Re: [MBZ] Octane and detonation....
Did the preview and was overwhelmed. There is just way too much stuff that somebody needs. The engines were looking really good. Used a bit, but clean enough. A few old DOD genset. I suspect with the weather we have today, most of the metal bits will go for scrap prices. On Jan 8, 2007, at 8:24 PM, Craig McCluskey wrote: On Mon, 8 Jan 2007 11:38:16 -0800 Redghost <[EMAIL PROTECTED]> wrote: There are a number of Lister motors available at this upcoming auction. That and a few 200-300amp gen sets. You can even bid live online. For those trapped at a desk. I am going to preview the site Tuesday. A two day affair to get all the toys sold. Bound to be truck loads of tools and supplies going for pennies Thursday. Whole rooms and shelf units loaded. This sounds interesting: 531 1 each KATO 30KW, 208-240/416- 480V, 3PH-120/240V, 1PH DETROIT DIESEL DRIVE No affiliation, just sporting big wood for this auction. Not sure what you mean by this phrase ... Craig ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com -- Clay Seattle Bioburner 1972 220D - Gump 1995 E300D - Cleo 1987 300SDL - POS - DOA The FSM would drive a Diesel Benz
Re: [MBZ] Octane and detonation....
That _is_ full of woody goodness! Maybe that's mourning wood, since I ain't-a gonna get to go. -- Jim
Re: [MBZ] Octane and detonation....
On Mon, 08 Jan 2007 23:33:19 -0500 Mitch Haley <[EMAIL PROTECTED]> wrote: > > > Craig McCluskey wrote: > > > > Not sure what you mean by this phrase ... > > If this were the "banned" list I'd spell it out for you. Oh.
Re: [MBZ] Octane and detonation....
Craig McCluskey wrote: > > Not sure what you mean by this phrase ... If this were the "banned" list I'd spell it out for you.
Re: [MBZ] Octane and detonation....
On Mon, 8 Jan 2007 11:38:16 -0800 Redghost <[EMAIL PROTECTED]> wrote: > > > There are a number of Lister motors available at this upcoming auction. > That and a few 200-300amp gen sets. You can even bid live online. > For those trapped at a desk. > > I am going to preview the site Tuesday. A two day affair to get all > the toys sold. Bound to be truck loads of tools and supplies going for > pennies Thursday. Whole rooms and shelf units loaded. This sounds interesting: 531 1 each KATO 30KW, 208-240/416- 480V, 3PH-120/240V, 1PH DETROIT DIESEL DRIVE > No affiliation, just sporting big wood for this auction. Not sure what you mean by this phrase ... Craig
Re: [MBZ] Octane and detonation....
PacindustrialCat.pdf Description: Adobe PDF document There are a number of Lister motors available at this upcoming auction. That and a few 200-300amp gen sets. You can even bid live online. For those trapped at a desk. I am going to preview the site Tuesday. A two day affair to get all the toys sold. Bound to be truck loads of tools and supplies going for pennies Thursday. Whole rooms and shelf units loaded. No affiliation, just sporting big wood for this auction. On Jan 7, 2007, at 10:38 PM, John M McIntosh wrote: On Jan 7, 2007, at 9:23 PM, Jim Cathey wrote: Lister cycle engines are low compression, dirty, and make lots of smoke along with burning quite a bit of fuel for the output generated. My understanding is that they are actually quite fuel-efficient, at least as used for modest amounts of backup power. And they run forever. -- Jim Well I've seen some number tossed about first, a baseline oak ridge national labs ORNL/TM-1999/213 advanced power generation systems "Modern reciprocating diesel engine fuel consumption can be as low as 190 g/kWh (45% efficiency) but usually falls in the 200- to 300-g/kWh (43 to 35% efficiency) range depending upon design and operating conditions." Some one can wander off and calculate om615/om617 and modern 2007 diesel engine consumption I'm sure. Also good to have some I sure rational numbers available to test make believe numbers with. Also found this graph http://lerch.no-ip.com/ChangFa_Gen/Day_07/Gen_Compare_Liter.gif Saw a claim for changfa 1cyl 12hp at 0.251 g/kwh, but the gif above quotes as low as 0.35 liter/kwh or at 0.85 density 298 g/kwh so I'd say this 0.251 number is optimistic. From elsewhere I see lister 419 g/kwh at 3kw, but perhaps on vegetable oil which has different density and BTUS, thus more fuel needed I believe kubota lists their 11Kw at 75% consuming 319 g/kwh or 340 g/kwh at 50% mmm say .375 liters/kwh which is more efficient than most of the mainstream diesel generators in the GIF. ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com -- Clay Seattle Bioburner 1972 220D - Gump 1995 E300D - Cleo 1987 300SDL - POS - DOA The FSM would drive a Diesel Benz
Re: [MBZ] Octane and detonation....
On Jan 7, 2007, at 9:23 PM, Jim Cathey wrote: Lister cycle engines are low compression, dirty, and make lots of smoke along with burning quite a bit of fuel for the output generated. My understanding is that they are actually quite fuel-efficient, at least as used for modest amounts of backup power. And they run forever. -- Jim Well I've seen some number tossed about first, a baseline oak ridge national labs ORNL/TM-1999/213 advanced power generation systems "Modern reciprocating diesel engine fuel consumption can be as low as 190 g/kWh (45% efficiency) but usually falls in the 200- to 300-g/kWh (43 to 35% efficiency) range depending upon design and operating conditions." Some one can wander off and calculate om615/om617 and modern 2007 diesel engine consumption I'm sure. Also good to have some I sure rational numbers available to test make believe numbers with. Also found this graph http://lerch.no-ip.com/ChangFa_Gen/Day_07/Gen_Compare_Liter.gif Saw a claim for changfa 1cyl 12hp at 0.251 g/kwh, but the gif above quotes as low as 0.35 liter/kwh or at 0.85 density 298 g/kwh so I'd say this 0.251 number is optimistic. From elsewhere I see lister 419 g/kwh at 3kw, but perhaps on vegetable oil which has different density and BTUS, thus more fuel needed I believe kubota lists their 11Kw at 75% consuming 319 g/kwh or 340 g/kwh at 50% mmm say .375 liters/kwh which is more efficient than most of the mainstream diesel generators in the GIF.
Re: [MBZ] Octane and detonation....
Lister cycle engines are low compression, dirty, and make lots of smoke along with burning quite a bit of fuel for the output generated. My understanding is that they are actually quite fuel-efficient, at least as used for modest amounts of backup power. And they run forever. -- Jim
Re: [MBZ] Octane and detonation....
Lister cycle engines are low compression, dirty, and make lots of smoke along with burning quite a bit of fuel for the output generated. Simple to make and repair, which is why they are in use in the third world, but very much an environmental problem. Peter
Re: [MBZ] Octane and detonation....
That makes sense from a safety standpoint, and is part of the barrier to entry. Chris Kueny ([EMAIL PROTECTED]) 78 Chevy Custom deluxe '85 300TD '02 Subaru Outback You are also required to use an approved disconnect that uncouples your generator if the grid power fails. They are expensive. You cannot use a simple volt/amp measurement trigger, because you will be measuring your own generator's output and may not detect a power failure of the grid in a timely manner. -Dave Walton
Re: [MBZ] Octane and detonation....
Here in Ohio, the utility companies are only required to pay the wholesale rate if you generate excess and run the meter backwards (2-3cents per kwh). You are also required to use an approved disconnect that uncouples your generator if the grid power fails. They are expensive. You cannot use a simple volt/amp measurement trigger, because you will be measuring your own generator's output and may not detect a power failure of the grid in a timely manner. -Dave Walton On 1/7/07, John M McIntosh <[EMAIL PROTECTED]> wrote: On Jan 7, 2007, at 9:53 AM, Chris Kueny wrote: > The Lister engines available from India today use no spark. ... > See www.utterpower.comfor all the details. > > Chris K > Cayce, SC After clocking 60 hours of gas generator use in dec here in the pacific NW I look at the various generator options just to understand the market. Mind this all has changed now due to the EPA jan 2007 regulations where most of the solutions might not even be allowed to be imported anymore in the USA or Canada. There are basically: a) Lister based options (huge debate ongoing about ability to import to usa now) b) 12-20 hp (about) HP single cylinder engines from china based on a german design, water cooled. c) multiple cyl large water cooled diesels made in china (20Kw+) d) A thousand and one vendors rebranding kipo or kipo clone 6-6.5 kw single cyl diesel generators, enclosed on wheels or non-enclosed, the manuals are quite funny to read, thank goodness we don't need to let diesel settle in 55 gallon drums to deal with the dirt and water before usage. Mmm depends I guess on your supplier. Pricing for these guys (same engine) varies from $900 to $4000 btw. e) very nice kuboto, yamaha, japan diesel engine base systems for . If for example you have a farm where you grow oil based products you can with a press generate vegetable oil and with a lister based system be totally off the grid, and if lucky sell power back to the utility. Otherwise here with electricity at 6.33 cents a kwh it's hard to consider alternatives because utility electricity is so cheap, baring of course outages. Still of course if I could trip over a nice diesel yamaha/honda generator mis-listed on ebay somewhere for a song why the loud gas powered 6.5kw genrac I have would get resold... John 1983 300TDt 374k Kilometers (mobil 1 Delvac) 1990's 300TDt 172k Kilometers (mobil 1 Delvac) 1993 500SEL 185k Kilometers (mobil 1 Delvac) ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] Octane and detonation....
The USA EPA changed the rules for small engines in January 2007. It's possible many engines made outside of the USA can no longer be imported. Testing and modifications of course takes time and $, also maybe the supplier couldn't careless about selling small engines into the USA anymore. Canada has decided to march lockstep mostly with the USA rules also starting in 2007. The debate is if Lister engines can be imported anymore to the USA. On Jan 7, 2007, at 4:05 PM, Chris Kueny wrote: My last commercial power bill had me paying 9.349 cents/kwh. Tell me more about the Lister debate...when I can finally get one, I don't want to be shut out. Chris Kueny ([EMAIL PROTECTED]) 78 Chevy Custom deluxe '85 300TD '02 Subaru Outback Otherwise here with electricity at 6.33 cents a kwh it's hard to consider alternatives because utility electricity is so cheap, baring of course outages.
Re: [MBZ] Octane and detonation....
My last commercial power bill had me paying 9.349 cents/kwh. Tell me more about the Lister debate...when I can finally get one, I don't want to be shut out. Chris Kueny ([EMAIL PROTECTED]) 78 Chevy Custom deluxe '85 300TD '02 Subaru Outback Otherwise here with electricity at 6.33 cents a kwh it's hard to consider alternatives because utility electricity is so cheap, baring of course outages.
Re: [MBZ] Octane and detonation....
On Jan 7, 2007, at 9:53 AM, Chris Kueny wrote: The Lister engines available from India today use no spark. ... See www.utterpower.comfor all the details. Chris K Cayce, SC After clocking 60 hours of gas generator use in dec here in the pacific NW I look at the various generator options just to understand the market. Mind this all has changed now due to the EPA jan 2007 regulations where most of the solutions might not even be allowed to be imported anymore in the USA or Canada. There are basically: a) Lister based options (huge debate ongoing about ability to import to usa now) b) 12-20 hp (about) HP single cylinder engines from china based on a german design, water cooled. c) multiple cyl large water cooled diesels made in china (20Kw+) d) A thousand and one vendors rebranding kipo or kipo clone 6-6.5 kw single cyl diesel generators, enclosed on wheels or non-enclosed, the manuals are quite funny to read, thank goodness we don't need to let diesel settle in 55 gallon drums to deal with the dirt and water before usage. Mmm depends I guess on your supplier. Pricing for these guys (same engine) varies from $900 to $4000 btw. e) very nice kuboto, yamaha, japan diesel engine base systems for . If for example you have a farm where you grow oil based products you can with a press generate vegetable oil and with a lister based system be totally off the grid, and if lucky sell power back to the utility. Otherwise here with electricity at 6.33 cents a kwh it's hard to consider alternatives because utility electricity is so cheap, baring of course outages. Still of course if I could trip over a nice diesel yamaha/honda generator mis-listed on ebay somewhere for a song why the loud gas powered 6.5kw genrac I have would get resold... John 1983 300TDt 374k Kilometers (mobil 1 Delvac) 1990's 300TDt 172k Kilometers (mobil 1 Delvac) 1993 500SEL 185k Kilometers (mobil 1 Delvac)
Re: [MBZ] Octane and detonation....
On high compression diesels (above 19:1), propane can ignite BEFORE the fuel is injected if the mixture is rich enough to be burnable. I would not recommend propane "fumigation" on anything with a compression ratio above 16:1 nor under high load with a turbocharger running, the risk of premature ignition (which will be much like detonation) is too high. Peter On Jan 7, 2007, at 2:04 PM, David Brodbeck wrote: Peter Frederick wrote: Diesels WILL run with a fuel/air mix, but there is no control over the ignition timing that way. I know at least one person who had a VW diesel get return holes in the head plugged up, and when the oil filled the valve cover and spilled over into the intake on the highway had QUITE a full throttle run until it all burned out That sometimes happens with VW diesels when they get bad rings, too. The blowby can drive enough oil mist through the valve cover breather vent and into the intake to cause runaway. Some of VW's gas engines have a plastic baffle between the cam and valve cover. Retrofitting that helps keep the oil out of the breather. Propane injection is used by hot-rodders to increase power on diesels, these days. The propane is mixed with the intake air, and it ignites with the diesel fuel when injection occurs. ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] Octane and detonation....
Peter Frederick wrote: > Diesels WILL run with a fuel/air mix, but there is no control over the > ignition timing that way. I know at least one person who had a VW > diesel get return holes in the head plugged up, and when the oil filled > the valve cover and spilled over into the intake on the highway had > QUITE a full throttle run until it all burned out That sometimes happens with VW diesels when they get bad rings, too. The blowby can drive enough oil mist through the valve cover breather vent and into the intake to cause runaway. Some of VW's gas engines have a plastic baffle between the cam and valve cover. Retrofitting that helps keep the oil out of the breather. Propane injection is used by hot-rodders to increase power on diesels, these days. The propane is mixed with the intake air, and it ignites with the diesel fuel when injection occurs.
Re: [MBZ] Octane and detonation....
The Jacobs R755 that was in Dad's Cessna 195 had two plugs per cylinder. Each set of plugs were fired by a seperate magnito - and they were timed about two degrees apart, IIRC. The left mag at 6 degrees BTDC, and the right mag at 8 degrees BTDC, for example. I don't remember the exact specs. During the pre-take-off engine run-up and check, you switched from both mags, to left only then right only and watched the RPM drops. One mag dropped a little more than the other. On 1/7/07, Peter Frederick <[EMAIL PROTECTED]> wrote: That I do not know -- I would GUESS that the most ignitable portion of the fuel/air mix is in different locations in the cylinder under different operating condition, and low power output/miss is a result with a single plug. There might also be a quench area that prevents proper flame propagation, or the chamber may simple be too large for a single flame front to burn all the fuel in the correct time frame (this is why, I think, that aircraft engines had 4 plugs per cylinder -- 4360 ci x 32 cylinders -- pretty big jugs!). I would assume they fire at the same time, but don't know that for a fact. -- OK Don, KD5NRO Norman, OK "Even if you're on the right track, you'll get run over if you just sit there." Will Rogers '90 300D, '87 300SDL, '81 240D, '78 450SLC, '97 Ply Grand Voyager
Re: [MBZ] Octane and detonation....
If I were Kaleb, I would preface this with 'Bzzzt, wrong.' But I am not so I won't. The Lister engines available from India today use no spark. You open a valve to relieve compression, turn the heavy flywheel until you get some stored inertial energy, close the valve and open the fuel start injecting fuel. Keep turning the wheel until it starts. No gasoline, no spark. I hope to get one once I have a spare $1500, engine hoist, and coupla weeks for a new hobby. Paired with a gen head, and running on 50-50 diesel/recycled veggie oil, you could save a bit on electricity. If we had net billing here. See www.utterpower.comfor all the details. Chris K Cayce, SC Lister cylcle engines use compression ignition by atomizing diesel fuel into the air and igniting it by compression of the mixture AND a spark, not by injection, which is why they must be started on gasoline with a spark ignition. Low compression, to say the least.
Re: [MBZ] Octane and detonation....
That I do not know -- I would GUESS that the most ignitable portion of the fuel/air mix is in different locations in the cylinder under different operating condition, and low power output/miss is a result with a single plug. There might also be a quench area that prevents proper flame propagation, or the chamber may simple be too large for a single flame front to burn all the fuel in the correct time frame (this is why, I think, that aircraft engines had 4 plugs per cylinder -- 4360 ci x 32 cylinders -- pretty big jugs!). I would assume they fire at the same time, but don't know that for a fact. Peter On Jan 7, 2007, at 9:48 AM, LarryT wrote: Thanks Peter - for that excellent explanation/ On a similar topic - when a cylinder head uses twin plugs - like some competition Porsches - when does the 2nd SP fire? At the same time as the 1st? Slightly afterward? Thx - Larry T (67 MGB, 74 911, 78 240D, 91 300D)
Re: [MBZ] Octane and detonation....
Ah, but there is no fuel in the cylinder until the injection pump "fires" it in! This is the secret of diesels, and the basis of R. Diesels patents. Lister cylcle engines use compression ignition by atomizing diesel fuel into the air and igniting it by compression of the mixture AND a spark, not by injection, which is why they must be started on gasoline with a spark ignition. Low compression, to say the least. Diesels WILL run with a fuel/air mix, but there is no control over the ignition timing that way. I know at least one person who had a VW diesel get return holes in the head plugged up, and when the oil filled the valve cover and spilled over into the intake on the highway had QUITE a full throttle run until it all burned out Peter
Re: [MBZ] Octane and detonation....
What amazes me is how diesel is refined precisely so a pre-determined ignition can be obtained allowing diesel to be used on everything from a Peterbuilt to a Isuzu Diesel. But I guess all diesels must operate at/near the same pressures. Ha! Precise refining? How about thinly-strained dinosaur? At least, that's how it used to be when diesel engines were first deployed. That's the beauty of injecting fuel only when you're ready for it to burn. No detonation at all, all you need is enough compression, and extra doesn't really hurt. (Except mechanically.) Hence the 1-4 atm. of turbo pressure in turbodiesels. -- Jim
Re: [MBZ] Octane and detonation....
Thanks Peter - for that excellent explanation/
On a similar topic - when a cylinder head uses twin plugs - like some
competition Porsches - when does the 2nd SP fire? At the same time as the
1st? Slightly afterward?
Thx -
Larry T (67 MGB, 74 911, 78 240D, 91 300D)
www.youroil.net for Oil Analysis and Weber Parts
Test Results http://members.rennlist.com/oil
PORSCHE POSTERS! youroil.net
Weber Carb Info http://members.rennlist.com/webercarbs
Porsche Road Test http://members.rennlist.com/roadtest/
.
- Original Message -
From: "Peter Frederick" <[EMAIL PROTECTED]>
To: "Mercedes Discussion List" ; <[EMAIL PROTECTED]>
Sent: Sunday, January 07, 2007 1:43 AM
Subject: Re: [MBZ] Octane and detonation
Proper combustion in a spark ignition engine is for the spark to ignite
the air/fuel mixture at the correct time for peak pressure to occur a
few degrees after TDC, and for the fuel mixture to burn at the correct
rate for the flame front to consume the vast majority of the fuel
before being quenched by contact with the head, cylinder walls, or a
space too small for the flame front to continue to propagate (the
quench zone in a wedge head design).
The key here is that the combustion MUST be slow enough to produce a
pulse of pressure that drives the piston down for as long as possible
during the power stroke -- when combustion becomes too rapid, pressure
and temperature rise too fast and the cylinder will become filled with
a combustion gas mixture too hot for the materials.
Detonation is just that -- and explosion of the air/fuel mixture,
usually not triggered by the timed ignition spark. In the worst case,
it is triggered by an overheated spark plug long enough before TDC to
produce a very high temperature zone extending out from the spark plug,
acting as a superheated torch. The heat from the flame thus produced
can burn a hole right through the pistons if the spark plug points at
them -- this was a problem with Alfa Romeo twin-cam hemi-heads in the
60s and 70s -- a tank full of regular gas and a highway run would
produce holes in the pistons about 1/4" in diameter that looked as if
machined there. Nasty.
The overpressure before TDC from detonation (which cannot be heard at
highway speeds, unlike spark knock or premature ignition) does a number
of other bad things -- it can cause enough crankpin pressure to wipe
the oil film off the crank journals, causing bearing failure, it can
melt piston crowns (or drill holes in them into the crankcase), can
seriously overheat valves, and can even cause flame cutting of piston
rings, where the flame from detonation (again, usually extending
straight out from the spark plug) can burn down the side of the piston
and cause ring failure.
Not pretty.
Higher octane fuels indeed burn slower. They are also harder to
ignite, so are more resistant to compression ignition. The slower
combustion rate reduces the tendency to detonate, will reduce or
eliminate premature combustion ("spark knock"), and lower peak
temperatures and pressures while extending the high pressure duration
during the power stroke.
Peter
___
http://www.okiebenz.com
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For used parts email [EMAIL PROTECTED]
To Unsubscribe or change delivery options go to:
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Re: [MBZ] Octane and detonation....
Thanks Royce, You wrote:> Detonation to me always meant: the fuel is compressed as the piston rises, and the pressure of the compression generates heat and ignites low octane fuels - which may be what you said in different wording. This is why accurate valve adjustment and rings in good condition is so important in diesels. Higher octane fuels resist this pre-ignition (as detonation is also called I believe) and allows higher compression and therefore higher horsepower. What amazes me is how diesel is refined precisely so a pre-determined ignition can be obtained allowing diesel to be used on everything from a Peterbuilt to a Isuzu Diesel. But I guess all diesels must operate at/near the same pressures. Larry T (67 MGB, 74 911, 78 240D, 91 300D) www.youroil.net for Oil Analysis and Weber Parts Test Results http://members.rennlist.com/oil PORSCHE POSTERS! youroil.net Weber Carb Info http://members.rennlist.com/webercarbs Porsche Road Test http://members.rennlist.com/roadtest/ . - Original Message - From: "Royce Engler" <[EMAIL PROTECTED]> To: "LarryT" <[EMAIL PROTECTED]>; "Mercedes Discussion List" Sent: Saturday, January 06, 2007 10:41 PM Subject: RE: [MBZ] Re: Octane and detonation Larry said... You wrote about octane and detonation: <> Hi Royce, Is that your way of saying the higher octane detonates later and therefore closer to the time when the piston reaches TDC - or almost? - I'm assuming TDC is the best place to ignite the mixture for max HP and other ignition points are preferable if lower emissions, etc are the objective? >> Hi Larry, Bear in mind that I'm not an automotive engineer, and my petroleum engineering experience was focused on how to get more of it out of the ground. Having said that, it is my understanding that the optimal way for fuel to burn in the cylinder is for it to burn smoothly through the cylinder space. Detonation occurs when the fuel air mixture "explodes"...i.e. burns in multiple places at the same time. This can happen when the fuel mixture contains components that ignite much like a diesel..i.e. it reaches a combustion temperature and pressure and "cooks off". When that happens, more of the fuel energy is converted to heat, rather than doing useful work like driving the piston down. A smooth combustion results in maximum energy conversion from fuel energy to pressure energy. I don't have the experience to say which ignition points are more preferable, or where the optimal ignition point is in the cycleI was just impressed by the concept that adding more "heavy" components would improve performance by making the mixture burn more slowly (-:. Royce Engler 1985 300TD Turbo 293K -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.410 / Virus Database: 268.16.6/617 - Release Date: 1/5/2007
Re: [MBZ] Octane and detonation....
Peter,
THANK YOU for that illuminating explanation. I knew some of the basics, but
your explanation filled in a LOT of holeskind of a gestalt...to use the
German term ;-)
Royce Engler
1985 300TD Turbo 293K
-Original Message-
From: Peter Frederick [mailto:[EMAIL PROTECTED]
Sent: Sunday, January 07, 2007 12:43 AM
To: Mercedes Discussion List; [EMAIL PROTECTED]
Subject: Re: [MBZ] Octane and detonation
Proper combustion in a spark ignition engine is for the spark to ignite
the air/fuel mixture at the correct time for peak pressure to occur a
few degrees after TDC, and for the fuel mixture to burn at the correct
rate for the flame front to consume the vast majority of the fuel
before being quenched by contact with the head, cylinder walls, or a
space too small for the flame front to continue to propagate (the
quench zone in a wedge head design).
The key here is that the combustion MUST be slow enough to produce a
pulse of pressure that drives the piston down for as long as possible
during the power stroke -- when combustion becomes too rapid, pressure
and temperature rise too fast and the cylinder will become filled with
a combustion gas mixture too hot for the materials.
Detonation is just that -- and explosion of the air/fuel mixture,
usually not triggered by the timed ignition spark. In the worst case,
it is triggered by an overheated spark plug long enough before TDC to
produce a very high temperature zone extending out from the spark plug,
acting as a superheated torch. The heat from the flame thus produced
can burn a hole right through the pistons if the spark plug points at
them -- this was a problem with Alfa Romeo twin-cam hemi-heads in the
60s and 70s -- a tank full of regular gas and a highway run would
produce holes in the pistons about 1/4" in diameter that looked as if
machined there. Nasty.
The overpressure before TDC from detonation (which cannot be heard at
highway speeds, unlike spark knock or premature ignition) does a number
of other bad things -- it can cause enough crankpin pressure to wipe
the oil film off the crank journals, causing bearing failure, it can
melt piston crowns (or drill holes in them into the crankcase), can
seriously overheat valves, and can even cause flame cutting of piston
rings, where the flame from detonation (again, usually extending
straight out from the spark plug) can burn down the side of the piston
and cause ring failure.
Not pretty.
Higher octane fuels indeed burn slower. They are also harder to
ignite, so are more resistant to compression ignition. The slower
combustion rate reduces the tendency to detonate, will reduce or
eliminate premature combustion ("spark knock"), and lower peak
temperatures and pressures while extending the high pressure duration
during the power stroke.
Peter
Re: [MBZ] Octane and detonation....
Proper combustion in a spark ignition engine is for the spark to ignite
the air/fuel mixture at the correct time for peak pressure to occur a
few degrees after TDC, and for the fuel mixture to burn at the correct
rate for the flame front to consume the vast majority of the fuel
before being quenched by contact with the head, cylinder walls, or a
space too small for the flame front to continue to propagate (the
quench zone in a wedge head design).
The key here is that the combustion MUST be slow enough to produce a
pulse of pressure that drives the piston down for as long as possible
during the power stroke -- when combustion becomes too rapid, pressure
and temperature rise too fast and the cylinder will become filled with
a combustion gas mixture too hot for the materials.
Detonation is just that -- and explosion of the air/fuel mixture,
usually not triggered by the timed ignition spark. In the worst case,
it is triggered by an overheated spark plug long enough before TDC to
produce a very high temperature zone extending out from the spark plug,
acting as a superheated torch. The heat from the flame thus produced
can burn a hole right through the pistons if the spark plug points at
them -- this was a problem with Alfa Romeo twin-cam hemi-heads in the
60s and 70s -- a tank full of regular gas and a highway run would
produce holes in the pistons about 1/4" in diameter that looked as if
machined there. Nasty.
The overpressure before TDC from detonation (which cannot be heard at
highway speeds, unlike spark knock or premature ignition) does a number
of other bad things -- it can cause enough crankpin pressure to wipe
the oil film off the crank journals, causing bearing failure, it can
melt piston crowns (or drill holes in them into the crankcase), can
seriously overheat valves, and can even cause flame cutting of piston
rings, where the flame from detonation (again, usually extending
straight out from the spark plug) can burn down the side of the piston
and cause ring failure.
Not pretty.
Higher octane fuels indeed burn slower. They are also harder to
ignite, so are more resistant to compression ignition. The slower
combustion rate reduces the tendency to detonate, will reduce or
eliminate premature combustion ("spark knock"), and lower peak
temperatures and pressures while extending the high pressure duration
during the power stroke.
Peter
Re: [MBZ] Octane and detonation....
space. Detonation occurs when the fuel air mixture "explodes"...i.e. burns in multiple places at the same time. This can happen when the fuel mixture contains components that ignite much like a diesel..i.e. it reaches a combustion temperature and pressure and "cooks off". When that happens, more of the fuel energy is converted to heat, rather than doing useful work like driving the piston down. A smooth combustion results in maximum energy conversion from fuel energy to pressure energy. Heat _is_ what provides useful work. But too fast/soon and it ends up making cylinder pressure where the crankshaft can't extract the energy from it, so that energy goes into beating the engine apart instead. -- Jim
Re: [MBZ] Octane and detonation....
Larry said... You wrote about octane and detonation: <> Hi Royce, Is that your way of saying the higher octane detonates later and therefore closer to the time when the piston reaches TDC - or almost? - I'm assuming TDC is the best place to ignite the mixture for max HP and other ignition points are preferable if lower emissions, etc are the objective? >> Hi Larry, Bear in mind that I'm not an automotive engineer, and my petroleum engineering experience was focused on how to get more of it out of the ground. Having said that, it is my understanding that the optimal way for fuel to burn in the cylinder is for it to burn smoothly through the cylinder space. Detonation occurs when the fuel air mixture "explodes"...i.e. burns in multiple places at the same time. This can happen when the fuel mixture contains components that ignite much like a diesel..i.e. it reaches a combustion temperature and pressure and "cooks off". When that happens, more of the fuel energy is converted to heat, rather than doing useful work like driving the piston down. A smooth combustion results in maximum energy conversion from fuel energy to pressure energy. I don't have the experience to say which ignition points are more preferable, or where the optimal ignition point is in the cycleI was just impressed by the concept that adding more "heavy" components would improve performance by making the mixture burn more slowly (-:. Royce Engler 1985 300TD Turbo 293K
