I don't think you can talk about the engines being the problem if the supposed alternative to kerosene-type fuels are methane and alcohol - the engines are prob

I don't think you can talk about the engines being the problem if the supposed alternative to kerosene-type fuels are methane and alcohol - the engines are probably the easy part of the problem there; it's the pressurization or cryogenic requirement for methane and the significantly lower (~half?) mass energy density for alcohol fuels.