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Thu, Sep 19, 2002

'Apple Jelly' Fuel Contaminant Identified

A team of investigators headed by Southwest Research Institute (SwRI) has identified the cause of a long-standing jet fuel contamination problem.

SwRI scientists traced the dark, gelatinous material, frequently called "apple jelly," to an anti-icing additive that becomes a potent solvent when mixed with water.

The military, particularly the U.S. Air Force, has struggled with jelly-like contaminants in fuel-handling systems for almost 50 years. Despite studies to isolate its cause, the problem has persisted, becoming a maintenance nightmare. Although the substance has been found in aircraft wing tanks, it is not believed to have caused any engine failure or crashes.

In 2001, the Defense Energy Support Center (DESC), the federal agency responsible for procuring and distributing fuel to the Department of Defense, asked SwRI to determine what apple jelly was, how it forms, and how it can be prevented or reduced.

After a year-long study, Institute scientists determined that apple jelly is caused by diethylene glycol methyl ether (DiEGME) interacting with water and other fuel system contaminants. DiEGME, an anti-icing inhibitor added to JP-8 jet fuel, prevents free water in a plane's fuel system from freezing at high altitudes. SwRI demonstrated that apple jelly is a complex mixture with varying viscosity, color, and other properties.

The term probably dates to the middle 1980s when a presentation to a subcommittee of the American Standards of Testing and Materials referred to a contaminant found in the Alberta Products Pipeline (APPL) as "APPL jelly." Since that time, the name has evolved to apple jelly and has been applied to a range of contaminants found in aviation fuel-delivery systems.

"After DiEGME joins with water, it forms a very aggressive solvent," explained Program Manager Steve Westbrook, manager of the Petroleum Products Technology section in SwRI's Engine and Vehicle Research Division. "When added to the fuel, DiEGME combines with free water and then reacts with dirt, rust, paint, fuel components, elastomers, and other contaminants in pipelines and fuel storage tanks. The resulting DiEGME-based mixture, with varying viscosity, color, texture, and appearance, is frequently identified as 'apple jelly.'

"When this blend reacts with polyacrylate polymers used to manufacture water-absorbing fuel filters used in some military fuel-handling systems, it forms the thick, gooey, sticky substance known as 'thick apple jelly.'"

SwRI headed a team that included Consulting for Energy Efficiency and Environmental Excellence (C4e) and Martin & Associates. The team conducted 31 onsite military base visits and examined 139 samples of apple jelly, fuel, and other types of samples related to apple jelly contamination.

To help prevent the contamination, SwRI recommended improved fuel-handling procedures and facilities designed to remove water from the fuel-distribution system and to ensure proper mixing of additives in the fuel.

FMI: www.desc.dla.mil/DCM/DCMPage.asp?LinkID=DESCPublications

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