small diesel engine cat con ??

[brutus1955]

ok, here is the scoop

a single cylinder diesel test engine, driving a fixed
load of 8kwatts (generator) at a fixed speed of 1800rpm
the exhaust gas leaving the exhaust port is 640 degrees F

the exhaust is going into a prototype heat exchanger

i would like to insert a small catalytic converter between the exhaust port and the heat exchanger

can i use a cat made for a gas engine?

if not why not? if maybe how long will it last?

any input would be appreciated

what i am trying to determine is if i can do some cleaning of the exhaust stream and in doing so improve the quality of the exhaust stream heat.

the engine will also be used in a dual fuel mode, wherein it will be fueled ~90% with propane or natural gas.

if the gas cat will not work at all, where can i get a 1.75"
cat that will work on a diesel engine?

bob g

http://www.microcogen.info

 

[BrianPetersen]

A catalyst made for a gasoline engine will probably clog with soot very quickly.

The catalyst from a VW TDI diesel is the smallest diesel one that I know of.

 

[MikeHalloran]

Uh, 640F is in the low range, even for a turbo Diesel. Is that engine lightly loaded? That may make soot control more difficult.




Mike Halloran
Pembroke Pines, FL, USA

 

[brutus1955]

thats full load at 640 as measured on the pipe about one inch out from the port with a laser temp gun,, so probably the exhaust flow itself is a bit higher?

i am a bit concerned with particulate clogging as well, and am thinking of secondary injection to do a periodic burn off.

are the cats able to burn some soot?

or do i need a filter before the cat that can be periodically burned off?

thanks
bob g

http://www.microcogen.info

 

[IceStationZebra]

Be careful with that "laser" temp gun. Infrared temp guns are not good at measuring shiny things including chrome and galvanized coatings, unless you recalibrate the emissivity. One trick is to get a better (though not totally accurate) reading is to cover an area with non-metallic paint or masking tape. In your case, even if you do this, I would only take the reading with a grain of salt since the exhaust system is acting as a thermal sink and the exhaust temp could well be hotter. You really need a probe for accurate data.

ISZ

 

[SomptingGuy]

A gasoline cat will be a TWC, which is inappropriate for a diesel engine. You probably want a DPF - not much else comes out of a diesel engine that might interfere with your prototype. There are many strategies for kicking off a regen (burning off the trapped carbon). Secondary injection is quite common.

- Steve

 

[ivymike]

steve beat me to it. a three-way catalyst will not be appropriate for a lean combustion scenario, soot aside.

You want an oxidation catalyst (25% soot reduction) or a catalyzed diesel particulate filter (95% or more reduction). You can talk to Miratech, DCL, CleanAIR Systems, Johnson Mathey, and countless other suppliers about getting one.

 

[GregLocock]

And to be a bit obvious, you need more or less the right size cat for your engine, a small engine will struggle to get a normal automotive cat up to temp.




Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SomptingGuy]

A DPF "up to temp"?

- Steve

 

[ivymike]

well, if you've got a CDPF, you'll need to get it into the right temp range (at least periodically, but preferably continuously) to oxidize the soot. The right range will depend on the specifics of the design.

 

[BrianPetersen]

If the 640 F was measured from the outside of the pipe, I guarantee that the gases inside will be much, much hotter, and for an oxidizing catalyst or DPF, that is good. 640 F won't be enough to make it "light up".

The catalyst on earlier VW TDI's was an oxidizing catalyst, which didn't do much, because engine-out HC and CO emissions from a properly-tuned direct-injection diesel are ordinarily already rather low. The new ones (2009+) have an extremely sophisticated system with an oxidizing catalyst and DPF in the same housing mounted as close to the engine as possible, since both of those function best when they are hot. There is a de-NOx catalyst a carefully selected distance down the pipe, since that device wants to operate in a lower temperature range. This is combined with an extremely complex engine control strategy because both the DPF and the de-NOx catalysts require periodic regeneration, which is done by making the engine operate differently, even under the same load conditions. Regenerating the DPF requires raising the exhaust temperature under lean operating conditions at intervals (imagine trying to set the soot on fire - it's not quite like that, but it's analogous - you need oxygen and heat) and regenerating the de-NOx catalyst requires running stoichiometric at intervals. The two regeneration intervals are not the same.

I'm not sure if the original poster wants to open that can of worms, or just use an oxidizing catalyst, which will be largely a cosmetic device if the engine is properly tuned.

 

[brutus1955]

thanks one and all for you input, i have done a bit more
reading and now understand about enough to be dangerous
but hopefully enough to do what i am wanting to do.

because the engine runs at steady state, under full load
i can maintain temperatures without issue, and due to other control systems being designed and used on the engine adding a regeneration cycle is not much trouble.

as for adding fuel to burn off, that is probably the direction i will go because the burned fuel does not equate to loss, but rather the added heat will be recovered in the heat exchanger downstream anyway.

thanks
bob g

http://www.microcogen.info

 

[GregLocock]

"A DPF "up to temp"?"

Fair call. I know very little. The one I've seen has some little cats near the header and some big ones under the floor. That is just about the full extent of my knowledge about diesel cats, all I really know is they get in the way of 'my' suspension and fuel tank.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.