ABSTRACT

The unavailability and cost of certain fuels commonly used by the U.S. Coast Guard sometimes promotes the use of alternative fuel choices to operate their gas turbine engines. This paper evaluates the effects of an alternative fuel on the Type II hot corrosion resistance of representative materials used in current gas turbine engines by the use of low-velocity burner rig (LVBR) tests. These materials consist of certain high-temperature nickel-based and cobalt-based alloys with an appropriate thermal barrier coating. Hot corrosion results using the alternative fuel were compared to LVBR hot corrosion tests using the preferred marine diesel fuel grade.

INTRODUCTION

The US Coast Guard (USCG) serves as the chief agency for the protection of life and property and enforcement of maritime laws on the high seas and navigable waters of the United States. The coast Guard has worldwide duties. Ice breakers clear clogged harbors on the North Atlantic and Alaskan coasts and on inland lakes, rivers, and canals. The Coast Guard locates icebergs in the shipping lanes of the North Atlantic and warns ships about them. The Coast Guard and the Navy work together in Greenland, Iceland, and other Arctic and Antarctic regions. The Coast Guard is heavily involved in enforcement of illegal immigration by sea and in interdiction of drugs into the United States. Its often unique maritime and enforcement responsibilities spread Coast Guard cutters and patrol boats to various ports and stations around the world.

To fulfill its mission, the Coast Guard has a fleet of several hundred vessels ranging from small patrol boats to 420-fft., 16,700-ton Healy class icebreakers. Various diesel and gas turbine engines power these ships. Because the Coast Guard often operates in lowly populated or remote areas around the world, USCG ships sometimes need to refuel where standard Navy fuel is unavailable. Typical Navy fuel is JP5 aviation turbine fuel covered by MIL-T-5624 specifications [1] and NATO F-76 Naval distillate fuel covered by MIL-F-16884J [2]. These fuels require separate storage facilities and transfer procedures and have specific physical and chemical specifications that promote long-term fuel stability for Naval gas turbines. These requirements necessitate storage at large depots to control costs. When Naval fuels are unavailable and to minimize operational impact, the USCG has sometimes resorted to commercial or Contract Marine Gas Oil (MGO) to continue its mission. Navy Purchase Description (NPD) MGO fuel is subject to standard commercial practice quality control rather than the extensive handling and storage requirements specified for MIL-SPEC fuels. There have been several reports that use of MGO has increased hot corrosion of gas turbine components and that it has limited physical stability. A conservative estimate of six weeks has been established for the complete use of MGO aboard USCG ships; this use limitation is viewed as operationally unrealistic. NATO F-76, on the other hand, has a historical storage life of 3 years before degradation. Three distinct mechanisms have been suggested for fuel destabilization: (1) biological contamination; (2) chemical destabilization of the fuel itself; and (3) potential for incompatibility when new fuel is mixed with remaining fuel in tanks. Any residual MGO in storage tanks can act as a catalyst to degrade new introduced fuel.

To increase fuel availability, the USCG is trying to define the operational and maintenance impact of using MGO versus NATO F-76 fuel. Detailed fuel requirements have been compiled by the various engine manufacturers especially for NATO F-76 and MGO fuels. Fuel usage rates, storage considerations, and purification capabilities hav

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