Army testing fire resistant fuels for combat vehicles.

• Author: Schmitigal, Joel A.
• Position: Army Technology

Fuel fires in combat vehicles have long been a difficult if not impossible problem to resolve.

In response to the growing threat of roadside bombs to military vehicles and troops, the Army currently is working on various projects to develop a fire resistant fuel.

Over the past decades, the Army has conducted research to make diesel fuel resistant to unwanted fire. This research involved a variety of approaches to reduce the flammability of diesel fuel.

The compression ignition or diesel engine which powers a large percentage of the Army ground vehicles has a fuel delivery system that returns a portion of the fuel from the injectors back to the fuel tank. This recirculation heats the fuel--typically raising the temperature of the fuel in the tank to above its flash point, and making it more susceptible to being ignited.

This heating, when combined with any direct or indirect ballistic penetration near the fuel tank or fuel line, significantly increases the potential for a catastrophic fire. Having a fuel that would not ignite under these conditions would have obvious benefits.

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Researchers evaluated emulsified fuel, halogenated additives, antimisting additives, and water-in-fuel microemulsions, with the latter showing the most promise. In a water-in-fuel microemulsion, the individual water droplets are completely surrounded by the fuel.

The fire resistant fuel that was developed--referred to as fire-safe fuel--was a clear to hazy microemulsion consisting of water, emulsifier premix (equal amounts of the emulsifier and an aromatic concentrate), and diesel fuel. This microemulsion performed satisfactorily both in diesel and turbine engine systems and could be easily prepared in the field.

Although it did not eliminate the initial mist fireball that occurs when a projectile impacts the vehicle, it significantly reduced the fuel fire threat by retarding the flame spread rate and self extinguishing any spilled fuel, which eliminates residual pool burning.

One problem with this approach was that the purity of the water that is needed for ensuring a stable microemulsion was considerably lower than the purity of the water typically generated by the Army's purification units.

Eventually, the urgency for the development of a fire-safe fuel diminished, and funding was discontinued.

With the start of the conflicts in Iraq and Afghanistan, attention again returned to the fuel fire threat as improvised explosive devices began to take...