(09-09-2013, 03:04 PM)Dum-Dum Wrote: Why though, surely denser fuel is more effieient?
Diesel has to heat up to burn when it reaches the cylinder, it doesn't just explode like petrol with a spark, theres a time delay before this happens, if the fuel is already hotter, that time delay is shorter, so it burns quicker and more efficiently. Denser fuel also doesn't atomise as well when it's injected, which is necessary for complete combustion.
Think about what happens when you start a diesel without glow plugs - cold cylinder, only part burnt fuel and poor efficiency. Runs like crap until it heats up a bit. It's the same effect.