RE: Tiny Long Lived Diesel Engine?
I have some background with this sort of thing. The first question is how much power do you need? You have to look at your application to see if it makes sense. If sunlight is available, solar might be a better choice. If you're camping for a few days or even a week, there are probably better choices, maybe even just batteries. If you'll be off grid for a month it would be worth considering a generator if solar doesn't make sense.
Cell and iPod charging is a couple watts. If the engine makes 40-50W and 80-90% is wasted the overall fuel conversion will be less than 1% and you'll have much more headache than bringing a large LiIon pack to charge from.