Why arent Diesel Cars Supercharged??

[BUSA]

Was Just wondering today, that most diesel cars are turbocharged and hence they have tremendous turbolag at low RPM. Then why dont manufacturers Supercharge diesel engines? This way the lag can be eliminated as well.

What are your inputs. Can it be done or its not possible due to some technical reason.

[arunforu1]

Hi BUSA, Turbo charging is essentially a way of supercharging but in an efficient manner.

If the design of super charger takes power from engine, then it will put a load on the engine, thus reducing the efficiency.

Turbocharging is a type of supercharging which utilise enery of escaping exhaust gases, thereby a more efficient method. You are right turbo lag is there at lower RPM's as turbine needs minimum input velocity to run compressor efficiently.

But this can be corrected by an optimised design solution, the modern diesels are getting lighter with advancement in material technology, thus helping in reducing inertia of moving parts so that engine can use higher rpm's allowing turbo to work properly.

I have used modern Volkswagen Golf 5, with 1.9 diesel turbo, i never felt turbo lag.

Our indian vehicles are getting turbo's as add on parts on older tech engines which were designed to run at low RPM's at idle, owing to heavy parts causing inertia problem. But an enigne design keeping in mind with turbo technology reduces Lag to unoticable range.

Also turbine & compress tech has improved a lot, i hope sooner we will get turbo diesels made in india, & very efficient ones.....our industry is maturing fast.

[vid6639]

Superchargers run off engine power. The supercharger uses engine power almost 1/3rd to provide boost to the engine.

The turbocharger is more efficient as it uses exhaust gases to provide the boost. these exhaust gases would normally be wasted so the turbo doesnt use the engine's power.

The supercharger since it's generally driven by a belt or pulley will have better throttle response intantaneously since it's using the engine power.

The turbo needs to spool up. This results in turbolag. Overall efficiency wise and performance wise the turbo is better. but if you need throttle response the supercharger is better.

Also the supercharger will consume more fuel.

hence not used as commonly as a turbo.

[deepakhon]

Isn't the new 1.4 ltr engine from VW both supercharged and turbocharged?

[arunforu1]

Originally Posted by deepakhon

Isn't the new 1.4 ltr engine from VW both supercharged and turbocharged?

Dear deepak, I am talking about VW Golf 5th generation, which is latest one, i have seen 2 options 1.6 FSI petrol, & 1.9 TDI diesel.

I am not aware of 1.4 variant, it may be used in polo, but i never have used a polo.

For golf i have used both 1.6 petrol & 1.9TDi for few moths.

[theMAG]

Most high-performance trucks such as MAN, CAT, Mercedes-Benz, Scania etc. come with supercharged diesel engines. They cant afford to have turbo lag while pulling loads. Even certain lightweight aircraft use SCed diesels.

In cars other considerations also crop up - such as small engines sizes and the need for those engines to run at a lower rpm. Besides a TC is more modular and robs the engine of no power.

[BUSA]

Originally Posted by deepakhon

Isn't the new 1.4 ltr engine from VW both supercharged and turbocharged?

Thats a Petrol.

Thanx for your input guys, i am aware how a supercharger & turbocharger works but i want to know why manufacturers dont use it on Diesel cars. Petrol cars do have it e.g Mercedes C200 Kompressor.

[iraghava]

IIRC the supercharger in the SL55 engine robs the engine of 100+bhp. So if it were more efficient the engine could ahve turned out 600+bhp.

Originally Posted by deepakhon

Isn't the new 1.4 ltr engine from VW both supercharged and turbocharged?

Yes, there is one such engine being sold in the Golf range.

[vid6639]

cause it's not as efficient as a turbo and turbo's are more easier to fit than superchargers which need the pulleys or belts to run off the engine.

efficiency is lesser both ways it wastes engine power and it will inturn use more fuel.

the only advantage is no turbolag.

[tsk1979]

Supercharging a diesel engine will give out lot less power than a turbo-intercooler combo. Hence it is employed only in trucks.
In case of petrol engines, even normally aspirated 1.5 lt engines can make 110-120bhp, so adding a bold on supercharger gives the performance without any turbo lag.
Since a diesel engine is all about efficiency, its mostly turbo in diesel land, and turbo lag is combatted using VGT etc.

[ac 427]

arent the Skoda Diesels Supercharged ??????

[tsk1979]

No, they are turbocharged.

[Rehaan]

Hmmmm..... good question BUSA!

I dont know the answer, but i can guess / remember some discussion about (might be wrong) deisels being MUCH better to turbo as opposed to supercharge due to something to do with the exhaust .... could it be the higher EGT? Higher compression engine ? something like that....... im sure Mpower will know.

Also, i seem to remember reading that Forced Induction on a deisel is much more advantageous than on a petrol (% of power increase per unit boost wise). Any confirmations?

cya
R

[Rehaan]

Heres another discussion with the exact same Q - PH: Why dont we get Supercharged Diesel car engines?

Kinda related, interesting read - DieselBike.net Supercharged Diesel Motorcycle

cya
R

[Mpower]

Originally Posted by Rehaan

Hmmmm..... good question BUSA!

I dont know the answer, but i can guess / remember some discussion about (might be wrong) deisels being MUCH better to turbo as opposed to supercharge due to something to do with the exhaust .... could it be the higher EGT? Higher compression engine ? something like that....... im sure Mpower will know.

Ya, thanks for putting me on the spot Rehaan...I was hoping I could weasel out of this one.

Me no expert here, but the thing is that diesels run very high Air Fuel Ratios some thing like 90:1 at low load and probably 30:1 at full load. But their calorific values are pretty similar (within 10%)

Therefore for every gram of fuel you have a to flow a lot more air through a diesel than a petrol....which means the cylinders are pumping out (negative work) humongus amounts of air at all times(not just at full throttle..remember there is no throttle plate) which can be recovered by a turbo and this air is really needed at the intake side. So it really complements the engine working principle. In fact turbos are a must for modern diesels not just an option.

As far as superchargers, they can be used in theory..it may not be as efficient. Since the primary motive for diesels is fuel economy nobody found it worthwile to do one. With VGTs and dual stage turbos, its really makes no sense anymore.