Propane (lpg) fumigation for noise reduction???

[coachgeo]

...trick to stop the knock using a small amount of LPG "Being very careful" which is "really important" ...

Very intresting. So your saying fumigating with a tiny amount of LPG stops the knock.. hmm..

Does it "stop it" or "significantly reduce it" ?

Are you fumigating thru the intake of the carb or air cleaner orrr??

"Very carefull" to prevent??? over rev's, melting engine parts,?? explosion in the shop orr?

{this is a spinn off from this thread- viewtopic.php?f=3&t=963&p=6031#p6031 }

[andrewaust]

Very intresting. So your saying fumigating with a tiny amount of LPG stops the knock.. hmm..

Does it "stop it" or "significantly reduce it" ?

It will virtually stop the diesel knock at idle and raise the rpm a little

Are you fumigating thru the intake of the carb or air cleaner orrr??

Through the air cleaner

"Very carefull" to prevent??? over rev's, melting engine parts,?? explosion in the shop orr?It will virtually stop the diesel knock at idle and raise the rpm a little

Yes explosion, some silly buggers absolutely pour gas in which could lead to all sorts of problems - I use a small hand held butane "now lpg filled" heating torch, natually not lit .... lol, you may have to take out the very small orifice jet to get enough gas to go in.

It quietens the engine down so much so it sounds like a petrol engine, I do this to listen to bearings etc, you'll never be able to hear anything over the knock, well not with the yanclones anyway.

Just be cautious when dealing with gas. I guess acetylene or any other combustible gas would do the trick, I've only tried lpg.





A

[coachgeo]

this is very interesting. Did not know it reduced knock. Would be interesting to experement with this as a means of making the whole bike (or other diesel project) quieter. I know it increases efficency of the engine. LPG to diesel is like nitrious to a petrol engine.

Had considered the possibility of a lpg small camping bottle mounted on my Tiger and plumb it to a home brewed coolant heater. Fully warm the engine prior to starting engine thus significantly reducing potential for coking when using veg. oil fuels. This could be another reason to do this. Have a "stealth mode" LPG fumigation for when evading police lol. No for like when rolling thru a nice quiet neighbor hood.


Hmmmm.... My home's batteries (Im off the grid) are charged w/a Diesel Genny. Might be a way to make it more quite..... hmmm.

Now the other side of the coin is... some diesel gurus say; when using veg oil fuels, a quet engine is NOT actually good. They suggest adjusting IP timing to get it back to normal noise. Less noise means less effcient burn of the fuel is their reasoning. Wonder if that applies here at all. The resulting raise in RPM you noted would seem to say no.

[Diesel Dave]

LPG fumigation is not like Nitrous Oxide in a petrol engine, it's the exact opposite.

Nitrous adds oxygen, LPG adds fuel.

Fumigating adds a low level of another slower burning fuel to the combustion process, mixing this with the diesel ignition process essentially slows down the burn and thus reduces knock.

Fumigating for extra power relies on there being sufficient oxygen available in the charge to make use of the extra fuel, if your already injecting the maximum amount of diesel fuel that can be burned by the available oxygen then no gain will be realised. This is why it generally works with Turbo setups because there is much more air/oxygen available.

So, if you wan the ultimate in chemical enhancement then go the same way as the VW TDI 'Max Power' boys and add both Nitrous Oxide and LPG = fuel and oxygen in a measured system.

If you want to reduce knock at idle then fumigating will work well, diesel burns really fast and with fixed timing this produces the heavy idle knock. Adding LPG effectively elongates the burn time, it will also increase the idle speed unless adjusted as your adding fuel in the same way that opening the twistgrip will!

A word of warning, engines don't like to be fumigated when cold - try it and see with your blowlamp!

There are other duel fuel options that may be more effective, Methanol carries a reasonable amount of it's own oxygen and water too so acts as a water & fuel injection system, you could use a std carb with the slide removed and just use the idle circuit to porvide a low level fumigation.

The possibilities are endless.

BTW adding Veg oil to your Derv also adds oxygen and changes the ignition qualities - effectively changing the timing.

Cheers
Dave

[coachgeo]

LPG fumigation is not like Nitrous Oxide in a petrol engine, it's the exact opposite.

Nitrous adds oxygen, LPG adds fuel........

Yes generaly speaking its the same.

. You push a button,
. the gas is expelled into the engine...
. you go faster

thats the only way I was making a simularity.

[balboa_71]

Dave,
Okay, lets go over this use of a carb on a diesel to inject water to slow down (reduce) engine knock. I've read about this elsewhere (can't remember where, however), where it ol' boy had a carb on his diesel and some water going into the engine. I think he may be a member of the group and live in Az. USA. My first impression with water in a carb is white rust (bummer), and removing the slide is something I'm not familiar with.... Help us out here.

Thanks,
Cris

[Diesel Dave]

Blocking off the main jet and removing the slide in a traditional bike carb would leave just the idle circuit in place to feed methanol into the motor.

You don't want to restrict the air so binning the slide leaves a clear path for the air to pass through.

You can get specific methanol carbs but essentially they have a varnish coating to stop the white oxidation forming.

Dual fueling in this way can produce good results, you have 2 different fuel burn rates that create extra turbulence in the combustion process that helps scavange all the available oxygen. It's doomed as a commercial venture 'cos nobody would want the hassle of two fuel systems to refill CORRECTLY.

Water seems to reduce knock by creating a buffer for the piston, some of this may be due to 'masking' the available airborne oxygen fractionally and this would show up mostly at idle hence the softer idle sound.

Cheers
Dave

[andrewaust]

Yes it is a tricky one, having such light castings with these single cylinder engines some of us are using don't help, it's really the only running problem too! If the knock was "Knocked out ..... lol" the bike would be very quiet.

I've noticed when pulling up a hill and fueling of the engine is increased the knock drops a fair bit, it gets really loud when coasting and leaning the fuel to keep the engine power stable "remembering a diesel is a lean burn engine" .

Some of the singles like the Robin's etc had lower compressions "from memory" and still knocked.

I think variable timing is a goer, some engines have it, hopefully it will be available to refit other engines.


A

[balboa_71]

Thanks for the explanation regarding using a carb to add another fuel to the engine. I could go with water, but do not wish carry tanks of explosive gas around on my bike. I did find one problem that was contributing to the racket: loose Comet drive unit I had slid a 1mm Ø piece of wire in next to my home made key, which somehow had become non effective and the unit could be rotated on the crank a degree or two. After fixing the problem, my engine idles with much less noise. Until we get variable timing, as you all have mentioned, we're stuck with a lot of racket

Thanks,
Cris

[Sphere]

Or just don't idle at traffic lights so much, but drive top speed across backroads

[chevy43]

From what I have read Diesel "Knock" is caused by delay in the fuel burning which then lets the fuel build up for a fraction of a second which then ignites all at once. Propane causes it to burn immediatley reducing knock. Delay is what causes a cold diesel to make a louder knock than a warmed up engine.

I have played with propane on diesels too. It works great at increasing power and reducing smoke to a point - then you get preignition of the propane and it is very hard on the engine.

[TedV]

I have played with propane on diesels too. It works great at increasing power and reducing smoke to a point - then you get preignition of the propane and it is very hard on the engine.

esp. hard on diesels with the pre-cup chambers.