It's interesting that this card has generated this much discussion.
As the card is, I'd consider it underpowered. First of all, assuming you manage to get 1 out on the first turn with Momentum (2 card combo), over 10 turns you have dealt an average of 5.5 damage per turn, which will still leave the opponent with 45 health.
For an accelerator, it's quite slow. The condition for it to damage in order to grow seems good, but I'd probably increase it to +2 | 0 each time it triggers and the cost can stay. Even if the card were given Momentum and Quintessence, that would be a 3 card combo for something which Steam Machine can do with more potential.