The role and value of dieseling in springers

[Basu]

I recall that Tirths RIP had adviced me not to use light oil in chamber in case if I am desparate for power but to soak the pellet in oil and fire to get extra yards.Dropping lubricant in chamber might cause bulging of compression area.
For a power monger , it is better not to drop oil in receiver .
Benne..there is no way to deny that in springers ...dieseling is part of the system and effort should be made to regulate it to the best possible extent.

Basu

[timmy]

I am currently using WD 40

Does it show signs of dieseling.
Is it better than the usual barell oil.

That's interesting. I didn't know that and assumed it was a straight chain. Maybe I am wrong but this "compact" molecule seems to offer up more opportunities for the Hydrogen atoms to bump into nearby Oxygen atoms and go bang!

in diesel engines the detonation does not take place due to direct injection of fuel.

"Detonation" is a term used in ignition engines to indicate what happens when the air/fuel mixture is ignited by excessive heat and/or pressure in the combustion chamber too early, so the rise in pressure pushes back on the piston and makes the crankshaft want to turn backwards. This can be caused by too much spark advance (mixture ignited too early), or a hot spot in the cylinder igniting the mixture before the spark (usually a hot exhaust valve or sharp edge in the chamber, like a spark plug thread), or using gasoline with too low of an octane rating.

Detonation doesn't have too much to do with a diesel engine: there is normally no fuel in the cylinder until it is injected near top dead center. However, a diesel can "run on" (as ignition engines do when hot and after the spark is shut off) in a way that is the same as an air gun. In this case, it is caused by lubricating oil in the cylinder.

The compactness of the molecule stabilizes the free radical more hence it tempers the runaway combustion which otherwise becomes a detonation in a gasoline IC engines.

Free radical?

Refineries may use a free radical (in this case, a hydrogen atom without an electron) to combine an alkene with a molecule like methane to produce something like isobutane.

Where are you seeing free radicals as affecting detonation?

[bennedose]

.Dropping lubricant in chamber might cause bulging of compression area.

Putting a drop of oil in the pellet skirt is a time honoured way of causing detonation. Personal experience suggests that it is not easy to make the compression area bulge using mere lubricant oil in the compression chamber. However more dangerous oils - like petrol or diesel might make a person require a new air rifle after he gets out of hospital, provided he is not in jail..

[mercury]

no digression really given the similarities....oil , air , pressure , temperature and a compression / combustion chamber.

In airguns i would think that it has to be looked at differently. ideally the lubes present..in air gun chambers, on combustion are meant to slow burn ( if there is such a term ! ) and not fire up. using or excessive use of wrong oils / lube could trigger the fire up leading to a dieseling effect.

There are some interesting examples of airguns with the express intention of inducing dieseling. As bulky as early combustion engines too !!

http://www.pyramydair.com/blog/2006/5/w ... air-rifle/

there is another airgun which had a hole situated at the rear end of the compression chamber through which oil could be added directly into the compression chamber.forgotten the manufacturers name though.

Briha raises an interesting point on the location of the combustion in air guns . what about detonation ?? where does that occur?? inside the compression chamber ??reason for all those bulging tubes we hear about ??

Bennedose using heavy pellets does help to control mild dieseling. The only reason i can think of would be that the heavier pellet will slow done the piston..even if fractionally...easing up the pressure thus inducing a slow burn ( ??) rather than explosive temperatures.

[Basu]

Dear mercury,
I am surprised to note, with reference to the link in you post that ARs Fps go up to 30% then its normal velocity.
The jump in Fpe to this effect would be very high as well.
I know benne is left with two junk guns with rifled and plain bores so expect him to undergo a systematic test with chronograph and enlighten us the outcome.
I found it quite intriguing and hope for others too.
I am sure while doing the experiment..benne being a practicing surgeon , will take all possible precautions to avoid any uncalled for incident.

Basu

[bennedose]

Briha raises an interesting point on the location of the combustion in air guns . what about detonation ?? where does that occur?? inside the compression chamber ??reason for all those bulging tubes we hear about ??

I think Briha mentioned that combustion occurs at the transfer port and IIRC this is exactly what the Cardews found. Thinking about it - I had a sudden "aha" moment. Every rocket engine is an explosion in a closed chamber but the vast mass of flame appears outside starting from the "transfer port" of the rocket (the rocket nozzle). This may be because the net gas fow is towards the direction in which the pressure s being released.

It occurs to me that a detonation would be such a sudden rise in pressure that there is not enough time for it to vent towards the transfer port and would probably occur in the comprssion chamber and do bad things to the piston and seal.

[bennedose]

I know benne is left with two junk guns with rifled and plain bores so expect him to undergo a systematic test with chronograph and enlighten us the outcome.

If I am lucky - I will be the owner of a Chrony in March. Let's see. I am giving away one of my junk air rifles, but I still have one for diseling/power tests.

[ganeshn]

Dear mercury,
I am surprised to note, with reference to the link in you post that ARs Fps go up to 30% then its normal velocity.
The jump in Fpe to this effect would be very high as well.
I know benne is left with two junk guns with rifled and plain bores so expect him to undergo a systematic test with chronograph and enlighten us the outcome.
I found it quite intriguing and hope for others too.
I am sure while doing the experiment..benne being a practicing surgeon , will take all possible precautions to avoid any uncalled for incident.

Basu

Surely watching this space Basuda, crony+two spare guns+aptitude = v.interesting stuff.

[Basu]

I am sure benne's test would discover many details which are not available on the forum.
My only concern is that he is very fond of metric units and KMPH.

Basu

[brihacharan]

I am sure benne's test would discover many details which are not available on the forum.
My only concern is that he is very fond of metric units and KMPH.
Basu

Why are we "re-inventing the wheel"
It's a proven fact that 'dieseling' results in damage to the AR (receiver / transfer port / breech joint / piston & seal)
Now establishing the variance in 'velocities' before & after dieseling is an exercise in the realm of 'syncopated academics'...
Wake Up - Basu...Pounds & mph are 'passe'...its the age of 'metric system'
Man's curiosity & inquisitiveness is perennial....When the board in the park bench says "WET PAINT" he has to touch it to find out or rather reassert the message
Briha

[ganeshn]

Free radical?
.........
.........
Where are you seeing free radicals as affecting detonation?

let me take help of tetra ethyl lead in explaining the role of radicals below.

http://en.m.wikipedia.org/wiki/Tetraethyllead

" A noteworthy feature of TEL is the weakness of its four C–Pb bonds. At the temperatures found in internal combustion engines, (CH3CH2)4Pb decomposes completely into lead and lead oxides as well as combustible, short-lived ethyl radicals. Lead and lead oxide scavenge radical intermediates in combustion reactions. "

http://en.m.wikipedia.org/wiki/Radical_%28chemistry%29

"Free radicals play an important role in combustion, atmospheric chemistry, polymerization, plasma chemistry, biochemistry, and many other chemical processes"

Refineries may use a free radical (in this case, a hydrogen atom without an electron) to combine an alkene with a molecule like methane to produce something like isobutane.

This actually happens all the time in the refineries(with a slight modification to the above)

http://www.chemguide.co.uk/organicprops ... cking.html

" In thermal cracking, high temperatures (typically in the range of 450°C to 750°C) and pressures (up to about 70 atmospheres) are used to break the large hydrocarbons into smaller ones. Thermal cracking gives mixtures of products containing high proportions of hydrocarbons with double bonds - alkenes.

(
Warning! This is a gross oversimplification, and is written to satisfy the needs of one of the UK A level Exam Boards (AQA). In fact, there are several versions of thermal cracking designed to produce different mixtures of products. These use completely different sets of conditions.
If you need to know about thermal cracking in detail, a Google search on thermal cracking will throw up lots of useful leads. Be careful to go to industry (or similarly reliable) sources.
)

Thermal cracking doesn't go via ionic intermediates like catalytic cracking. Instead, carbon-carbon bonds are broken so that each carbon atom ends up with a single electron. In other words, free radicals are formed"



At high temperature and pressures pyrolysis generates free radicals.the more stable ones i.e, the branched ones give rise to more stable free radicals which prevent the pre-ignition also known as detonation, there is complex chemistry giving rise to branched chain, cyclic, heterocyclic compounds and carbon allotropes(diamonds not ruled out).
there is a reason why iso-octane is a role model of sorts here (its relatively compact molecule afterall,layman terms).

Such reactions do not lend themselves to straightjacket as textbook inspired .
hydrocarbon +O2 ----> CO2+ H2O+ Heat.

in diesel engines the detonation does not take place due to direct injection of fuel.

"Detonation" is a term used in ignition engines to indicate what happens when the air/fuel mixture is ignited by excessive heat and/or pressure in the combustion chamber too early, so the rise in pressure pushes back on the piston and makes the crankshaft want to turn backwards. This can be caused by too much spark advance (mixture ignited too early)
.........
.........
Detonation doesn't have too much to do with a diesel engine: there is normally no fuel in the cylinder until it is injected near top dead center. However, a diesel can "run on" (as ignition engines do when hot and after the spark is shut off) in a way that is the same as an air gun. In this case, it is caused by lubricating oil in the cylinder.

As long as the ECM dumps the diesel(direct injection, I do not know of any port injection diesel engines) after TDC there is no way detonation can happen in diesel engine.
In gasoline engine the timing is advanced only to a extent allowed by ECM thru the knock sensor.The diesel run-on may be hum of radiator fan doing its solemn duty, by definition presence of oil BTDC is detonation which will stop the crank dead in its tracks.
My guess is we are on the same page here.

I personally prefer a two liner over treatise any day.

[mercury]

these attachments are a two part article written by Cardew for Airgun World. Cardew expands on some of the points written in his books. since Cardew has been quoted in this post and if one does not have access to his books..this article kind of brings it to gather.

his thought on piston seals are interesting too....

( MODs: from the net.. NOT.. Airgun World Magazine.)

[timmy]

Ganeshn -- thanks for this, it is really better than two liners. I enjoyed the role of tetraethyl lead. You may know that it was developed by General Motors and my perspective of it comes from Indianapolis racing. Back in the early 20s, Thomas Midgley, a research scientist at General Motors, discovered the anti-knock capabilities of tetraethyl lead. None other than CF Kettering gave some to the famous racer Tommy Milton for the 1922 Indianapolis race, and Milton won using it in 1923. The tetraethyl lead allowed him to run the amazing compression ratio of 7.5:1!

Racers also used benzene and toluene as an octane booster -- something still done today.

My thinking was going along the lines of strict single chain hydrocarbons, and did not take into account double carbon chains as present in aromatics and alkenes. The workings of tetraethyl lead in that one wiki are especially appreciated. I will go back and study some of this and refining as well -- thank you for the leads.

Regarding diesels and running on, this is a well-known phenomenon -- anything combustable in the engine will make it run on. It may not be common in new cars, but consider that diesel marine engines and other such stuff, like stationaries or even some old Lister CS running a saw mill in the boondocks of Madhya Pradesh or powering a Jugaad in Punjab could be subject to this. (I would like to get an Indian-made "Listeroid" for generating power from vegetable oil as a retirement project, when they put me out to pasture soon.)

There are no factory diesels with port injection that I can think of, unless you count the tiny model aircraft engines that are called "diesels." I do know that here in the USA, hotrodders of diesel trucks will inject propane into the intake manifold for increased power, which would be theoretical port injection.

So here, no, I'm not talking about a cooling fan running!

Ignition before BTDC, whether compression ignition or spark ignition, is the way to go and is what is used. The idea is to have the majority of the pressure rise after TDC, where the work is done. There is a whole bunch of stuff on this that you may find interesting if you look into the Atkinson Cycle and the Miller Cycle, with reference to the Toyota Prius. Also, you might find Henry Ford's dear old De Saxe principle interesting, and I read somewhere where some car maker was bringing that back. But all ignition takes place BTDC that I can think of, but the inertia of the running engine carries the rotation through before the pressure rise opposes that rotation significantly.

Of course, when the engine is starting, some retard of the spark is needed -- my Grandfather lost his thumb cranking a woman's car who did not retard the spark.

You have given me a lot to read and think about here, ganeshn, thanks! I would like to revisit this in the future if you are amenable!

[Basu]

Dear mercury,
Very interesting references.
Quite informative.
Thanks for sharing.

Basu

[bennedose]

these attachments are a two part article written by Cardew for Airgun World. Cardew expands on some of the points written in his books. since Cardew has been quoted in this post and if one does not have access to his books..this article kind of brings it to gather.

his thought on piston seals are interesting too....

( MODs: from the net.. NOT.. Airgun World Magazine.)

What can I say? Brilliant! Brilliant! Many thanks for posting