why no supercharged diesels ? - Diesel Forum

hapaschold · 11-18-2006, 05:37 AM

any thoughts ?

ICP · 11-18-2006, 05:43 AM

What do you mean? right now?
There were before, Detroits were superchargedd

AaronSEIA · 11-18-2006, 07:19 AM

From what I gather, the Detroits were all 2 stroke and were supercharged to a bit over atmospheric pressire to scavage exhaust gases. Big problem that I see with a SC is limited boost. Unless I am wrong, a SC is always building the same amount of boost or almost the same up to a preset psi. That would limit the fuel that an electric diesel could inject and thus limit horsepower.
Aaron SEIA

Birken Vogt · 11-18-2006, 09:36 AM

Detroits are NOT supercharged as a function of their design. The blower on a Detroit rather takes the place of the intake and exhaust stroke on a 4 cycle engine. But put a Detroit blower on a 4 cycle engine and then that engine will be supercharged. Some constant speed Detroits could be supercharged by just the blower such as generators if they increased the air flow and fooled with the valve timing.

Now anyway, back in the 50s or 60s Cummins had what they called an "iron lung" which was a blower on the side of the engine supercharging. But as was stated above a mechanical supercharger always gives the same boost whether needed or not thus wasting power most of the time. Better suited for constant speed applications if at all.

With the advent of turbo technlogy (which is properly called a turbosupercharger) all engine driven supercharging disappeared anywhere money is to be made, as exhaust driven supercharging utilizes power from the hot gas stream that would otherwise be wasted, thus improving efficiency.

Birken

frashdog · 11-18-2006, 09:42 AM

Right now they are being offered for boats. I went to a boat show this year and found some diesels I-6 with supercharger and turbo. They were the power plant for the new direct drive lowerunits. Looks like a inboard out board lowerunit, but it is mounted directly beneith the motor like an inboard. Oh, and the prop is out front, pulling! Helps dock these bigger boats, they can drive sideways. They are designed for 30+foot cabin cruisers, 250-350hp with all kindas torque.

So back to the motor. The super charger works the boost up at low rpms out of the turbos range to help, once the turbo spools up the supercharger gets bypassed a bit. Make an over all more effecient unit as I was told by the sales dude. He did tell me the variable vane turbos coming out were going to make the roll of the supercharger in this application obsolete.

CowKiller · 11-18-2006, 12:02 PM

also blowers or superchargers rob power from the engine to rotate them.lot less efficent

2006CTDAUTO · 11-18-2006, 12:12 PM

The supercharger robs power from the crankshaft to generate the boost thus decreasing fuel efficiency. Why take power from the crank that can go to the flywheel when you can just use free energy in the exhaust?

The supercharger's boost also does not change based on load, only with engine RPM.

Birken Vogt · 11-18-2006, 01:36 PM

[ QUOTE ]
So back to the motor. The super charger works the boost up at low rpms out of the turbos range to help, once the turbo spools up the supercharger gets bypassed a bit. Make an over all more effecient unit as I was told by the sales dude.

[/ QUOTE ]

That sounds more like a Detroit Diesel 2-cycle with a bypass blower, maybe they are still selling them in boats. Also the EMD engines have a centrifugal supercharger that is driven by the engine at low speeds and the exhaust at high speeds, again a 2 cycle engine but you say 200-300 hp so I am guessing Detroit, again not really supercharged by the blower.

Birken

Gone Fishen · 11-18-2006, 09:12 PM

Berkin is correct on the EMD engine. There was a diesel gen set at our shop and it had a turbo + a supercharger. Rolls Royce diesel, turbo'd and the supercharger supplied air to the turbo. The turbo was driven by the exhaust from the engine and the supercharger was driven by the exhaust from the turbo. Shop sold it.

mudguppy · 11-19-2006, 01:16 PM

[ QUOTE ]
...The turbo was driven by the exhaust from the engine and the supercharger was driven by the exhaust from the turbo....

[/ QUOTE ]

um, no. [img]/ubbthreads/images/graemlins/vulnerable.gif[/img]

a supercharger (or blower) is driven mechanically via belt or gear, not by exhaust. if it is driven by the exhaust, it needs a turbine to transfer the energy, and then it is by definition a turbosupercharger. and i don't think we are talking about a roots-type blower, here. not possible. centrifugal compressor only.

and the only "supercharger" set-ups that i've seen are on 2-cycle applications with the blower driven mechanically and the turbo feeding into the blower, not the other way around.

not saying that it doesn't exist or that i've seen every diesel in the world, but it just wouldn't make sense any other way. you wouldn't generally supercharge a 4-cycle. the effeciency and maintenance is so much better and easier w/ a turbo on a 4-cycle.

my opinion. [img]/ubbthreads/images/graemlins/biggrin.gif[/img]

Gone Fishen · 11-19-2006, 02:38 PM

Correct as spoken, however I don't like the blowers on the 2 cycle DDA engines having a refered as a supercharger. As for the engine I spoke of, the only way the 'supercharger was receiving any drive, was either the oil pressure, oil drain, or the exhaust to the supercharger or the outlet from the supercharger. Maybe I missed something in my observation of the genset. Since it is no longer in inventory and I cannot go back and look at that piece of equipment I will therefor suceed this call on that generator set. I must have missed the drive mechanism. My bad.
All of the 'supercharger's' I saw while I was in the oil field workings were mechanically driven with a clutch to drop out when the purpose was no longer needed as in the case of 2 12V EMD's and 1 V8-EMD engine.
All of the 2 cycle engine I worked on for 25+ years and even today were DDA engines and none of them ever had a supercharger. All were blowers and were refered to in all the overhaul books as blowers. All were driven by a shaft or gears directly from the gear train. All of these were always driven, no clutches or any means of not being being driven. None were supercharged.
[img]/ubbthreads/images/graemlins/grin.gif[/img]

mudguppy · 11-19-2006, 02:58 PM

[ QUOTE ]
...were mechanically driven with a clutch to drop out when the purpose was no longer needed as in the case of 2 12V EMD's and 1 V8-EMD engine....

[/ QUOTE ]

really? were they roots type blowers?? i'm just wondering how that wouldn't cause problems if the blower vanes no longer were driven. i guess i'm looking at it as if the vanes weren't turning than they would basically block the intake air flow and the turbo would have to force the charge through the vanes.

or, is it the case that since the clutch disengages while running, so that means that the intake charge keeps the blower vanes turning, but really just kinda "coasting"????

i guess i could see that better if it were a centrifugal compressor/blower, but doing that to a positive displacement roots-type seems strange to me.

but a lot of things seem strange to me.... [img]/ubbthreads/images/graemlins/biggrin.gif[/img]

frashdog · 11-19-2006, 06:31 PM

Well who'd thought volvo made the supercharged, turbo diesel motors back in 2003, see here

Still using them here Did not see this motor on the IPS drives

Yehaw · 11-19-2006, 06:31 PM

[ QUOTE ]
The supercharger robs power from the crankshaft to generate the boost thus decreasing fuel efficiency. Why take power from the crank that can go to the flywheel when you can just use free energy in the exhaust?

[/ QUOTE ]Nope......Driving a turbo causes exhaust back pressure which in turn causes higher cylinder pressures on the exhaust stroke...It's not free energy, but the increase in power outweigh the losses if properly designed.

Birken Vogt · 11-20-2006, 12:58 PM

[ QUOTE ]
[ QUOTE ]
The supercharger robs power from the crankshaft to generate the boost thus decreasing fuel efficiency. Why take power from the crank that can go to the flywheel when you can just use free energy in the exhaust?

[/ QUOTE ]Nope......Driving a turbo causes exhaust back pressure which in turn causes higher cylinder pressures on the exhaust stroke...It's not free energy, but the increase in power outweigh the losses if properly designed.

[/ QUOTE ]

It's not entirely "free" but it does not take as much power from the engine crank shaft to drive it as the power you are getting out the compressor side. Most of the power from an exhaust driven turbocharger is taken from the extra energy of the exhaust gases and not the engine crank shaft. Now a mechanically driven supercharger takes 100% of its energy from the crank shaft and therefore is not an "energy scavenger" like the exhaust driven turbo.

Birken