* Disclaimer: I am an employee of Alphabet or one of its subsidiaries, but I do not work on this team, and didn't know anything about it prior to reading this article.
JP-7 has a very high ignition temperature (it was actually used as a coolant/heat sink for the rest of the aircraft), so TEB combusting once it hit the air is used to light the engines.
SR-71s only had a limited amount of TEB to use each flight. I believe it was 13 shots per engine. TEB was used each time the engines were lit and also when afterburners were lit. While the SR-71's routes were built around refueling, the number of TEB shots remaining were the true limiting factor of the SR-71's flight time.
Note: I'm not affiliated with Veertu, but I recently came across the product and found it very interesting. If you're interested in OS X's Hypervisor.framework, it was added as part of OS X Yosemite: https://developer.apple.com/library/mac/releasenotes/MacOSX/...