Progress on gas-fuelled two-strokes

MAN’s GI-fitted ME research engine MAN’s GI-fitted ME research engine

The pressure to find alternative fuels, driven by both emissions legislation and the resulting commercial pressures that threaten to drive up the cost of low-sulphur fuel oils, is impacting on the low speed engine market.

Both of the main engine designers are addressing this question by developing large dual-fuel two-stroke designs. According to one, Wärtsilä, finding a single solution that can ensure compliance with impending SOx and NOx limits has so far proven to be elusive.

The company believes it has found an answer to IMO Tier III NOx regulations, starting in 2016, and the 2015 imposition of 0.1% SOx limits in ECAs. Wärtsilä’s ‘single solution’ to the two differing requirements is based on dual-fuel low-pressure gas engine technology. The company ways it has demonstrated that there will be no requirement for additional equipment, such as exhaust gas after treatment (catalytic reduction and sulphur scrubbers), to meet Tier III NOx regulations while running on gas. And for operation in ECAs, running on gas will satisfy the sulphur limits without recourse to costly distillate fuel, which currently carries a cost premium of 50% over high sulphur bunker fuel.

As well as offering ship operators an alternative solution to costly bunker fuel bills while fulfilling the emission regulations, Wärtsilä says its dual-fuel engine installations offer sought-after flexibility, allowing operators to switch between gas and residual or distillate fuels, depending upon price and bunkering availability. Despite the infancy of LNG bunkering, its longer term potential is becoming increasingly clear. As a result, the development of the LNG bunkering infrastructure will support organic growth until the use of LNG as a fuel becomes widespread practice. According to Wärtsilä, this is being demonstrated by many proposals for new LNG bunkering stations in northern Europe.

Natural gas is the alternative fuel offering the greatest potential considering the upcoming environmental regulations. Wärtsilä believes natural gas shows the greatest potential of all alternative fuels, and points to its record of over 6 million running hours in both land-based and marine applications with medium speed dual fuel engines and its experience of dual-fuel LNG carrier engines since 2005.

In late 2010, Wärtsilä initiated a major project to extend its leadership for dual-fuel engines by adapting the low pressure gas engine technology to the low-speed engine portfolio. A new RTX-5 test engine (based on a commercially available six-cylinder RT-flex50 engine) was installed in the Trieste engine laboratory in Italy in March 2011. This has demonstrated that low-speed engine performance can fully comply with Tier III NOx limits while operating on gas.

Wärtsilä plans to make its low pressure two-stroke gas engine technology available for commercial use from 2014.

High pressure GI engines

MAN Diesel & Turbo, meanwhile, favours the high-pressure gas injection solution for its low speed dual-fuel engines. The company believes that this offers certain benefits compared with other dual-fuel low-speed engine technologies, such as no power reduction, no methane slip, and no knocking. MAN cites 10 years experience operating a 12K90MC-GI-S engine in a power plant application using the same basic technology developed for its current ME-series engines.

Test results from the company’s research engine are said to show that engine performance is identical running on gas or oil fuel, and the expected efficiency improvement on gas has been confirmed. Operating on gas, NOx has been reduced by 30%, well below Tier II requirements, with the highest reduction at high engine loads. By tuning the engine for optimum SFOC, it is possible to achieve reductions in SFOC of 3.1, 5.7 and 1.9g/kWh at 75%, 50% and 25% engine load respectively, with a slight NOx penalty below about 70% load but a significant improvement in NOx at full load. Methane slip is restricted to 0.2g/kWh at 25% to 100% load, resulting in a reduction in global warming potential of about 20% for the ME-GI. To meet Tier III NOx limits with the ME-GI it will probably be necessary to employ exhaust gas recirculation (EGR).

As a result, the ME-GI add-on platform is being made available for all ME engine types.

Two MAN Diesel licensees, Hyundai Heavy Industries in Korea and Mitsui Engineering & Shipbuilding in Japan, have announced projects where existing S70ME engines are being converted to gas injection (GI) operation for demonstration purposes. HHI said its engine was expected to start running in November 2012, with the MES engine coming on stream a few months later.

MAN Diesel regards these licensee initiatives as acknowledgement of customer interest in the ME-GI engine for new projects. Ole Grøne, senior vice president low-speed promotion & sales says: “It is immensely encouraging that some of our biggest licensees, based in the greatest shipbuilding countries in the world, are showing such tangible interest in this gas engine.”

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