This fairly in depth but here goes
LPG has a calorific value of 46.1 MJ/kg and petrol is 45.8 MJ/kg so in weight has a higher value. However, its energy density per volume unit of 26 MJ/L is lower than that of petrol (about 0.5–0.58 kg/L, compared to 0.71–0.77 kg/L
This means we need to put more LPG in than petrol to make the same power
1) no we are putting in practaly the same energy (what is lost is the tiny amount of air lost that is replaced with the extra fuel)
2) see above
3) As the CR is the same for petrol and LPG no power is lost.
4) It is possible with some ECU's to advance the timing or it can be done via seperate processors. The gain is so small on LPG it is rare to be done but is essential with CNG
5) The power loss with mixers systems comes from teh restriction on teh air intake introduced by the LPG mixer
6) LPG could make a fraction more power at WOT but we are only talking a small amount. Where a higher CR would really come into play would be at part throttle and would make the engine more efficient with the higher effective CR under part throttle.
7) a) LPG does not need more advance but can use it
b) either way things will be slightly comprimised for one or the fuels. Either way the CR is striking a balance between part and full throttle. Timing advance for LPG is an option to get the most of what is there but the improvemnt is so small its bearly worth it. The advance that can be used is in mid range.
With LPG the engine will work perfectly fine under all conditions as it has been set for running petrol. With CNG that is not the case, it needs a lot more advance to run correctly
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