Turbo or no....

[Henning]

Turbos, do one thing. They wear out engines prematurely, period.
(...)
just ask, people who do this for a living, not opinions, from laymen, just COMMON SENSE, from engine rebuilders..

I actually do this for a living, but anyway... the example you give of premature wear in jimmies is related to higher power densities, not the mere presence of a turbocharger.

 

[sunchaser]

Hi,

I stumbled onto the Trawler Forums while looking for information on Becker rudders, and started reading this thread as I have considered de-turboing my main engine. I finally registered in the hope of dispelling a couple of common myths about turbocharges.

#1 - Turbodiesels are inherently less fuel efficient: They're not, as evidenced by commonly available data. As for why, a common (and partially correct) assumption is that the smaller engine size for a given power level leads to reduced mechanical losses. There is a different and more important explanation, tough: A significant portion of the mechanical energy generated by the piston is lost to pumping air through the engine. Because a centrifugal impeller compressor is much more efficient than a piston pump at these low delta-p numbers, adding a turbo to any given diesel engine (and dropping compression by a point or two) tends to yield a fuel efficiency increase around 2-3% for a given power level.

2 - Turbocharging an engine leads to increased EGTs: Anyone who has lost a turbo on a non-compensated engine knows how wrong that is (EGTs instantly go through the roof). In fact, just adding a turbo to an engine (as above) will lead to higher lambda, which leads directly to lower EGT. That being said, turbocharged engines are generally able to sustain higher EGTs by maintaining combustion efficiency at higher power densities, as well as having marginally better piston cooling for a given EGT, which is why turbodiesels tend to run hotter exhaust.

3 - Turbodiesels wear out quicker: Again, empirical evidence suggests otherwise. Take my main engine as an example; It's a FIAT 8281 17 liter V8 @ 500-ish hp. The same engine delivers 310 bhp @ 1700 rpm NA (16:1 compression, injection fixed at 18 degrees btdc). The continuous duty turbo version (no intercooler) delivers 370 bhp @ 1800 rpm, with 15:1 compression and injection start 26 degrees btdc. The latter configuration has a typical TBO of 25k hours, and I know of one concrete example that ran almost 50k hours on a set of rings (although that was pushing it). That's quite a bit, no? Furthermore, a lot of medium speed marine engines have scheduled liner replacement at 50k hours, and they're all turbocharged these days.

That being said, the turbocharger itself has a much shorter life span than the engine, and you'd be lucky to get 10k hours out of one. Short cycling without pre-heating and pre-lubrication drastically reduces that number, and I've seen plenty of pleasure use turbos die "natural" deaths before they reach 1.500 hours. I actually murdered my own turbos even sooner than that, by a lot of really short run cycles (<1hr), hence the interest in de-turboing despite the expected drop in fuel economy.

I'm sure the diesel engine builders would have an opposing comment or two. Having been involved with Cat dyno testing on many diesels, my experience is very different than you have noted.

The last before I retired was with 4000 HP engines operating at 15.000 feet. Fuel efficiencies and HP obtained matched performance at sea level. This would not have been possible without 21st century engineering including computer controls and very interesting quad turbo intake design. Cooling at these altitudes is a huge challenge.

Last but not least, I've seen turbos easily go 15,000 hours or more in off the road commercial operation. Dozens of them. Never a concern except when lubrication is lost due to fitting or hose issues.

 

[Hotrod]

I actually do this for a living, but anyway... the example you give of premature wear in jimmies is related to higher power densities, not the mere presence of a turbocharger.

I did this for a living also. The reason manufacturers, put boost was to increase power, and hence, more fuel, by bigger injectors, that is why it was done, which increased Temps, compression heat, etc, which shortened life.

 

[Rebel112r]

Dont all the 71 series have blowers?

 

[Hotrod]

Dont all the 71 series have blowers?

Sir, 671 naturals, will run and run. The power density, is only achieved, by more fuel, from blowers added, or they will run too lean, hence bigger injectors. And hence , wears pistons, rods, crank, etc.

 

[Henning]

Last but not least, I've seen turbos easily go 15,000 hours or more in off the road commercial operation. Dozens of them. Never a concern except when lubrication is lost due to fitting or hose issues.

Fair point; There are bunches of factors affecting turbo longevity, and larger turbos do live longer - my experience is far from all-encompassing there. I do stand by my statement that the life of the turbo itself is the limiting factor with turbocharged diesel engines, though.

As for the rest, I don't really understand your objection to my argument. Your experience with normalizing large Cats relates to it how? And how does your experience differ from what I say? I'm sincerely curious.

 

[Henning]

Dont all the 71 series have blowers?

Indeed they do, as do the 92s (and I believe the 53s and 149s) but not the 51s. However, blower displacement is closely matched to scavenging air demand, so there isn't really much over pressure being made. The blower is there to ensure somewhat acceptable scavenging when the engine is operating off its ideal speed range.

When the engines are turbo charged, the turbo is added in-line with the blower.

 

[twistedtree]

Indeed they do, as do the 92s (and I believe the 53s and 149s) but not the 51s. However, blower displacement is closely matched to scavenging air demand, so there isn't really much over pressure being made. The blower is there to ensure somewhat acceptable scavenging when the engine is operating off its ideal speed range.

When the engines are turbo charged, the turbo is added in-line with the blower.

So a blower and a turbo charger are different things? I assumed blower was slang for a turbo charger.

 

[stubones99]

So a blower and a turbo charger are different things? I assumed blower was slang for a turbo charger.

No, a blower is either belt or gear driven pump that pressurizes the incoming air for the engine.


A turbo is powered by the exhaust to pressurize the incoming air.

A blower does not have turbo lag, but spins at engine rpm speeds. A turbo spins up only after you throttle down, and the exhaust spins the turbine, spinning the pressure side faster, and increasing air flow and pressure.

 

[BruceK]

No, a blower is either belt or gear driven pump that pressurizes the incoming air for the engine.


A turbo is powered by the exhaust to pressurize the incoming air.

A blower does not have turbo lag, but spins at engine rpm speeds. A turbo spins up only after you throttle down, and the exhaust spins the turbine, spinning the pressure side faster, and increasing air flow and pressure.

Are you talking about a supercharger?
And engines fitted with both supercharger and turbocharger?

 

[Ski in NC]

A little geek speak: A turbo is in tech speak a "exhaust gas turbine driven centrifugal super charger".

Anything that pushes more air into the engine than it would draw on its own is a "super charger". Can be a turbo, a blower, something driven electrically, whatever.

Blowers are most commonly the roots style mechanical like used as a scavenging blower on a Detroit two stroke. On those engines it is used to push air through to get the smoke out, it does not super charge. The engine will not run without it. Strap that same blower on a Chevy car engine, now it does super charge.

Some Volvo marine engines have both a turbo and a mechanically driven blower. Both are super chargers. Blower to get low end torque, turbo takes over for higher rpm.

 

[stubones99]

Engines are seldom fitted with both turbo and supercharger.

 

[stubones99]

I wonder when the excess energy of the turbos will drive alternators, like some of the big boys do... According to what I've read, there is often much more power in the exhaust turbine to not only spin the compressor turbine and an alternator. Of course, it will be spinning fast!

Interesting note that most turbos only generate boost when operating over 100,000 RPM. IF you can hear them whistle, it's loping along and not generating much boost.

 

[BruceK]

Ford Lehmans. No turbo, no blower, no supercharger. And yes, not so much power. But sweet as

 

[Henning]

@Ski in NC: Very well put. I'm curious, though - are you sure that a DD won't run with the blower taken off? I know for a fact that a B&W Alfa will run with the reed plates taken out of the scavenging air pump, albeit like absolute fecal matter. That one uses loop scavenging, and the DD's longitudinal scavenging scheme is even better suited to function dynamically, so I always assumed that it would run without the blower, just not very nicely.
</pedantry>

@stubones99: Interesting thought, but I somehow doubt it's going to happen. Small engines in general operate under such varying load conditions as to make it impractical, and belt driven alternators are very inexpensive and easy to deal with as long as they're not too big.

 

[sunchaser]

Ford Lehmans. No turbo, no blower, no supercharger. And yes, not so much power. But sweet as

Yes, kinda like my sweet old dearly departed Sunbeam Tiger. No longer made darn it.

 

[BruceK]

Yes, kinda like my sweet old dearly departed Sunbeam Tiger. No longer made darn it.

Not sure but was the Tiger a V8, the last model development of the 4 cylinder Sunbeam Alpine? Same era as the Daimler SP250?
Compare D4 Volvo output, 300hp out of 3.75L capacity. That`s 2.5x the output, from around 40% less cubic capacity of the venerable Lehman. Turbo Volvo D4s work hard.

 

[Simi 60]

Engines are seldom fitted with both turbo and supercharger.

True but I remember working on one back in the day with twin V16 Detroits
Not sure if I got it right but what I remember was every bank of 8 having a superchasrger and every bank of 4 having a turbocharger.
It was awesome

 

[Hotrod]

Ford Lehmans. No turbo, no blower, no supercharger. And yes, not so much power. But sweet as

Sir, I believe you are dead on, correct. When trawlers first came on the scene, early, Grand banks, marine trader, defever, all ran Lehmans 120 or 135 hp.I believe the whole concept was to push along with an easy riding hull, at 6 to 8 knots, with very low fuel consumption, and very simple maintenance. Less was considered more, which gave affordability, distance, etc.if these engines were run under load, at 1600 to 1800 rpm, and ran at 180 degrees, and serviced regularly, 10,000 hours or more were not unusual, with very modest fuel consumption. Keep the fuel clean, constantly pet the cooling system, and off you gn the other hand, the velvet drive, was a little different story, but not terrible, in my opinion.

 

[FF]

"On the other hand, the velvet drive, was a little different story, but not terrible, in my opinion."

A Twin Disc cold have been fitted , but the boats cost would have been higher.

 

[Hotrod]

A pet peeve of mine also is, these new style rail engines, that require that you MUST, call manufacturer, for a PLUG IN, analysis, when the engines act up. It is no wonder that people started walking away from this life style, due to this nonsense of control, and making it difficult for self repair, and insane expense, due to having to call them for repair, and diagnosis. MaybeTed Kazisinki, the unabomber, was correct, the worst thing for mankind is technology , at least in some cases.

 

[stubones99]

@stubones99: Interesting thought, but I somehow doubt it's going to happen. Small engines in general operate under such varying load conditions as to make it impractical, and belt driven alternators are very inexpensive and easy to deal with as long as they're not too big.[/QUOTE]

Wartsila and some other vendor collaborated on a solution for large container ships that no longer needs to run another APU or genset. Of course, this is a much larger scale than trawlers, but the article I read said that almost all turbos had much more power than the compressor needed.

I would never suggest a belt drive on a turbo shaft since the small pulley would be turning as much as 130,000 RPM and I don't think they make rubber belts that could stand the centrifugal force of having to change directions that fast without flinging rubber in all directions. It would either have to have a step down gear train or build the alternator around the center part of the shaft between the hot side and the compressor side, with windings to run at that speed. You might want to put an explosion proof wrap around it, just in case... No telling what a rare earth magnet would do if spun off the shaft at 130,000 RPM.

Dealing with the variable speeds is a fairly easy device. In the voltage regulator, you take whatever voltage coming off the windings and make it what you need for your systems. It might be 500v or 30v, who knows.

The one thing it will need is a speed sensor, since putting too much load on the turbo when it is idling will stall it, overheating one side of the turbo and never letting it get to speed to operate. So it should only work while the turbo is loaded and generating boost.

I'll try to find the article and post a link to that on here.

stu

 

[Henning]

@stubones99:

I think you misunderstand me. I would never suggest driving a rubber belt of any kind off a turbo. Allow me to rephrase:

Varying load conditions on small / short haul engines pose a challenge because exhaust turbine driven power generation would only be available at higher load levels. Thus, development of such technology for small / recreational engines is unlikely, especially since our existing solution of crankshaft driven rubber belts solves the problem so cheaply and easily up to ~2 kW.

 

[stubones99]

Here is a link, and I was wrong... it was Mitsubishi

https://www.vesselfinder.com/news/5...-wins-Energy-Conserving-Machinery-Award-Video

 

[Henning]

Interesting. That does at least provide some packaging benefits over Wärtsilä's system, which uses an entirely separate turbine for electricity generation.

I wonder how this scales down? I suppose it might find a niche in short-haul applications in combination with a clutchable PTO generator, although it would make for a relatively expensive system...

Cool stuffs

 

[stubones99]

turbo powered generator

Interesting. That does at least provide some packaging benefits over Wärtsilä's system, which uses an entirely separate turbine for electricity generation.

I wonder how this scales down? I suppose it might find a niche in short-haul applications in combination with a clutchable PTO generator, although it would make for a relatively expensive system...

Assuming the generator is actually an alternator, it could vary the excitation current to the stator and vary the load on the turbo drive. zero excitation current = zero load.

The coolest thing is using the generator as a motor, spinning up the turbo before the engine runs, providing boost early and lowering emissions. That makes it more of an electric supercharger, which converts to turbo + generator once the engine is under load.

If you're doing the motor thing, it can't be an alternator, but milling the shaft to hold rare earth magnets for the generator would be a simple thing. It will be a few years til we see something like that in marine engines though.

What I'd like to see is the flywheel generator / starter, so you do without the starter Bendix. I've heard several boaters trying to start already running engines and that's not a good sound. On the other hand, any problem with a flywheel generator / starter means you have to drop the transmission to get to the flywheel. I wonder what the stats are between the separate starter, integrated flywheel starter are in real life. I've not heard of a hybrid car with a starter problem yet.

 

[Ski in NC]

130,000rpm is the realm of tiny car turbos. They are made tiny so that they spool very quickly, try to avoid turbo "lag". Larger turbos spin much slower, not sure of exact numbers. And you can design a turbine with small blades on a larger diameter wheel to get whatever rpm you desire, suitable for direct drive on a generator, certainly do-able.

From an above post, the Detroits often had blowers and turbos. Both are not superchargers. The blowers are scavenging blowers, doing the get the smoke out thing for starting and light load ops. Once on load, the turbos not only supercharge but take over the scavenging duty also. Some have bypass valves that open up around the blower, so while it remains spinning, at least some air is vented around it to reduce parasitic loads.

A similar two stroke, the larger EMD engines common in loco's and tugboats, some have a turbo that is geared and clutched to the crankshaft. As engine starts, turbo is mechanically driven to scavange. Once under load, turbo gets driven by exhaust and an over-run clutch opens up to disconnect drive from crank.

I like the idea of a exhaust turbine being used for other useful work, be it gennie or going back to the crank. On small engines not really worth it. On freighters, heck yea.

This was done in the 40's and 50's on big recip aero engines. Called turbo/compound or something like that. Exhaust turbines geared to crank, supercharging done with gear driven centrifugal blower. Later (??) evolved to the turbos we are now familiar with. Tech faded as the gas turbine jet, turbofan and turbo props got developed and retired the big recips.

 

[sunchaser]

Let's talk recreational marine diesels for a brief moment where there are few if any options to avoid a turbo if you are considering a new to 15 year old engine. Theory, trucks, dozers buses, freighters etc are one thing but a newer Mainship, GB, DeFever, Nordhavn etc quite another.

Over a very long period of time and having spent lots of money on engine related maintenance, not one red cent has been spent on turbo repair. Some argue that turbos wear out engines. Hah, in my low boost 200 hour a year usage the boat, base engine and gel coat will outlive many attentive owners.

I do know those who run their diesels at high RPMs and over propped. They are oblivious to soot on the transom and even desultory ER checks. These owners are boat yard and rebuild shop dreams and don't mind paying to play.

 

[FF]

"newer Mainship, GB, DeFever, Nordhavn etc quite another."

All these boats need about 100 - 150HP engines to operate properly if displacement boats.

Car diesels are tiny and their service life stinks in a marine HD application.

A truck engine of about 350-400 CI would be grand but many are turboed to please both the air police and owners that want hill climbing ability. Cost and complexity to no purpose.

The cruising low speed market is way to small to have an engine created and millions spent for Tier whatever for the air police.

Best we can do is use one of the 4 engines mentioned and set it up right for the boats requirements.

For many boats , esp at 200 hours a year , a modern gasoline engine could be best choice. Esp if we finally get rid of the ethanol in the gasoline.

 

[Henning]

Let's talk recreational marine diesels for a brief moment where there are few if any options to avoid a turbo if you are considering a new to 15 year old engine. (...)

Deutz manufactures a range of oil cooled NA diesel engines that are well suited for marine use. They are popular in standby applications (lifeboats, emergency gennies, large vessel thrusters, etc) because the absence of water in the cooling jacket makes for superior resistance to neglect, which is also a major worry with recreational marine engines.

They're packaged for recreational use by Vetus, and it must surely be possible to get one in your new yacht if you so desire. I put one in a Nauticat 33 once, and it was one of the sweetest running mechanically injected high speed engines I ever had the pleasure to deal with. It also has a very nice "quality feel" to it, although that's harder to define. Sadly, they're too expensive to ever become common.