Help to put in Laymens terms

[platinum01]

Hello and Happy Turkey day. Have a Question and hope that ya'll can help to put into Laymens Terms for me. I was talking with somebody earlier in the day and we were talking about turbos and twin turbos . He then asked me how come they don't put belt driven Prochargers or Superchargers on diesels. I explained to him the best that I could, be he still looked at me like I had two heads and then asked if I could put it in Laymens Terms. He is a big old school motor head but not really defined on diesels. I told him that I would post the question on the best web page ever and then see what ya'll have to say. Thanks

 

[BamaSixGun]

is he talkin bout a blower? like you would see on a dragster?

 

[Tail_Gunner]

He then asked me how come they don't put belt driven Prochargers or Superchargers on diesels.

Parasitic power loss?

A supercharger or blower will put a strain on the engine for what ever amount of power it takes to turn the blower unit. That amount of power will be power spent turning the blower and not turning the rear wheels whether it be 50, 75 or 100hp.

A turbo charger doesn't have such a parasitic power loss because it is driven by exhaust gasses and not the crankshaft. The trade-off is that the turbo does take slightly longer to build power, i.e. turbo lag.

That's my best guess.

 

[Roland_Jenkins]

Blowers typically produce less additional power (vs. turbo/powerpacking) because, unlike turbochargers, they use engine power to run themselves. Blowers create more heat while compressing the air which reduces the air density, producing less power and possibly causing engine damage.

source; http://www.dieselpage.com/tipsdgt.htm

FWIW department. The old two stroke Detroit's had a blower. They also were often equipped with both, a blower and a turbo sometimes twin turbos.

 

[JLDickmon]

Well to begin with, turbocharging IS a form of supercharging.

In a gasoline engine, you vary the amount of throttle by basically controlling airflow (always near 14.7:1 air/fuel).

In a Diesel engine, you throttle it by controlling the amount of fuel, airflow is always full-flow.

Turbo's run off exhaust heat; displacement varies with the amount of load applied to the engine. More load is more heat, is more boost.

Roots-style and Paxton superchargers (blowers) are belt driven, and the displacement varies with engine rpm. So to get boost, you would ALWAYS have to be making boost. This is very hard on an engine. You are always producing excess heat (that's why you see it's use limited to ultra-high performance applications where the RPM window is very small, like powerboat racing and drag racing). And like Kent said, parasitic power loss is incredible. You may be able to bolt on 150 hosepower, but you're going to lose 100 of that just running the blower.

Next lesson, Otto-cycle piston engines vs Felix Wankel's rotary engine...

 

[roosterdiesel]

ProChargers are centrifugal chargers like Paxton and Vortech chargers. Not roots type blowers like a 6-71 sticking out of the hood of an old hot rod.


I don't think ProCharger or others make a charger big enough to produce the CFM we need for our engines. Add the parasitic loss and the only way to go is a turbocharger.

 

[platinum01]

Awsome. Thanks you all for the quick response. With all that was said I will be able to pass this along and let him know the reasons that BLOWERS and PROCHARGERS are not used on diesels. Again I want to say this is a great site, and thanks to all.

 

[roosterdiesel]

Next lesson, Otto-cycle piston engines vs Felix Wankel's rotary engine...

He said Wankel!



The Wankel is a VERY efficient engine, just add more rotors, housings, air(turbo) and fuel for whatever powerlevel you want. Only problem is that apex seals wear out.

 

[Hoss 350]

There are several reasons above and beyond what was mentioned.

1.) Efficiency. This one was already mentioned in a way, in the form of parasitic loss, etc, but I will put it into even more layman terms. Supers take horsepower to drive them. They result in a net increase in horsepower, but at the cost of adding a BIG load on the engine to do so, and so a loss of fuel efficiency. In an industry where MILLIONS of dollars are made on a difference of one mile per gallon, supers just don't add up. Turbos add (more or less) FREE power to the engine by using scavanged exhaust pulses to drive boost. Net result is BETTER fuel economy and BETTER power.
Just for reference, I understand supers put a parasitic loss of somwhere between 25 and 50 percent on an engine, where a turbo can be as little as 2 to 15 percent (mostly due to exhaust backpressure)

2.) LOAD SENSITIVE BOOSTING. This is a HUGE one that many people miss. A super, being crank driven, makes boost via engine RPM, not via engine load. So, to get maximum boost, you have to be at redline. Diesel engines make peak torque at somewhere around 30 to 50% of redline RPM, so they would only be at 30 to 50% boost in peak torque range. Wnat max boost? You're at redline where the torque has dropped off and you're efficieny sucks! Turbos make boost based on your right foot. More throttle, more boost. You can have maximum boost right in the sweet spot of the torque range, and run your diesel where it wants to be all day long at max power and max boost, not at redline (where we all know diesels don't need or want to be!) Think of a bog cat diesel, which will pull out of 500 RPMs all day long. With a turbo, it can make big boost at that RPM level. With a super, it is barely above atmospheric pressure!

3.) Diesel RPMs are too low. As described above, you would have to overdrive a super on a low RPM diesel to get any sort of boost numbers out of it, and that just increases parasitic loss by giving the super a leverage advantage on the crank.

4.) And finally, THEY DID use superchargers on diesels. on 2-stroke diesels, blowers were an intergral part of the engine design. they wouldn't run without one, because the stroker relied on the blower for intake and exhaust scavanging. But they were never meant to be power adders because at the low RPMs of a diesel, they only made a peak boost of 3 psi!

 

[Mike K]

Superchargers, Turbos, Detroits, black smoke..... arg arg arg....

-popcorn