[G00LA5H]

TEB to start up the engines, one at a time

TriEthylBorane used as a "starter" fuel for the SR-71 Blackbirds

The Engines used on the SR-71 were Pratt & Whitney J58s, these engines operated as 'turbo-ramjets' meaning that beyond a particular speed, the majority of the compression is achieved through the ramming of high velocity air into the front end of the engine where pressure recovery is achieved by those huge variable inlet cones.

Because of the fact that the aircraft flies supersonic-ally for the majority of its mission time, the engine and the air frame heats up greatly, the conventional JP-4 fuel used in military jets would vaporize and pressurize the fuel containers, creating fuel feed problems and all kinds of related mayhem, the JP-7 fuel used on the Blackbird has a much higher flash-point (auto ignition ) temperature, (and weight for weight happens to be as expensive as champagne). This solves one problem, but creates another.

At the speeds at which the SR-71 operates, lighting the afterburner has been equated to "keeping a candle lit in a hurricane". the higher boiling point of JP-7 keeps it from vaporising readily, and the exhaust velocity is pretty high, making sustained combustion problematic. A reliable method had to be found to ignite the excess fuel dumped into the combustion chamber, TriEthylBorane ignites spontaneously in contact with oxygen generating very high temperatures thus ensuring that the engine 'catches' on the first strike.

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