The down side is capacitors charge so slow each cylinder will need probably 60 capacitors charging so they can discharge in, 1, 2, 3, order each time the piston is in the firing position. My capacitor bank is 3 caps in parallel, 5000 VDC 18,000. amps each = 54,000. amps total = 270,000,000. watts discharge. These 3 caps weight close to 100 lbs total. A vehicle will need to pull a 100 ft trailer full of capacitor but this could be done with a stationary engine with a building full of capacitors. Experimenting will be required to determine minimum capacitor size and water injection into a insulated discharge cup. RPM of the engine will be determined by the number of capacitors being charged. My cap bank takes about 40 seconds to charge, 60 caps charging will allow the piston to fire 1 time per second = 60 RPMs. When my capacitor bank discharges it will vaporize 4 ft of solid 1/8" diameter steel wire, it flashes as bright as the sun and sounds like as 30-06 rifle. A much smaller cap bank can be used to vaporize 1 or 2 drops of water for each cylinder.
I had a used 5000w airport runway landing light this cap bank flashed it 1 time the entire light bulb vaporizes even the glass was gone.
View attachment 131954