Gas vs PSD
Hotshot
Joined: Dec 2003
Posts: 18,423
Likes: 9
From: iowa
Moving air is not spooling a turbo. Making the turbine move and spooling are two different things. A turbo will not spool without heat unless its mated to an air pump so large that it would be pointless to hook it up cuz the intake side of the turbo would move less air than the source pump is giving it. . . .in other words turbos,like every other machine on earth, is not 100% efficient. If turbos move air. . .the movement of air cannot be the source of energy spooling it. They cannot run without heat. Period.
To put this in more understandable means. . .
Anyone competant individual who's ever owned or perhaps even driven a turbo vehicle without a throttle body (turbos can actually create vacuum with throttle body equipped motors, like gassers) knows the turbo wont build boost without load on the motor. I.e. heat production. . . . .you can downshift all the way to redline (max airflow from motor) and it wont build boost. The turbos rpm is increased (can hear it increase) but no boost is made. There is no boost, and there is no heat (no combustion on downshifts).
Another example is free revving the motor. I can build 2-3 psi with a free rev (more can be achived with twins but its still a fraction of max boost). This is a little boost, with only a small amount of heat.
As load increases, egts increase not only in their max possible temp. . .but also the acceleration to the max temp. This is why turbo vehicles love the highway. The high load/high heat makes for a fast spooling turbo.
It would take a miracle for a turbo to spool without heat. It just wont.
To put this in more understandable means. . .
Anyone competant individual who's ever owned or perhaps even driven a turbo vehicle without a throttle body (turbos can actually create vacuum with throttle body equipped motors, like gassers) knows the turbo wont build boost without load on the motor. I.e. heat production. . . . .you can downshift all the way to redline (max airflow from motor) and it wont build boost. The turbos rpm is increased (can hear it increase) but no boost is made. There is no boost, and there is no heat (no combustion on downshifts).
Another example is free revving the motor. I can build 2-3 psi with a free rev (more can be achived with twins but its still a fraction of max boost). This is a little boost, with only a small amount of heat.
As load increases, egts increase not only in their max possible temp. . .but also the acceleration to the max temp. This is why turbo vehicles love the highway. The high load/high heat makes for a fast spooling turbo.
It would take a miracle for a turbo to spool without heat. It just wont.
You uncork the turbo and you can put all the heat you want through it and it won't build an bit of boost. Boost like vacuum is built by a restriction. You CAN build boost if you use a big enough air pump to spin the turbine side of it and put a smaller motor on the compressor side and it will build boost.
The act of compressing air does build heat which is why intercoolers are used but it's NOT a requirement of the turbo in order to build boost to have heat.
Your confusing the fact that under load an engine produces more heated exhaust gases that are expanding with needing that heat to spin the turbo. the turbo needs air flow plain and simple. you put the turbo off of my 7.3 onto a 3.0L 4cylinder and it will hardly build any boost even tho you might get a large amount of heat. The reason is the smaller displacment engine won't produce enough volume of air to spin the turbine fast enough to let the compressor actually pump more air then the engine can use (which is what builds boost)
FTE Leadership Emeritus
Joined: May 2004
Posts: 18,787
Likes: 30
From: Melbourne, Aus
However, I still fail to see where exhaust flow is "radiated out to the environment". It's a purely physical action. The turbo is not consuming BTUs to produce energy, it's consuming velocity which happens to cool off the exhaust gas AFTER the turbo, yet also heats up the gas BEFORE the turbo because of compression.
Go back to the PV=nRT.
I know that part is hard to get your head around - its a mechanical device, how does it consume thermal energy? It does it the same way that the engine does it to begin with.
Now, I would also say "there ain't no such thing as a free lunch" - TANSTAAFL
Any mechanic energy that the turbo uses to drive it's shaft, is lost exhaust gas velocity. The effect of that lost velocity is a pressure build-up before the turbo, acting back on the head of the piston as it rises on the exhaust stroke (backpressure).
Any mechanic energy that the turbo uses to drive it's shaft, is lost exhaust gas velocity. The effect of that lost velocity is a pressure build-up before the turbo, acting back on the head of the piston as it rises on the exhaust stroke (backpressure).
A good example of this is the thickness of an engine block to a turbo manifold that needs to support their respective pressures.
So yes, it does add backpressure - but the backpressure doesn't have as big of an impact on the exhaust gas flowing out of the engine. Most turbo's run most efficiently on the turbine side run at a 2-2.5:1 pressure ratio. Meaning about a 30-37psi gauge pressure.
Bearing in mind that combustion pressure (even at BDC) is around 1000 gauge psi, its influence is in the order of a few percentage points.
It's not FREE energy driving that turbo. It's a positive-feedback in terms of putting more O2 into the cylinder that far exceeds the loss to exhaust backpressure, but it's still there.
The engine's ability to extract power from what is a relatively low pressure differential (20 odd gauge psi) is minimal, but a turbine type device like a turbo is very efficient at the high flow/low pressure environments.
FTE Leadership Emeritus
Joined: May 2004
Posts: 18,787
Likes: 30
From: Melbourne, Aus
absolutely 100% wrong all the way around.
You uncork the turbo and you can put all the heat you want through it and it won't build an bit of boost. Boost like vacuum is built by a restriction. You CAN build boost if you use a big enough air pump to spin the turbine side of it and put a smaller motor on the compressor side and it will build boost.
The act of compressing air does build heat which is why intercoolers are used but it's NOT a requirement of the turbo in order to build boost to have heat.
Your confusing the fact that under load an engine produces more heated exhaust gases that are expanding with needing that heat to spin the turbo. the turbo needs air flow plain and simple. you put the turbo off of my 7.3 onto a 3.0L 4cylinder and it will hardly build any boost even tho you might get a large amount of heat. The reason is the smaller displacment engine won't produce enough volume of air to spin the turbine fast enough to let the compressor actually pump more air then the engine can use (which is what builds boost)
You uncork the turbo and you can put all the heat you want through it and it won't build an bit of boost. Boost like vacuum is built by a restriction. You CAN build boost if you use a big enough air pump to spin the turbine side of it and put a smaller motor on the compressor side and it will build boost.
The act of compressing air does build heat which is why intercoolers are used but it's NOT a requirement of the turbo in order to build boost to have heat.
Your confusing the fact that under load an engine produces more heated exhaust gases that are expanding with needing that heat to spin the turbo. the turbo needs air flow plain and simple. you put the turbo off of my 7.3 onto a 3.0L 4cylinder and it will hardly build any boost even tho you might get a large amount of heat. The reason is the smaller displacment engine won't produce enough volume of air to spin the turbine fast enough to let the compressor actually pump more air then the engine can use (which is what builds boost)
Yes, you can create a restriction and it will build pressure, but in the case of your 7.3, if you didn't have the temperature in the exhaust gases to begin with - the turbo on your 7.3 would be way too big as well, and it is VERY dependent on heat being there to build the pressure.
I hope that makes cents
Lead Driver
Joined: May 2011
Posts: 5,775
Likes: 443
absolutely 100% wrong all the way around.
You uncork the turbo and you can put all the heat you want through it and it won't build an bit of boost. Boost like vacuum is built by a restriction. You CAN build boost if you use a big enough air pump to spin the turbine side of it and put a smaller motor on the compressor side and it will build boost.
The act of compressing air does build heat which is why intercoolers are used but it's NOT a requirement of the turbo in order to build boost to have heat.
Your confusing the fact that under load an engine produces more heated exhaust gases that are expanding with needing that heat to spin the turbo. the turbo needs air flow plain and simple. you put the turbo off of my 7.3 onto a 3.0L 4cylinder and it will hardly build any boost even tho you might get a large amount of heat. The reason is the smaller displacment engine won't produce enough volume of air to spin the turbine fast enough to let the compressor actually pump more air then the engine can use (which is what builds boost)
You uncork the turbo and you can put all the heat you want through it and it won't build an bit of boost. Boost like vacuum is built by a restriction. You CAN build boost if you use a big enough air pump to spin the turbine side of it and put a smaller motor on the compressor side and it will build boost.
The act of compressing air does build heat which is why intercoolers are used but it's NOT a requirement of the turbo in order to build boost to have heat.
Your confusing the fact that under load an engine produces more heated exhaust gases that are expanding with needing that heat to spin the turbo. the turbo needs air flow plain and simple. you put the turbo off of my 7.3 onto a 3.0L 4cylinder and it will hardly build any boost even tho you might get a large amount of heat. The reason is the smaller displacment engine won't produce enough volume of air to spin the turbine fast enough to let the compressor actually pump more air then the engine can use (which is what builds boost)
Lead Driver
Joined: May 2011
Posts: 5,775
Likes: 443
The airflow comes from the mechanical motion of the pistons, which i've already proved isn't enough to spool a turbo with my free rev/downshift examples. The massive amounts of thermal energy released through the turbo comes.from the"leftovers" of combustion. That thermal energy is what operates the turbo (not just moving the wheels, but actually spooling turb)o. The airflow is just the vessel that carries the energy. And. . .it would be impossible for drive/boost pressure to be 1:1 if airflow from motor spooled turbo by itself.
Lead Driver
Joined: Jan 2006
Posts: 6,267
Likes: 5
YouTube - ‪Beer+old turbo=home made jet engine‬‏
In this setup, a flame tube in the system burns fuel, causing rapid expansion of gasses, and causes the turbocharger to run like a jet engine.
While our trucks make heat during combustion, you can't deny that the engine itself is an air pump, and this drastically changes a few key operating facts about the turbocharger, which in my mind rule out calling it an "engine"
1. It will spin using any exhaust temperature, using proper vanes and sizing. It will because the airflow force can still be exerted on the vanes at any temperature.
2. You could rip a chunk of IC tube out and the turbo still spins. In this instance, it is easy to see that it is being "powered" by exhaust, rather than acting as an engine.
3. In a jet engine configuration, the more heat you add, the faster it spools and the more combustion happens - which is almost the same as our trucks, except that our combustion takes place in a positive displacement pump.
This is my thinking on why we're all disagreeing so much. This is not a jet engine. While science and laws of thermodynamics are all present, just remember that theres a twist put into the system, being a positive displacement pump, and it will operate slightly different.
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Lead Driver
Joined: Jan 2006
Posts: 6,267
Likes: 5
The turbo is running from air pressure, which is the air pumped through the engine and expelled at high temperatures. In this configuration, it is being powered 100% by exhaust pressure / flow.
If you wanted to get a turbocharger spinning from heat alone, I think you could, you'd need to set it up like a jet engine and replace the combustion tube with an air-air heat exchanger which the exhaust would flow through.
Postmaster
Joined: Apr 2006
Posts: 3,524
Likes: 2
From: CA Bay Area
I think the idea with making turbo into jet engine inside your garage would be great for checking with "Myth Busters"
The clip might be titled like "Can I take the whole neighborhood with my danger projects, or only my own house?"
The clip might be titled like "Can I take the whole neighborhood with my danger projects, or only my own house?"
Postmaster
Joined: Apr 2006
Posts: 3,524
Likes: 2
From: CA Bay Area
I've been playing with miniature engines in my teens and have seen miniature jet engines operating safely on flying models.
But having that red hot pipe working inside garage 3 feet above gas can with bunch of people observing FROM INSIDE
But having that red hot pipe working inside garage 3 feet above gas can with bunch of people observing FROM INSIDE