What exactly are you trying to say? One strikes up a conversation.

Instead of "spark up", "burning like a fiery geyser" could work. Some other possibilities only really work in the past tense. There were many of us - ignited like a fiery geyser. There were many of us - extinguished like a fiery geyser. Aflame, ablaze? Since there aren't so many geysers of any kind in North America (and probably England too), we tend to say "went up in flames" as in a house that went up in flames. When we talk about people getting burned to death, the word "scorched" could work. But I suspect the simile is about the sudden, tragic, painful death of so many rather than the notion that they literally burned to death. "There were many of us - lives that went up in flames" would be my choice, although I have no clue of the actual meaning of the original. I am better with headlines than poetry :>)

You definitely can use spark up in other contexts - it’s maybe less normal, but still. I sometimes hear people say spark up in the context of smoking