Why no supercharged diesels?

[Deleted member 37751]

Had a good look at my friends C36 AMG restoration today and we were chatting about the new Bi-Turbo engines and ended up on about the supercharged AMG's and I was wondering why no-one manufactures a supercharged diesel?
And if not, technically speaking why not?

 

[Haris]

Never really thought about that, a supercharger would definately make a diesel sound much better!

 

[moonloops]

IIRC diesels generate a lot of exhaust gas flow compared to petrol hence turbos are much more efficient on diesels than superchargers

 

[LTD]

Isn't heat generation an issue too ?

 

[219]

I'd imagine there would be less of a benefit , compared to petrol engines .

The main advantage of supercharging over turbocharging , by my limited understanding , is that there is a useful boost even at low revs with a permanently engaged supercharger .

Since Diesel engines , relatively speaking , tend to have greater torque at low revs than a similar sized petrol engine , there is arguably less of a need for supercharging ? Once the turbo spins up , the boost is there to be exploited at higher revs .

Hopefully , Dieselman will be along as this , I think , is his area of expertise .

 

[Frankie]

I had a google and found that Mazda did the 626 with a 2.0 supercharged diesel engine. I wonder why they took that route instead of turbo.

 

[markjay]

Pontoneer is right.

Turbochargers provide boost only at the higher engine rev range, while superchargers work all the way from very low revs, and are not as efficient at high revs because they are mechanically driven by the engine. This is why Diesel engines, who are very torquey at the lower rev range but naturally asthmatic at high engine rev, benefit more from turbochargers more than from superchargers.

In fact, turbochargers are generally not ideally suited for road-going cars, because the reduced compression ratio on turbocharged engines means that they are less powerful at low engine revs than a comparable naturally aspirated (but with higher compression ratio) engine. However thanks to ongoing development, modern turbocharged petrol engine hardly have any noticeable turbo lag.

 

[rf065]

I had a google and found that Mazda did the 626 with a 2.0 supercharged diesel engine. I wonder why they took that route instead of turbo.

They used a comprex supercharger, it was driven by a belt & also used the exhaust gases to drive it too, unlike any other superchargers. Sounds as though it was more of a supercharger/turbo hybrid that just a supercharger.

Russ

 

[Mactech]

Pontoneer is right.

Turbochargers provide boost only at the higher engine rev range, while superchargers work all the way from very low revs, and are not as efficient at high revs because they are mechanically driven by the engine. This is why Diesel engines, who are very torquey at the lower rev range but naturally asthmatic at high engine rev, benefit more from turbochargers more than from superchargers.

Spot on Markjay! The reason that most of us have diesel engines is now one of effciency, so to add extra mechanical drag to drive the supercharger when the waste exhaust gases can be had pretty much 'for free' to provide the drive for a turbo, goes against the real ethos of diesel.

 

[RBYCC]

Actually diesels were supercharged long before being turbocharged.

General Motors Detroit Diesel Division developed the most famous supercharger, the 6-71 in 1938.

It was a Roots type and used on heavy duty diesels for both stationary and transportation ( rail ) use.

The 6-71 was the "blower" of choice starting in the 50's for both gas and fuel dragsters..

Link below to "Marinediesel" which manufactures supercharged diesel engines for commercial and military use.
Marinediesel AB

"TSC-series – With twin Lysholm superchargers

With twin Lysholm superchargers this engine is not like anything the world propulsion market has ever witnessed. The engine is specifically designed for applications where ultra fast throttle and torque response is required such as boarding missions etc.
The engine is still under development."

I would think that the application of turbos in automotive use is primarily for production cost and efficiency which equates to profit.
High performance considerations are secondary to production design practicality.

 

[219]

Historically , the first superchargers were fitted to Aero engines to allow the same performance at altitudes , where the air is 'thinner' , as at ground level .

 

[markjay]

Correct me if I am wrong, but I believe that (the much simpler) supercharger technology existed much before turbochargers did, which probably explains why earlier engines - diesel and petrol - were supercharged rather than turbocharged...?

 

[219]

I am sure that is correct : supercharging certainly existed in the 1920's ( plenty of Mercedes cars of that era were so equipped - especially the ones designed by Dr Porsche when he worked for Mercedes ) , however , I think the technique was developed for WW1 fighter aircraft , as mentioned above .

Turbocharging , as far as I am aware was first heard of in the 1970's with the SAAB 99 Turbo and the Porsche 911 Turbo being the first two so equipped cars I am aware of . The BMW 2002 tii was in there somewhere too , but I 'think' it came slightly later ?

I stand to be corrected on any of the above .

 

[Dryce]

I think the technique was developed for WW1 fighter aircraft , as mentioned above .

That sounds early. Supercharging as a principle predates WW1.

But I don't recall seeing any mention of supercharged aero engines until the 20s and they don't really emerge properly until the 30s.

 

[Value Motering]

Supercharger - Wikipedia, the free encyclopedia
...
1860 ??? that makes em about 151 years old, Wiki and interwebb are too clever.

 

[lupi]

Actually diesels were supercharged long before being turbocharged.

General Motors Detroit Diesel Division developed the most famous supercharger, the 6-71 in 1938.

It was a Roots type and used on heavy duty diesels for both stationary and transportation ( rail ) use.

The 6-71 was the "blower" of choice starting in the 50's for both gas and fuel dragsters..

Link below to "Marinediesel" which manufactures supercharged diesel engines for commercial and military use.


Marinediesel AB

"TSC-series – With twin Lysholm superchargers

With twin Lysholm superchargers this engine is not like anything the world propulsion market has ever witnessed. The engine is specifically designed for applications where ultra fast throttle and torque response is required such as boarding missions etc.
The engine is still under development."

I would think that the application of turbos in automotive use is primarily for production cost and efficiency which equates to profit.
High performance considerations are secondary to production design practicality.

Back in 1994, I had a couple of Volvo`s 230bhp (straight six cyl.)
diesels on 32ft Princesss boat, these engines were developed from
the 200bph also straight six and same cubic capacity, the development was a compressor, belt drivin by the crankshaft pulley,
the compressor supercharged the engine from 1400 rpm up to cut
off 2500 rpm,the idea was to get boats on the plain much quicker,
both the 200bhp and 230bhp had turbos and both had a 4000 rpm.

So I think it is not impossible to have something similar, obviously
the subject may be different between cars and boats.

 

[markjay]

I believe that some high performance cars did have both superchargers and turbochargers... but while this may sound like 'the best of both worlds', it is probably not really ideal because of the additional weight at the front of the car (assuming front-engine and RWD), and because - when mated to a v8 or v12 - it would make the engine bay a very busy (and very hot) environment... and a plumber's nightmare.

And I don't envy anyone servicing such an engine, especially when shoe-stringed into a smaller car - replacing the alternator for example is likely to be quite challenging...

 

[Colin_b]

I believe that some high performance cars did have both superchargers and turbochargers... but while this may sound like 'the best of both worlds', it is probably not really ideal because of the additional weight at the front of the car (assuming front-engine and RWD), and because - when mated to a v8 or v12 - it would make the engine bay a very busy (and very hot) environment... and a plumber's nightmare.

And I don't envy anyone servicing such an engine, especially when shoe-stringed into a smaller car - replacing the alternator for example is likely to be quite challenging...

I think it was Lancia (at least) that had low engine rpm direct drive superchargers to cover the poor performance of the exhaust drive supercharger. Engine drive was inefficient, and technology fixed the exhaust drive problems like lag, over-run and fuel regulation.

The now known as turbo has just become another component, as anonymous as a camshaft.

Until it goes wrong

 

[grober]

The exhaust gas turbocharger was "invented" on 16 November 1905 when Swiss engineer Dr. Alfred Büchi received patent No. 204630 from the Imperial Patent Office of the German Reich for a "combustion machine consisting of a compressor (turbine compressor), a piston engine, and a turbine in sequential arrangement". He had to wait a long time until his invention was first able to enter practical use in large marine engines installed in the German "Danzig" and "Preussen" passenger liners in 1923. Each had twin ten-cylinder diesel engines with output boosted by turbocharger technology from 1750 to 2500 horsepower. My bet is that it was simply the development of better material science that finally allowed the turbocharger to flourish. Perhaps the lower thermal efficiency of the supercharger was compensated by the fact they would last longer in the early days. The intrinsically higher thermal efficiency [ and hence fuel economy]of the turbocharger is the reason Mercedes has given for abandoning their KOMPRESSOR petrol engines in favour of turbocharged ones in their latest models. In the early 90's Mercedes vowed never to turbocharge their petrol engines as they said it made them unreliable! Changed days!

 

[markjay]

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