Turbocharged Engine exhaust Systems
 

Exhaust System Technology: Science and Implementation of High Performance Exhaust Systems

An interesting technical article on engines, which got me thinking about exhaust systems. There are numerous companies around the world who market header systems for naturally aspirated engines, some claiming anything up to 15% increase in Hp. But has anyone tried it with a turbocharged engine.

Looking at a typical Chieftain, Cirrus turbo engine shows the exhaust primary tube is a simple log type manifold. One would assume there would be loots of counterproductive interference with the exhaust pulses. I was wondering about the efficiency of these OEM exhausts and do they cause a little or significant increase in fuel consumption compared with a perfect header type system.

N/A engine needs a tuned length to scavage the exhaust gas out of the chamber to let the incoming change in. In a blower engine this is not require as it has a positive px that's why it's not as important the exhaust system is tuned It all about the inlet.
Cheers

Ok, I stand corrected. I had thought that but discarded it. So when you say inlet, are we talking about the inlet to the exhaust side of the turbo or the induction side of the engine as a whole?

No the inlet valve for charged air with fuel. That's the inlet and exhaust valve is what it says.
Cheers

The high claims for special exhausts are something that I take with a pinch of salt without back to back Dyno data.

As you can imagine I have some info on this from George Braly, one of the few folk who has actually done a fair bit of Dyno work on Piston Aero engines, and quite likely more than anyone else on the planet.

His discovery for several exhausts on NA TCM 6 cylinder engines is the torque peak moves around a bit, so at a particular RPM you get a small gain but lose it say at 2700.

When asked he refers people to the guys who buy up all the NA exhausts of Cirrus and Beech that buy them from TAT when they do a turbo upgrade.

Read between the lines :ok:

For Turbo engines all the best gains come from intercoolers and ones that are engineered with higher efficiency. Every turbo should not just have one but a good one. Problem is most will never get one coz the cost of paperwork and R&D.

Cheers
:ok:

PS if Walter and JD wander past they might have some good first hand info to share. ;)

There lots fitted up this end of the world pilots seam to like them they notice a preformance gain in the heat.
Cheers

Your engine is just a big air pump, the better it flows the better it works

Whilst the materials are of good quality the design is quite poor given the reduction of room they have to work with.

Exhausts with turbocharged engines are a bit of a compromise.
In terms of heat energy you want the turbo to be as close to the engine as possible to minimise losses, and that usually means simple log-style manifold.
But in terms of pressure recovery you want a good straight length after the collector to help smooth out the pressure pulses that the turbine section receives, again for best power & efficiency.
A well-designed set of extractors (header is the US terminology) must be very difficult in an aeroplanes engine cowling due to the lack of room available. So a simple log-style of manifold is often used and they work just fine for the application.

The turbo needs velocity its not px this is a myth that it require px, Small tube in large tube out.
Cheers

Fixed that for you.

The original is more correct, I would say. It doesn't matter how hot it is, or how high pressure, if the exhaust gases are not moving through the turbine it's not going to do anything.

The velocity through the turbine comes from the difference in pressure from one side to the other. If you have no difference in pressure you can have the same or more energy (pressure, heat), but no rotation.

At 2700 rpm, the idea that gas flow restrictions in a manifold are a significant source of losses is ludicrous provided the manifold is adequately sized, you might just as well make it out of water pipe with right angle elbows. *

If you were running Four valves at 5000 rpm with much higher gas velocities it would be different.


* this begs the question of equal air fuel distribution which is a different matter.

Sorry sunfish you are totally in correct.
Cheers

Andrew, PV = NRT where n is quantity, r is the universal gas constant and T is temperature.

work is the integral of P with respect to V

Hot high pressure gas at one side of the wheel, cold low pressure gas on the other side.

The turbine in the turbo is an airfoil and the greater the velocity the faster it will spin. It's no different to a wing. Faster the airflow the greater the lift. It's not about px it velocity.
Cheers

yrwrong. The gas can be stationary upstream, it expands, accelerating through the turbo causing the turbo wheel to react against the accelerating gas F = MA.

The greatest restriction in airflow in an IC engine is the intake port around the valve seat. This is why racing engines often have up to 5 different angles cut in the seat face, to ensure smoother flow.

Sunfish suggest you study bgt namely GG and GH. V increase PX decrease temp decrease.
The scroll increase velocity into the turbine ( divergent duct ) iT moves across the turbine airfoil this creating rotation (ie lift ) then exits velocity decreases pressure increases temp increases.

Inlet side
Compressor opening is large into the comp it is compressed velocity is increased px decreased temp decreases as it passes through the scroll divergent now velocity decreases px increases temp increase
The compressed gas will only compress if the engine cannot use all of the flow that it is at it's use.
Simple basic gas.

Cheers

The 1971 book by Smith & Morrison " The scientific Design of Intake & Exhaust Systems" is still the bible.

The scientific design of exhaust and intake systems - Philip Hubert Smith, John Cruickshank Morrison - Google Books

Turbo chargers extract energy from the exhaust stream by lowering its pressure as it expands though the turbine. Known as an impulse turbine . This has the undesirable side-effect of increasing the back-pressure in the engine, which decreases scavenging of the exhaust gas from the cylinders and thereby lowers the efficiency of the piston portion.

Design and Function of a Turbocharger - Turbine | BorgWarner Turbo Systems

Turbo compound engines, on the other hand, operate on the "blow down" principle, which extract energy only from the momentum of the rapidly moving exhaust gasses. Although less efficient than the impulse turbine, it has the benefit of not effecting the operation of the piston side of the system, since there is little to no back pressure.

www.dtic.mil/dtic/tr/fulltext/u2/b807167.pdf‎

In summary, the turbocharger is a pressure turbine, a power recovery turbine is a velocity one.

Velocity is transformed across the turbine blade as in a wing that produces lift to px. Velocity is increased in the turbo scoll (divergent duct) from the exhaust. Px in the exhaust pipe from valve to the scoll is not relevant as it velocity that is required and not px.


A compound charger is the same transform's across the blade but instead of driving a compressor it drive a shaft onto the crankshaft.

Cheers

So explain the science behind waste gate operation, does it bleed off velocity or pressure from the system?

This quote from a turbo-charger manufacturer;

So what gives you the px differential across a wing ? Speed / velocity. Velocity across the blade. No difference to any gas turbine. Velocity transformed not px. If it was just px there would be no need for a divergent scroll would there.

Cheers

Remember
Velocity increase. Px decreases temp decrease.

Or

Velocity decreases. Px increases temp increases

Gas law for subsonic flow.

Unless they got that wrong as we'll

Cheers

You are confusing a gas turbine engine with a turbocharger they operate on different principles.

The turbine section of a "jet" engine has stators and rotors, the stators expand the air and accelerate it focusing on the rotors. These are aerofoil shaped and act like a wing turning the shaft.

In the basic turbocharger gas pressure builds up against it and the act of the pressure flowing through the unit to the exhaust drives the shaft.

It's exactly the same the convergent duct in a turbine to increase velocity is the scroll in a turbo. Turbine wheels on a turbo also have airfoils

That's why you can make a jet engine out of a turbo and why anti lag as in a WRC rally car injected fuel into the turbo to increase velocity of the gas flow.

Cheers

A turbine is a divergent duct, not convergent - otherwise known as a nozzle.

Whether it's axial, radial or mixed flow, the principles are the same - expanding gas through a nozzle allows you to capture some kinetic energy that would otherwise be released as heat.

I'm afraid you don't understand the basic principles involved. One operates on the basis of Newtons second law of motion, and the other on the basis of Newtons third law. I'll leave you to figure which might be which.

So the burner can is divergent is it guess better have a closer look. The 1st wheel is the smallest then wheel size increases proportional up to balance size against force as the energy is released
Cheers

no - burner can is (theoretically) the constant pressure part of the brayton cycle.

Bummer can exit is convergent to increase volicity into the I
1st Ngv. From that point onwards it starts to go divergent thought the rest of the engine to get maximum energy recovery. Last point before air enters the bummer can it goes divergent to increase px and slow volicity. Why is this. So you don't blow the flame out
Cheers

Last time I look at a turbo charger ext gas entered the scroll in a convergent duct. Last time I saw a compound disc was approx 8"inches in dia and had on top of it wait for a convergent scroll to once again increase volicity or in your world dose a convergent duct not do that ?
Cheers

And Ngv do several things as the pass the gas flow though the engine. The increase in dia they flow the air onto the next disc at the correct aoa. And they have a convergent duct between the vanes to increase the the volicity of the air passing through the Ngv.

Cheers

Could you please learn to speak english. You posts are completely and totally unintelligible.

Nah they fine if you know what your talking about I just showed the apprentice and he could work it out.
Dia diameter
Aoa angle of attract
Convergent large to small
Divergent small to large
Ngv nozzle guild vane

Cheers

Now that last post made me smile!

:p

He suffers from a very rare affliction known as ABSuRD: Apparently Selective But Random Dyslexia.

He's actually responsible for maintaining aero engines (apparently..), well, those customers who don't have their perfectly maintained burnt valves lying allover the floor that is...

He also suffers from delusions of grandeur