I thnk you have a great idea here. Have you thought about reshooting it? Maybe a bit tighter on the composition and darken the rest of the area to make the spark plug and spark stand out? I see some noise which makes me thing that you boosted the exposure or used the shadow/highlight tool. EIther way that did leave you a little flat on the lighting.
Still even with all of this I don't think you deserved your sub 4 score.
Let me know if you ever try this one agan, I would like to see it.
the spark of the plug that ignites the gas that drives piston that spins the wheel of civilization. The spark of life. I like the metaphor, but I'm an engineer. I doubt most people will have no idea of what this is.