I’ve been looking on the web, using GOOGLE, for a site which explains the mechanics involved with the operation of a comprex supercharger…an engine boosting device which uses the energy of exhaust pulses to compress the intake charge.
Anyone knows of such a site? I’ve found sites about specific companies marketing a particular engine, and a couple of sites with a simple definition like mine, but no real detail.
Umm… maybe I’m not getting something here… but the
name of the thing that uses the energy of exhaust gasses
to compress the incoming air is… a turbocharger.
All supercharger arrangements I’ve ever seen have
the compressor (whatever kind it is) powered by a
belt that is driven by the crankshaft.
I’m sure there’s nothing stopping anyone from making
a supercharger whose compressor is powered by a fan
that is spun by exhaust gasses. But you’d probably
get better efficiency, add less weight, and get more
boost out of a normal turbocharger.
I am not an automotive engineer (though I play one
on the SDMB ;]), but this sure sound like a gimmick to me.
-Ben
Hm, well, it’s more legit than I thought. I just threw
“comprex supercharger” into Google, and found this page:
http://www.pml.com.sg/showroom/glossary_detail.asp?start_letter=c&id=17
It looks like a hybrid turbocharger/supercharger. It
says it was designed specially for diesel engines. Why
you would want to put this thing on a gasoline engine
I don’t know.
-Ben
No direct knowledge of this thing, but it looks like a tuning/maintenance nightmare to me. Aside from heating the intake charge and increasing exhaust backpressure, it would have to be timed to the valvetrain, and would only work really well in a narrow rpm range. I would also think that you would either be recycling a lot of exhaust or exhausting a lot of unburned fuel.
Until Anthracite gets here to point out my errors, I’d say stick with a turbo or centrifugal blower.
True enough, a Comprex Supercharger (or Compie) is indeed a sort-of hybrid between turbo and super chargers. It is indeed primarily used on Diesel engines, specificaly those that operate within a certain, stable RPM range, such as those on a Diesel train engine, or even a generator. They aren’t TOO bad to maintain, but they are an absolute bitch to install and calibrate. I suppose you could install one on a gasoline engine if you really wanted to, since they aren’t fuel-dependent. If you put it on a car, though, I would expect a shorter-than-average lifespan for the unit since it wasn’t really designed with that sort of operation on mind. If you do, then I’d be interested to know how it turns out.
catmandu42 is correct. They use the assistance of the pressure waves in the exhaust gas to help the compression effect. They work really, really well within a very tight RPM range. Outside of that range, they can have little positive effect, and (reputedly) even sometimes reduce the power output of the engine, unless you have a really complicated closed-loop feedback system on them to adjust and dynamically re-calibrate them.
Oh, I see. Kind of like those funny shaped exhaust pipes on 2-stroke engines.
Well, Anth glossed over them, so I’ll pick a bit.
A heated intake charge on a diesel engine is not a problem, as hot air has a greater potential, and a diesel engine cannot overheat or detonate. The exhaust backpressure would be increased, but the effect is overridden by the performance gains of the increased intake charge. Exhaust is not recirculated, it exists the vehicle normally. You would not exhaust unburnt fuel unless your vehicle was improperly tuned.
–Tim
Expansion chamber on 2-strokes.
They are actually a series of chambers divided by baffles whose purpose is to produce a back pressure wave to help keep in the inlet mixture and yet produce a vacuum to scavenge out the burnt gases.
Each chamber is of a differant volume so as to time these pressure waves to be at the right place at a specific range of engine revs which helps to widen the power band, in efect they are tuned to certain revs.
You will also find on 2-stroke motorcycles, that the end pipe is nearly always around 20mm in diameter whcih helps give the restriction that allows the expansion chamber to develop the pressure waves, smaller and it is too restrictive, larger and its not restrictive enough.
Homer, heated intake air is less dense, and so provides less reaction mass per given volume. So you are automatically undoing part of the compression even as it is occurring. I maintain that it is not a good thing. And unless I missed something, the Comprex supercharger brings the intake charge into direct contact with the exhaust. Some mixing would seem inevitable. Also, unless timed perfectly I doubt the gasses would magically stay in their intended paths without any “overlap”. You are correct about fuel not being exhausted though (I forgot about O2 sensors).
Again, I’ve not seen one of these IRL. Does it intentionally dump part of the intake charge to the exhaust side? That would minimize both of these problems.