Consider this when setting the pop pressure, fuel setting and timing of the IP. Lately, there has been alot of post's/discussion on this.
This is my theory of how a Diesel engine should work... I'm certainly not a Diesel Engineer, and my Math may be off. As the saying goes, For 20 yr I can't say en gin near now I are one.
The 7.3 IDI is basically a square stroker. Bore 4.110" Stroke 4.180" Gasser's are short stroker's. Bore is larger than stroke.
Timing is set at 2000 RPM. At that RPM you have 2000 RPM / 60 Sec. = 33.3 RPS / 8 = 4.1625 / 2 = 2.08 #1 cyl. fires every 2.08 seconds.
I assume its set there because the max torque is between ~1800 and ~2000 RPM.
If the timing is set at 8.5* to 9.5* BTDC. The piston @ (8.5*) is .084 (thousands) from TDC when fuel is injected at the recommended 1850 PSI. The burn starts immediately, the full load of injected fuel is in micro seconds. At 8.5* fuel injection starts at ~.023 (thousands) of a second BTDC, The IP injection curve effects the length of time of injection. Injector nozzle size and IP fuel setting determines fuel quantity injected. When the piston reaches half stroke upward it slows down due to the throw of the crank, and for an instant stops as it goes over TDC, then gains speed Of course the fuel continues to burn until the exhaust valve opens at ~ BDC. The Cam grind profile determines when and how long the valves open and close. Just imagine how fast the valves have to actuate. That leaves ~1 second for power stroke and ~1 second for exhaust stroke.
By setting an increase of fuel from the IP more than can be burned in ~1second, that would produce black smoke.
Black smoke is ignited but not fully burned. Waste of power and fuel.
White smoke is when the fuel does not ignite at all, but just heated close to autoignition point
Diesel fuel flash points vary between 52 °C and 96 °C (126 °F to 204 °F). Diesel is designed for use in a high-compression engine. Air is compressed until it has been heated above the autoignition temperature of diesel; then the fuel is injected as a high-pressure spray, keeping the fuel-air mix within the flammable limits of diesel. There is no ignition source. Therefore, diesel is required to have a high flash point and a low autoignition temperature. Autoignition temperature is ~410*. The cylinder temperature reaches ~840*+, most all this energy is contained in the precup and released thru the small spout opening of the precup.
Diesel fuel doesn't explode like gasoline, it burns, the energy is released by expanding hot gas continually throughout the stroke.
A turbo engine induces more air/pressure to each cylinder, which takes longer to compress and raises the cylinder temperature higher ~980*, hence the one degree more advanced (9.5*) for fuel injection which allows more time for fuel to be injected.
There are six sizes of plungers in th DB2 IP's identified by the 2nd model number, (25) .250 (27) .270 (29) .290 (31) .310 (33) .330 (35) .350
The IP injection curve would effect the length of time for injection, and IP plunger size would determine the amount of fuel along with the injector nozzel size.
All that air and fuel is squeezed/compressed into a very small space approx. 4.110 X .075 thick, plus the precombustion chamber volume, 6.9 is 18.34 CU and 7.3 is 20.42 CU.
Too much fuel or poor atomization would cause a knock.
I guess to sum it all up, at 2000 RPM a power stroke happens in such a short time, all things have to be right for a good running engine.
Am I figuring this right? Comments welcomed.