Don Stauffer wrote:


I wouldn't say the ENTIRE expansion phase. That would not be that great
for efficiency- sort of like a steam engine running with no cutoff. And
if one injects fuel into the cylinder at the instant just before BDC,
that fuel would be pretty much wasted. I was under the impression that
the cycle would look something like the steam (Rankine) cycle in that
the way Diesel envisoned it it would be either constant enthalpy or
constant pressure of part of the expansion phase, adiabatic during the
rest. The point where it changed would correspond to what would be the
throttle opening on a steam or SI engine. At full "throttle" the
changeover would be late in stroke, light load early in stroke.

True, although diesel engine manufacturers of late have discovered that
they can do things like reduce the injection flow rate instead of just
reducing injection duration. That has the nice side-effect of REALLY
quieting diesel "rattle" at light throttle openings, as most clearly
evidenced by the current Cummins diesel in the Dodge Ram. The flow
rate/duration combination can be played with to do really neat things to
the torque curve also. The stumbling block that prevented this for many,
many years was the camshaft-driven fuel injection pump, and its limited
ability to vary injection timing and volume. Once the move was made to
computer control and use of electronically controlled engine
oil-pressure activated unit injectors, a lot of possibilities opened up.