EVAP System
EVAP System
(OP)
I'm trying to find more information about the EVAP system, and I'm having trouble. In addition to the exhaust system which I'm designing (which a number of you have helped me out on, thanks for that) I'm also doing the fuel system, and the engine we're using (Rotax 4 cylinder 4-stroke Aircraft Engine, carbureted, not FI) has obviously never needed an EVAP system. If anyone could steer me in the right direction for some more info, as well as some sources for parts, I would greatly appreciate it.





RE: EVAP System
RE: EVAP System
If at all possible, we'd like to meet the California LEV standard for passenger vehicles
RE: EVAP System
http://www.obdii.com/background.html
and check with the California Air Resources Board for specific requirements.
Franz
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: EVAP System
Maybe I'm wrong, but I get the feeling someone is about to tell me I'm going to have to have fuel injection for this one
RE: EVAP System
If I remember correctly, OBD (2 at least) requires that you be able to monitor and adjust the fuel delivery to achieve correct levels on an ongoing basis.
RE: EVAP System
RE: EVAP System
RE: EVAP System
You are going to need to control fuel vapour emissions from:
- Refuelling activities
- Storage (are you using a plastic tank? How are you connecting the tank to the engine?)
- All fuel line connectors
_ The vapour storage cannister (if your project really needs it)
And your vapour cannister will need to be purged occasionally, when the operating conditions of the engine allow. An EFI system controller will normally have a calibratable control strategy to do this, how will your carburetted system cope if you only have an electronic spark system?
Do you think it would be worth studying a mass-produced motorcycle system for ideas?
What exactly is the project?
Bill
RE: EVAP System
RE: EVAP System
Since you state you are doing a composite vehicle and not a motorcycle, other requirements probably apply. Somewhere you will have to do SHED emissions testing as well, something that has been a problem for vehicles with certain non-metallic body parts and paint compositions.
The reason for fuel injection is that a carburetion system cannot provide the long term hands-off emission control required by the EPA for model year 1996 and newer vehicles.
Franz
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: EVAP System
RE: EVAP System
I dont want to be the bearer of bad news but I think that you are going to seriously struggle with this.
For a start, if you are trying to use a carb for fuelling control you are going to fail on the fedral/carb tailpipe out emissions tests, even with a cat. A situation that will only be exacerbated by you purging the charcoal canister.
If you decide to use an aftermarket EFI system you will probably still be a country mile away from where you need to be. These systems just do not posses the functionality that you require.
My best advice would be to speak to a automotive consultancy such as Ricardo, Lotus, Mahle, AVL, FEV, IAV etc etc to see what their take is on your plans.....
MS
RE: EVAP System
If so I strongly recommend that you hook into the forums there.
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: EVAP System
RE: EVAP System
and as Franzh says, SHED can be an issue with 'conventionally' built vehicles, let alone something with high proportions of composites in its structure.
From what I can remember, legislation (may vary with geographical/political location) requires any new vehicle to be evaluated for certain chemical emissions over simulated environmental cycling periods.
The test result will include emissions from tyres, trim, polymer-based materials (dash panel, seat foam, door and glass seals, etc., etc.) in addition to stuff that you may have expected, like the engine and fuel system. So beware, products of curing processes that may be part of your hybrid body could be an issue.
And mattsooty is right. I don't know about the USA, but unless your vehicle is destined to be such a low manufacturing volume that special legal 'get outs' exist, as they can for one-offs or machinery, carburettors aren't going to figure anywhere in a serious attempt to get something into production.
Bill
RE: EVAP System
In the US, ALL volume manufacturers must perform the SHED test along with a full EPA certified FTP-75/US-06 emission test. Small volume manufacturers have such tight restrictions on what constitutes a small volume as to be almost impractical (50 cars at 1.5 million each, or 5000 cars at $15,000 each, guess which one has a higher cost recovery ratio?)
1) To qualify for LEV or any level below that, you will HAVE to use a catalyst.
2) To keep the catalyst in its sweet spot, you will HAVE to use fuel injection.
3) To keep the fuel injection operating in its optimum range for catalyst efficiency, the electronic controls suite will have to be extensively refined. You are NOT going to find an off the shelf unit, it MUST be refined for your EXACT application. For example, the engine calibration for a 2006 Ford F-150 4.6 L engine is different than a 2006 Ford E-150 4.6.
You havent even gotten into crash testing yet.
I dont intend to dispel any good intentions you have, but to let you know what you are setting yourself up for.
Franz
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: EVAP System
In terms of exemptions, truthfully, we were hoping we could get one for this vehicle. The carbureted engine is really just for our Proof-of-concept vehicle, which is just to prove to people that the thing actually works like we say it wlil. After that, when we hit production, we would switch to a FI engine (or even, GASP, a diesel!). But I'm fairly certain that if we were to even have a chance at getting an exemption, we'd need to demonstrate that we actually attempted to do our level best to meet the emissions standards, and we would say "Look, we tried really hard, we did everything we could in this situation to meet emissions standards, we promise we're going to change it as soon as we move into production so that it definitely will, but right now we're really poor and can't afford a different engine, etc. etc."
So on that note, if anyone knows of someone I could speak with regarding exemptions, that would be awesome.
RE: EVAP System
RE: EVAP System
I dare say there are many more in the USA than here in Europe, but even when you find one, you may also find that you could be sheduled well into the future as the type of testing can be in high depand. Don't expect it to be readily available.
I'm sure your countrymen will know, but Southwest Research in Texas might be a place to start.
Bill
RE: EVAP System
Southwest Research Institute in San Antonio, Texas, is a testing lab held in high esteem worldwide. They can do all emission testing for you, but at a cost, as will any lab.
Note for the record: I am not affiliated with SWRI but I personally know many of the automotive engineers there and have worked with them in the past.
There are other testing labs in the US that are recognized by the EPA.
Franz
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: EVAP System
RE: EVAP System
Also, do you have any contacts at the EPA that could point me in the right direction with regards to an exemption?
RE: EVAP System
Thanks
RE: EVAP System
I feel you are putting WAY too much emphasis on the evap system when that is only a small part of the project. Its sort of asking for an apple pie but only taking the crust and leaving out the apples.
Like the old song, "Love and Marriage", you cant have one without the other.
If you want to explore a vehicle for production, you need to explore the entire envelope, not just the evap.
Time for a project reassessment and identify the priorities. The last time I worked on a total vehicle package, the evap system was almost the last thing we did for the ECM programming.
Franz
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: EVAP System
I agree with you. Thus far, the pieces of the puzzle that apply to this particular vehicle (given that its going to have this carbureted engine for our proof-of-concept no matter what), are a cat (which wont work as well as it can, i know), the evap system, the fuel vapor recovery system....and thats all I've come up with. We're a startup, and the engine we have is going to be the one we use for the first prototype because we're too poor to go out and buy another engine. I've made it very clear to my boss that we will never pass emissions stuff with a carbureted engine, and he acknowledges it and agrees with me, and we know we'll switch to a FI engine for production, but right now I'm just trying to get a handle on all of the systems we'll need for production, even if we switch to a different engine. So, other than those three, is there anything else?
RE: EVAP System
The evap system on a modern OBD-II vehicle includes complicated actuators and sensors to check whether the fuel system is sealed, and solenoid valves for purging out the evap (charcoal) canister, etc. In your carbureted proof-of-concept application, none of that is going to happen.
Here is the simplified "gist" of how the system works on a California motorcycle, which is not subject to OBD-II. There is an evap canister (charcoal canister) and a couple of check valves and a bunch of hoses, THAT'S IT. The fuel tank cap is sealed. There is a hose going from the top of the fuel tank to the "dirty" end of the evap canister (no check valve), and there is another hose going from the "dirty" end of the evap canister to a vacuum port on the throttle bodies through an out-only check valve that's usually part of another gizmo that I'll get to later. There are check valves letting air "in" if the system drops even slightly below atmospheric, and another letting air out of the "clean" side of the evap canister if the pressure goes much above atmospheric. These check valves may be built into the evap canister, or in the fuel tank cap, or as part of another gizmo to be explained later, or separate items, depending on system layout.
On to how it works. When the vehicle is sitting still, and gets parked out in the sun, fuel evaporation goes out from the fuel tank into the "dirty" side of the evap canister. No check valve in that hose, air can go back and forth between fuel tank and "dirty" side of evap canister freely. The air has to go somewhere, and the check valve on the "clean" side of the evap canister is designed to be the first one to open. So, fumes go from the tank, through the canister which absorbs them, then the air gets vented out (usually this connection is to the clean side of the engine's air filter housing). The purge connection stays closed because there's not enough pressure/vacuum for that system to do anything.
When you start the engine, vacuum gets applied to the connection to the throttle bodies and this opens the check valve and sucks fumes from the "dirty" side of the canister. This puts the canister under a very slight vacuum, which opens the "in" check valve on the "clean" side, and this draws air through and purges the canister. The air is drawn in from the engine's air filter housing so that dirt doesn't get in.
When the engine is stopped and the fuel tank cools off, the suction gets applied through the evap canister and a check valve mentioned above breaks the vacuum by letting air in through the "clean" side.
On to one more complicating factor; on a bike the design of the filler neck doesn't completely eliminate the possibility of liquid fuel spillage into what's normally the vent line. Liquid fuel into an evap canister is BAD news. Usually there is a liquid-vapor separator housing in the line from the fuel tank to the evap canister, and a little vacuum-operated diaphragm pump to pump the liquid back into the fuel tank. On motorcycle engines, they almost invariably use one throttle per cylinder, giving lots of vacuum pulsation in that connection to the throttle body, and this gizmo uses that same pulsation to operate the return pump and to activate the purge system.
With that ... here is an example from a 1994 Kawasaki ZX9R.
http://h
Part number 16165 in that diagram is the vapor/liquid separator.
The place labelled "Ref. Cylinder Head" is the connection into one of the engine's intake ports downstream of the throttle - with pulsating vacuum to operate the pump inside that separator.
Part number 16164 is the evap canister itself.
RE: EVAP System
Any other additives like stabilisers and release agents and possibly colours and flame retardants as well are also migrating and being released. This is also happening from paint, other plastics and fabrics and lubricants and fuel.
As well as volatiles migrating and releasing, the more solid components are degrading due to exposure to air, light and heat. Some of the products of decomposition are also volatiles and therefore emitted from the surface as gas or even as tiny solid particles.
This applies to all components from tail light lenses to windscreen wiper blades to insulating materials on any electric motors, to door seals and upholstery fabrics to name just a very few.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: EVAP System
That was very helpful, thank you.
Pat-
I agree that there will be some off-gassing even after we cure, but we're using high-temp pre-preg, so I'd think that most of it is going to get cooked off, and its not like we have a super resin-rich part like we would with a wet layup. As a result, I'm curious as to how huge a problem the carbon is actually going to be for a SHED test, as you're not the first person to have expressed some concern with that regard...there are other fully composite vehicles on the road (granted, not very many, but there are a handful) so I'm assuming they have passed the SHED testing, so what did they have to do special, or did they just get lucky and managed?
RE: EVAP System
Treating at moderately elevated temperatures under vacuum would certainly help, but the cost would be through the roof I expect as it would require a very large vessel and vacuum pump.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: EVAP System
RE: EVAP System
You will still get out gassing, but you certainly have taken some very serious steps to minimise it. Time after treating under vacuum will also have an effect. I expect out gassing will be at a minimum immediately after vacuum treatment, then will slowly increase of a moderate time then will slowly decrease over a very long time
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.