Two-stroke low-speed marine engines are direct-coupled crosshead diesels that still power nearly all deep-sea cargo ships, with the largest unit rated 75,570 kW. Three designers, Everllence, WinGD and J-ENG, now sell LNG, methanol and ammonia variants, and the first ammonia-fuelled two-stroke ships entered service in 2026.
What it is and how it works
A two-stroke low-speed marine engine is a crosshead diesel that fires once per revolution, runs at roughly 80 rpm and is bolted directly to the propeller shaft. This architecture powers almost every container ship, bulk carrier, tanker and gas carrier in deep-sea trade. The largest example, the 11-cylinder MAN B&W G95ME-C9.5, is rated 75,570 kW and entered service in 2016 on a 19,437 TEU container ship. The G95 delivers 6,870 kW per cylinder at 80 rpm and 21 bar mean effective pressure, as MarineLink reported. A 1995 technical abstract indexed by TRID states that two-stroke marine diesels exceed 50% thermal efficiency; no current OEM percentage could be fetched during this research, so treat that figure as historical.
Three designers share the market: Everllence (formerly MAN Energy Solutions, renamed in 2025), WinGD of Switzerland and Japan's J-ENG, which builds the Mitsubishi UE lineage in its own factory.
Why it matters now
Efficiency gains in mature diesels are now incremental. The G80ME-C10.5 upgrade reduced specific fuel oil consumption by 2 g/kWh across the load range, roughly a 1% improvement, as Veus Shipping reported. The bigger lever is fuel switching, and every alternative fuel reaches the deep-sea fleet first as a two-stroke variant. Everllence's dual-fuel two-stroke portfolio (ME-GI methane, ME-LGIM methanol, ME-GIE ethane, ME-LGIP LPG and ME-LGIA ammonia) passed 2,000 cumulative orders in 2025, up from 1,000 in November 2022. The demand backdrop is LNG-heavy: DNV data show 275 alternative-fuel ships ordered in 2025, of which LNG took 188, methanol 61, ammonia 5 and hydrogen 4.
Key players and products
WinGD's low-pressure, lean-burn X-DF had more than 800 engines in service or on order and over 8 million running hours by December 2024, according to WinGD. The company claimed a 36% share of the global two-stroke market and 59% of the dual-fuel market by capacity at end-2020 (TradeWinds), and its CEO has claimed around 70% of LNG-fuelled propulsion; both are company claims. WinGD's X-DF2.0 variable-compression-ratio technology cut methane emissions by about 30% in shop tests and has passed 100 VCR orders, as Cyprus Shipping News reported.
Everllence's ME-LGIM methanol engine had more than 230 orders and over 600,000 methanol running hours by September 2025. WinGD's X-DF-M methanol platform had 56 engines on order and delivered the largest methanol engine built to date, a 10-cylinder 92-bore unit, in early 2025.
Figures that matter
An ME-GI LNG carrier burns about 100 t/day against 125-130 t/day for a comparable four-stroke DFDE plant, although an ABB study argues an optimised DFDE plant can beat a two-stroke mechanical solution. J-ENG's 7UEC50LSJA completed official tests in August 2025 with ammonia-mode thermal efficiency equal to or above HFO mode, NOx about half that of an HFO engine, near-zero unburned ammonia after SCR and more than 90% GHG reduction at 95% ammonia energy share, as Hydrocarbon Processing reported.
| Metric | Value | Source type | Source |
|---|---|---|---|
| Largest two-stroke rating (G95ME-C9.5) | 75,570 kW | trade-press | — |
| G95 output per cylinder | 6,870 kW at 80 rpm, 21 bar MEP | trade-press | MarineLink |
| Everllence dual-fuel two-stroke orders | 2,000+ cumulative | vendor | Everllence |
| WinGD X-DF engines in service or on order | 800+ (Dec 2024) | vendor | WinGD |
| ME-GI vs DFDE fuel use on an LNG carrier | about 100 vs 125-130 t/day | trade-press | — |
| J-ENG ammonia engine GHG reduction | more than 90% at 95% ammonia share | vendor | Hydrocarbon Processing |
| Alternative-fuel ship orders, 2025 | 275 (LNG 188, methanol 61, ammonia 5) | aggregator | DNV |
Developments 2023-2026
- January 2025: Everllence's full-scale ME-LGIA runs at 100% load for the first time (Everllence).
- Mid-2025: the X52DF-A, the first ammonia two-stroke to complete type approval and factory acceptance, is installed on Exmar's ships; the first vessel, Antwerpen, delivered in June 2026 (AJOT).
- April 2026: the first commercial 6G60ME-LGIA passes its factory acceptance test in South Korea (Turbomachinery Magazine); the 93,000 m3 VLAC Terra Clove is named at HD Hyundai in late October 2026.
- June 2026: WinGD's X72DF-A receives its first approval for a 210,000 dwt CMB.TECH bulk carrier and the X-DF-A orderbook rises to about 40 engines.
- 2026: J-ENG's 6UEC35LSGH, the first full-scale hydrogen two-stroke for an actual vessel, reaches at least 95% hydrogen co-firing with more than 95% GHG reduction in ClassNK-witnessed factory tests, for installation on a 17,500 dwt MOL ship from January 2027.
Outlook
Engine availability now runs well ahead of the ship orderbook. DNV counted only three ammonia-capable ships in the world fleet at end-2025 (Manifold Times), so near-term ammonia volume will come from gas carriers that carry the fuel as cargo. LNG two-strokes remain the volume product, methanol-capable tonnage keeps growing through 2027-2028 on orders already placed, and the next efficiency gains will come from methane-slip control and waste heat recovery rather than from the base diesel cycle.
