guy321

Makes sense to me, like a peltier semiconductor.

i just like typing the word peltier

Turbine_pwr

Hymee,

Of course, you are quite right. I was using a fairly crude approach... mostly to show the affect of intercooling. I would like to find a set of compressor maps for supercharger and turbocharger designs and incorporate them into a real thermodnamic analysis program that includes duct losses and intercooler effects (ideally effectiveness maps and pressure loss relationships). Turbo maps are easy to come by but supercharger maps are a bit harder to find. It may take a while but I'm considering going back to basics and using basic design equations for an axial compressor to evaulate it's utility in a supercharger application. On the far right of the spreasheet I posted earlier... I show that a direct drive axial compressor or for that matter centrifugal compressor supercharger would have to operate over a very wide speed range (approx 10-100% speed) in the Renesis. This is a much wider operating range then is typically used in gas turbines. As a result, it may introduce operability problems. I'm curious if anyone has looked into this subject before??? Comments anyone?

Hymee

iTrader: (1)

Turbine,

Your right about the speeds of centrifigual compressors currently uded in automotive apps. If you look inside them there is a pair of step-up gears, and there is a BIG difference in the size of the two.




I imagine the mechanical force needed to spin one up is a bit like those old hand operated air-raid sirens!

I haven't seen much about axial flow in automotive terms, but I suspect it is what is used in gas-turbines? I can't recall details, but my memory seems to recall this term in relation to WWII aero engines - such as the Rolls Royce Merlin, having a "axial flow" supercharger mounted on the front of the crank. I just guessed it was a variant of centrifugal type.

Some beautiful pictures here of a 1/5 scale Rolls Royce Merlin here, including the crank-driven supercharger (16-18PSI)

I would like to get a hold of all the data/specs/curves for a variety of these devices (centigugal/screw) etc.

I like the twin-screw for the following reasons:

Constant boost
Efficient at high RPM's = wide operating range
Higher efficiencies (both mechanial and thermal)
Allows for a fre-flowing exhaust (manifold) design (compared to a turbo).

I would like to make a comparison, investigating many of the variables we talk about. Including non-intercooling and the trade off in having less advance. I'm not doubting the effectiveness of a well designed intercooler. But it introduces complexities, and it also introduces other factors - such as the reduction in boost (your analysis correctly factored in). Sure - you can add more boost to make up for it. Then you have raised the temp again, and require even more HP to drive the blower. This is a bit of a vicious circle! The fun would be working out an ideal situation/trade-off between all the things working against it.

I guess at the end of the day, it is practical experience that will count. But I'm sure that the theory equipped with the operating data will help get something close to a good starting point.

Here is another question - What is really suspect to breakage inside a 13B due to high torque? A PD blower will theoretically raise the Torque curve by a % across the board. Normally it is too high RPM that busts engines - when talking about reciprocating ones. We don't have that problem as such, but I guess there are other gotchas lurking! I would like to raise the HP without raising the RPM. Getting a fatter area under then curve, rather than just a pointier peak.

Cheers,
Hymee.

babylou

This is not what you stated earlier. Earlier you said the intercooler would "store air". I see now that you meant "store heat".

Anyways, the above explanation of yours is only correct if the engine bay temp is higher than the outlet temp from the compressor. Under hood static temps are usually in the 140 F range. Under significant boost a compressor outlet temp will be in the 200 F range. Therefore your theory is good on paper but not in practice.

Xyntax

ok... so whatever happened to this smokinjoe supercharger? Did these forum arguments give them a headache?

rotarygod

Yup I reread it. I said store air instead of store heat. That's what I meant. Typos happen.

You still aren't understanding it though. I'm about to have to draw a picture. The engine bay temp is irrelevant. It doesn't matter where the intercooler is mounted. This applies to intercoolers that have zero or poor airflow across them. If the intercooler can not get rid of heat it keeps it. Since the air coming out of the turbo when under boost is hot, we'll say 200 F from your post, the intercooler has the potential to also reach 200 F. This is only if it does not have ventilation and can not get rid of this heat. The intercooler has to absorb heat so it can pass it on to the surrounding air. If it can't pass it on, it keeps it. Once this happens, it takes a while to cool back down. Most intercooler systems do have adequate ventilation and airflow across them so this isn't an issue. It can happen though in theory and most certainly in practice and it does happen. If there is no airflow across the core, there is very little heat rejection. If there is poor airflow across the core, there is little heat rejection and more stored heat. More stored heat is less dense air. Less dense air is less air. Less air is less power. This is how an intercooler has the potential to hurt power. It is only if the system was designed badly. Luckily most of them help.

Drewstein

Proper intercooling is not bad, it's aftercooling that isn't really worth it as far as "adding power. Proper cooling just helps the motor run closer to "perfect" conditions. You're saying there is room for more air, but how does that air get there? With a swin screw blower fixed to your motor, the only air entering the motor must pass through it. This means that the volume of air is fixed once it passes through your supercharger wether it's cool or not. If it is cooled then there will be more room for more air molecules, but no molecules are going to show up or magically appear. However if the air was cooler before entering the supercharger where it can get more dense because it's not sealed off from outside air, then you would see an increase in volume at a given psi. So since the baloon does get smaller, the only thing you can ad more of is fuel. I don't know if that's good or bad, but it's the only substance that can be introduced once the air passes through the blower.

Now by using a twin screw over a roots, your air temps drop causing volume to increase. That is just one advantage over the roots. Also, since the 8 can use low end grunt and top end pull equally, it makes more sense to use these over centrafugal blowers. Making constant boost at 1000rpm through 9000rpm would fatten up that curve nicely.

Hymee

iTrader: (1)

Aftercooling and Intercooling are really the same thing in normal usage of the words. They both cool the charge after it has been compressed. It is the compressor that heats it up.

I'm a twin screw fan.

Cheers,
Hymee.

IKnowNot'ing

Cost AND mass-production capacities

IKN

bureau13

This balloon analogy is bugging me, and here's why (I may be all wrong, so if I am let me know). The supercharger is constantly taking a handful of air molecules, compressing them, and shoving them into the engine. The engine itself is constantly taking mouthfuls of air molecules that are sitting there (under pressure). However, these two events aren't really linked in any sort of 1:1 ratio, right? The "balloon" full of compressed air that shoots through the supercharger at a given moment is not necessarily the exact amount needed in the next intake cycle. The air waiting for the engine to take it is at a pretty constant pressure, assuming you're at full boost, so its not like the SC puts the air in the balloon, the engine takes exactly that balloon full of air, and then the SC gets another one ready. Its constantly shoving them towards the engine faster than the engine can take it (hence the greater-than-atmospheric pressure) and so the more you cool it down, the larger the percentage of the available pressurized air the engine can take in a given intake cycle.

Right?

jds

babylou

To make the intercooler core peak temperature greater than the peak compressor outlet temperature one would viollate the laws of thermodynamics. The only way your above scenario does not violate the laws of thermodynamics is:

1. Run the system at high boost for a lengthy period of time to heat the intercooler mass to the same temp as the compressor outlet temp. Lets' say 200 F. For simplicity we will ignore the cooling due to convection currents and radiation.
2. Let off the throttle and run at a lower compressor boost and therefore a lower compressor outlet temperature of say 150 F. Now the 200 F intercooler is heating the 150 F intake charge.

The only problem with the above theory is you are only reducing the part throttle intake charge density. At full throttle and full boost the compressor outlet temp is already 200F and cannot be heated more. Therefore, power output is not affected.

If you know a way to make the intercooler have a higher temp than the max outlet temp of the compressor please let me know. I will then congratulate you because you have just invented a perpetual motion machine.

rotarygod

You may not realize it but you actually just completely agreed with me!

If people still don't understand then I give up. It's not my fault if others can't learn. It is so simple that it baffles me why people don't get it. Think harder. Actually, don't think so hard. Maybe that's the problem.

Reeko

I think what RotaryGod is saying is that the intercooler needs to disappate heat.
If there is not enough ventilation, it disappates the heat very slowly. If it is not disappating the heat, it is not helping anymore (once it hits peak temp), and is actually hurting at partial throttle settings.

Hymee

iTrader: (1)

Reeko,

Nice summary!

Cheers,
Hymee.

olddragger

iTrader: (3)

dang Guys ,
Seems simple to me. More fuel in, the bigger the explosion, the more power you have. I know, I know the timing and a/f ratio and all that stuff has to be right BUT, the more fuel in (properly) the more power you have. end of story. Now will someone please build a supercharger system for this car!? I would be extremely happy with only 275-300 whp!
Ya want to talk about heat? Hell we already have a heat problem. In georgia in the summer the air temp inside the airbox is over a hundred degrees.!
olddragger

babylou

The heck if I agreed with you. Also, your responses of "you need to think more" is simply saying I am an idiot and is not helping to prove your point. Let's stick to science.

Earlier you stated: "If there is no airflow across the core, there is very little heat rejection. If there is poor airflow across the core, there is little heat rejection and more stored heat. More stored heat is less dense air. Less dense air is less air. Less air is less power. This is how an intercooler has the potential to hurt power."

The last sentence clearly stated an intercooler has the potential to hurt power due to thermal reasons. As I explained earlier this is thermodynamically impossible except during part throttle operation after a long period of full throttle operation. In case you are unfamiliar with the scientific methods of testing an engine I will tell you that engine power is tested at full throttle. Also, if for some reason your engine is loping along at part throttle and you are wanting more power just push the throttle pedal a bit closer to the floor. By the time the pedal touches the metal the power will be the same. Unless of course Isaac Newton was wrong with all those laws he discovered.

Hymee

iTrader: (1)

I'm keen. If I new I had critical mass of customers I'd take deposits right away!

Cheers,
Hymee.

rotarygod

I never said or implied that you are an idiot. That was all you buddy! What I did say is that you are either overthinking the situation or are overlooking something. Nowhere did I say anything about your intelligence level. Smart people miss things too! Forget science. Let's stick to common sense! Science won't help me cross a street during traffic and it won't help here either.

It's obvious I'm going to have to pull out the good old automotive based book from Corky Bell to quote rather then a science book to quote from. This first example is how an intercooler "could" be setup to not be worth it's presence. Lets say you place an intercooler in the engine bay behind the radiator. Not a good idea. The only ventilation it gets is from the hot radiator air. Let's say that ambient outside air temperature is 90 degrees and the air after it has passed through the intercooler is at 140 degrees. Just a figure so don't get into actual numbers. This air will do a lousy job of trying to cool anything. At low or no boost levels the supercharger or turbocharger may not have an outlet temperature that is as high as the ambient intercooler heat. Therefore the air gains heat as it passes through the core. In this scenario it becomes an "interheater" as it is adding heat to the system. When boost rises to the point that the temperature of the charge exceeds the underhood temperature, the intercooler will begin doing some work but will forever suffer from a severe efficiency loss. If the small reduction that it is still giving in temperature is not enough of a gain to overcome the pressure loss through the core and piping, then there was no point in having it there in the first place. Most importantly, the engine bay is no place for an intercooler. That is only ONE possible scenario.

The same thing can occur in a system that has very poor ventilation but is not in the engine bay. This could include any nonfront mount type of system that has inadequate ventilation. The amount of heat that the intercooler can pick up from the turbo can not be dissipated very efficiently with no air flow. This will store it. When the engine is under little to no boost where air temperatures are below that of the stored heat in the core, it again becomes an "interheater". When the intercooler cools down enough that it is at ambient temperature to the air flowing through it, it is no longer an interheater.

Here's a real world scenario. My best friend's '93 RX-7 is about to get a new engine. (It's a 3rd gen, of course it is!) The air duct to the intercooler is removed. The stock intercooler sits in the engine bay. There is little to no ventilation across it. At least not cool air. The car is fastest after it is first started. The intercooler hasn't had time to heat up yet. After a few minutes the car starts to get slower. The intercooler isn't getting rid of the heat. It becomes sluggish on the street. Under full boost, it still does something but it isn't terribly effective.

When an intercooler system is designed and installed properly, it has little pressure loss internally and is properly ducted to receive good airflow. This high amount of airflow easily serves to help heat escape from the core when under boost. The more heat that can get out of the cooler, the more heat can enter it and the more heat that can be taken away from the air inside of it. Any cooling benefit of an intercooler is an advantage for power over using no intercooler as long as there is not a huge pressure drop that is offset by the denser air gain. This is how every successful intercooler system works and how most everyone does it. When done properly, there are no drawbacks as far as power production is concerned to using an intercooler and only gains to be had. Any issues with drivability are minimal. Again this assumes a good design.

Another thing which happens is heat soak. This applies whether turbocharged, supercharged, intercooled or not. When the engine has been under boost really hard, the hot air through the system eventually starts to build up. This is true as long as the intercooler can not dissipate the added heat fast enough. At this point everything in the intake system starts to get hot and hold heat. The pipes, intercooler, intake manifold, etc. all start getting hotter. This heat in the system makes the car a little slower. The only solution once that happens is to not drive so hard until the car cools down or to redesign the intercooling system. This usually applies to track driven street cars. It can also happen to any car when sitting still in traffic. Hot air from the radiator fan is blowing into the engine bay but there is little airflow through the intake runners to help dissipate the heat. Let your car idle for a while sometime with the hood closed and then open it and touch the manifold. It's hot. Then go for a drive and immediately touch the manifold after you stop (of course after you stop!). It is much cooler. This was heat soak and for a short time even the manifold worked as an "interheater". It happens everyday to every car.

You are interpreting the "interheater" statement to imply that it is always heating up the air like an oven when it is a part time phenomenon. You are so concerned with trying to prove me wrong that you are entirely overlooking the fact that you already have it figured out. I didn't say you were an idiot. You are overlooking the obvious though. Put down the science books for a while an use common sense. At the very least pick up an automotive based book that deals directly with the topic rather the the physics behind it. There was another thread on here where the members were trying to argue how coefficient of drag and tire width were the reason why another members car slows down more when going down hill than another car. Thie arguments were ludicrous and pointeless. The real issue is that something mechanical in the vehicle is slowing it down such as brakes dragging, etc. Those guys were obviously intelligent in the ways of science, but overlooking the obvious in the real world. I said it over there but I'll say it again here.

"That's why we have mechanics. It's because scientists don't know anything about cars!"

Do you understand now? And stop taking it so damn personally!

babylou

rotarygod,

You keep changing your what ifs. I see in scenario number one now the cooling air is hotter than the charge air. This was never discussed before.

Also, all you talk about is part throttle effects and how the power is being reduced at part throttle. Like I said before why don't you push the pedal farther? Once at full throttle you will be at the same exact power. Why do you refuse to discuss this?

In your sixth paragraph you again revisit the topic of building up air. Are we talking about a car or a hot air balloon here?

Your real world scenario showing that the car loses power after the intercooler heats up is worthless. Your example does nothing to show an intercooler is losing power versus no intercooler. It simply shows how a hot intercooler loses power versus a cold intercooler. Study up on the scientific method.

I'm glad you possess common sense mechanics and Corky's book(s). Since it appears I have no common sense I am forced to stick with my science based education of thermodynamics and heat transfer that I studied, the same as Corky Bell, at Texas A&M University.

Hymee

iTrader: (1)

C'mon guys,

Don't ruin a good thread. Just agree to disagree

Cheers,
Hymee.

rotarygod

I'll throw in the towel. It's obvious you can't teach some people.

I have not once contradicted myself or changed my story especially clear when I make it clear that I am describing one of many possible scenarios. You just constantly fail to comprehend. It baffles me how such a simple obvious scenario cannot be understood. Hymee summed it all up in 2 lines. It can't be any more obvious. I'm actually dumbfounded! I'm not sure if knowing Corky neccessarily gives credibility at this point.

FWIW: Anyone can pass a test on paper. Eductation does not guarantee intelligence.

To make you happy, you win! I'm done. Be proud.

Rotarian_SC

That the cooling air being hotter than the charge air is what I understood from earlier posts.

I think for part throttle he is just listing another scenario where it can happen. If it is happening in street driving you can't always be at full throttle though.

I thought he said car and FI engine in the 6th paragraph.

I am pretty sure this is going down to common sense because I am positive that you have a much better thermodynamics educaton than I do.

babylou

No, part throttle is not "another scenario" but the only scenario where approach applies. Also, this scenario is only correct after a long blast at high boost. At full boost there is no loss. Period.

Who cares about part throttle? At full throttle an intercooler that is 100% heat soaked will make the exact same power as a non-intercooled system. Even after 1000 blasts down a quarter mile.

I just don't get how anyone thinks the intercooler can get hotter than the charge air at full boost. It cannot. And full boost is when we care about power. Not at 50% throttle/50% boost.

Let's try this common sense thing I've been told I lack: Put a TV dinner in the oven at 400 F. What is the max temp the TV dinner can reach? 400 F.

Now engine compartment air is ~140 F. I've tested this on maybe 10 different vehicles.

Knowing that charge air at full boost will be ~200 F please tell me what's the temp of the air entering the engine on a non-intercooled system. Yup 200 F. Okay?

Now we add an intercooler to the same engine. We run the engine at full boost for 1 hour. Remember the charge air is ~200 F at full boost. The intercooler system was designed by a scientist that lacks common sense, like me and unlike a mechanic, therefore is placed in stagnant underhood air at 140 F. What is the temp of the intercooler? Remember that the air flowing in the intercooler is 200 F and the stagnant air around the exterior of the intercooler is 140 F. The intercooler can reach a maxiumum of 200 F. Now what is the temp of 200 F air passing through an intercooler at 200 F? 200 F

All of the above ignores any losses due to flow related effects (profile and skin drag effects). These losses have never been part of this heat soak topic.

Hymee

iTrader: (1)

Which is exactly what Rotarygod is saying.

Cheers,
Hymee.

babylou

It seemed to me that rotarygod was saying a poorly designed intercooler will become so hot it will actually heat the charge air and therefore actually reduce power potential versus a non-intercooled engine. I believe he coined the term "interheater".