A way of reducing knock??

[tappy]

Just an idea I thought I'd throw into the mix:

The various static diesel engines people are using suffer from knock at low rpm. The large injection advance BTDC is necessary for power, but at low rpm the high compression, rapid burn effectively happens "too early".
It seems to me that the effect could be reduced by reducing compression ratio slightly - this will slow the burn, effectively retarding it.
BUT, for power the high compression is still needed.
So why not lower an engine's compression very slightly, then fit a low pressure turbo? At low rpm the turbo will not be doing much so the engine will have low compression and smoother running. At higher power the turbo pressure boost will raise effective compression and return the power..

I've not yet looked into how much the compression would need to be reduced to reduce knock.
The other side effect of lower compression might be starting problems, tho' it should at least be easier for the motor / battery to crank the engine over.

So - any thoughts?

[andrewaust]

Yes good observation, lowering the compression would reduce the knock a little, although as you said starting would be more difficult and you wouldn't get such a clean burn of the fuel. I remember working on diesels with 16:1 compression which you would find hard to pass emission laws as they are really smoky, you'd work them hard and clean up the exhaust, then once idled down the smoke would return = bugger. I always liked the old Detroit diesels, they are one of the engines to be hit by emission laws, the humble 555 & 903 Cummins have found it difficult to pass emission standards.

A turbo would be a great idea to boost compression and fuel burn, singles do not turbo well, although a engine driven blower would work. The best thing to see would be some kind of advancing unit on these fixed injection pumps that alters the timing.

I think my yanclone has close to 21:1 compression, which is really high for a direct injection engine, you usually find this kind of compression with indirect injected diesels, its all to make them run efficient, but that knock can be a pain "I'm use to it but the neighbours don't think to well of it".

So we have the high compression to deal with emission laws and keep the greenies happy with smokeless exhaust most of the time, the one thing the engine manufacturers could address is variable injection timing.



A

[Diesel Dave]

I might try popping the injection pump with the retard notch into the bike's engine and see what happens.

I would also swap the injector in case the break pressures are different.

The only painful bit is re-timing the pump - takes me ages to do properly and I'm thinking that a high speed video camera would help as I could whip the motor over by hand with the injector rigged up outside the head and film both the flywheel position and the injector at the same time. Then when it fires you will be able to see the timing clearly.

Dave

[Pat Pending]

Hi,
Thought it may be of interest to those concerned regarding the Diesel knock issue on the fixed timing Yan clone Chinese engines.
Having recently completed an Enfield conversion using a Kama 186 (now done around 1000 miles) I spent a few hours with shims subjectively investigating the relationship between audible knock, perceived performance and timing.
Calculations based upon some very basic drawings indicated that 0.1mm increase in thickness of shim gave in the region of 1 deg retardation in injection timing (this is only a crude approximation but a good starting point). After a number of iterations of shim thickness (using varying thickness if gasket papers) I concluded the best running was obtained with 0.7mm of additional shimming (compromise between knock & performance).
Given that the original static injection timing was somewhere around 16-18 degs BTDC (best I could estimate turning the engine over by hand on the bench - high speed photography would indeed be of benefit) I would guess I am currently running somewhere around 10degs. This gives a good compromise, the low speed 'knock' is not now as harsh and at high speed (50ish mph) not too noticeable at all (engine not quite as crisp at full throttle as originally though). Not a perfect solution, but a good compromise. I am happy to live with it anyway - especially at 160mpg.

Currently trying a blend of straight veg oil with diesel (about 10-15 % so far) but no noticeable difference in performance or knock/smoke at all.

Regards Pat Pending

[sbrumby]

Could I just ask why are you trying a blend of SVO & derv. As veg oil is dearer than derv & derv carries 60%tax.

[cumorglas]

i don't know how it works in merry olde england but here the veg oil is free if you don't mind that the chinese restaurant used it first.

[coachgeo]

i don't know how it works in merry olde england but here the veg oil is free if you don't mind that the chinese restaurant used it first.

Nope... not free. It varies to time of year, region, state, city etc.. It is often free but not allways.

[arnaud]

There are 3 ways of easily reducing the knocking, as far as i know.
1 add salad oil to the diesel
2 add an extra copper gasket under the fuel pump cover(as stated in a yanclone manual) but realize this will cost performance in the upper rpm range
3 add a shim under the injector spring, this also will retard the beginning of injection and make it stop earlier.

But, they need running in. Afetr 15K it will run much smoother. Kickstarting gets easier.
It will always be loud, that's the design.
Get good earplugs!

We're just back form our holiday, on the 418 enfield diesel with the wife and luggage from the north side of the Netherlands to the belgian and french ardennes, the Vosges area (nice mountain passes) the Swiss area and Austria, were we got applause when we reached the highest (nowadays called 'biker meeting point' as every parking place people can earn money from bikersin Austria)parking place of the GrossGlockner.
Getting the overloaded bike over small hairpins there was a big effort!
It has run over 40K. now.

[TedV]

I might try popping the injection pump with the retard notch into the bike's engine and see what happens.

I would also swap the injector in case the break pressures are different.

Is there a post with the exploded workings of the injector pump around someplace? ::edit:: yup, just had the time to search "variable timing" and came up with plenty of posts. The post on building a diesel engine from a bike motor got me thinking about just a change to the static pump would be easier and work wonders. How hard is it to change the yanclones to variable timing?

I've seen DIY on how to build injector pop testers on the web using cheap bottle jacks, high presure pipe fittings and gauge, but not gotten around to making one. google turned up these:
http://www.peachparts.com/shopforum/sho ... ?p=2134929
http://www.peachparts.com/shopforum/sho ... p?t=251436

[mamboman]

Another way to reduce knock is water injection, with the added benefit of steam cleaning your engines innards... conversely, supposedly it allows you to raise the compression without knock.

[oldbmw]

Another way to reduce knock is water injection, with the added benefit of steam cleaning your engines innards... conversely, supposedly it allows you to raise the compression without knock.

Alternatively, you could ride when it is misty

[Sphere]

Ha! Ride a bike, when it's humid outside?
Whatever will people think

[mamboman]

Form the first page of the wikipedia article about water injection:

In internal combustion engines, water injection, also known as anti-detonant injection, is a method for cooling the combustion chambers of engines by adding water to the cylinder or incoming fuel-air mixture, allowing for greater compression ratios and largely eliminating the problem of engine knocking (detonation).

full article http://en.wikipedia.org/wiki/Water_injection_(engines)

I wonder why, if water injection really has all the advantages it is hyped to have, it isnt seen more often on petrol/diesel engines. Water, after all, is pretty cheap.