Lister Engine Forum
How to / DIY => Engines => Topic started by: Twinscrew on September 28, 2006, 12:52:36 AM
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Is anyone hear familiar with Somender Singh? http://somender-singh.com/ I am curious as to how some of you, especially Guy Fawkes and Mobile Bob, feel about his work. This is open to anyone with an opinion, good or bad. So, let's have it.
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Something that *sounds* so much like snake oil is something I'd avoid until it becomes a standard in OEM or race engines.
But that's just my nature. ::)
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For diesels, I dunno.
But I do know that in petrol engines less fuel in an engine means more air, higher combustion temperatures, and thus more heat to drive the reaction of Nitrogen and Oxygen to form NOx which is a major contributor to photochemical smog and acid rain.
This is why modern engines have an EGR valve, to recycle some of the exhaust to basically smother the combustion a little, keeping the temps down and the NOx levels low. That thing ain't in there for performance -far from it- it's needed for emission control.
So I'd say that if the methodology worked, you would lower CO2 production, but increase NOx production a lot.
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Sounds like 2 thumbs down so far. Anyone else?
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Well, sounds like there are a few things to comment on here. First is the "groove" concept, of cutting one or more grooves in the squish area of the head. The other is the "nitrogen" question, which confusingly is what is referenced on the main page. The site certainly has the tinfoil-hat look and feel, with lots of strange incomplete thoughts and undocumented assertions. However, digging a bit through the chaff does seem to have some interesting tidbits of actual, real data. The gains are small, but certainly seem realistic. There is no good diesel data, however, so this might be misleading to those of us working with the heavier fuels... I would say that it seems like the modifications seem to have some adherents, and if you have an inexpensive 6/1 head or whatever laying around in which cutting a groove sounds like an OK thing to do, then I'd be interested in hearing what the results are. I don't know what the downside would be - I'm not smart enough to do the math to see what kind of compression changes would happen from removing a cubic centimeter or so of metal out of the inside of the head. My gut says "not a big deal, so give it a shot" but someone who is better at those calculations should take a swing at it. Certainly, the Lister(oid) community has a much better chance of empirically proving any of these "fringe" energy efficiency theories - our engines stay at exactly one RPM setting once started, and they produce an extremely predictable amount of power in a stationary setting, and are very easily monitored for various temperatures, outputs, and inputs requirements. Should be a quick determination as to what works and what doesn't, no?
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Squish and quench areas in cylinder heads were common on 1960's non emsission controlled engines. This improved performance by reducing knock a dnping but at the cost of high emmisions. When cars went to open combustion chanmbers and unleaded gas in the 70's compression ratios had to drop....
No idea how this can be aplied to diesel.....
Doug
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No idea how this can be aplied to diesel.....
I'm not thinking that it can. The topic was intended to initiate a dialog of opinions about these theories. They are being applied, so far, to 2 & 4 stroke gasoline engines. There are some very knowledgeable folks posting regularly on this forum. Conversely, there are some not so knowledgeable folks posting as well. I would like to get opinions from EVERYONE here. I am not concerned with quantification, just opinion. Come on guys, if this were a negative thread with mud slinging it would have pages of replies by now. So, out with it...........
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Ok, paraphrasing the web page.
Nitrogen makes up a large percentage of what is known as air.
Turbulence increases mixing of fuel and oxygen resulting in more complete combustion.
Both of these have been known for at least 200 years.
So nothing new.
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Re: squish and quench areas, yes they were common on SI engines from about 1950 until the advent of regulated HC emissions circa 1967 or thereabouts. Properly done, they help an SI engine approximate an IDI diesel in combustion efficiency. The modern pentroof chamber is a compromise in this direction with an open design. You need turbulence to homogenize the fuel-air mixture and blow it past the spark plug to encourage rapid flame front travel. You need a compact combustion chamber (the comet spherical chamber is ideal for combustion - there's just this little heat transfer problem in the transfer port) to get efficient and rapid combustion both for better efficiency (both combustion efficiency and efficient energy transfer to piston) and to burn most/all the mixture so quickly that you can't get end-gas combustion away from the flame front (knock, ping or detonation).
The downside to squish/quench areas on SI engines is that they have an irreduceable minimum amount of unburned hydrocarbons (except for the Honda CVCC system, which worked great, until NOx was regulated). Back in the days when the first compression ring was 1/8" down the piston, unburned HC wasn't such a big deal. Nowadays, you can't sell a car with such an engine in it in a first-world country. Any engine with high compression will have NOx issues as well. If you get the chamber temp high enough, you will oxidize the nitrogen in air. Simple as that. EGR allows current engine designers to have their cake and eat it too - they can design in a compact (pentroof) chamber and a high CR, and then use the EGR to reduce the free nitrogen content in the chamber at low throttle to small enough values that the remaining NOx is easily reduced in the three-way catalyst. EGR also has a powerful antiknock capability similar to water injection, so active managed EGR is now an indispensable tool in the recip SI engine designer's bag.
If you look at DI diesel designs, you see all kinds of pockets in piston heads and the like. These are the same sort of squish/quench area and combustion pocket an SI engine uses. In the diesel, of course, there's no unburned HC problem because there's nothing but compressed air in the squish areas if the injection pattern is properly placed. With diesels, though, you want to disperse the injected mass of fuel into the air in an even dispersion to avoid rich spots. High pressure common rail injection is part of this strategy, and combustion chamber design is the other part. If you look at http://en.wikipedia.org/wiki/Image:VAG_1.9_TDI_engine.jpg this cutaway of the VW TDI engine, you'll see there's a sort of compressed toroid combustion chamber in the center of the piston. Given the good numbers the TDI engine gives, it's a safe assumption that there's some pretty good computational fluid dynamics analysis behind that shape. If you want a clearer view, check out the Wartsila-Sulzer photos posted a while ago. Pistons the diameter of lister flywheels still have the same chamber shape requirements as the little TDI Volkswagen.
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we can get into all sorts of theory here, but may be stopped cold by the simple fact that any grooving will reduce compression ratio. how much i don't know without some computation.
i am not sure the end result would be a measurable decrease in emmissions of a typical listeroid or any measurable increase in power. likely though there might be a slight improvement in lower emmissions if done properly (by reduction of combustion temps) but with a loss in power.
just my guess
bob g
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Thanks Bob. Lets suppose that combustion chamber size, and subsequently static compression, would remain the same as before the groove modification, by performing a minimal surface milling of the head.
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correct me if i am wrong, but diesel heads start out flat, no chamber
so surfacing the head would not restore the compression ratio, unless it decreased the grooving volume, in which case don't groove so deep to minimize loss of compression, but then you lose whatever possible gains there might be from grooving.
i don't think we are going to see these grooves doing much to increase power, reduce emmissions or reduce fuel consumption.
my thinking here is pretty simple, (i know this will ellicit a storm of responce)
if this technology was good for diesels we would have seen it in offerings from detroit, cummins or cat.
with the epa reg's horrendous competition for market share etc, these manufactures likely have tried everything from grooves to dog turds. there is no status quo in the diesel industry.
if you want high efficiency, low emmisions from your roid, think HUI, but get ready to spend 10 times what you did on the engine to impliment it.
then it aint simple no more.
for now i can't see the grooves as being a good thing or something i would spend much time on.
but that is just me,,, if you are interested by all means check it out.
bob g
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if this technology was good for diesels we would have seen it in offerings from detroit, cummins or cat.
I don't think this theory would apply to a diesel at all. Just gas engines. So, why the question on a diesel forum? Just because of the level of intellect floating around here.
Also, I know of a few horsepower junkies posting here. So Bob, do you believe the grooves would improve performance in say, a 500 inch twin turbo Caddy engine? Assuming, of course, that you could get traction even without the grooves. ;D
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lol
i doubt it
:)
bob g
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Bob:
I'd like your take on the turbulance area in the intake port of the Petteroid....
Basicaly its a ridge counter sunk under the valve seat just above the top of the runner. I've seen something like this on other DI engines but I have to wonder if this realy makes a difference or would it be better to simple grind most of it out. Does the difference in turbulance make up for the loss in VE?
Doug
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Doug:
frankly there has been volumes written on the subject of port design and redesign.
the long and short of it, is more damage to flow can be done by getting in there and grinding out without knowing specifically what and where to grind.
if there is flashing, go ahead and grind it out, if it looks like a purposely placed part of the casting i wiould hesitate removing it.
if you have port to manifold mismatch, go ahead and match em up. i would grind on the intake more though. you never know when you are going to hit water in the head port.
got any pictures of the port and this particular detail?
bob g
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Can do Bob, some time today
Doug
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Here Bob:
http://www.putfile.com/dougwp
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I made a file all about the Petter project and moved everything to the new file along with a few other picture of some of the more gruesome details....
http://www.putfile.com/dougwp/images/31565
Doug
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Doug:
while that seemingly looks like an obstruction, it may well be there purposely to help swirl the intake charge of air to help scavenge the cylinder.
i would not remove it until i could document whether the original used this feature.
even so, if you figure the actual cross section under the open valve based on lift and area, you may find that this "obstruction" really does not hamper flow in either event.
bob g
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Bob:
I'd like your take on the turbulance area in the intake port of the Petteroid....
Basicaly its a ridge counter sunk under the valve seat just above the top of the runner. I've seen something like this on other DI engines but I have to wonder if this realy makes a difference or would it be better to simple grind most of it out. Does the difference in turbulance make up for the loss in VE?
Doug
For what is basically a relatively low-speed diesel, with low BMEP etc., this sort of thing in the inlet tract is not going to make a big difference with the (relatively) slow air-flow going through it.
As diesels normally work with unthrottled intakes the inlet side of things is usually fairly unsophisticated on idustrial stuff, compared with a diesel like the VW or BMW auto diesels (for example)
Peter
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It looked to me like this was intentional and part of the design but I had to ask the experst if they thought a little smoothign and cleaning might help.
Thank you guys....
This still leaves me with a spare head that has a minor offset intake runner castign defect....
I'm kind of tempted to remove these obstructions and use this head with a modified intake as a producer gas head of I can figure out how to squeeze a spark plug into that injector port....
Doug