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December 1, 2009

Gas fuel options open up

Tightening emission regulations under the IMO Tier II & III and ECA zone implementations, and volatile fuel prices mean that ship owners and operators are facing serious challenges. One solution for complying with new environmental rules while maintaining cost-efficient operations is to use natural gas as a fuel.

Now Wärtsilä is making this option more feasible at the lower end of the power spectrum.

Its latest dual-fuel offering, the Wärtsilä 20DF engine, is a compact unit that brings the advantages of fuel flexibility to auxiliary applications, such as generating sets or as the prime mover in smaller vessels.

With the launch of the 20DF, Wärtsilä is extending the benefits of dual-fuel (DF) technology to cover the entire power range. Based on the well proven Wärtsilä 20 diesel engine introduced in the early 1990s the engine can be optimized for constant speed generating sets, as well as variable speed mechanical drives, for main engine applications.

Installed alongside Wärtsilä 34DF or 50DF main propulsion machinery, a Wärtsilä 20DF generating set completes the multi-fuel engine room concept. Compact and light, the Wärtsilä 20DF is intended for use in those vessel types where the Wärtsilä 20 is currently installed.

As well as being an ideal mechanical-drive prime mover in smaller applications, such as small cargo vessels, ferries or tug boats, it is also suitable for harbor generating set applications in a wide range of vessel types.

Main fuel flexibility

Fuel flexibility enables owners and operators to opt for the most suitable fuel, taking account local environmental restrictions, fuel price variations, and fuel bunkering availability. A unique feature of the Wärtsilä DF dual-fuel engines is their ability to run on Natural Gas, Marine Diesel Oil (MDO), Heavy Fuel Oil (HFO) and Bio Fuels, thereby providing maximum flexibility in fuel choice.

In marine applications, fuel flexibility also represents a significant safety feature. In the case of an interruption to the gas supply, Wärtsilä DF engines automatically switch to diesel operation without any loss in speed or power output. Single-fuel installations do not have this additional level of operational safety.

Keeping emissions under control

When a DF engine is running in gas mode, CO2 emissions are reduced by approximately 20% since natural gas has a lower carbon content than liquid fuels. The lean-burn combustion process employed means that NOX emissions are reduced by approximately 80%, while SOX emissions are completely eliminated as natural gas does not contain any sulphur. The production of particulates is practically non-existent as natural gas has virtually no residuals.

Lean-burn combustion technology results in extremely-low emission values and very-high engine efficiency. In this process, the combustion of a lean air-gas mixture is initiated by injecting a very small amount of MDO as pilot fuel. To obtain the best efficiency and lowest emissions, each cylinder is individually controlled to ensure operation at the correct air-fuel ratio, and with the correct amount and timing of pilot fuel injection.

Wärtsilä has further developed UNIC, an electronic control system that controls combustion in each cylinder, while ensuring optimal performance in terms of efficiency and emissions under all conditions. Stable and well-controlled combustion also contributes to less mechanical and thermal load on the engine components.

In gas mode, Wärtsilä DF engines are already compliant with the forthcoming IMO Tier III regulations without the need for any secondary exhaust gas purification systems. In liquid fuel oil mode, all Wärtsilä DF engines are fully compliant with the IMO Tier II exhaust emission regulations set out in Annex VI of the MARPOL 73/78 convention.

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