What are you trying to ignite? If you are trying to fire a auto spark plug, all you need is a mosfet and a coil. an arduino is capable of timing the spark, especially if you are reading a hall effect sensor off the cam. a water ignitor is a open flame ignitor, not a closed cylinder under compression ignitor.
Actually that is what they used to fire up the space shuttle engines but sometimes it wouldn't work so then the would send in a technician with a zippo lighter to get the shuttle going. The problem was they always had the replace the technician.
