NIIGATA Power Systems Co., Ltd., (Niigata) received an order for the first unit of the new dual fuel engine 6L28AHX-DF from Keihin Dock Co., Ltd., used as the main engine for the LNG-fueled tugboat built by NYK Lines, which runs either on diesel fuel or liquefied natural gas (LNG). The tugboat is the first ship fueled by LNG in Japan other than the LNG carrier, and the order for the engine is the first gas engine for marine application in Japan.

The 28AHX-DF is a dual fuel engine that has diesel and gas fuel operation mode. The engine was developed as a medium-speed marine engine to meet the environmental regulations of the International Maritime Organization (IMO) Tier III NOx regulations by using gas fuel. NOx emissions are reduced by approximately 75% from the previous IMO Tier II compliant engines of Niigata, and the environmental impact is reduced substantially.

This is a gas engine leading the industry developed to operate with a direct connection to the fixed pitch propeller (FPP) with comparable load-following capability from the diesel engine, which has been a problem in gas operation. This engine is used as the prime mover of the 360-degree steerable Z-Peller propulsion system with more than 4000 units delivered, which has expanded the lineup of environmentally friendly products from Niigata for use principally in tugboats and offshore support vessels.

Advantages of 28AHX-DF engine are as follows.
(1) Quick start up in gas operation
Quick acceleration from startup to 100% load operation is an important factor for the marine engine. It was understood that the gas engine is not as good as the diesel engine for load increase rate. The load increase rate of the AHX-DF in gas operation is substantially improved and comparable with the diesel engine.

(2) Switching between gas operation and diesel operation possible at any time from startup to 100% load operation
Conventional dual fuel engines switching between gas operation and diesel operation was only possible when the engine ran below 80% load. In the case of the AHX-DF, switching of operation mode is possible at 100% load, which allows continued safe ship operation by switching the operation mode in an emergency.

(3) Stable operation during rapid load increase in gas operation
It was understood that stable ship operation was difficult with a gas engine due to possible abnormal combustion during rapid load increases. Technologies to control abnormal combustion of gas engine generator sets developed by NPS are used in the AHX-DF to reduce abnormal combustion during rapid load increases.

(4) Allows selection of suitable operation mode depending on the sea area
The dual fuel feature of the AHX-DF allows flexible selection of operation mode: gas operation in sea areas where IMO Tier III NOx regulations apply and diesel operation in other sea areas. This makes compliance with IMO Tier III NOx regulations with reduced fuel consumption.

28AHX-DF

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