Generator and Webasto exhaust in same tube?

[rv_safetyman]

As any of you folks who have Webastos know, the exhaust is quite noisy when the burner is on.  We could try to be good neighbors and have a generator stack (for both noise and smell), but then have the same problem with the Webasto exhaust. 
Right now, we have both coming out close to each other on the driver side about mid-bus.  I am thinking about making an adapter to put them both in one tube and run it along the bus exiting close to the rear wheels.  Might even think about going clear to the rear of the bus.

Both my Webasto and Generator have 1.5 inch exhaust pipes.  In total that is about 3.5 square inches of opening.  A two inch exhaust pipe would have an area of 3.14 square inches and a 2.5 inch pipe would be 4.9 square inches.

So, the questions: 

1)  Has anyone combined the exhausts of these units?

2)  Any opinions on pros and cons of this approach?

3)  If it looks like a good idea, which size combined pipe would you use?  (I doubt that this decision would affected by exhaust pulses like a high performance engine)

Jim

[luvrbus]

Jim, Webasto and the other diesel fired units are real touchy about the size and length of the exhaust and at 600 degrees from the Webasto I would want the shortest route  good luck

[JackConrad]

Not sure about Webasto, but ProHeat reccomends no more than 5' for exhaust and no more than 90 degrees of bends. I have heard that more exhaust causes more carbon build up in the burners.  Jack

[Nick Badame Refrig/ACC]

Hi Jim,

Your Webasto will bleed through!  Meaning, that if your generator makes positive pressure in the webasto exhaust, the gen exhaust will travel

through the webasto and end up in the make-up air of the webasto. That might be in the bay of your bus... There are no pistons in a webasto

to stop back feed. Please make sure your webasto has fresh air make-up sealed to the outside!  I think your asking for trouble if you combine the two.

Good Luck
Nick-

[gus]

Jim,

I assume you mean by exhausting near the rear wheels that it is under the bus. I sure wouldn't recommend any low exhaust near the bedroom or anywhere for that matter.

I wouldn't be comfortable with any low exhaust while sleeping. I don't run mine when sleeping but am going to make a removable rooftop height exhaust stack.

[Sean]

Jim,

Webasto mandates a separate exhaust system.

I'm with Nick on this -- with the Webasto off, the exhaust from the generator can (and some will) back up through the Webasto combustion chamber, past the fan (which is off), and out through the intake under the unit.

Even when talking about engines, where this is not a factor, engineering 2-into-1 exhaust systems is something of a black art.  Anything downstream, even a bend in the pipe, can cause backpressure issues, even if you make everything, from the "Y" on down, at least as big as the sum of the cross-sectional areas of the two inputs (and, without engineering data, I would not go smaller than that anyway).

FWIW, we have an unmuffled exhaust from our Webasto, and it's a short pipe with just one 90 in it, exiting the rear of the coach (under the bedroom, to Gus's horror).  We don't find the sound level to be bothersome either inside or outside the coach.

It should go without saying that you should have a CO detector in your bedroom, in any case.

-Sean
http://ourodyssey.blogspot.com

[Sojourner]

About merging mixed exhaust system into one.

Agree with Nick...ICE (internal combustion engine) is positive pressure (pulse) exhaust.

Webasto, ProHeat or any furnace air exhaust is a very low-compressive mode without pulse check valve. In other words if you blocked the non ICE's exhaust...you cause the reduction or stop the intake of oxygen/air to complete the proper A/F combustible mixture.

All non ICE furnace's combustion chamber are tuned with proper exhaust restriction.

Otherwise it maybe in unfavorable air-fuel ratio to optimize BTU/gal fuel setting to cause poor or hot starting or burn-out combustion's chamber or soot-ed with carbon to a point of non starting mode.

In other word never merge non-compress-exhaust with another or exhaust pulse system.

However you can add any number of ICE cylinder to another ICE as long the exhaust is design for the given exhaust flow rate. Such as 1, 2, 3, 4, or more cylinders ICE.

Agree with Sean for the safety.

However after you understand the nature of it combustion design for max BTU/fuel ecomcony...you never want to tap into another exhaust in the first place.

Sojourn for Christ, Gerald

[gus]

Sean,

Your bedroom is so high in that big rig of yours that the exhaust can never reach you!!

[gumpy]

I agree with Nick and Sean on this. Don't combine them.

I considered this myself and came to the conclusion that if I ran them to the same place and exited under the coach next to each other, I could build a double stack that I could hook to a single location on the roof (drip rail) and attach to both pipes coming from under the bus. Done right, it should look good, and well as work well.

I just posted a reply to Ace's post regarding generator usage. I found I have a CO problem with my generator, so will be working on the exhaust in the next few weeks. I'll be running it back next to the aquahot exhaust and will make up a stack for them after that.

Keep them separate.

craig

[buswarrior]

What about a combined and vented up-pipe? For camp use, of course...

Bring the two exhausts out the side close together, and capture them with an open pipe combiner, such that more air is free to join the skyward pointing giant pipe.

Some experiment of having some tighter fitting pieces to grab the more forceful gen exhaust to ensure it heads up the pipe and helps with the venturi/sucking...

I agree, the Webasto might not be the best hooked together with the generator, with no where else for the pressure to go.

happy coaching!
buswarrior

[gumpy]

What about a combined and vented up-pipe? For camp use, of course...

Bring the two exhausts out the side close together, and capture them with an open pipe combiner, such that more air is free to join the skyward pointing giant pipe.

Some experiment of having some tighter fitting pieces to grab the more forceful gen exhaust to ensure it heads up the pipe and helps with the venturi/sucking...

I agree, the Webasto might not be the best hooked together with the generator, with no where else for the pressure to go.

happy coaching!
buswarrior

Interesting idea.  I'll have to think about this for awhile. On the surface it seems like it might work.

One of the issues I have with my 2-pipe stack design is storage. I'm desperately low on bay space as it is. With your idea, it would only mean parts of a single pipe. Maybe 2 or 3 section, but still only one pipe width, where mine would be 2 wide.  Might be easier to store.

Now if I can only figure out how to make a telescoping stack.

craig

[BG6]

As any of you folks who have Webastos know, the exhaust is quite noisy when the burner is on.  We could try to be good neighbors and have a generator stack (for both noise and smell), but then have the same problem with the Webasto exhaust. 

Combining exhausts is way up there on the Bad-Idea-that-Looks-Good-O-Meter.  You NEVER see this done when there is any other option.  The only reason they do it on your engine is because they don't have room for 8 exhaust stacks, and even then they have to spend a lot of time solving problems with scavenging from far ends of the manifold.  That that's on an engine where all exhaust ports have the same pressure, temperature and volume of expelled gases.

If you want to quiet the WeBeasto, give it a separate exhaust stack.  If it's that close to the genset, you can run the two exhausts together under a common heat guard.

[TomC]

No matter what you're using, whether it be the main engine, generator, Webasto, etc, they should all have separate exhausts.  Each piece of equipment has different exhaust pressures, flows, temperatures, back pressure, back flow requirements that makes combining them a risky venture into unneeded repair venue.  I had a Hot Box on my truck (gasoline fired version of the Webasto) and it had a muffler on it for silent operation.  I would put a free flowing muffler on the Webasto, pipe directly outide, then use a venturi type up exhaust for zero back pressure when camped.  Good Luck, TomC
P.S.- The only approved combination of exhausts has happened between Onan and Cummins (they are owned together) where on big rigs they plumb the trucks APU into the big engine exhaust before the particulate trap so the Onan engine is flowing through the particulate trap.  California has the wonderful rule that if a big rig has an auxiliary engine for either generating, running HVAC, or refer unit, if the truck engine has a particulate trap the small engine has to also.  Good Luck, TomC

[rv_safetyman]

Thanks for all the input.  Guess this was not one of my better ideas

Jim