Author Topic: Turbocharger power input (consumption)  (Read 1456 times)

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Offline langwadt

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Re: Turbocharger power input (consumption)
« Reply #25 on: March 25, 2020, 10:58:12 pm »
it is not quite so simple, the turbine is driven by the kinetic energy of the exhaust stream not just pressure
It sure isn't simple! I've often wondered about the effect of having a large plenum right at the inlet to the turbine similar to one commonly used at the compressor outlet where the inlet pipes branch from. That would spread and reduce the amplitude of the kinetic energy of the pulsating waves to more of a smooth flow, similar to the effect of a series choke with rectified DC current flow. The turbo might have to be resized to suit the new circumstances, but I wonder if there would be any benefit. Somewhat similar to a transformer not having to handle the peak currents of a capacitor input filter? Far fetched maybe, but sometimes physics has some interesting parallels.

kinetic energy is velocity squared so I think it'll reduce power

 

Online joeqsmith

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Re: Turbocharger power input (consumption)
« Reply #26 on: March 25, 2020, 11:04:25 pm »
Also, I wouldn’t say the power to drive a turbo is free. If you have pressure at the compressor outlet then you are also going to have pressure at the exhaust turbine inlet. This exhaust back pressure is something the rising piston has to push against on the exhaust stroke, therefore stealing crankshaft power. Of course, this might be partially countered by the inlet boost pressure helping to force the piston down on the inlet stroke. To get it right is engineer’s stuff, not a shade tree mechanic.

I try to match this at 1:1.   So 30 PSI on the intake, 30 PSI in the exhaust.   To measure the exhaust pressure,  I use about a foot of stainless tubing to connect the sensor.   

With higher pressures, I have had the valves want to open.   Of course there have been many other problems to solve along the way. 
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Offline NiHaoMike

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Re: Turbocharger power input (consumption)
« Reply #27 on: March 25, 2020, 11:11:54 pm »
In the realm of racing, how does a turbocharged/supercharged engine compare to a jet engine?
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Offline langwadt

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Re: Turbocharger power input (consumption)
« Reply #28 on: March 25, 2020, 11:38:58 pm »
In the realm of racing, how does a turbocharged/supercharged engine compare to a jet engine?

jet engines are  powerful for their size and weight, but thirsty and only really efficient at +90% power

 

Online joeqsmith

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Re: Turbocharger power input (consumption)
« Reply #29 on: March 26, 2020, 12:04:38 am »
In the realm of racing, how does a turbocharged/supercharged engine compare to a jet engine?

You saw a lot more innovation back then.

How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Online Someone

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Re: Turbocharger power input (consumption)
« Reply #30 on: March 26, 2020, 12:18:01 am »
In the realm of racing, how does a turbocharged/supercharged engine compare to a jet engine?
Mechanically they have a lot of similarities. Scrapheap challenge showed at least 2 DIY jet engines based around turbochargers:
https://youtu.be/z0iigOmActU
https://youtu.be/9GCBCdMOFpE
Rudimentary antilag systems basically use the turbo directly as a jet engine...

Guy in the UK, can't recall the name just now, used an interesting method of eliminating turbo lag on his Ford BDT (If I recall correctly) powered hill climb special.  He used a jet turbine APU to assist driving the turbo, so the turbo had a constant feed of exhaust gas, therefore boost was constant!!  The thing is crazy fast off the line, as it is also AWD, and everywhere else!!  Not exactly practical or fuel efficient for road use, but for it's intended use, amazing.
I've watched it run a few times and it's quite an experience, with the sound of a jet engine and a 4 cylinder turbo motor. Oh yeah, he built it all himself!!
Antilag has many implementations:
https://en.wikipedia.org/wiki/Antilag_system
 

Online Circlotron

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Re: Turbocharger power input (consumption)
« Reply #31 on: March 26, 2020, 01:09:20 am »
I try to match this at 1:1.   So 30 PSI on the intake, 30 PSI in the exhaust.
I imagine that if intake pressure was much higher than exhaust pressure you would get blow-through during valve overlap. A 1:1 pressure ratio wouldn't work very well for a turbo converted to a jet engine though! Inlet pressure would have to be higher than exhaust for the air + fuel to flow in the right direction. I've heard a single turbo with no air filter on an 855hp V8 on a dynamometer from a distance of about 20 metres. That convinced me that there was plenty of action going on! Living proof of advances in material science.
 

Offline langwadt

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Re: Turbocharger power input (consumption)
« Reply #32 on: March 26, 2020, 01:51:20 am »
I try to match this at 1:1.   So 30 PSI on the intake, 30 PSI in the exhaust.
I imagine that if intake pressure was much higher than exhaust pressure you would get blow-through during valve overlap. A 1:1 pressure ratio wouldn't work very well for a turbo converted to a jet engine though! Inlet pressure would have to be higher than exhaust for the air + fuel to flow in the right direction. I've heard a single turbo with no air filter on an 855hp V8 on a dynamometer from a distance of about 20 metres. That convinced me that there was plenty of action going on! Living proof of advances in material science.


modern efficient turbofans are more like 40-50:1, a 50 year old turbojet ~12:1
 
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Offline firewalker

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Re: Turbocharger power input (consumption)
« Reply #33 on: March 26, 2020, 08:02:10 am »
For an EE forum we are doing pretty well! I guess engineering is engineering! :D :D :D

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Offline mzzj

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Re: Turbocharger power input (consumption)
« Reply #34 on: March 26, 2020, 08:19:45 am »
it is not quite so simple, the turbine is driven by the kinetic energy of the exhaust stream not just pressure
It sure isn't simple! I've often wondered about the effect of having a large plenum right at the inlet to the turbine similar to one commonly used at the compressor outlet where the inlet pipes branch from. That would spread and reduce the amplitude of the kinetic energy of the pulsating waves to more of a smooth flow, similar to the effect of a series choke with rectified DC current flow. The turbo might have to be resized to suit the new circumstances, but I wonder if there would be any benefit. Somewhat similar to a transformer not having to handle the peak currents of a capacitor input filter? Far fetched maybe, but sometimes physics has some interesting parallels.
Bad business, you want to keep the exhaust gas as hot as possible and large plenum would be difficult to insulate. (hot gas is flowing faster and energy is lost when it cools down) 
If you google "twin scroll turbocharger" it has almost opposite idea, maintain the kinetic energy and pressure spikes from each cylinder as well as possible.
 

Offline firewalker

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Re: Turbocharger power input (consumption)
« Reply #35 on: March 26, 2020, 12:34:31 pm »
With many assumption made. A 2000 cm3 engine at 6000 RPM with a "pump" driving the intake at 0.5 bar (50000 Pa). Every revolution the engine needs 1000 cm3 of air. This means 50000 cm3 or 0.05 m3  every second. The power the fluid takes from the pump is P=0.05*50000 = 2500 Watt.

This is without taking in account the vacuum of the engine that the pump should overcome. This means that the pressure differential is in reality 1.5 bar or more for 0.5 pressure. And is just the power of the fluid.

Alexander.
Become a realist, stay a dreamer.

 

Offline SilverSolder

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Re: Turbocharger power input (consumption)
« Reply #36 on: March 26, 2020, 01:11:04 pm »
Had to find that guys name!!  Nick Mann, heres his website with full details :-

https://raceenginedesign.co.uk/the-manic-beattie/

Really interesting if you're a petrol head.

Batshit crazy.  Love it!  :D
 

Online Circlotron

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Re: Turbocharger power input (consumption)
« Reply #37 on: March 26, 2020, 09:52:50 pm »
Okay, back to the original topic.
Let’s try it again for a 3 litre engine at 6000rpm with 15 psig. Instead of a turbo, say our compressor is a very long cylinder and piston with a cross sectional area of 1/15 square inch. That means this piston needs 1 pound force against 15 psi. The engine will consume 9000 litres per minute of air, but at double normal density. 9,000,000,000 cubic mm. The piston in our long compressor cylinder has a surface area of 1/15 sq  inch or 43 sq mm so to displace 9G cubic mm per minute it would move at 9G/43 = 209,302,325 mm per minute or 686,687 feet per minute, against 1 pound force, so 686,687 foot pounds per minute. 686,687/33,000 = 20.8hp = 15.52kW. That’s pretty simplistic, but it’s a starting point.
 
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Offline james_s

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Re: Turbocharger power input (consumption)
« Reply #38 on: March 26, 2020, 10:23:55 pm »
The whole point of a turbocharger is that it recovers otherwise wasted energy from the exhaust and uses that to drive the compressor wheel that supercharges the engine. If you want to know how much energy that takes, you'd likely have more luck looking at engine driven superchargers as the parasitic load they draw is likely to be better documented.

I don't know how well it translates to car sized engines but I recall reading that the supercharger used on the RR Merlin aircraft engine draws about 500HP from the crankshaft so the ~1300HP engine was actually producing closer to 1800HP. A mechanically driven supercharger is simpler, easier to build and cheaper but the fact that a turbocharger uses mostly otherwise wasted energy makes it significantly more efficient.
 

Offline james_s

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Re: Turbocharger power input (consumption)
« Reply #39 on: March 26, 2020, 10:26:10 pm »
https://en.wikipedia.org/wiki/Antilag_system

I actually kind of like the lag in my old Volvo, that kick in the pants when the turbo finally spools up is a lot of fun, it's like the whole car suddenly wakes up and leaps forward.
 

Offline langwadt

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Re: Turbocharger power input (consumption)
« Reply #40 on: March 26, 2020, 10:58:04 pm »
Okay, back to the original topic.
Let’s try it again for a 3 litre engine at 6000rpm with 15 psig. Instead of a turbo, say our compressor is a very long cylinder and piston with a cross sectional area of 1/15 square inch. That means this piston needs 1 pound force against 15 psi. The engine will consume 9000 litres per minute of air, but at double normal density. 9,000,000,000 cubic mm. The piston in our long compressor cylinder has a surface area of 1/15 sq  inch or 43 sq mm so to displace 9G cubic mm per minute it would move at 9G/43 = 209,302,325 mm per minute or 686,687 feet per minute, against 1 pound force, so 686,687 foot pounds per minute. 686,687/33,000 = 20.8hp = 15.52kW. That’s pretty simplistic, but it’s a starting point.

it is a starting point, some of the pressure would come from the increase in temperature

https://checalc.com/calc/compress.html

 

Offline JPortici

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Re: Turbocharger power input (consumption)
« Reply #41 on: March 27, 2020, 07:26:22 am »
Is the amount of power a turbocharger need the main reason for not having electrically driven turbines?

Alexander.
a conventional exhaust driven turbocharger in full power turns at 100k+ RPM and at the same time is way hotter than 150 °C :) that will add some complexity
« Last Edit: March 27, 2020, 07:28:42 am by JPortici »
 
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Offline tautech

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Re: Turbocharger power input (consumption)
« Reply #42 on: March 27, 2020, 08:18:56 am »
I imagine that if intake pressure was much higher than exhaust pressure you would get blow-through during valve overlap.
Exactly this is the great advantage with turbo'ed diesels. The proper cylinder scavenging promotes cleaner and better burns.

Some good general reading on turbochargers are books by Hugh MacInnes from way back in the 80's.
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Offline langwadt

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Re: Turbocharger power input (consumption)
« Reply #43 on: March 27, 2020, 09:05:37 am »
I imagine that if intake pressure was much higher than exhaust pressure you would get blow-through during valve overlap.
Exactly this is the great advantage with turbo'ed diesels. The proper cylinder scavenging promotes cleaner and better burns.

if efficiency was the only object maybe

but exhaust gas recirculation to reduces the amount oxygen to reduce the amount of NOx. and since diesels
always run with excess oxygen in the exhaust a three-way catalyst won't work to reduce NOx so you need things like Adblue
 

Offline tautech

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Re: Turbocharger power input (consumption)
« Reply #44 on: March 27, 2020, 09:14:39 am »
I imagine that if intake pressure was much higher than exhaust pressure you would get blow-through during valve overlap.
Exactly this is the great advantage with turbo'ed diesels. The proper cylinder scavenging promotes cleaner and better burns.

if efficiency was the only object maybe

but exhaust gas recirculation to reduces the amount oxygen to reduce the amount of NOx. and since diesels
always run with excess oxygen in the exhaust a three-way catalyst won't work to reduce NOx so you need things like Adblue
EGR is something completely different where a portion of exhaust gasses are diverted into the intake manifold.
It uses a separate piped connection and valving to accomplish it.

EGR is quite different to engine valve overlap where boost pressure can momentarily pass from intake to exhaust when the valve timing overlaps and in doing so scavenges the combustion chamber of any remaining exhaust gasses.
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Offline langwadt

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Re: Turbocharger power input (consumption)
« Reply #45 on: March 27, 2020, 09:37:52 am »
I imagine that if intake pressure was much higher than exhaust pressure you would get blow-through during valve overlap.
Exactly this is the great advantage with turbo'ed diesels. The proper cylinder scavenging promotes cleaner and better burns.

if efficiency was the only object maybe

but exhaust gas recirculation to reduces the amount oxygen to reduce the amount of NOx. and since diesels
always run with excess oxygen in the exhaust a three-way catalyst won't work to reduce NOx so you need things like Adblue
EGR is something completely different where a portion of exhaust gasses are diverted into the intake manifold.
It uses a separate piped connection and valving to accomplish it.

EGR is quite different to engine valve overlap where boost pressure can momentarily pass from intake to exhaust when the valve timing overlaps and in doing so scavenges the combustion chamber of any remaining exhaust gasses.

yes EGR is the exact opposite. So why would it be and advantage to scavenge any remaining exhaust gasses only to add it back via the intake to meet emissions demand 

 

Offline tautech

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Re: Turbocharger power input (consumption)
« Reply #46 on: March 27, 2020, 09:41:02 am »
I imagine that if intake pressure was much higher than exhaust pressure you would get blow-through during valve overlap.
Exactly this is the great advantage with turbo'ed diesels. The proper cylinder scavenging promotes cleaner and better burns.

if efficiency was the only object maybe

but exhaust gas recirculation to reduces the amount oxygen to reduce the amount of NOx. and since diesels
always run with excess oxygen in the exhaust a three-way catalyst won't work to reduce NOx so you need things like Adblue
EGR is something completely different where a portion of exhaust gasses are diverted into the intake manifold.
It uses a separate piped connection and valving to accomplish it.

EGR is quite different to engine valve overlap where boost pressure can momentarily pass from intake to exhaust when the valve timing overlaps and in doing so scavenges the combustion chamber of any remaining exhaust gasses.

yes EGR is the exact opposite. So why would it be and advantage to scavenge any remaining exhaust gasses only to add it back via the intake to meet emissions demand
Some don't give a damn about emissions !  :-DD



« Last Edit: March 27, 2020, 09:44:05 am by tautech »
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Offline SilverSolder

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Re: Turbocharger power input (consumption)
« Reply #47 on: March 27, 2020, 04:27:00 pm »
I imagine that if intake pressure was much higher than exhaust pressure you would get blow-through during valve overlap.
Exactly this is the great advantage with turbo'ed diesels. The proper cylinder scavenging promotes cleaner and better burns.

if efficiency was the only object maybe

but exhaust gas recirculation to reduces the amount oxygen to reduce the amount of NOx. and since diesels
always run with excess oxygen in the exhaust a three-way catalyst won't work to reduce NOx so you need things like Adblue
EGR is something completely different where a portion of exhaust gasses are diverted into the intake manifold.
It uses a separate piped connection and valving to accomplish it.

EGR is quite different to engine valve overlap where boost pressure can momentarily pass from intake to exhaust when the valve timing overlaps and in doing so scavenges the combustion chamber of any remaining exhaust gasses.

yes EGR is the exact opposite. So why would it be and advantage to scavenge any remaining exhaust gasses only to add it back via the intake to meet emissions demand

EGR can be disabled by the computer during peak demand input (mashing the pedal to the metal).  The rest of the time, during normal driving, the emissions are then safely lowered with EGR without impacting performance.
 

Offline tautech

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Re: Turbocharger power input (consumption)
« Reply #48 on: March 27, 2020, 06:02:27 pm »
I imagine that if intake pressure was much higher than exhaust pressure you would get blow-through during valve overlap.
Exactly this is the great advantage with turbo'ed diesels. The proper cylinder scavenging promotes cleaner and better burns.

if efficiency was the only object maybe

but exhaust gas recirculation to reduces the amount oxygen to reduce the amount of NOx. and since diesels
always run with excess oxygen in the exhaust a three-way catalyst won't work to reduce NOx so you need things like Adblue
EGR is something completely different where a portion of exhaust gasses are diverted into the intake manifold.
It uses a separate piped connection and valving to accomplish it.

EGR is quite different to engine valve overlap where boost pressure can momentarily pass from intake to exhaust when the valve timing overlaps and in doing so scavenges the combustion chamber of any remaining exhaust gasses.

yes EGR is the exact opposite. So why would it be and advantage to scavenge any remaining exhaust gasses only to add it back via the intake to meet emissions demand

EGR can be disabled by the computer during peak demand input (mashing the pedal to the metal).  The rest of the time, during normal driving, the emissions are then safely lowered with EGR without impacting performance.
Little do you know of the negative effects on an engine of EGR in its attempt to mitigate emissions.
Special oils had to be developed that better withstand the exhaust contaminants recycled through the engine that decimated ordinary diesel engine oil life and risked engine damage.

There are many tricks to disable EGR that monitoring systems do not see.  ;)
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Offline james_s

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Re: Turbocharger power input (consumption)
« Reply #49 on: March 27, 2020, 06:43:20 pm »
EGR has benefits but it is certainly not without problems. It tends to really gum up intake manifolds, and I've had the EGR valves themselves get gummed up and stick. The crankcase vapor recovery also makes a mess of intakes, covering everything with hard black crust.
 
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