TA vs TI?

Cuttyhunk47 said:

OK, I thought I was with you until the argument came up about a turbocharger not necessarily using more fuel.

So, using a Cat 3208TA 375 hp for example. I was under the impression that the turbocharger "kicks in" at a certain rpm. So, am I wrong thinking that if I am underway at a lower rpm (before the turbocharger "kicks in"), that I would be using the same gph as a 3208na at that same speed. I know I am probably trying to get simple explanations for complex issues, so I will hope you will bear with me.

And your discussion about "hp down the shaft" threw me for another loop. How do you determine how much hp one needs down his shaft. Sounds like I am trying to be funny, but I'm serious.

My experience has been with Cat 3208na They would move my boat at about 9 knots at 2100 rpm and would consume 10 gph. If I needed to get off the water due to weather or other issues, I could punch them up to 2450 rpm and gain about 2 knots, but use about 16 gph. Can anyone hazard a guess how a 3208TA 375 hp Cat would have affected those numbers?

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Just realize in theory, turbochargers do not "kick in" at a certain RPM. They kick in at a certain load. It is heat that drives a turbocharger(not exhaust flow)....heat is energy. To give you an idea, an engine at idle will not drive up the boost because it is not loaded. Just to clarify things.

And Ski was just using 300hp arbitrarily. Don't let his "down the shaft" terminology throw you off. He just used 300hp as an example.

Now the main reason why turbocharged aftercooled/intercooled engines are more efficient in his example is because of the charge air volume and temperature. You are actually extracting more energy out of a parcel of fuel than you are in an NA engine. It really is as simple as that. And THAT IS THE REASON why turbodiesels dominate the current modern market. They are more efficient...hence they burn cleaner...hence less pollution.

Baker said:

It is heat that drives a turbocharger(not exhaust flow)....heat is energy. To give you an idea, an engine at idle will not drive up the boost because it is not loaded. Just to clarify things.

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OK, how does heat drive a turbocharger?

Exhaust pressure (due to engine combustion) is what spins the exhaust turbine which is close coupled to the intake compressor turbine. I know exhaust systems heat up based on fuel consumption = loading, but that isn't just heat.

you can heat up a turbine with a propane torch and it won't move... It is solely exhaust pressure, caused by the engine combustion (which generates heat and expansion of the gases) which are fed to the turbo.

Are we all agreeing in our own way?

English can be so ambiguous sometimes.

Stu

Ski:


I did it your way using the 370 hp engine data sheet and got the same result as you. My old eyes or parallax fooled me. So the NA and highly turbocharged Cummins engines both use the same fuel at low hp. Makes better sense to me.


Stu:


Combustion gas volume exiting the engine is influenced by these variables: the pounds of air sucked or pushed into the engine, the pounds of fuel burned and the temperature of the exhaust gas as it exits.


The chemical energy in a pound of fuel roughly is converted into 1/3 kinetic (rotational) energy, 1/3 exhaust gas temperature and 1/3 jacket cooling and convection radiant losses from the block.


So more fuel means more heat in the exhaust gas which means more volume of exhaust gas. PV=NRT, the ideal gas law. P=pressure, V=volume, N= ideal gas, N= number of moles which is related to pounds, R=ideal gas constant (sort of a fudge factor).


At idle or even higher rpms at no load, there is very little fuel injected. The air/fuel ratio is very high, maybe as much as 100:1. Remember the 1/3 rule of thumb above. If kinetic energy is very low (just parasitic losses) then it doesn't take much fuel to make it so the temperature will be low. But at high hp loading the pounds of air and fuel go up and the temperature goes up, therefore the exhaust gas volume is very high.


That's all the physics my tired brain can handle today. Let's talk about neat places to anchor out now.


David

Turbines work off volume flow rate and pressure differential.

Using the ideal gas law, most engines have about three times the volume of exhaust gas leaving the engine compared to air going in.

Temp has to be expressed in absolute terms, so I'll show my age and use Rankine:

Inlet air 70F + 460= 530R
Exhaust gas 1000F + 460= 1460R

So all else being equal in the ideal gas equation, exh volume 2.75 times intake air volume. Plus a little bit more from combustion products, so call it three.

What's nice about that is the boost can then be a good bit higher than the exhaust manifold pressure. Can't be three times as the turbine and compressor both have inefficiencies that add up.

It's true heat does not spin the turbine, it is flow volume and delta p that spin it. But heat that gas up and it works much better!!!

I have overhauled a turbo or two, and knew that regardless of the temperature, it wouldn't spin.

You guys are getting into the laws of thermodynamics and that kind of thing which I sort of grasp, but it has little to do with the mechanical side of things.

or perhaps my medication needs to be adjusted again

Stu

OK, so I thought I was walking through Harvard Square looking for a lobster-roll and I wandered into a room of professors discussing thermodynamics. I hope there isn't a final test on the details of your discussion, but you have been very helpful in correcting some of my misconceptions.

I am certainly less frightened by turbochargers. I am a little more aware of the positive boost that can be achieved if the electrical nurget is placed in front of the inter-cooler. I am being a smart a-- here, but it really has been very helpful. Thank you, sincerely.

I will maintain my initial statement!!! Turbochargers are driven by thermal energy...ie HEAT!!! Does E=MC2 ring a bell???? It is free "wasted" energy that would otherwise exit the exhaust pipe. Those with boost gauges please tell me the boost pressure with the transmission in neutral at a particular RPM versus a loaded engine at the same RPM. The boost pressure will not be the same....not even close!!!! And Stu, to answer your question versus a blow torch on a turbine wheel....if you were able to contain that heat in a confined chamber without burning everything, then, yes, you will get boost. But it takes a lot more than just aiming a blowtorch at a turbine wheel. I found this on youtube. I think it does a good job of explaining how a turbo works.

Thanks Mr. Baker,

I know how they work and have had a couple on the workbench (30 years ago). It was the thermodynamics lesson that threw me for a loop. I know engines are 'heat' engines, and the combustion causes expansion and drives the piston down which is translated to the crankshaft through the connecting rod, etc...

What I was trying to say was it isn't the 'heat' that causes it to spin the exhaust side turbine. The heat causes 3-4 x expansion and that expansion of exhaust gases cause the turbine to spin.

It is like looking up at a windmill in the midwest on a windless day. Despite the sun shining on that windmill, it won't turn unless there is wind. it isn't HEAT that makes it turn. That would be a thermal pile.

Ok, I know that sun shines and causes irregular heating / warming of the earth's crust which causes high and low pressure air zones which tend to cause windmills to turn... ok, back to heat

Too late for me to keep this up guys!

Enjoy the lesson in thermodymanics without me.

stubones99 said:

Thanks Mr. Baker,



What I was trying to say was it isn't the 'heat' that causes it to spin the exhaust side turbine. The heat causes 3-4 x expansion and that expansion of exhaust gases cause the turbine to spin.



Too late for me to keep this up guys!

Enjoy the lesson in thermodymanics without me.

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What you are trying to say is exactly what I was trying to say....the HEAT causes the 3-4x expansion.....if that heat is not there, THE BOOST DOES NOT HAPPEN!!!!.....PERIOD!!!!! Your analogies(windmills and blowtorches) are not relevant!!!!...because the heat in your analogies are not contained and directed!!!! Heat is energy!!!! And it is THAT ENERGY that you are capturing in the exhaust gases to spin the turbine!!!!

Ps....your windmill analogy might be a little more relevant. Wind is caused by the uneven heating of the Earth's surface.

Baker said:

I found this on youtube. I think it does a good job of explaining how a turbo works.

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That's a great little demo, Baker.Thanks.
It shows an intercooler at the 2:50-3:00 mark and, going back to my original starting post, we can call that an aftercooler as well, right?

Learned a bunch more than I asked for in this thread.

Hawgwash said:

That's a great little demo, Baker.Thanks.
It shows an intercooler at the 2:50-3:00 mark and, going back to my original starting post, we can call that an aftercooler as well, right?

Learned a bunch more than I asked for in this thread.

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In this case, I think intercooler and aftercooler are interchangeable....as stated in Ski's excellent post earlier(post #3).

"And THAT IS THE REASON why turbodiesels dominate the current modern market. They are more efficient...hence they burn cleaner...hence less pollution."

This is true for a modern industrial engine , installed and operated as it was designed.

Take a real 350 HP diesel and require 40HP for 99% of its life and there is no efficiency.

Only massive costs for the never seen high speed Most folks prefer 2-4GPH to 20+ GPH

For many folks the best use of a turbo is in their car. 3X the normal HP is required for 0-60 in under 4 seconds or 15 seconds to get to 155MPH.

Then the car goes back to 40mpg down the highway requiring 2 GPH at normal 80mph cruise.

A turboed 60-80 hp engine for our rec. trawler power requirements is hard to find!

FF said:

"And THAT IS THE REASON why turbodiesels dominate the current modern market. They are more efficient...hence they burn cleaner...hence less pollution."

This is true for a modern industrial engine , installed and operated as it was designed.

Take a real 350 HP diesel and require 40HP for 99% of its life and there is no efficiency

Only massive costs for the never seen high speed Most folks prefer 2-4GPH to 20+ GPH

For many folks the best use of a turbo is in their car. 3X the normal HP is required for 0-60 in under 4 seconds or 15 seconds to get to 155MPH.

Then the car goes back to 40mpg down the highway requiring 2 GPH at normal 80mph cruise.

A turboed 60-80 hp engine for our rec. trawler power requirements is hard to find!

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FF- Dave and I went into the numbers and found that a Cummins 6BTA 330 and 370, both highly turbocharged, make about 18hp/gph while running on the prop curve, making 50hp at 1400rpm. That is pretty dang good, probably better than a FL 120 NA engine making the same 50hp.

So there is is no basis for your statement highlighted in bold.

The 6BTA making 50hp in trawler service is quite efficient. If the extra hp in the top end is not used, it will not cost you fuel. And experience has shown that it also does not hurt the engine to run at that point.

Very similar to the duty cycle of similar B engine in a pickup truck, 1400rpm, 50hp, 2.8gph, say 60mph, that's 21mpg, which is about what they get in steady state.

I certainly support Ski's analysis above.


It would be nice if the recreational marine diesel manufacturer's made a slow turning, non aspirated, 100-150 hp engine today like the Lehman or the Perkins, which would be perfect for most slow trawlers. But they do not.


So you have to live with a 230 hp Cummins QSB, a D4 Volvo, etc for a new boat and run it low and slow. But as noted above, it will be efficient and environmentally sociable, albeit expensive.


David

These are the kinds of threads I like!!!

djmarchand said:

It would be nice if the recreational marine diesel manufacturer's made a slow turning, non aspirated, 100-150 hp engine today like the Lehman or the Perkins, which would be perfect for most slow trawlers. But they do not. So you have to live with a 230 hp Cummins QSB, a D4 Volvo, etc...

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David you read my mind.
I was just trying to formulate an easy to understand question about the need for big space occupying TAs in a 8-10 knot boat when there are FL, JD and Yanmars that would do the same and be easier to access...or would they??

Hawgwash said:

David you read my mind.
I was just trying to formulate an easy to understand question about the need for big space occupying TAs in a 8-10 knot boat when there are FL, JD and Yanmars that would do the same and be easier to access...or would they??

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NA engines of that size and power do not fit the EPA footprint for emissions. That is basically what put Bob Smith's 140hp Lehman replacement out of business....sadly!!!! What a perfectly great engine....contrary to what Marin thinks!!!!...

Baker said:

....contrary to what Marin thinks!!!!...

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Oh, ****! Here we go.

Actually I forgot about the John Deer 4.5 liter engine. Even though it has a turbocharger, it runs slow, about 2,400 rpm and the after cooler is jacket water cooled which minimizes corrosion problems. And even though it is a 4 cylinder, it should be fairly smooth as it has a balance shaft. It is also common rail injected, so it should be environmentally sociable.


Not surprisingly that engine is used on the smaller Nordhavns and would work with any trawler of 35' to 45' range if all you wanted was to go at displacement speed.


David

djmarchand said:

Actually I forgot about the John Deer 4.5 liter engine. Even though it has a turbocharger, it runs slow, about 2,400 rpm and the after cooler is jacket water cooled which minimizes corrosion problems. And even though it is a 4 cylinder, it should be fairly smooth as it has a balance shaft. It is also common rail injected, so it should be environmentally sociable.


Not surprisingly that engine is used on the smaller Nordhavns and would work with any trawler of 35' to 45' range if all you wanted was to go at displacement speed.


David

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I think that is what powers Mark Pierce's Coot.

Also I think OC Diver put a Deere 4045 in his. Probably the best option for true displacement hull boats. Deere stuff has a good reputation.

Frustrating, I looked at the Deere website to try to peel off some burn numbers, not easy to do from the graphs. I really get spoiled by the tabular data Cat and Cummins publish.

It looks like the M1 4045 is turbo, no aftercooler and a mechanical injection pump. So no electronics?? Data sheet is not very clear on tech details.

At 50hp, it looks like it is just under 3gph. Not super good, about 17hp/gph. Not bad either.

I went looking at Cummins for low hp versions that might be appropriate for trawlers, the lowest qsb is 230. At 43hp at 1400 it is 2.6gph, that's 16.5hp/gph. Not very good for all the high tech computer stuff and common rail. At 85hp at 1800, it gets a little better at 18hp/gph.

Since I am completely boooorrreed waiting again for the stupid framing crew to show up, NOT!!, and it is cold as crap outside, I looked at the QSL 9liter rated at 285hp/1800rpm. At 49hp at 1000rpm, it burns 2.6 fro 19hp/gph. Better than the smaller QSB!! At 107hp at 1300, it burns 5.5 for 19.5hp/gph.

So that big engine does better on fuel than the little 5.9liter. It is basically a C series 8.3 with longer stroke, and that engine for some reason has always had good burn numbers in all the ratings.

I think part of the unspectacular CR burn rate numbers stems from the NOx control, so I've heard. Later injection timing or such...

So if you want a big slow turning motor for making 50hp, that QSL is a pretty good prospect. Apparently available KC, not sure how they handle aftercooling, probably still SW, which would suck. Not sure how good for it it would be to loaf along at 1000rpm for it's whole life. I'd rather run a qsb or 4045 Deere at 1400-1600 and pay the tiny fuel penalty.

And that QSL is bound to be dang expensive!!

Does Cummins make a 4 cylinder QSB???

Baker said:

Does Cummins make a 4 cylinder QSB???

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QSB for Agriculture (Tier 2) - Cummins Engines
Wonder, do they Marinize it?

Baker said:

Does Cummins make a 4 cylinder QSB???

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If that is the same engine family that Dodge uses there is a 4 cylinder version used in small equipment. Had one fail in a Dresser dozer several years ago from lack of oil, it was being worked on a steep slope. Complete new engine was around $2,400.00, way less than parts and machine shop charges to rebuild.


Sent from my iPad using Trawler Forum

Yea, they make a qsb3.9 and qsb4.5, both four bangers, based on the 5.9 and 6.7 sixes. Have yet to see them offered in marine dress.

I went roving around the Volvo site. The D4 and D6 were around 18hp/gph at 50hp. I found a commercial engine, the D7A rated at 177hp and 1900rpm. This one was over 20hp/gph at around 50hp. But I don't think that one meets emissions as there was no tier 2 listed in its certs. Probably meant for third world export.

FF said:

"Take a real 350 HP diesel and"

What would you estimate the service life of that engine at its rated 350 hp?

Why is it not chosen when 350 HP is required 24/7?

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Not sure what your question is. If you are going to run the engine continuous at its rating, you would want an engine designed for that, they are called "continuous duty" or other similar term, and they are readily available.

The QSL9 around 300hp is rated to run at that hp 24/7/365. Most other brands have similar offerings.

And they are turbos with aftercoolers.

High output engines like those used in sportfish are rated to spend only a fraction of their hours at rated power. How long would they last at full? Crapshoot. I do know the mfr's dyno test preproduction engines at like 110% load for thousands of hours prior to releasing them, mostly to find weak spots and protect them from warranty exposure.

Given Baker's simple video and Ski's post 3;
TI: Turbo to cooler to blower to engine
TA: Turbo to blower to cooler to engine
is there a preferred, more efficient setup?

Hawgwash said:

Given Baker's simple video and Ski's post 3;
TI: Turbo to cooler to blower to engine
TA: Turbo to blower to cooler to engine
is there a preferred, more efficient setup?

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As I said earlier, I understand ours as turbo to cooler to engine, no extra blower involved.

-Chris

Hawgwash said:

Given Baker's simple video and Ski's post 3;
TI: Turbo to cooler to blower to engine
TA: Turbo to blower to cooler to engine
is there a preferred, more efficient setup?

Click to expand...

The above distinction between TI and TA applies only to Detroit two-strokes. TI preferred as air temps are lower, but that is just MHO.

Four strokes TI and TA mean the same thing.