Light Loading of Diesels -- How Harmful?

[a64pilot]

Originally Posted by Dockhead

"Decoking chemical"? I've never heard of that. Do you have any details?

There are several things people use, everything from Diesel fuel, to Kerosene, ATF and Sea Foam, Sea Foam has specific directions on the can on exactly how to do it.
Usually they amount to dribbling it into the intake, adding throttle to keep engine running, ignore copious amounts of smoke, shut down, let soak a while start engine and run the snot out of it.
With a turbo and an after cooler, I would recommend you not do it, course I think you have no problem, from what I can gather, you have a normal running Yanmar boat engine, although the ones I've had on little John Deere tractors never smoked at all, very clean burning, I don't know, maybe it's the cold exhaust manifold on a Marine engine that does it?

[poiu]

Running the engine flat out for a while - 15 mins or so helps reduce smoking and I believe does so by decoking the engine. I have found it to reduce (white) smoke noticeably in my engine.

I used to run at low speeds, but got a little concerned about that not being good for the engine, plus I was getting some smoke. I now try to run at just under the peak of torque curve. I run at the low end as the engine uses a ton of fuel if I run it faster. At peak torque the turbo is working effectively and the engine should be most efficient, so burning at its cleanest.

[Dockhead]

Originally Posted by poiu

Running the engine flat out for a while - 15 mins or so helps reduce smoking and I believe does so by decoking the engine. I have found it to reduce (white) smoke noticeably in my engine.

I used to run at low speeds, but got a little concerned about that not being good for the engine, plus I was getting some smoke. I now try to run at just under the peak of torque curve. I run at the low end as the engine uses a ton of fuel if I run it faster. At peak torque the turbo is working effectively and the engine should be most efficient, so burning at its cleanest.

Remind us what engine you have, Poiu?

These are helpful thoughts.

I started out using 2500 RPM as my cruising speed. That's somewhat below my engine's torque peak, but I think the turbo is already working pretty well. My engine is using 6 or 7 liters per hour at that speed.

As the years went by, I started running the engine slower and slower and slower, most recently with 1800 being a normal cruising speed in calm weather or motorsailing.

But now I'm starting to think better of it. Why have I been so greedy to save fuel? There is something psychological at play. It's not like fuel is my biggest expense. In fact I spend less on fuel -- which is not only propulsion, but light and heat as well -- than I spend just on electrical service to my apartment. What have I been thinking?

I wish I had a boost gauge to know when the turbo is working. I think it's definitely doing nothing at 1800. Maybe 2200 or so would be an ok cruising RPM.

[a64pilot]

A boost gauge and maybe a pyrometer, many gauges will do both, would be very beneficial in my opinion and is so easy to install, these modern engines. Are they Can-bus, if so dead easy to get surprisingly a lot of data on NMEA, I was astonished what all I got on my Mercury Verado outboard.
Anyway if you operate just where she is making a little boost and ignore RPM, then I think it will run forever. Boost isn't so much a function of RPM as it is load, but load and RPM on a boat are sort of tied together, except when we are motorsailing.
But and this is a really cool thing in my opinion, an Autoprop will increase pitch to keep a load on an engine, and this is a really nice feature, especially on a blown motor.

But maybe at some point we quit playing with these motors and start sailing

[poiu]

Originally Posted by Dockhead

Remind us what engine you have, Poiu?

These are helpful thoughts.

I started out using 2500 RPM as my cruising speed. That's somewhat below my engine's torque peak, but I think the turbo is already working pretty well. My engine is using 6 or 7 liters per hour at that speed.

As the years went by, I started running the engine slower and slower and slower, most recently with 1800 being a normal cruising speed in calm weather or motorsailing.

But now I'm starting to think better of it. Why have I been so greedy to save fuel? There is something psychological at play. It's not like fuel is my biggest expense. In fact I spend less on fuel -- which is not only propulsion, but light and heat as well -- than I spend just on electrical service to my apartment. What have I been thinking?

I wish I had a boost gauge to know when the turbo is working. I think it's definitely doing nothing at 1800. Maybe 2200 or so would be an ok cruising RPM.

I've got the Perkins M225ti.

You will see from the power curve, particularly the torque curve that there should be a steep rise as the turbo starts to work effectively and boosts power. If you are on the upside of that curve then your power is at optimum value for money.

As you say fuel costs don't matter too much within reason. If you increase the life of your engine that saving will probably compensate for any extra fuel costs on its own.

It's only when you get to near hull speed that fuel consumption goes ballistic and we're not talking about doing that. Running maybe too slow I will use 6 lt/hr for 6.5 kts. My engine is happier at 7 or 8 lt/hr, but will drink 40 lt/hr flat out, for very little more speed (that range corresponds to going from 7.5 to 10kt).

[Dockhead]

Originally Posted by a64pilot

A boost gauge and maybe a pyrometer, many gauges will do both, would be very beneficial in my opinion and is so easy to install, these modern engines. Are they Can-bus, if so dead easy to get surprisingly a lot of data on NMEA, I was astonished what all I got on my Mercury Verado outboard.
Anyway if you operate just where she is making a little boost and ignore RPM, then I think it will run forever. Boost isn't so much a function of RPM as it is load, but load and RPM on a boat are sort of tied together, except when we are motorsailing.
But and this is a really cool thing in my opinion, an Autoprop will increase pitch to keep a load on an engine, and this is a really nice feature, especially on a blown motor.

But maybe at some point we quit playing with these motors and start sailing

Ah, but playing with machinery is one of the great joys of cruising. You know, if you didn't like to play with machinery, a lot of the inevitable aspects of cruising would be torture.

I have a extremely complex NMEA2000 network, with something like 40 devices on it. It's so complex that it's split into two separate networks connected with a bridge. Despite that, I rejected the idea of adding pyrometers or boost sensors (I do have the EMS100 Yanmar connector, and the lovely Maretron fuel flow meters, though).

Now A64 has convinced me of my error. The pyrometer is dead simple; I already have the Maretron temperature module. Just need to buy the sensor and drill (eek!) and tap a hole in my exhaust manifold. For boost, there seems to be a stand alone Lowrance N2K sensor.

On my list. Thanks, A64!

[sartorst]

Black smoke is from an incomplete burn whether it be from, load,improper atomizing,low compression,poor fuel,too much fuel,not enough air,etc white smoke is from fuel that never even started to burn as in a misfire,blue is oil, and you can have a combination of all of the above

[Dockhead]

Originally Posted by poiu

I've got the Perkins M225ti.

You will see from the power curve, particularly the torque curve that there should be a steep rise as the turbo starts to work effectively and boosts power. If you are on the upside of that curve then your power is at optimum value for money.

As you say fuel costs don't matter too much within reason. If you increase the life of your engine that saving will probably compensate for any extra fuel costs on its own.

It's only when you get to near hull speed that fuel consumption goes ballistic and we're not talking about doing that. Running maybe too slow I will use 6 lt/hr for 6.5 kts. My engine is happier at 7 or 8 lt/hr, but will drink 40 lt/hr flat out, for very little more speed (that range corresponds to going from 7.5 to 10kt).

That's some engine-- a big more than half ton brute of a beast

Mine is very different -- lightweight, high speed.

The torque curve of my engine doesn't have any steep bits:




I think I'm going to need the boost gauge and pyrometer.

[Dockhead]

This is the torque curve from the naturally aspirated version of my engine:



Very interesting. Would seem to indicate that the turbo is already working at 2000 RPM.

Comparing these two curves is a really good illustration of what turbos do.

[model 10]

Originally Posted by Dockhead

I think I'm going to need the boost gauge and pyrometer.

You are choosing to use trucking terms for these 2 instruments. This a boat so if you have the choice you could use aviation terms instead. These would be manifold pressure and EGT (exhaust gas temp.) Sometimes they refer to EGT as TIT (turbine inlet temp). I like that better.

[poiu]

Originally Posted by Dockhead

This is the torque curve from the naturally aspirated version of my engine:

Attachment 112245

Very interesting. Would seem to indicate that the turbo is already working at 2000 RPM.

Comparing these two curves is a really good illustration of what turbos do.

The lower end of that curve is missing, which would show a steep rise in output as the turbo boost comes on. The turbo clearly is working well at 2000 rpm and the engine should be burning efficiently and cleanly. Assuming the turbo is working well down to 1800 or maybe less then I don't think you are operating it too slowly. Assuming also your prop is correctly matched. That said, I can't imagine long periods of very slow operation are too harmful. Your engine is probably similar - my engine is used widely in agricultural/construction equipment and buses for example and they routinely spend many hours at idle.

Peak efficiency and cleanest, leanest, hottest burning should be somewhere approaching the max torque of 2600rpm.

[HappyMdRSailor]

Boost/pyrometer indicator is a brilliant idea...

It would seem that maximizing boost for the particular load would save you a ton in unnecessary fuel... Back off the throttle after your boost starts to flatten out???

[IdoraKeeper]

I have the 4jh2te...it acts just like your 3te. I normally run it at 1650 to 1750 with dashes to 1800 or 2000. It's turning a highly pitched 18" wheel...have to use lower rpms due to cavitation caused by proximity to the surface. I had a dry exhaust on it. Replaced that with a larger diameter wet exhaust...smoking decreased markedly. Vibration also decreased. Now I can actually hear the shaft rumble.
MY .02, mechanical fuel control cannot compensate for anything but intake airflow based on crank rpm. The boost pressure is an analogue of crank rpm. If you allow back pressure in the exhaust your turbine speed will be low compared to a free flowing exhaust. Low turbine speed for a given crank rpm= rich mixture=smoke. In my case a better exhaust system eliminated soot in the area of the exhaust...nothing else was changed whatsoever.
I was going to ask about the Russian diesel but you brought it up and disposed of the question. I think the sweet spot for fuel flow v boat speed is pretty wide, even when we are making more smoke than we would like.

[Wotname]

Originally Posted by IdoraKeeper

.....
MY .02, mechanical fuel control cannot compensate for anyything but intake airflow based on crank rpm. The boost pressure is an analogue of crank rpm. If you allow back pressure in the exhaust your turbine speed will be low compared to a free flowing exhaust. Low turbine speed for a given crank rpm= rich mixture=smoke. In my case a better exhaust system eliminated soot in the area of the exhaust...nothing else was changed whatsoever.
I was going to ask about the Russian diesel but you brought it up and disposed of the question. I think the sweet spot for fuel flow v boat speed is pretty wide, even when we are making more smoke than we would like.

Your .02 makes a lot of intuitive good sense

[Kenomac]

I have the same Yanmar engine, same year. I think your issue is related to fuel quality or composition.

Ours does not smoke at all, not white, not black, not at idle or under load. Once early last summer, I did notice some soot build up near the generator and engine exhaust, but it cleared up entirely when I filled up the fuel tank half way through the summer. Probably due to a slightly different fuel mixture coming from the fuel dock. Nothing else changed.

Are you routinely revving your engine once every hour like the owners manual suggests? Place in neutral and revv over 3000rps five times or run at 3000+ for five minutes? We do, and no problems with smoke or soot.

Have you installed a fuel polishing system as I've suggested? We did, and it makes a HUGE difference and eliminates the possibility of contaminated fuel causing problems.

Seems to me like you're chasing your tail with these fuel issues.... Simply install a quality polishing system and eliminate most issues.