8V92T no cooler?

[Hawssie]

I was wondering if there is a reason why the 8V92Ts don't seem to be inner cooled. I know that they are 2 strokes and also inherently require a supercharger just to run, so maybe its a 2 stroke thing? 500 hp from a 12 liter diesel without being inner cooled is rather impressive. Just wondered if there was some gains to be had with one.

 

[BiffJ]

To the best of my knowledge the 8V92T series has an aftercooler which is also known as an Intercooler. I have no idea what an inner cooler is.....
The aftercooler runs the compressed air from the turbo and mechanical blower through a heat exchanger which is cooled by the liquid coolant from the engine. It sits between the roots blower and the engine block. Air passes through it and then into the cylinders via ports in the cylinder wall. According to some spec sheets its a two pass system so I guess it either goes through 2 exchangers or goes through twice. One of the reasons they're getting so much horsepower from this "little" 12 l engine is that its a blown, turbocharged 2 stroke and since it is intercooled (or aftercooled if you prefer) thats how it does it. Most the 8V92Ts I've seen are only rated at 435-455 HP though maybe marine engines are higher rated.

Hope that answers the question.

Frank

 

[tim292stro]

There are many variants T, TA, TTA - some have water after-coolers (after the roots scavenging blower), some don't. Marine engines are rated higher since they use the ocean as the cooling system. The real reason they get so much bang from the engine is that it's a two-stroke - every downward stroke is a power stroke, whereas with a 4-stroke one half of the downwards strokes are power. That's also the reason for the need to run a roots scavenging blower - this does not super-charge and engine, it simply blows the exhaust out the exhaust valves while the intake ports at the bottom of the cylinder stroke are open (letting pressurized air from the air-box into the cylinder).

Intercooler vs after cooler has to do with placement in the process. If you have an medium-to-medium (i.e. air-to-air) heat exchanger between two turbos or between a turbo and a supercharger (or roots scavenging blower) - then you have an intercooler (it cools between heating steps). If you have a medium-to-medium heat exchanger after the last device (turbo or super/roots-scavengine blower) - then you have an after cooler (it cools after the last heating step). Most cars and trucks have an aftercooler, which everyone calls an intercooler. If you want to be a smart-@$$, you can ask a guy with a single turbocharger then and aftercooler before the throttle-body who calls it an "intercooler" - "Where's your other turbo?"

All of this aside, I'd prefer to not use the general engine water circuit that DD uses in the aftercooler - it's subject to the thermostat's set-point, I'd rather put the coldest water I could find into that circuit. You could also add an intercooler after the turbo, but before the roots scavenging blower to further cool the charge. The risk here is over-cooling the engine by chilling the air charge (two strokes don't like to be too cold).

 

[DrillerSurplus]

Like Hawssie I had wondered about an after cooler and did some research. As tim292stro says, there are lots of variations, but most of the turbo 6V92 and 8V92 Detroits have the aftercooler located below the roots blower. Some also have an intercooler in a box between the turbo and the top of the roots blower.

Both of them use the engine coolant and I agree with the comment above about that not being optimal in a truck application since the best you would do is cooling air to the 180 degrees of the water temp. Looks like quite a few folks reached the same conclusion. One solution was to get rid of the after cooler and install a large air to air intercooler similar to what you see on modern diesel trucks.

Lots of talk in various marine and racing forums on 8V92 engines doing pretty well for reliability at 650 horsepower, and not very well at 750. Even 650 would be a 30% increase. These engines have been around a long time. so lots of knowledge out there on getting more horsepower.

 

[HETvet]

I think chemical cooling between the turbo and supercharger would be great. Then using a standalone cooling system in closed circuit to replace the factory system.

Or a twin turbo set up and a 4 core air to air intercooler (dual in puts and a single out put) that discharges in to the blower, a stand alone closed circuit cooling system to replace the factory one; and add a little water/methanol injection after that. If you need more oxygen, spray it with some nitrous. Fire ring the head and block, add a high volume/high pressure lift pump and do some work on the IP, install hotter injectors and you have a loads of power potential. Keeping it cool is going to be hard though. But with the newer technology, I think it can be done.

 

[BiffJ]

Chemical cooling is a good idea and has been done. Our indycar engines at one point (2001 or so????) used another injector spraying into the turbo outlet before the intake plenum. The methanol evaporating into this flow dropped the charge temp enough to be useful and added a few HP to the output. As for using cooling water to inter or after cool the charge it is better than nothing at all and when you find that the air temps downstream from the turbo are in the 300-400 deg F range its easy to see why even 180 deg coolant is a good medium for aftercooling. For the Roots blower you're pretty much stuck with the normal coolant setup. There isn't much of a way to get another cooler in there since the blower is part of the engine case. I don't know what the compression ratio is for the roots blower but I'm sure there is a pretty good temp rise there too.

Frank

 

[tim292stro]

...Looks like quite a few folks reached the same conclusion. One solution was to get rid of the after cooler and install a large air to air intercooler similar to what you see on modern diesel trucks...

It doesn't take long for the aftermarket and racing people to pick up a few books on thermodynamics in diesel engines to figure out how to squeeze a bunch more HP out. As with any I.C.E., it's basically an air pump with a combustion stage in the middle (really simple in principal). It's that combustion stage that is the most important though, since heat affects how everything else works. The simplified thermodynamc model for a water cooled diesel engine is "30, 30, 30, ballance", where 30% of the heat leaves the engine through the expansion of the cylinder volume (i.e. work being done), 30% though cooling water, 30% through the exhaust air, and the balance through radiation from the block to the environment. Take the fuel BTU/hr value, assume perfect combustion, and that gives you a way to figure out the power target you want (and thus a fuel rate). Once you know the fuel rate, you can work out how much air is needed to get a good air-fuel mix, at a given RPM so you can figure out how to size a turbo or blower (or both, or multiple combinations). Then you need to size your cooling system to account for the amount of heat you're going to be generating. The "magic" in racing is the hard work it takes to figure out how close you got to "perfect combustion", and figuring out how to get closer. This again is the 80/20 principal - 20% of the effort gets 80% of the work done - this is fine for Bob the Bus Driver, Sally the Soccer Mom, or Private Pimple Face. That last 20% of the work though requires the remaining 80% of the effort, and is why racing team/companies spend boat-loads of cash figuring this stuff out.

...I think chemical cooling between the turbo and supercharger would be great. Then using a standalone cooling system in closed circuit to replace the factory system...

For a DD 2-stroke, this is probably the most correct place to do any cooling - there is a bypass valve in the roots blower which allows a turbo charger before the blower to pressurize the air charge more that the gear-train driver blower can based on engine RPMs. Also since the turbo uses hot exhaust gasses to charge the air, there is some thermal coupling unless you have a turbo with a ceramic exhaust impeller and shaft.

 

[HETvet]

I also know fine mist of water can increase the compression due to it not being compressable. And I think keeping the factory charge cooler under the blower with its own dedicated coolant flow, lines, pump, and "radiator" would be great. A large surface area multi core radiator with great heat transfer abilities, and a fluid that also has great heat exchange rate. Maybe even some sort of water misting system on the aftercoolers.

 

[HETvet]

I personally think going with 2 turbos in to an after cooler, in to the blower, through the above described after cooler system for the blower would be the best way to reliably get IATs to ambient. I would also like to see EMP and IMP pressures here to see how efficient the system is. With it being a 2 stroke, I bet the EGTs are low due to the volume of air being used to discharge the cylinders of exhaust gasses. This leaves little to be used to spool the turbine. So I feel that exhaust wrapping would be use full here. Also going to the point of port matching and manifold smoothing.

 

[tim292stro]

It's as efficient as a 2-stroke diesel . That said as low revs there is hardly enough to spool a turbo, on my stock 6V92 in my bus it won't spool until 1400RPM - but it will eventually spool (this is turbo sizing). When combustion happens in an I.C.E., there is expansion beyond the volume that was put into the cylinder during compression - this is what pushes the cylinder down. For a two stroke, the exhaust valves should open a bit before the intake ports at the bottom of the piston stroke are revealed as a pressure relief. This prevents the exhaust gasses from pushing back into the intake plenum (air box under the roots blower). To get the best efficiency, on a two stroke DD you want the roots blower to be geared and sized just right so that there is at least as much air pressure in the air box as the cylinder when the exhaust ports are relieved - slightly higher. Any more pressure driven by the blower would add work to the gear train after all it takes effort to compress air, and this would be power you don't get to use at the flywheel.

Since the pressure is relieved before the intake ports are exposed, this means any positive pressure in the cylinder is let out the exhaust manifold and is available to power a turbo. This is also why it's very important not to over-fuel a 2-stroke, since all of the exhaust valves are at the top of the cylinder (in the head), so any incomplete combustion during the power portion of the stroke can continue as the exhaust gasses exit the cylinder, through the cylinder head, and out the exhaust manifold. This is a great way to burn up a 2-stroke (lugging, evidenced by billowing black smoke out the tail pipe), since the head and exhaust manifolds are cast iron and will warp or crack (which can let out your cooling water and leave you up a stinky creek without a propulsion device). If you have an EGT gauge on a 2-stroke and lug it, you will see a spike in temps. Exhaust wrapping will help keep the hot air in the header/pipes before the turbo so that the further expansion of the gasses as it passes through the power turbine cools only as it exits the tailpipe. The important thing with turbos is figuring out the air volumes (expanded exhaust gas vs intended air charge). This is a recursive calculation so hard to "just work out", but turbo manufactures have pretty good look-up tables for sizing based on engine volume and RPMs.


Again here, with I.C.E. the idea is to lose as little power to the movement of air volumes, while maximizing the amount of effort that pushes the pistons down (work produced). Things like moving air too fast will induce turbulence, which saps power. Tight bends are harder for air to go around than long sweeping bends with guide vanes (think of cartoon characters running into each other as they exit a room and make a turn in a hallway) - bigger pipes will slow down air speed for a given volume. The flip side there is that bigger pipes create a larger TOTAL volume, so there is a real balancing act for things like intercooler size and turbo to intercooler piping - a larger volume takes longer to get to a given pressure, so simply "going big" may actually be hurting performance. There's no such thing as too big an air filter or pre-turbo piping or too big an exhaust pipe after the turbo though - since you're not trying to compress that gas, any reduction in air-flow resistance is a net gain.

 

[tim292stro]

I guess the other important thing to point out is that an engine is a "system of systems", so making a change to one system without thining about the impact the all of the other systems is a recipe for a short engine life.

 

[HETvet]

I see your point with the blower and turbo thing. But where is the heat retention pre turbo? And "blowing" heat/exhaust out the ports should cool the exhaust. I think the limiting factor is the cam shaft fired injectors. I think with a different nozzle and higher pop pressure being fired off with electronics; we could get a hotter burn, more fuel burned, and more control of advanced e/retard. Instead of basicly just dumping fuel and hoping it burns; we should give it smaller injection pulses with a finer spray pattern delivering the same amount of fuel per combustion stroke. I think that would give the best results for power and effecenct. Any thing beyond that becomes a heat retention/heat disappointed game.

 

[tim292stro]

This'll get a bit more involved -and probably makes some people's eyes glaze over...

When the exhaust valves open there is a pressure wave that exits the cylinder most of the increased pressure in the cylinder is lost very fast, in fact the pressure should be slightly negative in the cylinder as it expands and the intake ports at the bottom of the stroke are revealed. The hot exhaust gasses leaving the cylinder through the head are still expanding a bit and cooling as a result of the expansion, but the majority of the cooler air entering the cylinder is not mixing with the hot combustion gasses, rather it's pushing the exhaust gasses out of the cylinder volume. For the sake of some simplicity, think of the hot combustion gasses and cold intake air as water and oil. You are merely displacing the oil which floats on top of the water out of the cylinder (this is the over-simplified elementary school demo, and is intended to illustrate the principal rather than explain how varying density and temperature media interacts at the interface front).

I'm not clear on what you are asking about the heat retention pre-turbo... Are you asking before the compressor or before the power turbine (just guessing the latter). As the exhaust gasses leave the cylinder, you want less of that heat to be absorbed into the walls of the exhaust passageways, and more of it contained in the gas itself. If you've ever let the air out of an air compressor, you'll note that it is cool or cold, this is an effect quantified by the Gay-Lussac gas law. Molecules running into each to other makes heat (like friction), so squeezing molecules closer together makes heat (since molecules can run into each other easier due to proximity). Cooling a compressed gas then reducing the pressure of that gas will cause molecules to spread out and not run into each other, and this cools the medium down. By the same effect, heating a gas which was at room temperature and ambient pressure (in a confined space), will cause the pressure to go up - this effect can be witnessed by putting a closed Tupper-ware in the microwave and watching the top blow off. The reverse is done in food packaging to "vacuum seal" food - it's heated well above room temp at ambient pressure, then a lid is put on and the food product is allowed to cool, this reduces the pressure in the container. By that last example, that is the effect you don't want to have happen mid-traversal of the exhaust header, and manifold - you want all of that pressure and heat (both interrelated) to appear at its earliest convenience at the fins of the power turbine, at as close the the exit pressure and temperature of the cylinder. This will provide the maximum amount of energy transfer to the fins of the power turbine as the gasses expand out to an un-constrained volume of the exhaust system and muffler (i.e. vent to open air). By the same measure, you don't want heat transfer from the hot side of the turbo to the cold side of the turbo, since that would heat the intake air at ambient pressure, which would make it act more like a spring than a fluid since it would want to spread out more (think of this like "vapor lock" for air).

In an efficient engine, you aren't spending a lot of time mixing things, rather it's better to segregate the gasses completely if possible. This is the reason for the move from 2-stroke to 4-stroke - it is more efficient, and easier to control how the gasses behave, since you can completely change the volume of air with very little interaction due to the addition of two distinct cycles (intake and exhaust). Greater separation allows for other systems like EGR to have simple expectations, so their design is easier. This also doubles the time per full cycle traversal (since there are twice as many), so it makes things like computer control easier. Software designers like their problems simple and constrained, especially on cheap hardware.

Higher fuel pressure means that you will be able to push more volume of fuel into the cylinder, electronic injectors do give you added control of timing and in some cases the ability to do multiple injections. In the first case, yes you are getting more fuel into the cylinder, but you can already do that with larger injectors (try the G90 injectors for the 8V92, that's 90cc of diesel per stroke). Good electronic control and higher popping pressure of the injector means that you get tighter control of the combustion timing, this again is great for software engineers since the equations they use to control the air-fuel mixture gets easier when there aren't uncontrolled variables. The ability to do more than one injection per power stroke helps keep the flame front from coming in contact with the piston (good for reliability), allows for internal shock-waves within the cylinder to mix the air so the likelihood of complete combustion is higher (lower emissions), keeps the combustion temperature lower (lower emissions, less heat soak), and actually makes the engine quieter (10x of .22 caliber rifle shots are a lot quieter than one .50 cal shot). Finer spray pattern also lets the air mix with the fuel - the term you are looking for here is "atomization", basically you want the fuel to mix with the combustion air at the correct air-fuel ratio, but also do so down to the molecular level.

This is beyond the design of a 2-stroke though - I think patracy had a thread in conversations about making things too complicated, really the DDEC systems are not great because they are trying to solve a problem that you really need a 4-stroke with. I'm in agreement with patracy about over complicating this if you're trying to add a system like DDEC or roll your own to a MUI 2-stroke - really what you want in that case is a modern 4-stroke that was designed that way

That said, by doing the simple things like keeping the air filter restriction low, and the exhaust back-pressure low, you will notice reasonable gain in performance, properly sizing the engine, turbo, injectors and radiator/intercooler will help too.

 

[Hawssie]

Holy smoke this is all above my head. Although I didn't specify earlier the vehicle I was referring to is a M1070. So what I am gathering is that a factory water to air cooler is already under the blower. With all that you guys have said, would a typical air to air cooler for the turbo help at all in this application? If you answered this already I apologize but it must have flew over my head!

 

[tim292stro]

Yeah, I was worried that it was a bit much

If your engine is turbo'd it probably has the aftercooler under the roots blower. The general consensus from after market modifiers is that you can remove the aftercooler, then install an intercooler in front of the radiator. This cools the air better than the hot water that is circulating through the aftercooler .

You can probably find an air-to-air intercooler from a commercial truck application that will squeeze between your grille and the radiator - I'm not that familiar with the M1070 component layout (I'd defer to the likes of DieselFreak88M for something like that), but you might need to shuffle so things to make space. Really not much you do is going to change the MPG, but you can get more power that way. I'm not really sure why you'd need more power with such a low-geared tractor. What are you dragging that's heavier than an M1A2?

 

[tim292stro]

If you're looking for a power modification to a V71 or V92 engine, I'd actually recommend a guy I've talked to from the Bus Conversion world: Don Fairchild. He comes highly recommended from all the people I've talked to, I invite you to do some checking too, as always YMMV and it's been years since the last time I spoke to him. They are in SoCAL - Don should be able to work with you for a parts list for a certain power level, and you might try going to a DD service center and picking up a copy of Detroit Diesel publication: 18SA0353 - Cooling System Guidelines for Radiator Cooled Engine Applications

don@cctskit.com

 

[HETvet]

I completely grasped what was said above. Than You for that explination. I feel that going to an intercooler after the turbo could net some gains. The compressor housing would need to be clocked 190 - ish degrees, hot side pipes going in to the heat exchanger then back in to the blower. It can be done, there is a lot of room to get it to fit. But I think that having the coolant being the final cooling system; it's going to negate any positive effect the air to air had. The first problem is by passing engine coolant neighborhood used as a charge air cooler. Once that has been accomplished, then the above intercooler would come in to play. And as I have said, the materials used to construct the stand alone liquid charge air cooler is going to have a great effect on final IATs.

 

[tim292stro]

And if you do that, you can locate the radiator for the aftercooler outside the existing engine air streams - this is similar to what was done on the A1, lot of coolers everywhere, not all of them stuck on the front of the radiator. After all, if you're spendinf the time to make sure that you aren't mixing engine temperatures, why not ensure you're not adding heat back in somewhere else?

I saw a NatGeo thing about transport deployment in Iraq, it seemed that the HET didn't do well with high ambient temps, this is probably a result of 110° ambient air being further heated by 180° "cooling" water in the aftercooler, then having things like the trans-cooler mounted in front of the radiator adding heat to the air the radiator was breathing.

 

[Hawssie]

I can now see how the Detroit is in a tough situation for cooling the air as it has the turbo that heats up the air then the roots blower. And it would only make sense that the cooling would be most efficiently done after the last addition of heat. So it sounds like the location of the cooler is in the right place, and leaving out wether the specific cooler is large enough or efficient enough, it seems that its main drawback is that its engine cooled. I am talking theoretical as I don't even know what the water to air cooler looks like in this application. But maybe you could provide it with its own radiator with a circulating pump? Not sure if it would be a good idea or not and wether its worth the trouble, but at least it wouldn't be dependent on the engine temperature. Then if you added a pre air to air cooler you wouldn't have the later addition of engine coolant heat.

 

[HETvet]

Your exactly right. What I'm talking about is basicly what Ford did on the GT. It's got a supercharged 5.4 that's mounted in the rear. It has a heat exchanger under the blower and coolant lines that run to the front of the car that are connected to another heat exchanger. This system operates by its self with its own electric pump. It's good enough to keep the IATs down to about 50-75 degrees above ambient @32 psi in a twin turbo application.