Ron Earp
Admin
Definitely more show than go - the equilvalent airflow and response could be accomplished by a variety of means. Those are TINY turbos!!!!! But, it is unique and cool, so go for it!
Turbo post
Turbo post
Turbocharger efficency
- Thread starter Ron Earp
- Start date
I'd never go for it, but hey if he's got the money... I think 2 is enough for most V8s... I'm interested though in the possibility of doing a 3-turbo setup... smaller ones to build quick boost and big ol' turbo to take over once it spools up. Eh, probably more trouble than it is worth.
John
John
Ron Earp
Admin
There are numerous methods to acheive this. One is the twin setup with a flapper valve that diverts exhaust gas to a larger turbo at a cetain RPM or boost level. This was used on a number of production cars, notably the Mazda RX7 3rd gen and the last version of the Toyota Supra. Both of these engines are fantastic and produce lots of power.
Another way to do it is with the variable geometry turbos that control pitch of the vanes (turbine side) or blade (compressor side) to change efficiency at different RPM ranges. Complicated and I don't know of too many applications.
R
Another way to do it is with the variable geometry turbos that control pitch of the vanes (turbine side) or blade (compressor side) to change efficiency at different RPM ranges. Complicated and I don't know of too many applications.
R
Jim Rosenthal
Supporter
Actually, many of the larger marine diesels had multi-stage turbocharging a few years back, with, as you say, smaller turbos to get boost quickly and larger ones which would take longer to turn up to boost level. These engines were very complex, though, and I think that their successors use electronic engine control to regulate how much fuel and air go in. These engines have some kind of device that opens the fuel-injection rack based on how much manifold pressure it sees. Do turboed gasoline engines have something similar to this, or is this accomplished automatically bythe EFI map based on manifold pressure?
Ron Earp
Admin
Most auto turbo engines have a fuel pressure regulator tied to the manifold pressure. So, up goes the boost, up goes the fuel pressure, and more fuel goes in. This is the simplest way, others using MAF adjust injector duty cycle in realtime or fire secondary injectors with increasing pressure. The Lotus is sort of a combination, having a fuel pressure increase and secondary injectors too. But, saddled with the old GM computer it uses it isn't very accurate nor flexible so the result is a very rich motor and lost power.
There are multistage compressor engines from the 30s and 40s - aircraft, auto, and marine. There are examples of two and three turbo stages along with examples of mechanical supercharger augmented by a exhaust driven turbocharger. Lots of neat stuff, but somewhat complex for auto use though.
I've always been intrigued by the possibility of using a Lysholm screw type supercharger in conjunction with a turbocharger. The screw blower provides instant boost, as long as its displacement is an appreciable fraction of the engine, and the turbo charger could be used to pick up the very high RPM range where you don't wish to drive the blower. It'd require some valving in the intake department that could be complex. One way would be to provide a relief valve for the blower that vents to atmosphere thus unloading it and at the same time closing a valve from the vented turbo allowing it to pressurize the manifold. Not sure what to do about a MAF system like this, would likely need a mapped system. Bet it wouldn't pay off in the end, but would be cool.
R
There are multistage compressor engines from the 30s and 40s - aircraft, auto, and marine. There are examples of two and three turbo stages along with examples of mechanical supercharger augmented by a exhaust driven turbocharger. Lots of neat stuff, but somewhat complex for auto use though.
I've always been intrigued by the possibility of using a Lysholm screw type supercharger in conjunction with a turbocharger. The screw blower provides instant boost, as long as its displacement is an appreciable fraction of the engine, and the turbo charger could be used to pick up the very high RPM range where you don't wish to drive the blower. It'd require some valving in the intake department that could be complex. One way would be to provide a relief valve for the blower that vents to atmosphere thus unloading it and at the same time closing a valve from the vented turbo allowing it to pressurize the manifold. Not sure what to do about a MAF system like this, would likely need a mapped system. Bet it wouldn't pay off in the end, but would be cool.
R
Trevor Booth
Lifetime Supporter
Adam, If your tables were directed at me ,thanks, but I already have a set and I know how to use them. For you and I the calculations are simple and they will provide a starting point but as you would know in an area of variables the results are not always as predicted,sure a turbo with a higher isentropic efficiency is less affected in an uncontrolled environment, but man can they be very frustrating. For those who have not had the same educational opportunities, the turbo manuf are the best starting point.
Ron Earp
Admin
I wouldn't expect the calcs to be 100% accurate and they don't need to be. I was just wanting a way to compare two very different compressors and get a rough idea for how inefficient one is compared to the other. The calculations I did bore a fairly close approximation to what I saw using a thermocouple a few years back while trying to tune a car.
R
R
[ QUOTE ]
Adam, If your tables were directed at me ,thanks, but I already have a set and I know how to use them.
[/ QUOTE ]
Actually none of my posts have been directed at you. The tables are for Ron, or anyone else that may want to try different inlet temps, pressure ratios, and efficiencies.
[ QUOTE ]
For you and I the calculations are simple and they will provide a starting point but as you would know in an area of variables the results are not always as predicted,sure a turbo with a higher isentropic efficiency is less affected in an uncontrolled environment, but man can they be very frustrating.
[/ QUOTE ]
Ron's original question was:
[ QUOTE ]
And, if so how can I use the efficiency number on a compressor map to make some calculations on discharge air temp?
[/ QUOTE ]
And that is exactly what I gave him.
[ QUOTE ]
For those who have not had the same educational opportunities, the turbo manuf are the best starting point.
[/ QUOTE ]
That is exactly the attitude we don't need around here. The more people can undestand of the fundamentals, the less voodoo and mystery there will be in the hobby, which is a good thing.
Adam, If your tables were directed at me ,thanks, but I already have a set and I know how to use them.
[/ QUOTE ]
Actually none of my posts have been directed at you. The tables are for Ron, or anyone else that may want to try different inlet temps, pressure ratios, and efficiencies.
[ QUOTE ]
For you and I the calculations are simple and they will provide a starting point but as you would know in an area of variables the results are not always as predicted,sure a turbo with a higher isentropic efficiency is less affected in an uncontrolled environment, but man can they be very frustrating.
[/ QUOTE ]
Ron's original question was:
[ QUOTE ]
And, if so how can I use the efficiency number on a compressor map to make some calculations on discharge air temp?
[/ QUOTE ]
And that is exactly what I gave him.
[ QUOTE ]
For those who have not had the same educational opportunities, the turbo manuf are the best starting point.
[/ QUOTE ]
That is exactly the attitude we don't need around here. The more people can undestand of the fundamentals, the less voodoo and mystery there will be in the hobby, which is a good thing.
Ron Earp
Admin
[ QUOTE ]
For those who have not had the same educational opportunities, the turbo manuf are the best starting point.
[/ QUOTE ]
I've got the education and mathematical background to handle any calcs - my doctorate is in Analytical Chemistry with a lot of physics/physical chemistry - so thermo is no problem. However, my knowledge of thermodynamics and associated topics is focused on non-automotive examples and Adam's post is just what I needed! /ubbthreads/images/graemlins/smile.gif
R
For those who have not had the same educational opportunities, the turbo manuf are the best starting point.
[/ QUOTE ]
I've got the education and mathematical background to handle any calcs - my doctorate is in Analytical Chemistry with a lot of physics/physical chemistry - so thermo is no problem. However, my knowledge of thermodynamics and associated topics is focused on non-automotive examples and Adam's post is just what I needed! /ubbthreads/images/graemlins/smile.gif
R
Trevor Booth
Lifetime Supporter
Gentleman, please accept my humble apology. No offence was meant nor intended, nor did I take any offence. Perhaps my choice of words could have been better chosen, but aussies tend to be a little direct and abrupt at times. I shall be more cautious in future. You will appreciate that it is difficult to know of the knowledge base of participants on this forum (although Adams was obvious)and my comments were of a general nature. As to the reference to educational opportunities, that was a slight on Adams words "any joe" used in an earlier post. I thought you would have picked that up. I am also a believer in breaking down the "voodoo" it gets more people involved and provides a beter understanding.
Once again my apology,
Trevor
Once again my apology,
Trevor
Ron,
one way I can think of to use a supercharger and turbo in conjunction like you mention is by using a magnetically engaging supercharger. I can't remember who makes them, but I remember seeing one awhile back... it was a roots type and the pulley works like a clutch driven fan, but is engaged by a very strong magnet... when it disengages, it just freewheels.
John
one way I can think of to use a supercharger and turbo in conjunction like you mention is by using a magnetically engaging supercharger. I can't remember who makes them, but I remember seeing one awhile back... it was a roots type and the pulley works like a clutch driven fan, but is engaged by a very strong magnet... when it disengages, it just freewheels.
John
Howard Jones
Supporter
Speaking of voodoo, Do any of you guys remember a system used for a very short time on the F1 Ferrari's around 1986-87 or so. This was the turbo 1.5L days and the red cars had a suppercharger system refered to as "comprex". I believe it was a turbo that was somehow driven by a clutch system at low exaust gas pressure and then released from being crank driven to normal exaust gas powered. The low engine speed configuration also had some sort of variable gearing to build a contant boost pressure at low to medium engine revs.
In the end the whole thing was to complex to sort out and around that same time frame F1 rules started to limmit boost pressure thus the beginning of the end of the turbo era.
In the end the whole thing was to complex to sort out and around that same time frame F1 rules started to limmit boost pressure thus the beginning of the end of the turbo era.
I'm not sure what they were using at that time, but the comprex works differently than how you are describing.
The comprex is a cylinder with passages in it something like a catalytic converter brick. The idea is simple, but the process is complicated to explain. Imagine each of these tubes filled with intake air. One side of the tube is opened to the exhaust mainifold. The higher exhaust pressure pushes the intake air to the other side of the tube, which is then opened to the intake manifold. The trick is to cut off the conection before the exhaust gas reaches the intake manifold. It won't attempt to describe the rest of the process, but it basically ends with the exhaust gases being pushed out and new fresh air brought into the tubes.
The comprex spins only to open the tubes to the correct manifolds at the correct time, so it is very different from a supercharger or turbo. It can be fery efficient and develops boost sooner than a turbo, but works best on small engines.
The comprex is a cylinder with passages in it something like a catalytic converter brick. The idea is simple, but the process is complicated to explain. Imagine each of these tubes filled with intake air. One side of the tube is opened to the exhaust mainifold. The higher exhaust pressure pushes the intake air to the other side of the tube, which is then opened to the intake manifold. The trick is to cut off the conection before the exhaust gas reaches the intake manifold. It won't attempt to describe the rest of the process, but it basically ends with the exhaust gases being pushed out and new fresh air brought into the tubes.
The comprex spins only to open the tubes to the correct manifolds at the correct time, so it is very different from a supercharger or turbo. It can be fery efficient and develops boost sooner than a turbo, but works best on small engines.
Howard Jones
Supporter
Adam, Now here is a perfect example of a back yard builder like myself trying to explain voodoo and being corrected by a real engineer. Thanks I have been wondering what the hell was in the back of that ferrrari for more than 20 years. What I wrote above was the only thing I could come up with to describe what I thought was going on. Interesting stuff, voodoo!
Thanks again. I started my 40 project because I wanted something to get my mind going. It's working! More voodoo!
Thanks again. I started my 40 project because I wanted something to get my mind going. It's working! More voodoo!
