err diesel doesnt hold more energy than petrol, the reason they remap to more power is becasue of the turbo.
fuel burns from ignition, diesel needs compression to burn, you can put a naked flame out with diesel, try it with petrol, then run
its pure physics. diesel is squirted at a much higher pressure than petrol, as it needs this high pressure to combust (hence why diesels run at much higher temps than petrol), there efficiant, because the fuel is heavier (more dense, less needed for the equivalent petrol), and the cars rev lower.
diesels are tuned for torque, not power, hence why trucks use them, they need low end pulling power.
dieselis not physically more powerfull than petrol
you need twice as much (hence the density) to get the same bang from petrol, and it burns much much slower, hence the economy, if im wrong, then im wrong, but my dad worked with diesel engine for about 30 years, and it pure economy and torque, not power.