Luke Scharf wrote:

Steve wrote:

But there are more and more small diesels that run just as fast as
gasoline engines. There's no fundamental limit thats any different
than a gasoline engine, really, but up until now there's not been a
demand for high-RPM diesels.


When I was reading about the Volkswagen TDI engine, I vaguely remember
coming across someone who said that the redline of that engine was set
by the speed which which the burning fuel expanded.

Sounds rather fundamental to me - but, then again, I'm a computer guy.

-Luke

In almost ALL real-world engines, the actual limit is set by the point
at which some mechanical component would fail. The engine's torque *may*
drop off well before the mechanical failure point if it can't ingest
enough fuel or air at high speed. In the case of a diesel, you can
pretty much increase the burn rate to as high as the mechanical parts
can tolerate by increasing turbocharger boost (and injection rate to
match). Since detonation isn't possible (no fuel exists in the cylinder
until combustion is supposed to begin anyway) the only limits to boost
pressure are mechanical in nature. In practical terms, no one really
wants or needs a 9000 RPM diesel, though.