More diesel efficiency discussion

No problem, it has been a meandering path, and I haven't followed much of it either.

Am curious about the KAMD44, did the computer maintain a charge air pressure at some constant level or did it boost it proportional to load by measuring rack vs rpm or something like that, along the lines of a smoke limiter? Was there a pressure "bump" up or down when the turbo took over?
I'd love to get hold of the books on that one, it sounds like it was a fun system for the Volvo guys to develop.

I drove a KAMD-44P (If I remember correctly) in a parasailing boat when they first came out. It was horrid for the task and frankly- unsafe. In less than two years the owner replaced the engine with a non supercharged Volvo. The reason was when you were at higher RPM and developed a high load the engine bogged down, and the turbo could not hold the rpm despite giving more "throttle". The supercharger would NOT kick in until the low end of the scale- ie 1600 rpm. By that time the people in the 'chute were dropping like rocks. We had to install a manual switch to kick the SC in, but even that was a hassle and not worth it. A couple near disastrous accidents in which the people could have died (but instead just got a bit wet...) made the decision to change the engine a easy one. I also took care of a 32 Stamas sport fish with a set of the same engines and in that application the engines were an excellent match.

"It was horrid for the task ..."

Was it rapid acceleration that was a problem then? It sounds almost like the turbo was large and optimized for constant high load. If the load had dropped off from what it took to keep the turbo spooled up then the time lag to catch up again was too long. Sort of a reverse "bootstrapping" situation.

I can see where a steady acceleration in the SF would more closely match the time constant of the charge air system. Interesting story, did other boats have that problem or was it just related to the way you had to haul the fares around?

When the people are in the air you can experience gusts, lulls, run downwind, across wind etc. All these create differing loads, as well as when you pull the folks in or out. When we were right at the end of the SC range if load increased greatly then the rpm went down, back into the SC range- but the SC would not come back on until rpm fell to around 1600. (I do not recall the upper end range- say 2500- it did not re-engage at 2500- it had to drop to 1500 then spooled up) This created situations that could see the people dropping quickly, and the operator needed to hold rpm/raise rpm to pull them up/stop the decent, but could not until rpm dropped close to 1600. If the waters surface came before 1600....
This may have changed with later versions of the engines- I do not know. Your "reverse bootstrapping" is right on if I read it correctly.

I thought highly of the engines in the sportfish however; with very quick spool up, and have not heard of applications that mimicked the parasailing quick load changes that caused negative performance.

superchargers

Parasail boats became larger and larger between the introduction of the 42, the 43 and then the 44 (not really an approved application in commercial use). They went to two people in the chutes and everything kept kept getting bigger, boats and the parasail chutes. Eventually the engine did not have the displacement needed. I saw what Bamboo is describing when the fuel system started to get work badly. The engine struggled to make power (and therefore turbo boost) and slowed. So then the compressor would kick in to save the day, but only for a few moments. The symptom was close to the same for fuel starvation as it was for just overloading, with the compressor cycling on and off at times. By the way, do NOT compare with the common rail D4 and D6 series.
Marmot the computer software strategies are held pretty tight. The manifold pressure is reported to the ECU via a boost sensor. The strategy is do not release too much fuel until there is enough manifold pressure. I would find boost at maybe 7 psi at dead idle if you energized the compressor, but normally go from 8-10 psi as you start to accelerate and go beyond 15 psi as the computer shuts it off and the turbocharger is taking over.

This is consistent even up through the new engines and horsepower ranges. The software tells the compressor to assist of rapid power demands and not let the engine produce smoke. I must say it does work and they keep making it quieter in the process.