THE emergence of LNG as a viable marine fuel in the 1990s represented the first step towards a new era of clean-burning fuels for ships.

In 2016, the WinGD X-DF dual-fuel, low-speed, low-pressure LNG marine engine entered the market. Since then, more than 400 engines have completed over 8.5m running hours of reliable operation, with a further 460 engines due to enter service.

The introduction of the X-DF engine was a game changer for the two-stroke, low-pressure engine market. Ships could now benefit from high engine efficiency with low overall capex. X-DF duly established market leadership in the LNG carrier segment, which is particularly sensitive to system capex, but also in other merchant sectors.

At around the same time, high-pressure engine manufacturers were also introducing dual-fuel equivalents claiming lower CO2 equivalent emission levels, albeit with higher investment and operating costs and — often overlooked — higher harmful local emissions such as NOx, sulphur and particulate matters.

With the latest innovations, X-DF engines are no longer competing with other low-pressure models, or solely on capex with high-pressure engines; instead, they reach overall emissions levels similar to their high-pressure counterparts while retaining a capex advantage. 

Step-by-step advances

The first improvement came in 2020 with the introduction of a second-generation X-DF engine technology, X-DF 2.0. Intelligent Control by Exhaust Recycling (iCER) technology enables enhanced combustion control using inert gas. As a result, in gas mode the X-DF 2.0 reduces energy consumption by 3% and in diesel mode, fuel consumption is lowered by up to 5%.

The improved combustion control also offered a vast reduction in methane slip, which occurs when some of the methane in LNG fails to burn during combustion and escapes into the atmosphere. X-DF2.0 technology delivered a reduction of up to 50%, resulting in methane emissions below 1% of energy consumed.

Combined with the ability to further reduce NOx emissions — with even Tier III achievable in diesel as well as gas modes — this technology represented notable progress in creating more sustainable shipping operations.

Variable Compression Ratio: In 2023, WinGD introduced its Variable Compression Ratio technology. Potential fuel and emissions savings from VCR are in the range of 3% in gas mode and up to 6% in diesel mode, further extending the X-DF advantage. Just one year after its introduction, VCR uptake speaks for itself. WinGD has secured more than 100 orders, coming from most of the LNG newbuildings ordered in the past year as well as from containerships, bulkers and car carriers.

Comparisons undertaken by WinGD highlight the impact that these advances have had when applied to the well-proven X-DF engine concept. In the LNG carrier sector, X-DF has extended its advantage over other low-pressure concepts, with X-DF powered vessels recording lower fuel consumption — meaning lower fuel spend and emissions — as well as competitive capex. The benefits are amplified when considered against the rare application of high-pressure engines on LNG carriers.

Outside of the LNG carrier sector, the latest X-DF engines are also competitive with the more widely deployed high-pressure engines, as illustrated in the case of a pure car and truck carrier. WinGD’s advances in reducing methane slip and improving fuel consumption mean that overall emissions are lower than for high-pressure engines.

X-DF has come a long way in eight years. The engine platform has been firmly established as a leader in important vessel segments — notably 100% of the LNG carrier newbuilding market in 2024, Step by step, X-DF is improving its attractiveness as a mainstream LNG dual-fuel solution. WinGD continues to improve the concept, with the aim of delivering the benefits of low-pressure, dual-fuel engine technology to the wider maritime market as it strives for a more sustainable future.