Do Exhaust Filters for 2-Strokes Exist?

[Brian Jackson]

Since 2-stroke engines are notoriously bad polluters, is there such a thing as an exhaust filter? Forgive my ignorance on engine-related topics, but I would imagine restricting the airflow by any kind of forced air filtration would de-tune the pipe, resulting in engine inefficiency. I'm wondering if any other methods of cleaning the exhaust air exist. I don't recall seeing something like that. 4-strokes seem to burn pretty clean but 2-strokes often leave a cloud of smoke. Thanks for any feedback.

 

[schmoe90]

There's been all sorts of work on scavenging the exhaust of a 2 stroke (the smoke is from the oil burning,) but I don't think anything could be added later. If you're really interested, look at the Orbital engine - I believe that's ended up in drones.

 

[Doug Riley]

One of the nastiest pollutants from 2-strokes is simply unburnt gas. We tune them a bit rich to prevent the pistons from melting. In effect they are partially fuel-cooled. Lean one out to the point where all the fuel is burned (stoichiometric fuel-air ratio) and it'll seize.

The exhaust scent from behind an aircraft 2-stroke is a delightful perfume to those of us who fly them -- but it's not especially good for you.

There has been talk for decades about making the combustion parts of engines out of ceramics instead of metal. This would allow higher internal operating temps without meltdown. It might even eliminate cooling systems -- which are a ridiculous waste of heat energy when you think about it.

AFAIK, no solution to the 2-stroke's unburnt-fuel problem has come to market, though.

Oil injection, in theory, should result in lower oil emissions, as it increases the fuel-oil ratio at low RPM, while premix necessarily features a fixed (and rich) fuel-oil ratio. Some of us pessimists, however, are leery of making out engine's lubrication (and hence possibly our lives) dependent on a little plastic gear and on our remembering to fill the injector tank.

 

[Tyger]

Re oil injection: the old Mazda rotary engines have a "metering pump" that injects ordinary engine oil into the carb or combustion chamber; the amount varies by engine rpms. It's not made of plastic, and there is no need to fill a separate oil-injector tank.

 

[Sv.grainne]

Where is the oil stored? Crankcase? What's the consumption rate?

 

[Tyger]

It's just taken from the ordinary engine oil in the pan. I want to say it consumes about a quart in 1000 miles, but don't quote me.
It's really the only way to get lubrication to the apex seals on the rotors.
OR, you can "premix" two-stroke oil into your gasoline...

 

[Martin W.]

In many ways 2 strokes have cleaned up a lot since the 1960's .... back then chain saws , lawnmowers and boats often called for light engine oil and gas at a 20 to 1 ratio ... they smoked continually and plug cleaning was routine . Not to mention carbon buildup.

Boat motors exited exhaust into the water .... and on a small lake or pond you could see the multi-colored oil sheen floating on the surface afterwards .... soon a lot of pristine fishing lakes banned gas motors altogether.

Then a more refined dedicated 2 stroke oil was developed which produced less smoke and was mixed at 30 to 1.

Now it is common to see 50 to 1 ratios and no smoke.

Aircraft are different because rich mixtures aid in cooling.

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