Successful tests of dual fuel LNG ship Wartsila engine
The LNG carrier is under construction at the French shipyard Chantiers de l'Atlantique for the Gaz de France. Due for delivery in 2004, it will be powered by four Wartsila 6L50DF dual-fuel engined generating sets which will meet all the ship's propulsion and shipboard electrical requirements. The Wartsila 6L50DF engines each develop 5,700 kW at 514 rev/min.
This will be the first LNG (liquefied natural gas) carrier to be powered by electric propulsion, and one of few to have internal-combustion engines instead of the more usual steam turbine plant.
The tests of the 50DF engine began in Finland early November 2002. The test program is designed to verify the functioning of the engine and for optimization of its performance. After thorough checks of all systems and running in, the initial data measurements were taken and the turbocharging system was optimized. The engine performance was then measured at steps from 15 to 100 percent load. Adjustment of all engine functions then followed, particularly for trip to diesel operation, transfer to gas fuel operation, load acceptance and load rejection. The engine was tested mostly on natural gas but it was also run on low heating value gas and on gas with a low methane number.
The factory acceptance test was witnessed by the shipowner, the ship operator, the shipbuilder and the classification society. The engine also successfully passed a type approval test witnessed by representatives from the classification society Bureau Veritas.
Both tests included operation on gas fuel and light fuel oil (LFO), with tripping to diesel operation, transfer to gas fuel operation, load acceptance, and load rejection. Again it was also run on low heating value gas and low methane number gas. An important aspect was that all safety systems were tested.
In August 2003, all four engines will be delivered to the shipyard for installation in the LNG carrier.
Technical background of the Wartsila 50DF engine
Compared with the alternative power plants, says Wartsila, 50DF engines have distinctive benefits in LNG carriers. While making maximum use of the gas fuel (boil-off from the cargo of liquefied natural gas) to develop useful power, the high efficiency of these engines calls for a much lower fuel consumption overall and thus lower operating costs than the conventional steam turbine plant. The Wartsila 50DF engines also have much lower stack emissions than a steam plant. Their low NOx emissions are about one-tenth those of the equivalent diesel engines. The combination of the engines' low fuel consumption and their maximum use of natural gas means the Wartsila 50DF engines also have low CO2 emissions.
Developed from Wartsila's successful type 46 diesel engines, the Wartsila 50DF engines have cylinder dimensions of 500 mm bore by 580 mm piston stroke. Available in configurations with six, eight and nine cylinders in line, and 12, 16 and 18 cylinders Vee-form, they develop 950 kW per cylinder MCR at 500 or 514 rev/min for 50Hz and 60Hz electricity generation respectively.
The Wartsila 50DF engines can be run alternatively in gas mode or liquid fuel mode. The engines are also fully capable of switching over from gas to liquid fuel (marine diesel oil) automatically should the gas supply be interrupted, while continuing to deliver full power.
Gas fuel is supplied at a low pressure (less than five bar) to the engines. In gas mode, the Wartsila 50DF engines operate according to the lean-burn Otto process. Gas is admitted into the air inlet channels of the individual cylinders during the intake stroke to give a lean, premixed air-gas mixture in the engine combustion chambers. Reliable ignition is obtained by injecting a small quantity of diesel oil directly into the combustion chambers as pilot fuel which ignites by compression ignition as in a conventional diesel engine.
The Wartsila 50DF engines use a "micro-pilot" injection with less than one percent of the fuel energy being required as liquid fuel at nominal load. Electronic control closely regulates the "micro-pilot" injection system and air-gas ratio to keep each cylinder at its correct operating point between the knock and misfiring limits.