how much power does a turbo make

[freebeard]

I love this thread.

[ChazInMT]

Originally Posted by ConnClark

The energy comes from the fuel, not the engine.

Could you explain how this works please, or point me to a website that says this and explains it.

Originally Posted by ConnClark

There is no rule in thermodynamics forbidding use of a turbo to improve the efficiency of an engine.

If you read what I wrote, I said the turbocharger improves the efficiency of the engine several times. So why do you write this?

[jamesqf]

Originally Posted by ChazInMT

Could you explain how this works please, or point me to a website that says this and explains it.

For a simple thought experiment, consider eliminating the engine, and spinning the turbocharger with a stream of hot gas generated by burning some sort of fuel. That's fairly easily done. There are lots of examples on the web, starting with this: The Junkyard Turbojet Engine - A Real Working Jet Engine Built From Junkyard Parts (The first hit of 2.4 million.)

So this can hardly be robbing power from the engine, since there is no engine.

[ChazInMT]

Well James. It looks like to me you just said you need energy to run the turbocharger in the form of burning fuel. So, the turbine side of the turbocharger you admit needs power. I understand we burn fuel in our engines, pretty basic stuff. But when it leaves the engine on a normally aspirated engine, it just goes out the exhaust pipe fairly freely. Lets for grins say that it is at 1psi at the exhaust manifold. If there is a restriction in the exhaust system like say...A Turbocharger....then the pressure is going to rise in the exhaust manifold to say 3psi. This pressure and restriction WILL place a load on the engine, requiring more power from the engine in order to operate. That is where the power is coming from, our engines are big air pumps, and if you restrict the flow on the outlet, it needs more energy to overcome that.

Something you have not thought to mention, is that the air being compressed raises the intake and cylinder pressure about as much as there is a restriction on the exhaust, therefore, it is kind of close to a zero net sum situation, so it really doesn't take much extra energy to run.

I will say this again.....Pay Attention. The Turbocharger makes the overall engine more efficient. It does not rob power and slow it down, it's benefits far outweigh its gains. If it didn't than nobody would ever put them on an engine.

My only point is, it does take some power from the engine in order to run. It is doing so by requiring more force on the piston during its exhaust stroke than it would require if there were no turbocharger in the line.

You do a thought experiment and tell me what the engine would run like if the compressor side of the turbocharger just dumped the air into free space instead of the intake manifold. The engine would deliver less power than if it were not installed due to the exhaust restriction.

This really is just a nuance I wanted to point out, it is a misconception that turbochargers run for free, as if they don't require energy to operate. They do, you admitted yourself that you need to use "a stream of hot gas generated by burning some sort of fuel" which makes my point exactly, turbochargers need energy to run.

[JETZcorp]

I always wanted to see a turbocompound setup on a car. I know it's impractical because turbine speed and crankshaft speed have very different requirements (not just in magnitude but also in dynamics) but I believe an exhaust turbine produces more shaft horsepower than it takes in restriction. Additional energy can be had from the exhaust stream by enlarging the turbine outlet relative to the inlet, increasing pressure differential across the turbine. That's why a catback is so much more effective on turbocharged cars than on N/A cars. Mechanical constraints make a true turbocompound setup unlikely in a passenger car, but I think it would do good things if rigged to charge an IMA battery.

[freebeard]

I don't deal with these things much—if the turbo muffles the exhaust, would it do it with more or less restriction than a passive muffler with equivalent effect? Could you 'tune' the turbo for maximum acoustical results?

[Occasionally6]

Originally Posted by ChazInMT

Well James. It looks like to me you just said you need energy to run the turbocharger in the form of burning fuel. So, the turbine side of the turbocharger you admit needs power. I understand we burn fuel in our engines, pretty basic stuff. But when it leaves the engine on a normally aspirated engine, it just goes out the exhaust pipe fairly freely. Lets for grins say that it is at 1psi at the exhaust manifold. If there is a restriction in the exhaust system like say...A Turbocharger....then the pressure is going to rise in the exhaust manifold to say 3psi. This pressure and restriction WILL place a load on the engine, requiring more power from the engine in order to operate. That is where the power is coming from, our engines are big air pumps, and if you restrict the flow on the outlet, it needs more energy to overcome that.

Something you have not thought to mention, is that the air being compressed raises the intake and cylinder pressure about as much as there is a restriction on the exhaust, therefore, it is kind of close to a zero net sum situation, so it really doesn't take much extra energy to run.

I will say this again.....Pay Attention. The Turbocharger makes the overall engine more efficient. It does not rob power and slow it down, it's benefits far outweigh its gains. If it didn't than nobody would ever put them on an engine.

My only point is, it does take some power from the engine in order to run. It is doing so by requiring more force on the piston during its exhaust stroke than it would require if there were no turbocharger in the line.

You do a thought experiment and tell me what the engine would run like if the compressor side of the turbocharger just dumped the air into free space instead of the intake manifold. The engine would deliver less power than if it were not installed due to the exhaust restriction.

This really is just a nuance I wanted to point out, it is a misconception that turbochargers run for free, as if they don't require energy to operate. They do, you admitted yourself that you need to use "a stream of hot gas generated by burning some sort of fuel" which makes my point exactly, turbochargers need energy to run.

There is some truth to the turbine increasing the exhaust pumping pressure but it's not true to say that the turbine wholly presents a restriction that would not otherwise be there.

It depends on the engine load and exhaust valve area but the exhaust gas in the cylinder is still at fairly high pressure relative to that in the exhaust manifold, particularly in the early part of the exhaust stroke, even absent forced induction. That means flow past the exhaust valve will be, at least for part of the exhaust stroke, in choked flow.

When that is the case, the pressure downstream of the exhaust valve can be a lot lower than that which will produce the maximum mass flow rate past the exhaust valve. There is some head room within which the exhaust manifold pressure can be increased and have no effect on the mass flow rate of the exhaust gas, and consequently the pressure in the cylinder, at least for part the exhaust stroke.

There can also be some pressure benefit, as freebeard is alluding to ^, in substituting the sound reduction of the turbo for a muffler i.e. you end up with a similar restriction whether with the turbine or muffler in place.

If you think the exhaust pumping work is substantially contributing to the turbine work, try another thought experiment. Run the engine as an air pump i.e. don't add the fuel or spark with a turbine in the exhaust. How much turbine work will be available then vs what is actually available when it is producing the hot, high pressure exhaust gas?

[mechman600]

F1 engines next year are apparently going to use turbo shaft energy to make electricity. In addition to the current KERS (Kinetic Energy Recovery System - AKA hybrid), they are talking about TERS (Thermal Energy Recovery System).

From this article: Honda confirms F1 return in 2015 as McLaren engine supplier - The Globe and Mail

Ito gave two examples of technologies that could be applied from race cars to road cars – regenerative energy from the turbo, which changes the turbo’s rotational energy to electricity, and downsizing the turbo.

And check out this thread in the F1 technical forum:
http://www.f1technical.net/forum/vie...134193b4bebc3b
An old thread, but still pretty cool stuff.

[pgfpro]

Very cool thread guys

[oil pan 4]

Originally Posted by freebeard

I don't deal with these things much—if the turbo muffles the exhaust, would it do it with more or less restriction than a passive muffler with equivalent effect? Could you 'tune' the turbo for maximum acoustical results?

I run a straight pipe on my turbos.
If you use a Holset, they are very quiet. When I was only running the Holset with the straight pipe it was quieter than when the engine was N/A with factory mufflers and full exhaust.
The Garretts are a little noisy.

From back pressure tests others have done with Holset HE351VE and HX40 turbos with a straight pipe during normal driving the back pressures are about the same as the back pressure I got when I had the factory mufflers on there.