.

H21/32, H21C and H21M: 210 mm bore generator engines

The H21/32 is HiMSEN’s 210 by 320 mm diesel and HFO engine, built mainly as a generator set. At 720 or 750 rpm, for 50 Hz and 60 Hz generators with eight- and ten-pole alternators, it carries 160 kW per cylinder as standard and 175 kW on the higher rating. At 900 or 1,000 rpm the figures rise to 200 and 220 kW. Five to nine cylinders give 800 to 1,980 kW per set. The propulsion version, H21/32P, is rated 200 kW per cylinder at 900 rpm for six to nine cylinders.

The H21C is not a revised H21/32 block. It has a 330 mm stroke against 320 mm, carries 240 kW per cylinder at 900 and 1,000 rpm, and covers 1,200 to 2,160 kW. HHI’s history page records the type approval test of the “HiMSEN H21C CLEAN Engine” in August 2015. The H21M is a single six-cylinder model at 800 or 960 kW at 720 rpm and 1,050 to 1,320 kW at 900 rpm.

H25/33 and H25/33V

The H25/33 passed its type approval test in October 2002, according to HHI’s 2001 to 2010 history. In-line versions run six to nine cylinders at 720, 750, 900 and 1,000 rpm, from 240 kW per cylinder at 720 rpm to 330 kW at 1,000 rpm, a band of 1,440 to 2,970 kW. The H25/33P propulsion rating is 290 kW per cylinder at 900 rpm, 1,740 to 2,610 kW.

The V version extends to twelve through twenty cylinders. Its marine and offshore generator rating is 340 kW per cylinder (4,080 to 6,800 kW); the stationary rating is 320 kW per cylinder (3,840 to 6,400 kW). HHI records an inclination type approval for the H25/33V in May 2013.

H32/40, H32/40V, H32C and H32CV

HHI began the type approval test of the H32/40 on 4 December 2006 and announced it in January 2007 as the fourth HiMSEN model. It is rated 500 kW per cylinder at 720 and 750 rpm, 3,000 to 4,500 kW in-line; the H32/40V, type tested in December 2008, covers twelve to twenty cylinders and 6,000 to 10,000 kW. Propulsion versions (H32/40P, H32/40VP) carry the same 500 kW per cylinder at 750 rpm.

The H32C is the Clean successor, lengthened to a 450 mm stroke and rated 600 kW per cylinder at 720 and 750 rpm: 3,600 to 5,400 kW in-line and 7,200 to 10,800 kW for the H32CV. The propulsion rating of the H32C is based on two-stage turbochargers. The H32C platform is also the base for the H32CDF-LA ammonia engine.

Offshore construction is one documented application. In February 2022 HHI announced that Eneti had selected HiMSEN engines for its wind turbine installation vessels: six engines per vessel, four 9H32/40 and two 7H21C, supplied with SCR units, powering both the vessel and its cranes.

H46/60 and H46/60V

The H46/60 is the largest diesel HiMSEN. In the 2026 program it appears with propulsion ratings only: the H46/60P at 1,250 kW per cylinder at 600 rpm (7,500 to 11,250 kW for six to nine cylinders) and the H46/60VP at the same per-cylinder figure for twelve, sixteen and eighteen cylinders (15,000 to 22,500 kW). A stationary H46/60V is listed at 1,150 kW per cylinder.

HHI’s November 2010 H46/60V brochure gave a different picture: twelve to twenty cylinders, 1,200 kW per cylinder at 500 and 514 rpm, 1,300 kW per cylinder at 600 rpm, a 50-degree bank angle, a maximum firing pressure of 250 bar, and 26,000 kW for the twenty-cylinder engine. HHI ran the H46/60V type approval test in March 2013. Engines built to the earlier ratings can still be in service, so the rating on the engine’s own technical file governs.

Dual-fuel LNG: H35DF, H27DF, H22CDF and H54DF

The H35DF was the first dual-fuel HiMSEN; HHI’s history dates its type approval test to November 2012. In gas mode it burns low-pressure natural gas ignited by a diesel pilot; it can switch to diesel at load. The generator rating is 480 kW per cylinder at 720 and 750 rpm (2,880 to 4,320 kW in-line, 5,760 to 9,600 kW in the H35DFV), and the propulsion rating is 500 kW per cylinder at 750 rpm (3,000 to 4,500 kW in-line, 6,000 to 10,000 kW in V form).

The H27DF followed with its type approval test in September 2014, at 270 by 330 mm and up to 310 kW per cylinder at 1,000 rpm. The H22CDF is the small-bore Clean dual-fuel engine, 215 kW per cylinder at 900 rpm and 220 kW at 1,000 rpm.

The H35CDF is the newest LNG dual-fuel HiMSEN. HHI ran its type approval test from 21 to 23 September 2026 at its Engine Techno Center, with KR, ABS, BV, DNV, ClassNK, Lloyd’s Register and RINA attending. HHI describes it as built on HiMSEN’s second-generation Clean engine platform from the H35DF’s technology, with variable valve timing to control the charge air, for lower fuel consumption and less methane slip than earlier models. HHI has not yet published its stroke or ratings, so it isn’t in the program table above; the 35 in the name gives a 350 mm bore under HHI’s designation key.

The H54DF is the largest HiMSEN of any type: 540 by 600 mm, 1,400 kW per cylinder at 600 rpm, 8,400 to 12,600 kW in-line and 16,800 to 22,400 kW for the twelve- to sixteen-cylinder H54DFV with two-stage turbocharging. HHI’s history describes its development in September 2019 as “the world’s most powerful HiMSEN Engine”. HHI announced on 23 January 2025 that the first factory acceptance test, of a 6H54DF for an Excelerate Energy floating storage and regasification unit, was complete; the test ran at HD Hyundai’s Yeongam engine works. HHI’s dual-fuel product page quotes 26,460 kW for the H54DFV, above the 22,400 kW in the program tables; the program figure is the one tied to a stated cylinder count and speed.

Methanol and ammonia: the LM and LA engines

The liquid-fuel engines inject methanol or ammonia at high pressure with a diesel pilot. The H32DF-LM completed its factory acceptance test at Ulsan on 15 December 2022 with Maersk attending. HHI reported the test unit as a 5,400 bhp generator set, and the first unit went to the 2,100 TEU container ship built by Hyundai Mipo Dockyard for Maersk. HHI reported 50 engines for 13 vessels on order by January 2023, and 352 H32DF-LM engines ordered and built by October 2024.

The H22CDF-LM extended methanol to the 220 mm bore. Its type approval test ran from 19 to 22 March 2024 with KR, ABS, BV, DNV, ClassNK, Lloyd’s Register and RINA, at 240 kW per cylinder and 1,440 to 2,160 kW. In October 2024 HHI announced a contract for 18 units of the 7H22CDF-LM for six 2,400 TEU container ships built by Huangpu Wenchong Shipbuilding for Evergreen. A month later the methanol HiMSEN was named among Korea’s Top 10 Mechanical Technologies.

The H22CDF-LA burns ammonia at the same bore and rating as the H22CDF-LM. It passed a type approval test from 30 September to 2 October 2024 and received approval from seven class societies. The H32CDF-LA, on the H32C platform, followed with its classification approval test from 29 September to 2 October 2025, again with KR, ABS, BV, DNV, ClassNK, Lloyd’s Register and RINA in attendance, at up to 5.4 MW. The 2026 program lists no propulsion version of the H32CDF-LA. The wider fuel-handling and safety picture is in methanol as a marine fuel and ammonia as a marine fuel.

Spark-ignition gas engines

The G engines burn gas alone with spark ignition and are sold mainly for power plants. The current H35G and H35GV run 480 kW per cylinder at 720 rpm and 500 kW at 750 rpm; the H54GV with two-stage turbocharging spans 16,800 to 22,400 kW. The 2010 catalog’s H35/40GV (480 kW per cylinder, methane number 73) and the H17/24G (91 kW per cylinder at 1,000 rpm, 110 at 1,200 rpm) are their predecessors; HHI dates the H17/24G’s development to November 2007.

Output intensity: BMEP and mean piston speed

Brake mean effective pressure lets a 170 mm and a 540 mm engine be compared on one scale. It is the cylinder’s brake work per cycle divided by its swept volume; for a four-stroke engine, which fires once every two revolutions, $k = 2$:

For one H21/32 cylinder the swept volume is $\frac{\pi}{4} \times 0.21^2 \times 0.32 = 0.01108\ \text{m}^3$. At 220 kW and 1,000 rpm:

The same arithmetic on the 2010 H46/60V rating of 1,200 kW per cylinder at 514 rpm gives 28.1 bar. HHI’s brochure prints 28.1 bar, though against the 600 rpm column; its own power-density row matches 28.1 bar at 514 rpm, so the printed BMEP row is shifted by one column. The BMEP calculator runs the sum for any engine.

Mean piston speed is the average speed of the piston over a stroke:

The gas-burning engines (H27DF, H35DF, H54DF) run 4 to 5 bar lower BMEP than the diesels of similar size. The C platforms buy their extra output mostly from stroke: the H21C gains 9 percent over the H21/32 at the same speed by adding 10 mm of stroke and 1.4 bar of BMEP. Mean piston speed for any engine can be checked with the mean piston speed calculator.

HiMSEN beside MAN and Wärtsilä engines of the same bore

HiMSEN, MAN and Wärtsilä all build medium-speed engines near 210, 320 and 460 mm bore, and their designations look alike on a nameplate. The table sets the HiMSEN models beside the MAN (Everllence Marine Engine Programme 2026) and Wärtsilä (product guides) engines of the same class. BMEP and mean piston speed are computed from each maker’s own rating with the formulas above.

The H21/32 and the MAN L21/31 share a bore and a rating; the HiMSEN’s extra 10 mm of stroke gives it a larger swept volume and so a lower BMEP for the same 220 kW. At 320 mm the Wärtsilä 32 extracts 580 kW from the same 320 by 400 mm cylinder that the H32/40 rates at 500 kW, which is 4.0 bar more BMEP. HHI’s answer to that gap is the H32C: it doesn’t raise the BMEP of the 400 mm stroke engine but adds 50 mm of stroke and reaches 600 kW, the same figure as MAN’s L32/44CR.

The designations differ in three ways that matter when reading a plate. MAN writes the configuration letter before the bore (9L21/31, 12V32/44CR); HiMSEN writes it after (12H32/40V). Wärtsilä gives the bore alone (9L32, 16V46F). And both MAN and HiMSEN use centimeters with a slash, so 21/31 and 21/32 differ by one digit and one maker letter. The engine model decoder reference sets out every maker’s grammar.

Development timeline from HHI’s records

HHI’s own history pages and the HiMSEN story page give the following dated milestones:

HHI puts the HiMSEN research and development period at ten years and the investment at more than 100 billion won. Before HiMSEN, HHI’s engine business built two-stroke and four-stroke engines under license, and it still builds two-strokes to the designs of Everllence (MAN B&W) and WinGD; the HHI-EMD article covers that corporate history, and the Hanwha Engine article covers the other Korean licensee.

Engine architecture

Every HiMSEN is a trunk-piston four-stroke: the piston drives the connecting rod through a gudgeon pin with no crosshead, which keeps the engine short enough to sit on a common bedplate with its alternator. The four-stroke cycle gives one power stroke per cylinder every two revolutions, which is why the $k = 2$ factor appears in the BMEP formula above, and why a medium-speed engine needs far more cylinder-revolutions than a slow-speed two-stroke to deliver the same power.

Stroke-to-bore ratios across the range run from 1.11 on the H54DF to 1.65 on the H17/28. The longer ratios of the small engines keep mean piston speed near 10 m/s at 1,000 rpm; the large engines run shorter ratios at 600 rpm and reach 12 m/s. The four-stroke fundamentals article explains the scavenging, valve-timing and turbocharging trade-offs common to all engines in this class.

Two-stage turbocharging is the one architectural feature HHI writes into the designation, as the TSTC token on the H54DFV and H54GV. It also underlies the H32C propulsion rating. The V engines in the 2010 H46/60V brochure use a 50-degree bank angle; HHI’s 2026 program doesn’t restate that angle for the current V models.

Generator and propulsion ratings

HHI publishes separate ratings for generator sets and for propulsion, and the difference matters when a figure is lifted from a datasheet. A generator rating is a constant-speed rating at 720 or 750 rpm (for 60 Hz and 50 Hz with ten and eight poles) or at 900 or 1,000 rpm (eight and six poles). A propulsion rating, marked P, is given at one speed and in HHI’s words is “based on CPP constant speed operation”; for a fixed-pitch propeller the program tells the buyer to contact HHI-EMD.

That distinction shows in the numbers. The H35DF is 480 kW per cylinder as a generator and 500 kW as a propulsion engine. The H25/33 reaches 330 kW per cylinder as a 1,000 rpm generator but 290 kW at 900 rpm as the H25/33P. A load or fuel-consumption calculation should use the rating that matches the duty; the medium-speed auxiliary engine calculator and the SFOC to thermal efficiency calculator both take the rated output as an input. The auxiliary engines and generators article covers how a ship’s generator plant is sized.

Sizing a HiMSEN generator plant: a worked example

The speed of a generator engine is fixed by the frequency and the alternator’s pole count, $n = 120 f / p$. That is why HHI rates its generator engines at four speeds: 720 rpm drives a ten-pole alternator at 60 Hz, 750 rpm an eight-pole alternator at 50 Hz, 900 rpm an eight-pole alternator at 60 Hz and 1,000 rpm a six-pole alternator at 50 Hz. The choice of speed changes the rating per cylinder, so it changes how many cylinders a set needs.

Take a 60 Hz ship whose electrical load at sea is 2,400 kW, with three generator sets sized so that any two carry the load. Each engine has to deliver at least 1,200 kW plus the alternator’s losses. HHI’s 2026 ratings give these candidates:

The six-cylinder H21/32 at 900 rpm leaves 120 kW above the requirement for alternator losses and margin, on the higher power rating that HHI offers for six to nine cylinders. The seven-cylinder engine at 720 rpm fails the test: HHI’s table gives 1,164 kWe at the alternator, below the 1,200 kWe each set must carry, although its piston speed is 20 percent lower. The five-cylinder H21C meets 1,200 kW exactly at the engine and leaves nothing for alternator losses, so in practice the H21C answer is a six-cylinder 6H21C at 1,440 kW. The H25/33 carries the largest margin at the lowest BMEP but brings a 250 mm bore engine into a plant that a 210 mm bore engine can serve.

The arithmetic is the total output formula the decoder applies, $P = n_{cyl} \times P_{cyl}$; the medium-speed auxiliary engine calculator takes the next step to load factor and fuel.

Fuels available at each HiMSEN bore

The 220 mm and 320 mm bores are the only ones offered on three fuels, and they are the two bores HHI chose for its methanol and ammonia engines.

NOx limits under MARPOL Annex VI Regulation 13

Every HiMSEN above 130 kW installed on a ship is certified against the NOx limits of MARPOL Annex VI Regulation 13, and the limit depends on the engine’s rated speed $n$. For engines between 130 and 2,000 rpm, Tier II allows $44 \cdot n^{-0.23}$ g/kWh and Tier III allows $9 \cdot n^{-0.2}$ g/kWh. Tier III applies inside an emission control area designated for NOx: to ships constructed on or after 1 January 2016 in the North American and United States Caribbean Sea areas, on or after 1 January 2021 in the Baltic Sea and North Sea areas, and, under MEPC.392(82) in force from 1 March 2026, on or after 1 January 2025 in the Canadian Arctic area. In the Norwegian Sea area, also designated by MEPC.392(82), Tier III applies to ships with a building contract placed on or after 1 March 2026, a keel laid on or after 1 September 2026, or delivery on or after 1 March 2030. A North-East Atlantic ECA has been proposed and is not yet adopted.

The Tier III limit is roughly a quarter of the Tier II limit at every HiMSEN speed. HHI’s program states Tier III compliance in gas mode for its dual-fuel engines; for diesel operation the documented route is SCR, as on the engines supplied for the Eneti vessels and on the H22CDF-LA. The Regulation 13 article covers certification under the NOx Technical Code, and the SCR article covers the aftertreatment. Where the ships trade is set out in emission control areas.

Production volume and market position

HHI’s production milestones are the firmest figures on HiMSEN’s scale: 10,000 engines in March 2016 and 15,000 on 29 January 2024. That is 5,000 engines in just under eight years, an average of about 630 a year.

HHI’s own pages give two different measures of reach. The HiMSEN story page cites “6,000 MW Total Capacity of 60 Countries”; the product pages cite “550 clients from 43 countries”. They measure different things, installed capacity by country against client count by country, and neither is independently audited. The story page also claims a 28 percent share of the four-stroke engine market and describes licensing of HiMSEN “engine blueprints”, including a joint venture in Saudi Arabia, SEMCO. Treat the share figure as HHI’s claim.

The competing medium-speed programs cover the same bores under different grammars, which is why a nameplate is easy to misread. MAN’s L21/31 and L32/44CR, Wärtsilä’s W32 and W46F, and Caterpillar’s MaK M-series all sit in HiMSEN’s bore range; see the MAN L21/31, MAN L32/44CR, Wärtsilä 32 and Wärtsilä 46F articles, and the marine engine makers overview. The medium-speed four-stroke article explains when a ship uses a medium-speed engine for propulsion rather than a slow-speed two-stroke.

Reading a HiMSEN nameplate in the field

A surveyor or superintendent identifying a HiMSEN usually has the model string, the serial number and the rated output on the plate, and the EIAPP certificate in the technical file. Four checks catch most errors:

1. Confirm the units. The digits are centimeters. A plate reading H21/32 is a 210 mm bore engine, not 21 mm, and a record that says otherwise has been transcribed from the wrong convention.
2. Check the cylinder count against the range. In-line HiMSEN engines run five to nine cylinders; V engines twelve to twenty. A 16H32/40 without a V is a typing error.
3. Match the rating to the duty. A P engine’s rated output is a propulsion rating; a generator datasheet for the same bore will show a different kW per cylinder.
4. Look for the stroke. If the model has C, DF, CDF or G after the bore, the stroke isn’t in the name. Look it up in the program: the H21C, H22CDF and H32C strokes differ from older engines with the same bore.

The marine engine model decoder applies these checks and flags a cylinder count that the program doesn’t list.

Limitations

The ratings here are the 2026 program’s. HHI has re-rated models over time, and it announces new models such as the H35CDF before their ratings appear in the program; the H46/60V moved from 1,300 kW per cylinder at 600 rpm in 2010 to 1,250 kW in the 2026 propulsion tables. An engine’s own EIAPP certificate and technical file give the rating it was certified at, and that is the figure for any compliance or load calculation.

The highest rating isn’t the usual one. The table gives each family’s highest standard per-cylinder rating. Many engines are sold at the standard rather than the higher-power rating, or at 720 or 750 rpm rather than 1,000 rpm.

HHI’s web pages and program tables disagree in places. The H54DFV is 22,400 kW in the program and 26,460 kW on the dual-fuel product page; the reach figures are 60 countries on one page and 43 on another. This article uses the program tables where a cylinder count and speed are stated.

Older HiMSEN data is reproduced from HHI documents found outside HHI’s own site. The 2010 catalog and the November 2010 H46/60V brochure figures (H21/32V, H35/40GV, H17/24G, the 514 rpm H46/60V rating) come from copies of HHI documents rather than from hyundai-engine.com.

Fuel consumption isn’t covered. HHI’s program gives SFOC per model and load point; this article doesn’t reproduce those figures, and they depend on the fuel, the Tier III arrangement and the ambient conditions defined in ISO 3046-1.

See also

• Marine engine model decoder calculator
• Marine engine model decoder reference: HiMSEN
• 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
• MARPOL Annex VI Regulation 13 NOx tiers
• Methanol as a marine fuel
• Ammonia as a marine fuel
• LNG as a marine fuel
• Marine engine makers

Related calculators:

• Marine engine model decoder
• BMEP calculator
• Mean piston speed calculator
• Medium-speed auxiliary engine calculator
• SFOC to thermal efficiency calculator