XLR8R

Intercooling is an excellent way to raise charge-air cooling efficiency to where enough air for big HP can be delivered by "towing" twins. If a primary operating at a 2:1 PR pushes 100*F air through an IC to a secondary operating at 3:1 PR, I would expect the hot & cold sides of the CAC to be 350*F & 125*F, respectively.

Of course, the secondary turbine would have to flow/bypass enough gas in relation to the primary compressor.

The point is, the key to power production with turbocharging is proper thermal management.

NoSeeUm

The "Total Boost" DF is refering in the formula is actually CAC inlet pressure. Still, if he assumes a negligable pressure drop across the CAC and then given that, the CAC temperature drop only effects mass flow rate not total boost.

The formula works because it determines the boost value that PR1 = PR2. Knowing the boost, then one can determine PR1 and PR2.

The CAC temperature drop is after both compressors.

The CAC inlet temperature I find useful for comparing different compressors, twin vs single, PR1 vs PR2, psi vs psi, configurations etc.....

Jim

NoSeeUm

I think you forgot to add fuel? Your corrected gas number would be 1-4 lbm/min higher. Your example assumes you are turnning the engine via a external source and you just want to focus on gas flow through the turbine?

I was going to to a Turbine 102, but to simplify things. You are correct, a turbine relies on mass flow to do work. In the simplest turns it needs mass flow and a differential pressure. The differential pressure is much more effective because the gas is hot and much more greatly resists depressurization.

This is why corrected gas flow works so well I hope I understand. It corrects and more accurately standardizes the mass rate for all conceivable gas temperatures and inlet pressures / differential pressure. The TDP for your example above is bascially zero so the PR is basically 1. In fact, is the turbine itself doing any net work because the compressor is not making any boost?

Now, lets add some fuel, make some Hp and get your turbo spooled....

Jim

Diesel- Dummy

Thanks Hohn, I think all of us understand that there is a trade off when it comes to "performance turbos " but to say that you cant build an efficient set of twins to tow well and make big power sounds like what people said 100 years ago about going to the moon . I think with time someone will come up with something to fill this need but for now compromises are required. Just one more thing what if an s-300 on top with an A.R. of .55 and a 65 mm ex wheel and a exturnal gate[ for more flow] setup say with a 62 mm comp wheel over a s-480 sound like a good compromise for 700 + hp ??

HOHN

DD--I guess in order to have meaningful discussion on your particular tangent, we'd have to accurately define what is "efficient" and what is "towing well".

The day may come where we find a good way to reliablu retrofit VGT into a compound setup. But that day isn't here yet, so we aren't going to the moon. Unlike the moon trip, this isn't a lack of technology-- it's that we can't figure a way around the laws of physics.

For example, I can find way to exert more force on turbine wheel, make it have less intertia, reduce CHRA friction and all that, but in the end, it still has mass, it still needs a certain amount of mass flow, and I can't get around those obstacles completely.

If you're going to push enough fuel for 700hp, I'd consider an 85 or 88mm inducer size primary. The 62mm secondary should flow enough to help get it spooled. You'd be surprised just how a slightly larger top charger allows a significantly larger primary to be used.

Mike Holmen

What kinda of truck is it going on p pump, vp or cp engine? What gears, tire size, do you tow? If so how heavy? What size of exhaust you planning on using? You shifting gears automatically or with a stick. As Hohn, stated you should go as big as you can manage for a primary. The S400, 74mm inducer is a good choice. Its rated to 500 to 800 HP out of air werk catalog. You can tweak the turbine housing via math or just try it out and see how it works. I find that the math will just get you into the ball park area. How hard you drive and how much load does the rest. I tow, so me personally I like the larger A/R ratio on the turbine housing, larger inducer and large wheel sizes (more air, less Pratio) and sometime less interia mass. Managing egt's is important. As Hohn stated, most of the time you only need a Pratio less than 3:1. Most large turbos do that easily.

HOHN

You assume more efficient compressors than I do, because I have that temp at 368. That cold side temp like good, but it's tricky to achieve that with twins.

It makes sense now that I see the assumption that PR1=PR2. Hence the PR1^2 term.

CAC inlet temp is useful, but not that useful. The same PRs with the same efficiencies will yield the same result, whether it's one stage, two stage, or three stage compression. For example, a single stage at PR4 and 70% gives the same result as two stages each at PR2 and 70%. Of course, finding a compressor that can pull off 70% at 4:1 is pretty rare.

There's just no getting around the fact that if you want to flow a large mass of air into a small, low revving engine, you have to have a lot pressure to cram the air in there, and you have to have a ton of intercooling CAC capability to recover the the density you lose from the compression heating.

Yes! I did forget fuel! Under high loads, I'd expect to see AFRs as rich as 15:1 (steady state), with cruising AFRs between 18 and 22. Transition AFRs of course can get super rich, hence the smoke some of us are trying to avoid.

What is the definition of work done by a turbine? The primary doesn't have to be making boost to be doing work. To make boost, it has to be doing ENOUGH work. If the secondary is demanding 40lb/min, and the primary is only supplying 20, then it's not doing enough work, even if we measure a slight delta enthalpy across the turbine.

Because of the staged nature of the compressors and turbines in a compound setup, though, I think it's safe to postulate that if you measure any PR more than 1.25 or so, you will have positive pressure in the cold pipe.

jmo

XLR8R

No assumption on the compressors' efficiency - just some empirical measurements: HE351 @ 45psi = 350*F at CAC inlet, Super B over S471 @ 60psi = 500*F, charge air temps in air/water IC cooled to 128*F with 100*F water and down to 87*F with 48*F chilled water.

So, it's feasible to supply the secondary compressor with pressurized air at @ ambient temperature; which is then further compressed at it's PR into the CAC to regain some of it's lost density... the HPCR CAC lowers the temps 225*F across it on a hot summer day.

OEM CAC has ~2psi drop across it, quality aftermarket is ~1psi...

HOHN

Data! Yes! There's nothing like empirical measurement to guide design...

Mike Holmen

XLR8R, you planning on using a interstage cooling on your twins? A liquid to air intercooler will mount nicely on the passager fender and you put a liquid tank and pump into the bed. Forget about using engine coolant, as your just heating up the air. My next set-up, I'm trying it out and see if it affects turbo spool-up. NOS, is the easiest way to cool off the air the leaves the primary. My spearco, hardly made any changes to egt's. It improved air flow, some.

XLR8R

Yes - the battery is going back in the toolbox with the 10 gallon water/meth tank. Trying to find a suitable core to use for the IC; haven't decided on it's radiator location yet, since I'm thinking of using coolant chilled by R134A.

NO2 won't do except to light the primary on the dyno, since this truck will still tow (that's why I need an IC)... Nathan got a pretty good laugh when I told him what we're doing!

HOHN

Do you think you could use a liquid to air CAC modified to serve as an A/C evaporator on the liquid side? I'd imagine some kind of restriction orifice would be required, but I haven't really thought about how this could be done. The other element to this is that the total quantity of heat you'd have to remove from the charge air would easily drown what can be handled with a regular A/C compressor. The huge compressor required would suck tons of hp when operating, too.

Doesn't Spearco have separate cores you can buy, and then configure the tanks yourself?

I agree that a small nitrous shot in the cold pipe would be the best way to go as far as true "inter"cooling, but even some water or water/meth would be beneficial (high latent heats of vaporization).

XLR8R

The refrigeration coil running through the IC's water jacket will need an orifice at it's inlet, and the coolant's thermal mass should be able to handle the heat load from the primary compressor long enough to Git-R-Done.

I will "bank" BTU capacity in the IC and expend it as quickly as possible at WOT... otherwise, the IC shedding heat to it's radiator at ambient will help full time.

I've found a number of core sources, but the economical ones don't have much in the way of specs.

Anyone ever heard of/dealt with Treadstone?

Mike Holmen

I found lots of liquid to air IC on the net for 1000hp range that will fit under the hood. You don't want too big as it will start to hurt your spool-up. I have two different sizes sitting on my bench at home just waiting for time to burn some wire. I want to put mine on top the passenger fender close to the primary. The lenght to the secondary is short as well. 3 1/2in and out so it be can't restrict air flow to much. I want to keep my batteries under the hood. I still use my box for work stuff.