[pontifier]

I've often wondered if "gravity feed" might be an option. In a tall liquid fueled rocket, Gravity, then thrust, could create arbitrarily high pressures at the nozzle if the column of fuel is tall enough.

[mateo1]

Well, I guess is is possible, but to get 100 bar at 1g you need a 1km+ column. At higher accelerations though it's not such a bad idea.