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Old 06-24-2012, 01:55 PM   #21
Tobin
 
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Quote:
Originally Posted by Fahlin Racing View Post
I was looking at haywood's book a while back, however I am not able to purchase his writing as of yet. On another forum, I had been involved in an engine thread that involved needing to know cylinder pressure and temperatures involving failures due to engine timing, I had collected part numbers from ISSPRO to assemble a testing tool, which I haven't been able to buy yet either.

Since there is less time at high rpms, would creating a slight lip going inward to the center of our bowl creating slight more turbulence hoping to influence a state where our atomized fuel turns into a equally spread mixture easier, albeit, squish action could be more benficial and just have the bowl wall meeting the piston crown top edge, with a radii be sufficient?

Our crown temps get fairly high, I sometimes think a lip would counteract combustion efficiency through acting as a heat-sink and overload the crown thermally. Hmmm ......
Were you going to assemble something that records pressure vs. crank angle?

How were you going to measure the pressure? Drill a hole in the block right below the deck?

Tobin
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Last edited by Tobin; 06-24-2012 at 01:56 PM.
 
Old 06-26-2012, 05:13 AM   #22
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I am still, when I have time, thinking about how to record the crank angle. I was hoping to use the glow plug holes for the engines designed like that, but I will have to machine holes in heads that don't. If the block is not a parent-bore, I will probably encounter coolant leaking more easily if I were to go through the cylinder. Plus I would have to make sure the probe wouldn't strike the piston crown upon approaching tdc and leaving tdc.

The crank position recorder is the current thought of how to although at the moment, I was just going to measure pressure & temperature on the fixed factory timing and move from there.

What would you do as far as analysing this?

What is your view of the chamber Tobin?
I am still developing my view on what high speed diesel combustion chambers could look like and its effects on combustion along with fuel mixture characteristics itself.
 
Old 06-26-2012, 07:08 AM   #23
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There are systems out there that are designed for measuring such pressures. I have seen a few on the Dyno very impressive
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Old 06-26-2012, 09:22 AM   #24
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Ive been reading about swirl and its importance in part-load operation, but I wonder what role compression has in the combustion process. Would you only need enough compression to heat the air to the ignition point before spray, or is more beneficial?
Lowering compression with an oversize gasket screws with part-load operation pretty good. Haze and lots of lag. Im guessing that compression has some effect on combustion heat and exhaust velocity.
The rule of thumb seems to be, lower compression and more boost. That optimizes the engine for the higher revs.
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Last edited by kawi600; 06-26-2012 at 09:24 AM.
 
Old 06-26-2012, 05:11 PM   #25
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Quote:
Originally Posted by kawi600 View Post
Ive been reading about swirl and its importance in part-load operation, but I wonder what role compression has in the combustion process. Would you only need enough compression to heat the air to the ignition point before spray, or is more beneficial?
Lowering compression with an oversize gasket screws with part-load operation pretty good. Haze and lots of lag. Im guessing that compression has some effect on combustion heat and exhaust velocity.
The rule of thumb seems to be, lower compression and more boost. That optimizes the engine for the higher revs.
I'm scratching my head right now.....your reading to much and thinking way to hard. Fuel+Air= Power. Keep it simple and dont overthink....More compression= more efficiency at low rpms, higher cylinder pressure/temps. Low compression and more boost has nothing to do with higher revs....
 
Old 06-26-2012, 05:32 PM   #26
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Mazda's SkyActive diesel runs 13:5-1 compression and has 4 main injection events before TDC. Has a 5k or 6k rpm limit on a V6...
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Old 06-26-2012, 11:17 PM   #27
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Quote:
Originally Posted by lenahan05 View Post
I'm scratching my head right now.....your reading to much and thinking way to hard. Fuel+Air= Power. Keep it simple and dont overthink....More compression= more efficiency at low rpms, higher cylinder pressure/temps. Low compression and more boost has nothing to do with higher revs....
Meh I don't want to start a chit storm but combustion optimization is a pretty complex subject...manufacturers have really just figured out how to make good power out of these things in the last 15 years. I equate the 2000's of diesel technology to the 60's of gasoline.

With that said, I think our best shot at good intel is from the tractor guys unless someone wants to drop $100,000 and test 10 different bowl/injector designs with the proper sensors. Wide bowl/spray angle seems to be the best bet. Injector hole count is up in the air, a larger orifice penetrates better for the wider bowls but will start to get so thick of a jet that the fuel/air mix gets super rich and poor efficiency follows. Perhaps past a certain point more holes with a smaller orifice will be the ticket?

Quote:
Originally Posted by oldestof11 View Post
Mazda's SkyActive diesel runs 13:5-1 compression and has 4 main injection events before TDC. Has a 5k or 6k rpm limit on a V6...
Generally newer diesels lower the compression ratio to bring cylinder temps down to control NOx emissions. However you can start injection event earlier and impart more work on the piston through a longer combustion event. This might allow for a better use of burn at high rpm, and keep cylinder pressure spikes down to avoid failure. Just speculating...

What I've seen on these forums is that the end result creates people's theory + hypothesis rather than the other way around.
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Old 06-27-2012, 06:13 AM   #28
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Yeah, I am not hypothesizing. Just stating an OEM is attempting this already.
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Old 06-27-2012, 06:30 AM   #29
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Maybe you should just go ask a tractor guy and see if they are really doing anything different then what the truck guys are doing now.
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Old 06-27-2012, 07:00 AM   #30
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Im pretty sure Ive experienced the issue of injectors with smaller orifices having more difficulty penetrating high pressure air. And this with stock bowls on the 12v. Ive tried some 7-hole nozzles and they killed the top end power. Great on the low end though.
With some serious pressure behind them I bet they would be good.
Thats pretty impressive with a diesel at 13.5:1. Guess when you can control the injection event so finely you can ramp up cyl pressure with pre-injection.
Only downside is these new diesels are too quiet!
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Old 06-27-2012, 03:31 PM   #31
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[QUOTE=straight 6 roar;1819321]Meh I don't want to start a chit storm but combustion optimization is a pretty complex subject...manufacturers have really just figured out how to make good power out of these things in the last 15 years. I equate the 2000's of diesel technology to the 60's of gasoline.[QUOTE]

your have a point with this statement except that this thread was intended on mechanical injection if i was to guess. correct me if im wrong fahlin. everyone makes it more complex than it has to be. were not talking about mazdas and effciency...most are wanting to make HP. Theres a big difference. you cant exactly compare 30,000psi and 3,500psi inj pressure. everything else is going to be basically the same. Bigger holes, less duration, wide patterns, lower timing and wide bowls= Higher peak HP with unforgiving low throttle response. applies to mechanical and CR.....notice i didnt include Injection pressure for a reason. tighter patterns and narrow deep bowls have better idle and throttle response usually. argue all you want but thats about as simple and factual as it gets.
 
Old 06-27-2012, 06:55 PM   #32
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Mechanical or HEUI etc. But since we just need a base perspective mechanical single shot is just fine. As for multi-point injections, I believe that is a whole new ball game. The new diesels are quieter because of multi-point injection fuel systems. I don't think he is thinking too much Lenhan, he just thinking. Granted things get pretty indepth sometimes but I think that him posting that thought has not only brought it to the minds of others, but it reminds what we have to comprehend to evaluate things.

There will be no 'chit storm' Straight 6 roar. Arguing is not only worthless on here it wouldn't provide a clear post for anyone if things are distracted. Professional only. If you have opinions or experiences, please do share.

Quote:
Im guessing that compression has some effect on combustion heat and exhaust velocity.
Compression, we have 2 types (1) being mechanical or static and (2) dynamic compression. The more heat we produce, the more pressure we create which entails a stronger force upon the crown. Now when we get really hot some end up using water or water/methanol to keep temps from melting and breaking things. What A LOT of people think you make power with water, but you can't burn water, we are just creating a bandaid that absorbs heat to allow the further heat production to not do damage. Plain and simple.

Compression plays a role with our heat, cylinder pressure and flame speed. As cylinder temperature rises, our flame speed becomes faster, the quicker we burn, the greater the pressure rise. This all depends on fuel attributes as well to burn at the right speed but also produce enough heat to turn out crankshaft effectively and efficiently. Exhaust gas temperature & velocity, the hotter it is the faster it will exit, not only from pressure differential from cylinder to exhaust manifold, but hot gases do flow faster than cooler. For now, let just concentrate on things within the chamber please.

Now if we have high compression dynamically, and low pressure injection, the atomization may take longer even with adequate swirl or tumble or swumble and cause an extended delay angle with a shallow bowl? Although, if we have a small bowl and the low pressure would only penetrate so far, would we only be fighting for the quality of a homogenous charge within our combustion chamber? Hmmm

Also what compression would be best to make the best power & torque for high rpm?.....
 
Old 06-28-2012, 12:00 AM   #33
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Scratching my head but I'm subscribed, this is a lot to take in.
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Old 06-28-2012, 06:07 AM   #34
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Why would you want lower injection pressure? The higher injection pressure is always better, better atomization. The higher pressures are required for the higher dynamic pressures. Also the higher the compression pressure, the better efficiency (only reason why Diesel is efficient). The water injection also helps with more mass flow through the engine. More mass flow = more power.

Tobin
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Old 06-28-2012, 09:45 AM   #35
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Quote:
Originally Posted by Tobin View Post
Why would you want lower injection pressure? The higher injection pressure is always better, better atomization. The higher pressures are required for the higher dynamic pressures. Also the higher the compression pressure, the better efficiency (only reason why Diesel is efficient). The water injection also helps with more mass flow through the engine. More mass flow = more power.

Tobin
Water injection technically robs a little power through what's known as "latent heat of vaporization". This is the energy it takes to separate the molecules of the water. It's a moot point of course because it allows us to add more fuel to cancel out this effect.
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Old 06-28-2012, 10:39 AM   #36
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Good info! this has me re-thinking some of the issues on my build for sure.
Wish there was an easy/cheap way to add static compression on these motors.
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Last edited by kawi600; 06-28-2012 at 10:40 AM.
 
Old 06-28-2012, 10:46 AM   #37
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Mazda has shown you don't need high compression for power or fuel economy. The catch though is modern fuel injection and combustion chamber prep. Personally I don't want a bit more compression ratio than I need to start it.
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Old 06-28-2012, 11:47 AM   #38
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Why would you want lower injection pressure? The higher injection pressure is always better, better atomization.
Injection pressure can be high enough to be counterproductive.
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Old 06-28-2012, 05:28 PM   #39
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Injection pressure can be high enough to be counterproductive.
Like when you get holes on the pistons on cr?
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Old 06-28-2012, 07:22 PM   #40
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Mazda has shown you don't need high compression for power or fuel economy. The catch though is modern fuel injection and combustion chamber prep. Personally I don't want a bit more compression ratio than I need to start it.
Static or Dynamic compression?

Tobin
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