Niigata’s engine solves DF problems

Japan’s first vessel – apart from LNG carriers – to be powered by LNG will be driven by the first example of Niigata Power Systems’ 6L28AHX-DF dual-fuel medium speed engine. The vessel will be a tug operated by NYK Line on order at Keihin Dock (see also page 34).

The 28AHX-DF was developed to meet IMO’s Tier III NOx regulations. The enginebuilder reports that these emissions are about 75 per cent less than from its previous IMO Tier II compliant engines. Niigata has also overcome what it said had been problems with other gas engines.

“Quick acceleration from start-up to 100 per cent load operation is an important factor for marine engines,” it said. “The load increase rate of the AHX-DF in gas operation is substantially improved and comparable with the diesel engine,” it added, but did not include details about how this had been achieved.

It has, however, published some information about the engine’s stable operation during rapid load increases in gas operation, another of the benefits claimed for the engine. Rapid load increases can be a problem with gas engines because of possible abnormal combustion. Niigata had previously developed technology to control abnormal combustion in gas engine generator sets and has applied this to the AHX-DF.

Another feature that Niigata has cited is the engine’s ability to switch between gas and diesel operation at any point, from start-up to full load. With conventional dual-fuel engines, this is only possible when the engine is running at below 80 per cent load. The possibility of switching at any load “allows continued safe ship operation by switching the operation mode in an emergency,” it said.

It also makes it possible to switch between gas and diesel operation as the vessel moves in and out of areas where IMO’s Tier III regulations apply. MP