TA vs TI?

I see DD often described as being TI, as in 8.2TI.
Is there really any difference between TA and TI?

There is, but I'm not the best one to describe it. Something about when/where exhaust gasses are being used in the specific system. In our current system (not DD), exhaust gasses drive the turbo which is before the aftercooler. Maybe in an intercooled system the cooler is before the turbo.


Maybe. Somebody with a better clue will chime in.

Anyway, FWIW, we had a DD 8.2T and I don't remember ever seeing that written with either an I or an A.

-Chris

All 8.2's have the same "charge air cooling", which is a better technical term than aftercooler, TA, or intercooler, TI. It's a four stroke so the cooler is simply a cooler between the turbo and intake manifold.

On DD two strokes, there is a difference. A TI has the charge air cooler between turbo and blower, a TA has the cooler between blower and engine.

TI: Turbo to cooler to blower to engine
TA: Turbo to blower to cooler to engine

In general, v-block two strokes the TI is lower hp rating and better for trawlers. TA for top ratings. The inline two strokes don't have room for a TA cooler, so they are all TI.

Lower hp ratings may have a turbo and no charge air cooling, those are "T". Like 8.2T, 6BT, 671T, etc. Even lower rating no turbo at all.

Depending on the market, be it cars, airplanes, boats, locomotives, ships, etc.. Some call a charge air cooler an intercooler, some call it an aftercooler. So it can be a little confusing. VW jetta calls it and intercooler. Cummins calls it an aftercooler. Plumbing wise, same thing. You can always call it a charge air cooler.

For some manufacturer's like Cummins the "A" means after cooled whether coolant or sea water. For Detroits the "I" and the "A" seem to mean the same thing depending on the year and model. "I" designates intercooled which means the same thing as after cooled.


I was typing this when Ski posted. His is a much better answer.


David

Thanks guys.
Pretty straight forward answers.
I was talking to the owner of an 8.2 TI boat that he has had for 20 years. Asked him the difference and he didn't know. Now I can tell him. ��

Follow up.
Which DD models are 2 stroke?

DD four strokes: 8.2, series 50, series 60.

DD two strokes: Anything 53, 71, 92, 110, 149. Those numbers are the cubic inch per cylinder, and came in lots of cylinder counts. Some in-line, some vee block.

For example, a 71 could be 1, 2, 3, 4 and 6cyl inline. And 6, 8, 12, 16 and 24 cyl vee block.

6-71 inline
6V-71 vee block

I really appreciate this thread from obviously knowledgeable members. Am I right in thinking that the after/inter coolers and the turbos are all efforts (or part of the design) to increase hp? When someone uses the term naturally aspirated in the 3208n, for example, is the aspiration referring to how the motor is cooled? It would make sense that if you do not have an after-cooler (or inter-cooler) and you do not have a turbo, there are just so many fewer things that can bite you in the butt regarding mechanical failure. And, I have heard great things about the Cat 3208TA 375hp engine, as far as being really sturdy and dependable. It is a turbo and the "A" refers to after-cooler I believe, so why is that engine so well thought of when a 425hp or higher hp Cat is somewhat suspect?

Turbos and aftercoolers relate to the intake air only, nothing to do with cooling the engine.

Turbos and aftercoolers both allow higher hp per pound of engine, and also somewhat increase efficiency.

If the power is increased too much, the engine can't handle it and reliability suffers. That was the case with the 3208TA 425, 435 and 450. Experience showed that the 375 could handle it, thus it's reputation.

Most modern engines are designed from the git go to be turbo'd, so there is no reliability penalty. Some more maintenance and some more failure points.

Always a good idea to look skeptically at the highest hp rating of a given engine block, generally the ones a few notches down from the top hold up better. But not always, some high hp versions do just fine.

Cuttyhunk47 said:

When someone uses the term naturally aspirated in the 3208n, for example, is the aspiration referring to how the motor is cooled?

Click to expand...

A naturally aspirated engine is one that has neither a turbocharger or a supercharger and it uses the intake vacuum of the cylinders to pull in fresh air for combustion.

Thank you both. I could write a book about what I don't know about diesels.

Here is a quick tutorial while I sit on the screened porch in Oriental, NC enjoying the warm weather, for now.

Initially and probably for the first 75-100 years, all diesels were naturally aspirated which means there is no turbo.

Then to digress a little bit the Detroit Diesel 2 cycle came along during the 40s. It requires a supercharger to push fresh air into the cylinders and scavenge the exhaust gasses. It can't be a turbocharger because turbos only work with significant exhaust gases going through which won't be the case at start up or at idle. So the supercharger is mechanically driven.

With that aberration behind us, in the 70s approximately, some diesels were made with a turbo charger to push more air into the cylinders so that more fuel could be injected and make more power.

But there is a limit because as air is compressed in the air side of the turbo charger it gets hot and heat kills engines. So the practical limitation is to add about 50% to the NA power.

Let's digress a bit more. A turbo charger has two housings and impeller wheels connected by a common shaft. The exhaust wheel turns when high volume exhaust gasses pass through and that turns the air wheel which is a compressor. Mild non aftercooled turbo charged engines boost about 10 psi. Any more will overheat the engine components.

But if you cool the exhaust gases then you can boost to a higher pressure which puts more air in the cylinder and with more fuel injected produces more horsepower. The first were probably cooled by jacket water which has a temperature of about 180 F. It will cool the compressed air down to the low 200s.

But to get even more horsepower you can cool it further if you use seawater which will cool to the low 100s.

So looking at the Cummins 6B series, the NA version produces about 150 hp, the turbo but non aftercooled version makes 210, the jacket water cooled version makes 250 hp and the sea water cooled version makes as much as 370 hp and its boost is about 30 psi.

To be honest it wasn't just the turbo charger that allowed the Cummins 6BTA to make two and a half times the horsepower of the NA version. it was also better valve materials, oil jet cooling on the bottom of the piston, etc. that let it go that high as well as higher rpm operation.

Automotive based engines like the VW/Mercury or the BMW/Yanmar are now up to almost 90 hp per liter at 4,000 rpm. Whether they can last long at high power loadings is another question.

And back to the Detroit 2 cycles. They have both a supercharger for startup and low rpms, but modern ones have a turbocharger before the supercharger.

David

All that thought and research invested so that we can get there sooner! Big ticket initial costs, increased costs to maintain and quadruple the fuel costs so that we can get off the water sooner? Can't wait until the next improvement! Being facetious of course.

And seriously, thank you for explaining the evolution for us diesel dummies.

Thanks for the information and clear explanations.

ken

ktdtx said:

Thanks for the information and clear explanations.
ken

Click to expand...

Yes, ditto.
I read Calder and it didn't sink in.
This crowd did it for me.
A hundred years ago when I was studying steam, I got knotted up on saturated and superheated then out of nowhere the light went on.

Aftercoolers and intercoolers only cool the intake air charge, not exhaust. Actually, keeping the exhaust hot into the turbo creates more boost. Older DDs with "dry" turbos made more hp than the later model same engine with the "wet snail" exhaust housing.. Some DDs are both after and inter cooled, with high flow bypass on the blower. The supercharger (blower) actually becomes a restriction at high turbo boost.

kulas44 said:

Aftercoolers and intercoolers only cool the intake air charge, not exhaust. Actually, keeping the exhaust hot into the turbo creates more boost. Older DDs with "dry" turbos made more hp than the later model same engine with the "wet snail" exhaust housing.. Some DDs are both after and inter cooled, with high flow bypass on the blower. The supercharger (blower) actually becomes a restriction at high turbo boost.

Click to expand...

Thanks for that clarification of the previous clarifications by djmarchand and ski, Kulas. I was really chuffed by David's explanations, and he had me until he said...

"But if you cool the exhaust gases then you can boost to a higher pressure which puts more air in the cylinder and with more fuel injected produces more horsepower.".

Now having owned turbocharged cars for the last 30 years, one with an intercooler, I knew that he probably meant the 'compressed intake air, and not exhaust gases, (which do the compressing, right?), was cooled in the intercooler, and then Ski confused me with the references to turbos and blowers, until I twigged by 'blower' he meant a supercharger in there as well.

Now it all makes sense. Previously when folk referred to aftercoolers I used to think, "why would you bother cooling the exhaust gases, other than thru the wet exhaust. Now I understand the terms intercooler and aftercooler are synoniminymous, that makes sense as well. Thanks all.

Turbos and all the goodies added to a NA are to increase the power.

This requires an increase in fuel burn.

An engine is considered to be able to burn a certain number of gal of fuel before its worn enough for a rebuild.

Burn fuel at 3 times the basic rate and the engine life in hours will be at least 3x shorter

If you need plenty of power to operate a sport fish the goodies will give it to you.

If you operate a displacement boat there is little need for the cost and complexity of turbos or anything else.

Just install a DD that operates at 60%+ of rated HP or more and enjoy the insane number of hours these NA engines can operate.

Happily the 1936 design allows some selection of rated HP by changing injectors or timing,if the vessel service changes.

Ski in NC said:

On DD two strokes, there is a difference. A TI has the charge air cooler between turbo and blower, a TA has the cooler between blower and engine.

TI: Turbo to cooler to blower to engine
TA: Turbo to blower to cooler to engine

Click to expand...

djmarchand said:

And back to the Detroit 2 cycles. They have both a supercharger for startup and low rpms, but modern ones have a turbocharger before the supercharger.

Click to expand...

Blower? As in supercharger? Those TI/TA descriptions specific for 2-stroke DDs, yes?

I'd have described ours -- Cummins 8.3CTA -- as turbo to cooler to engine...

-Chris

THE "blower" on any 2 style DD is in reality a method of exhaust savenging.

By blowing out the old spent gasses the efficiency is increased.

The cylinder is charged thru holes drilled in the cylinder walls so some modest push is helpful.

While there may be a pound or 3 of blower pressure these DD are never considered to be supercharged.

The blowers are great air pumps and have been bolted on to race cars to supercharge them.

FF said:

Turbos and all the goodies added to a NA are to increase the power.

This requires an increase in fuel burn.

An engine is considered to be able to burn a certain number of gal of fuel before its worn enough for a rebuild.

Burn fuel at 3 times the basic rate and the engine life in hours will be at least 3x shorter

If you need plenty of power to operate a sport fish the goodies will give it to you.

If you operate a displacement boat there is little need for the cost and complexity of turbos or anything else.

Just install a DD that operates at 60%+ of rated HP or more and enjoy the insane number of hours these NA engines can operate.

Happily the 1936 design allows some selection of rated HP by changing injectors or timing,if the vessel service changes.

Click to expand...

Turbos do not increase fuel burn. If you have a choice between a TA engine and and a NA engine to make say 300hp, the TA will burn less fuel doing the same job.

There's a good reason all modern industrial, commercial and ship engines are turbocharged with charge air cooling. Some ship engines run both high boost, up over 40psi, and log over 100,000hrs. Their goal is efficiency. Ferries, fishing trawlers, CG cutters, tugboats, etc... All turbo engines unless engines are from way-back.

In a trawler that only needs say 40hp on the shaft, an NA might be the best choice as the turbo engine optimized for that duty really does not exist on the market. Maybe a VW tdi running 2000rpm at high boost, but who wants such a tiny beast pushing a big slow boat.

Ski in NC said:

Turbos do not increase fuel burn. If you have a choice between a TA engine and and a NA engine to make say 300hp, the TA will burn less fuel doing the same job.

Click to expand...

OK Sky, you're right on this one. A turbo engine will not burn more fuel (at idle) but once you start extracting that extra horse power offered by the turbo, you pay for it in fuel costs and accelerated engine wear.

The reason why more engines are equipped with turbos are mainly due to environmental regulations requiring a more complete burn of the fuel. The secondary reason is you get more horsepower out of the same sized engine with nearly the same weight.

As my father used to say, if a candle burns twice as bright, it lasts half as long.

stubones99 said:

OK Sky, you're right on this one. A turbo engine will not burn more fuel (at idle) but once you start extracting that extra horse power offered by the turbo, you pay for it in fuel costs and accelerated engine wear.

The reason why more engines are equipped with turbos are mainly due to environmental regulations requiring a more complete burn of the fuel. The secondary reason is you get more horsepower out of the same sized engine with nearly the same weight.

As my father used to say, if a candle burns twice as bright, it lasts half as long.

Click to expand...

You didn't really read what I posted. If you need 300hp down the shaft, and have a choice between NA and TA engines to do it, the TA will burn less fuel.

And no, turbos have nothing to do a more complete burn of the fuel. Both NA and TA engines properly designed, in good shape, and operating in the middle of their map burn virtually all the fuel, cleanly.

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?

A turbo is progressive. At idle, it idles too, whirring along at 20,000 RPM or so.

As you rev up the engine, more exhaust gases are created which spins up the turbo and crams more air into the engine.

You decide how much HP you need with the throttle. Faster = More HP.

Your peak economy would be about the point of peak torque on the engine.

Stu

Thank you for helping me understand this better. I had incorrect assumptions for sure.

"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."

IF the engine is being operated at a slow speed , where there is NO turbo boost the turbo becomes another restriction in the exhaust and will increase fuel burn.

Additionally if the compression has been lowered (compared to the NA) with no boost the efficiency will also be harmed.

All engines have a set of BMEP curves which hopefully the NA that selected the engine understood , and the owner operates as it was designed.

The hassle today is the lack of real industrial diesels in the 100HP range that have been marinized., and are common enough to obtain parts for.

Is the Caterpillar 3054B still in production? That's a low power NA platform that's completely marinized.

The Cummins 6B series of engines gives you the ability to compare fuel consumption for a turbocharged and NA engine at the same horsepower.

The data sheets and performance curves for the 120 hp 6B and the 370 hp 6BTA are available on Boatdiesel's library. I picked 50 hp as a reasonable slow speed trawler cruising hp to compare. As best as I can read the curve and as you might appreciate the 6BTA curve is hard to read at 50 hp, the NA engine uses 3 gph and the highly turbocharged 6BTA uses 3.5 gph.


Interestingly the NA engine produces its 50 hp (propeller curve) at about 2,200 rpm and the 6BTA produces it at about 1,600 rpm. So the turbo is definitely at work at that low rpm. You can see the torque curve head upward sharply at about 1,400 rpm to confirm this.


The factors at work here are lower compression for the turbocharged engine requiring more fuel but it operates at a lower rpm to produce that power than the NA engine which should reduce parasitic losses. I suspect that the exhaust back pressure from the turbo is mostly balanced out by the boost it produces.


The difference should be more dramatic at lower rpms and power.


David

David- I found a curve for a 330 6BTA CPL 1975 that has the tabulated prop curve burn data. Got it from Boatdiesel. Using the 2.7 exponent, which is what they used, you can calc hp. Got 50hp at 2.8gph at 1400. Easier than trying to pick numbers off a curve like they have for the 6B 115. Anyway, that comes out to 18hp/gph which is not too shabby running an engine at way low power.

Also, that engine uses the Bosch P7100 pump which is known for very "crisp" injection which is good for economy. The CAV pump in my opinion is a bit sloppy and it tends to show up in the burn numbers. The 6B and 6BT are fine engines, but when I do the burn rate calcs, if I can get the raw data, they are decent but not stellar.