Since 2005, dual-fuel (DF) engines have been the preferred method of propulsion for liquefied natural gas (LNG) carriers, and are the most suitable for powering vessels operating in emission-controlled areas (ECAs).
With 4,000,000kW of DF technology expected to be in operation by 2010, the Wärtsilä 50DF engine is becoming one of the company’s fastest-growing products. Its application in the marine market dates back to the first ‘dual-fuel–electric’ (DF-E) LNG carriers, the Provalys, Gaselys (155 K) and Gaz de France Suez Global Energy (75K), all of which were delivered at the end of 2006. These Gaz de France Suez vessels have pioneered DF propulsion in the LNG shipping market, and have set a trend that, since then, has essentially been followed by all major players.
The Gaz de France Suez Global Energy has already completed more than 154 loaded voyages without suffering any delays, and the total fleet of LNG carriers propelled by Wärtsilä 50DF engines has, during this time, increased to 27 units, with 29 to be delivered in 2010–2011. In this context, Wärtsilä has been able to attain significant knowledge and experience as a result of the approximately 1,000,000 running hours so far accumulated by its 50DF engines in the marine market.
One of the reasons for the strong success of 50DF-based propulsion over the other alternatives is the superior propulsion efficiency of this solution. It quickly became apparent that the savings delivered by DF-E propulsion are even greater than was anticipated. In addition, the flexibility of a multiple-engine installation has proved to be even more advantageous in the current volatile marine market. Slow steaming does not affect the very high level of propulsion efficiency that is a feature of the 50DF. The benefits to owners and charterers operating DF-E LNG carriers have continued to increase, thereby emphasising even more the advantage over other alternatives.
Nevertheless, this success has not deterred Wärtsilä from further developing its DF technology, concept and related products. This engine improvement process has introduced the following features:
- Additional temperature sensors were added to the comprehensive electronic monitoring system mounted on the Wärtsilä 50DF engine in order to control the big end bearing lube oil temperature. These sensors are based on wireless technology and give the operator a better overview of the engine’s working parameters, adding accuracy to any needed root-cause analysis.
- Following the International Maritime Organization (IMO) guidelines on air pollution, Wärtsilä was able to fulfil the Tier II requirements regulating nitrogen oxide (NOx) emissions by introducing only small modifications to the engine parameters, such as:
- engine output increased to 975kW/cylinder;
- fuel consumption in gas mode remained constant; and
- engine efficiency improved by 1% (above 48%).
The combination of reduced NOx emissions, constant fuel gas consumption, better efficiency and an increase in power output represents a remarkable achievement.
The new W20DF, W34DF and W50DF engines are equipped with cylinder pressure sensors that monitor and control the combustion process of every cylinder independently. This technology represents the state of the art in combustion control. Previously, other engine parameters were utilised in order to control the combustion process, such as the cylinder exhaust gas temperature. Nowadays, the combustion pressure is directly measured and the working parameters are adjusted accordingly. This feature is already reaping operational benefits, since low load operation has historically been restricted for safety reasons. Operations below 15% of engine load were not allowed, due to the fact that a possible incomplete combustion could have led to a direct bypass of unburned gas to the exhaust stacks.
With the cylinder pressure sensors, the DF engines can run in gas mode without any restrictions, throughout the entire range of loads. Additionally, the improved availability of data promises beneficial repercussions for maintenance, reducing time and cost expenditures.
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