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supercharged diesel?
nick205 - 11/12/08 at 12:00 PM

Thinking aloud...!

Why don't we see supercharged diesel engines?

Plenty of torque to drive a charger, less/no power lag - what am I missing?

Neville Jones - 11/12/08 at 12:04 PM

Superchargers are common on trucks and commercial and industrial diesels. Turbos are more likely these days. GM were supercharging their engines from way way back in the 1900s. Some heavy machinery even have the turbo blowing into a supercharger.

hobbsy - 11/12/08 at 12:05 PM

There's not a great deal of lag on a modern turbocharged VNT diesel though anyway is there?

If you get max torque at 1500rpm then you can only really get it a few hundred RPM sooner surely even with a supercharger?

Else the supercharger would be running all nearly the time and sapping power the second you go above idle.

Supercharger clutch and gearing issues?

Also turbo's on diesels are very effective due to cylinder filling being very high at all times (no throttle) and so exhaust gas volume must also be high - hence low lag?


I'm sure you could make it work but a modern VNT turbo works so well and doesn't have any real parasitic losses....

cd.thomson - 11/12/08 at 12:06 PM

How come we aren't all using forced induction wankel engines?

I suspect, (I also expect to be corrected) that this is just linked to ease for the manufacturer. Some boffin has explained how turbo superchargers work and that they don't sap bhp as superchargers do and so manufacturers have just all gone down this development route. Once you start using turbos theres no need to invest in supercharger induction. (Cylinders work fine, so why bother investing in wankel engines?).

Modern diesels with modern turbos get enough throttle lag from the TPS and ECU settings to make the effect of turbo lag negligible.

Personally I think superchargers are a better idea, but its too late in production/investment terms.

[Edited on 11/12/08 by cd.thomson]

MikeRJ - 11/12/08 at 02:08 PM

quote:
Originally posted by cd.thomson
How come we aren't all using forced induction wankel engines?


Wankel engines are interesting, but ultimately flawed. The long narrow combustion chamber contributes to poor thermal efficiency and poor emmisions performance. The rotor tip sealing problems still give the engine questionable longevity compared to piston engines (though they are much better than they used to be).

Turbochargers are ideally suited to a four stroke diesel. Since a diesel has a relatively low operating RPM range, you can use a small turbo that starts producing usable boost at 1500 RPM or so without it running out of puff as the engine approaches it's maximum RPM. The turbocharger also wins out on overall efficiency, packaging and cost.

The most efficient diesel engines do use superchargers, but they are two strokes and require a supercharger for scavenging. They tend to be limited to huge engines on ships, and for power generation etc.

nick205 - 11/12/08 at 02:23 PM

Good discussion gents

C10CoryM - 11/12/08 at 02:56 PM

There have been a few good supercharged diesels for the HD truck and off road equip industry. Mostly 2 stroke.
Where do you think the classic 6-71 or 8-71 superchargers came from?
The 6-71/ 8-71 are the names of the diesel engines that they came off.
Cheers.

tomgregory2000 - 11/12/08 at 06:35 PM

One word 'COST'

Simon - 11/12/08 at 07:50 PM

quote:
Originally posted by C10CoryM
The 6-71/ 8-71 are the names of the diesel engines that they came off.
Cheers.


My understanding and it has been for best part of thirty years, that those designations were for the capacity of the engine they were designed for, such as 6 cyl of 71 cu.in.

Anyway, agree, good thread. Have wondered about it myself occassionally.

I think with the turbo (particulary the ecu controlled VNT) you can design in a bit where there will be no boost - my Espace is off boost till about 1800rpm which means car will be more fuel efficient at cruising speeds, whereas with a blower, it'll always be on boost.

ATB

Simon

C10CoryM - 12/12/08 at 03:35 AM

quote:
Originally posted by Simon
quote:
Originally posted by C10CoryM
The 6-71/ 8-71 are the names of the diesel engines that they came off.
Cheers.


My understanding and it has been for best part of thirty years, that those designations were for the capacity of the engine they were designed for, such as 6 cyl of 71 cu.in.


Yep, but the Detroit Diesel 6-71 is what used the roots type blower that is called a "6-71" blower. Same with the 8-71.
http://store.summitracing.com/partdetail.asp?autofilter=1&part=WND%2D7476P&N=700+317356+115&autoview=sku

Cheers.

NS Dev - 12/12/08 at 07:19 PM

..................and if you want to hear one of em, click this link!

A chap I know has just bought a limespreader with one of these engines in it and he doesn't listen to the radio now, just goes deaf listening to the engine, it just sings!!

detroit diesel truck

rusty nuts - 12/12/08 at 07:31 PM

The old Commer TS3 ? was a supercharged two stroke diesel IIRC it was a three cylinder, six piston engine and PPC did an article on it earlier this year