How does petrol damage the fuel pump?

The pump is an extremely sensitive precision instrument that gets the fuel
up to about 1800 bar. This is a VERY high pressure. Putting the wrong fuel
it will seriously throw the pump off balance.

Note that on a common rail engine, getting the pump up to pressure is much
more important to starting than glow plugs. The high pressure and efficiency
of atomisation means that common rail engines need very little temperature
to start, and may not even have glow plugs at all. However, they won't work
properly until the pressure has stabilised, so still need a head start,
unlike a petrol engine.

Christian.