The RS-68 is a LOX/LH2 engine. As part of the launch sequence, a fair bit of hydrogen is run through the engine, prior to actual ignition to cool down pumps, components, etc and condition the engine. The SSME (Space Shuttle Main Engine, RS-25) does the same thing.
With the D4H however, there is sufficient hydrogen run through, that at ignition, it ignites, and actually starts an awesome to see fire, running up the sides of the core modules, and the insulation on the outside gets quite charred.
In order to minimize this they have tried to start one engine first, then the other two, so as to burn off some of the hydrogen first.
Thus my question. On the Space Shuttle, there are sparklers that ignite as the SSME's go through their conditioning cycle to burn off the excess hydrogen gas. Why not use the same on the D4H launches?