Does quench affect power?

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Re: Does quench affect power?

Post by juuhanaa »

LotusElise wrote: Fri Sep 23, 2022 10:23 am
juuhanaa wrote: Fri Sep 23, 2022 9:39 am ...how about crazy slow lobe and better combustion chamber/piston shape?
You mean slow on valve lift, in such a way that scavenge phase get the name worth and lift harder later with the aim to let the piston design need no valve reliefs?

Two things why this won't be the optimum:
  • cam lobe design need very consistent acceleration, once you begin slow it is hard to get it back without going to the edge on materials, you would loose lift potential and duration, seating is one of the most sensitive moments for cam designers, the profile before dictate what it needs in the end to seat the valve smooth so that bounce is reduced to min. at high engine speeds. Otherwise we need even more FMEP eating valve springs. A smooth but stepped lobe profile isn't good for the wear and the dynamics of the valve and valvespring. What you do wrong in the beginning can only be healed with higher valve spring forces in some portion. Nothing we want have for highest power output everywhere.
  • TDC valve lifts of 5-7 mm are typical for NA engines in the 4-valve field. If you go lower you loose in the midrange engine speed. At 10,000 rpm you still see 3-4 mm@TDC with a R/S-ratio of 1.7 and a 86 mm stroke and a 13:1 CR in a 50 ccm head that means still touching the piston without reliefs
I fear this is not leading to the holy grail. I talk about 100 ftlb/liter torque. I've reached already with my first attempt in NA racing 104 ftlb/liter peak torque (almost 209 ftlb peak torque on a 2-Liter NA engine) and from 4500-8200 rpm over 96 ftlb/liter. I know to get there and still searching on ways to take that level to higher engine speeds for the next attempt I am working on.
Naah. Im just a stupid racer, done stupid things and trying to lear how to read burn patterns from 20€ piston.. My cams are like 258@seat/178@1mm and 9.3mm lift, so i dont have valve train issues.

On a 2-Liter NA engine .5mm lift@TDC is enough to make 1.5ft lbs/cid from 4000rpm-5500rpm. This is done using modified oem parts and 15-16bar cranking press measured by our gage. My experimental stuff has gone up to 19-20bar using similar cams. There is power hidden on a exhaust side...

Attached is a picture about chamber matching the piston above, approximately 1.3mm quench clearance. I just go for bigger exhaust valves.

Megane F7R BMW nural piston.png
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Re: Does quench affect power?

Post by Wetflow »

travis wrote: Fri Sep 23, 2022 10:04 am From my point of view, I appreciate the lengthy discussions of things like this.
I agree. These conversations not only help me to understand the processes that are taking place but to also consider how specific changes affect specific outcomes. These are some of my favorite posts.
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Re: Does quench affect power?

Post by David Redszus »

The conversations regarding the performance contribution of various squish clearances can easily lead to an over simplication of chamber turbulence during combustion.

Turbulence is not completely defined by clearance, squish area, and piston speed. Nor tumble or swirl.
What must additionally be considered is the shape of the chamber, piston dome, squish pad shape and turbulent conditions prior to the onset of squish effects.

It is importance to realize that turbulence is not a static effect that can be defined by a single value. The intensity and direction of turbulence changes with piston position, both before TDC and afterwards. It is a three dimensional process in which the changing chamber shape substantially alters the space in which various forms of turbelence can exist and for their duration.

If one has access to a solid model CAD program, it would be useful to draw the shape of the chamber at various piston positions. The shaped volume at 30deg BTC is quite different than that at 5deg BTC. And ATC as well.

If Solid Works is not available, a rubber mold can be made of the chamber with the piston in place.
It quickly becomes apparent that the combustion space and shape are widely different from engine to engine.

The combustion pressure curve can be drawn as a half sine wave. But two waves can contain the same areas bounded by completely different shapes. What makes them different? Combustion turbulence.
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Re: Does quench affect power?

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juuhanaa wrote: Fri Sep 23, 2022 11:44 am My cams are like 258@seat/178@1mm and 9.3mm lift, so i dont have valve train issues.
That's an interesting approach. What would be the redline of this engine with that cam duration?
juuhanaa wrote: Fri Sep 23, 2022 11:44 amOn a 2-Liter NA engine .5mm lift@TDC is enough to make 1.5ft lbs/cid from 4000rpm-5500rpm. This is done using modified oem parts and 15-16bar cranking press measured by our gage. My experimental stuff has gone up to 19-20bar using similar cams. There is power hidden on a exhaust side...
That would be 124 Nm/liter, sounds very good for a OEM-near setup. Congratulation for that achievement. On low speed cam my 2-Liter (200°@1 mm, 0.5 mm@TDC, 13.5 bar compression test pressure) has 120 Nm/liter@4400 rpm and at high speed cam 142 Nm/liter@7500 rpm (1.72 ftlb/cui). Was that with the F7R engine basis? These engines (undersquare design, 82.7x93 or like the later homoligation versions 84x90, nice low speed VE by the lower R/S-ratio) made a very nice job in the first years of STW and BTCC. Till 8500 rpm the 93 mm stroke worked perfectly and these were later well into the 310-315 hp level.

I work actually with 1.4 mm cold squish, which is in the range of the 1.3 mm of your engine. Combustion chamber will need some developement as the 51° valve angle is quite not optimal for a 12+:1 CR on a 86 mm stroke. I assume to find some potential :D. Anyway that is a very interesting engine setup concept you have there.

What is the block height of the F7R engine? What does the head flow at 9 mm valve lift? What CR do you run for 18 bar compression test (wet or dry) value?
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Re: Does quench affect power?

Post by juuhanaa »

LotusElise wrote: Fri Sep 23, 2022 5:22 pm
juuhanaa wrote: Fri Sep 23, 2022 11:44 am My cams are like 258@seat/178@1mm and 9.3mm lift, so i dont have valve train issues.
That's an interesting approach. What would be the redline of this engine with that cam duration?
juuhanaa wrote: Fri Sep 23, 2022 11:44 amOn a 2-Liter NA engine .5mm lift@TDC is enough to make 1.5ft lbs/cid from 4000rpm-5500rpm. This is done using modified oem parts and 15-16bar cranking press measured by our gage. My experimental stuff has gone up to 19-20bar using similar cams. There is power hidden on a exhaust side...
That would be 124 Nm/liter, sounds very good for a OEM-near setup. Congratulation for that achievement. On low speed cam my 2-Liter (200°@1 mm, 0.5 mm@TDC, 13.5 bar compression test pressure) has 120 Nm/liter@4400 rpm and at high speed cam 142 Nm/liter@7500 rpm (1.72 ftlb/cui). Was that with the F7R engine basis? These engines (undersquare design, 82.7x93 or like the later homoligation versions 84x90, nice low speed VE by the lower R/S-ratio) made a very nice job in the first years of STW and BTCC. Till 8500 rpm the 93 mm stroke worked perfectly and these were later well into the 310-315 hp level.

I work actually with 1.4 mm cold squish, which is in the range of the 1.3 mm of your engine. Combustion chamber will need some developement as the 51° valve angle is quite not optimal for a 12+:1 CR on a 86 mm stroke. I assume to find some potential :D. Anyway that is a very interesting engine setup concept you have there.

What is the block height of the F7R engine? What does the head flow at 9 mm valve lift? What CR do you run for 18 bar compression test (wet or dry) value?
Thank you,

Yes engive can rev 8k, but with a 258@seat cams i have shifted close 7500 with a different intake setup, but i never dyno that combo, so i just dont know what output it made..

Yes mainly F7R engine basis. I have little experiment about earlier model F7P stuff which has drastically different cylinder head, but using 82.7x93 and 84x92.5 bottom ends, because of cid rule.

OEM-near setup had stock pistons and lowered deck height, so cold squish was reduced from approx 1.3mm. Megane stock cams are 248@seat, 170@1mm and 9.1lift which helps raising the DCR. By cranking pressure i mean turning the engine using its own starter at WOT.

Static CR is around 11 range, when measured 18,19,20bar cranking pressures. Attached a picture about "mule engine" which had different style 84mm dished pistons with approx std deck height and cold squish. Its originally a BMW turbo piston with excess material for NA deal above top piston ring, and it has valve cutouts which i dont necessarily need... I have 147mm long rods from MB M102/M111 engine, and im going to modify that dished piston for those longer rods and end up like same clevis volume that i previously had with a different BMW piston.

I have a swirl meter that i need to hook up into my flow bench.. I like measure flows across the chamber (one of those things not sure what im doing and i need to work my flow sheet), only problem im not a piston designer aand im a hobby guy. :oops:

IMG_20210422_170534.jpg
IMG_20210422_014155.jpg


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Re: Does quench affect power?

Post by ptuomov »

“ approximately 1.3mm quench clearance.”
75E05FF7-BD28-4588-B29F-EF619028BD47.jpeg
B7826A3D-7B78-4F20-AB9A-B04B76133CFA.png
This engine has basically zero squish but a lot of tumble with intake port angle normal to the exhaust valve and no piston crown, tumble which will be well broken down to small eddies near TDC by the combustion chamber shape.
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Re: Does quench affect power?

Post by David Redszus »

So far, the conversation has focused on squish band clearance and to a lesser extent
on Squish Area Ratio, and a little on piston speed.

Calculations based on the above will only yield average velocities.
Actually, local squish velocities are determined by the shape of the squish edge window
and adjacent area. The resulting squish jets can increase swirl or negate swirl patterns.

Vertically angled squish pads can produce jets that assist tumble, especially locally.

Increasingly, it appears we really need tools like CFD to help understand chamber
turbulence and its affect on the combustion process.
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Re: Does quench affect power?

Post by juuhanaa »

ptuomov wrote: Sat Sep 24, 2022 11:32 am “ approximately 1.3mm quench clearance.”

75E05FF7-BD28-4588-B29F-EF619028BD47.jpeg

B7826A3D-7B78-4F20-AB9A-B04B76133CFA.png

This engine has basically zero squish but a lot of tumble with intake port angle normal to the exhaust valve and no piston crown, tumble which will be well broken down to small eddies near TDC by the combustion chamber shape.
Those parts were not ran together. I didn't show matching cylinder head, or burn marks for the valve pocket version. I used smaller chamber head, which can also create swirl due to port orientation. 84mm bore was +2mm bigger than chamber was wide, so i needed mill piston bads to fit them inside the chamber, but i have small squish area around the combustion chamber and round dish in a piston.

Look the picture about cylinder head and piston without valve pockets. The squish clearance was approx 1.3mm between flat surfaces, and piston burn pattern indicates that area did squish, because there is no carbon residual. Megane has same part number for the crankshaft than diesel engine :wink:
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Re: Does quench affect power?

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juuhanaa wrote: Sat Sep 24, 2022 4:40 am Yes engive can rev 8k, but with a 258@seat cams i have shifted close 7500 with a different intake setup, but i never dyno that combo, so i just dont know what output it made..
The 7500 rpm sounds interesting. Do you have an assumption from the but-meter where peak power was?
juuhanaa wrote: Sat Sep 24, 2022 4:40 amYes mainly F7R engine basis. I have little experiment about earlier model F7P stuff which has drastically different cylinder head, but using 82.7x93 and 84x92.5 bottom ends, because of cid rule.
I really like the under-square design of the F7R engine, as it has a great VE support below 8500 rpm when budget starts rising to keep the forces handable. Some application don't need or allow not a higher redline (e.g. STW).
juuhanaa wrote: Sat Sep 24, 2022 4:40 amOEM-near setup had stock pistons and lowered deck height, so cold squish was reduced from approx 1.3mm. Megane stock cams are 248@seat, 170@1mm and 9.1lift which helps raising the DCR. By cranking pressure i mean turning the engine using its own starter at WOT.
How much was the squish area on that chamber? I saw a sort of spheric cut out in that block upper face picture. Is that a negative dome directed spheric area?
juuhanaa wrote: Sat Sep 24, 2022 4:40 amStatic CR is around 11 range, when measured 18,19,20bar cranking pressures.
Short overlap duration helps. But despite that it is very high. What liner-piston clearance does it have?

juuhanaa wrote: Sat Sep 24, 2022 4:40 amAttached a picture about "mule engine" which had different style 84mm dished pistons with approx std deck height and cold squish. Its originally a BMW turbo piston with excess material for NA deal above top piston ring, and it has valve cutouts which i dont necessarily need... I have 147mm long rods from MB M102/M111 engine, and im going to modify that dished piston for those longer rods and end up like same clevis volume that i previously had with a different BMW piston.
Awesome approach. Like my buddy, who mixes also different engine model parts to one engine to save money and time. Block height was 222 mm or what compression height does the BMW stuff has?
juuhanaa wrote: Sat Sep 24, 2022 4:40 amI have a swirl meter that i need to hook up into my flow bench.. I like measure flows across the chamber (one of those things not sure what im doing and i need to work my flow sheet), only problem im not a piston designer aand im a hobby guy. :oops:
You mean you want to improve the swirl number or why do you measure the swirl number?


IMG_20210422_170534.jpg


IMG_20210422_014155.jpg



-juhana
[/quote]
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Re: Does quench affect power?

Post by ptuomov »

Why would anyone want swirl in a four valve engine operating at WOT near peak power rpm? That’s would be very inefficient stuffing of a square peg in a round hole.

At low rpm and part load, swirl makes a lot of sense in a four valve head from combustion efficiency perspective. If you can turn one intake valve “off”, that’ll help. Or if you can use a throttle valve to turn one intake valve port off, that also helps. They help by both increasing flow velocity thru they what is now half the flow area and by creating swirl motion.

At high rpm WOT, obviously none of this swirl motion makes sense because the four valve head is naturally so efficient at producing tumble.

Right?
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Re: Does quench affect power?

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ptuomov wrote: Sat Sep 24, 2022 11:32 am This engine has basically zero squish but a lot of tumble with intake port angle normal to the exhaust valve and no piston crown, tumble which will be well broken down to small eddies near TDC by the combustion chamber shape.
Yeah, the huge stroke helps to reduce the dome volume massively when keeping CR constant and varying stroke to see the influence...

I wouldn't say it has zero squish velocity, at 7500 rpm it is about almost 10 m/s, assuming 15 % squish area of the bore area. Preserving tumble on low dome volume (higher strokes) is indeed easier, especially your approach uses maybe squish as tumble supporter. Mazda used a similar approach like yours for the SkyActive Otto engine (14:1 CR), just more concentrated bowl volume below spark plug. In their MTZ paper they mentioned it supports the preservation of combustion temperature during start. I discussed this once with Larry Widmer, he was very short about it and spoke it has disadvantages on the weight of the piston. He likely didn't test it ;). From my experience, the combustion process development is quite individual, general rules don't apply, application depended considerations have to be done. But what Mazda stated is somehow a general guideline, whenever distance to spark plug can be increased. On a 86 mm stroke engine there is not much room, as the 10,000+ rpm need quite a duration at intake side and hence an adapted CR.

I know many run huge durations in the drag race scene, which are not based optimal design approaches, but on the alternation of load design, typically used in the NA scene. As strokes of up to 108 mm at almost 10,000 rpm are used that design drawback doesn't get aware. The suction efficiency and cam duration need of a 108 mm stroke@10 krpm is indeed bigger compared to an 86 mm stroke.

On the NASCAR wedge heads and huge bores the 0.1 mm operated squish height would reassemble in a velocity of around 150 m/s, assuming a 30 % squish area of the 106 mm bore. This contradicts what G.P. Blair recommended as cold squish velocity would be at least 45 m/s. Another example was the STW race series, where almost zero squish height was aimed at redline. The engine speeds there were still in an area where knock can apply to because of low engine speeds. For me it is still not clear what is the aimed one for certain conditions. Squish velocity is a game of area, height, engine speed, material expansion, ...

...BTW, I validated my model of reduction of squish height by engine speed and heating at 3 examples, which fits quite well for alu and iron block systems. All 3 had evidences of sligthly light piston-head-kissing, which is the best validation case. From there I can definitely say, elongation of block and crank assembly is not compensated to zero, there is a leading difference, coming from temperature and inertia force driven portion.
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4000 rpm bandwidth of at least 192 ftlb
310 hp@8200 rpm
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Re: Does quench affect power?

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Awesome approach. Like my buddy, who mixes also different engine model parts to one engine to save money and time. Block height was 222 mm or what compression height does the BMW stuff has?
Thank you kind words. Folkrace is fun class where i can do soft head stuff, and those experiments serve other series like rally and sprint. MB 147 rods has 22 top for BMW piston and 51.6 lower for Renault stock 93 crank. This combo with std block height ends up roughly 4mm material above top piston ring and no valve pockets, but this is yet to come.

IMG_20220925_204902.jpg
Meganen veivi ja bemarin 84mm mäntä jonka puristuskorkeus tulee 1.75mm dekin yläpuolelle ennen koneistusta VS Vakio veivi ja 82mm mäntä.JPG
24 meganen oma veivi johon sovitus bemarin 84mm männälle (22mm tappi ja kiila muoto).JPG
29 bemarin mäntä jyrsitty muotoon (paljealue 1,3mm).JPG
28 kevennetty tilipitappi.JPG
IMG_20220925_205727.jpg
Short overlap duration helps. But despite that it is very high. What liner-piston clearance does it have?
BMW piston has more pin off set than OEM Renault. I have no idea what material 20€ piston is, but guide clearance was 3.3 hundred. I told my machinist to set it 5.5. It ran just fine :D I ran one summer tarmac sprint using JE -pistons and 8.1 hundred guide clearance for 82.7 bore, ran ok too. Valves need also attention. I had wider seats, but i probably try some coatings to handle heat better..

IMG_20220925_204432.jpg
How much was the squish area on that chamber? I saw a sort of spheric cut out in that block upper face picture. Is that a negative dome directed spheric area?
Block milling using OEM -pistons and 15 range cranking press.. BMW piston was milled using tools i happened to have at that point #-o

Screenshot_20220925-210206.jpg
You mean you want to improve the swirl number or why do you measure the swirl number?
I think its a factor to be considered and on a rally classes no port filling allowed. Its also an hobby for me and first ill just keep an eye on it.
Do you have an assumption from the but-meter where peak power was?
Attached calculus regarding intake harmonics :)

but dyno.png


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Re: Does quench affect power?

Post by juuhanaa »

ptuomov wrote: Sun Sep 25, 2022 1:04 pm Why would anyone want swirl in a four valve engine operating at WOT near peak power rpm? That’s would be very inefficient stuffing of a square peg in a round hole.

At low rpm and part load, swirl makes a lot of sense in a four valve head from combustion efficiency perspective. If you can turn one intake valve “off”, that’ll help. Or if you can use a throttle valve to turn one intake valve port off, that also helps. They help by both increasing flow velocity thru they what is now half the flow area and by creating swirl motion.

At high rpm WOT, obviously none of this swirl motion makes sense because the four valve head is naturally so efficient at producing tumble.

Right?
By looking how Renault did things from the factory (which must be taken into account due to the rules) aand what the F3 head may look like, i think there are different ways to skin a cat...

Renault F7P.png
Renault F3 engine 2.jpg


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Re: Does quench affect power?

Post by LotusElise »

David Redszus wrote: Sat Sep 24, 2022 1:41 pm So far, the conversation has focused on squish band clearance and to a lesser extent
on Squish Area Ratio, and a little on piston speed.

Calculations based on the above will only yield average velocities.
Actually, local squish velocities are determined by the shape of the squish edge window
and adjacent area. The resulting squish jets can increase swirl or negate swirl patterns.
Yeah, squish velocity is a product out of piston speed, squish area and height and yes, the direction of the squish flow has an effect on support or elimination of actual other flow regimes.

I concentrate only on the maximum squish velocity to see how big the impulse can be. My 0D-model uses the approach of G.P. Blair, which gives a rough idea what is happening in the chamber and when it happens. Of course a 3D-approach would clarify all the interaction, but this is out of my budget and time.
DAMPFHAMMER engine:
2000 ccm, Honda K20 NA engine
4000 rpm bandwidth of at least 192 ftlb
310 hp@8200 rpm
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Re: Does quench affect power?

Post by LotusElise »

juuhanaa wrote: Sun Sep 25, 2022 3:27 pm Thank you kind words. Folkrace is fun class where i can do soft head stuff, and those experiments serve other series like rally and sprint. MB 147 rods has 22 top for BMW piston and 51.6 lower for Renault stock 93 crank. This combo with std block height ends up roughly 4mm material above top piston ring and no valve pockets, but this is yet to come.
That sounds like a really nice playground for different approaches. Do you have a cylinder pressure indication system to find out more about the heat release over crank angle curve?
juuhanaa wrote: Sun Sep 25, 2022 3:27 pmBMW piston has more pin off set than OEM Renault. I have no idea what material 20€ piston is, but guide clearance was 3.3 hundred. I told my machinist to set it 5.5. It ran just fine :D I ran one summer tarmac sprint using JE -pistons and 8.1 hundred guide clearance for 82.7 bore, ran ok too. Valves need also attention. I had wider seats, but i probably try some coatings to handle heat better..
Thanks for your response on the clearance. How much was fireland height? Do you have an idea what the BMW pistons does have on squish area ratio?
juuhanaa wrote: Sun Sep 25, 2022 3:27 pmI think its a factor to be considered and on a rally classes no port filling allowed. Its also an hobby for me and first ill just keep an eye on it.
I see your point, knowhow gain in everything which can gatered =D>.
juuhanaa wrote: Sun Sep 25, 2022 3:27 pmAttached calculus regarding intake harmonics :)
Ok, thence it would be around 7200 rpm.

My actual 180 hp/liter-NA approach on the Honda K-series need about a 12.5+:1 CR because of the cam duration needed at 10,000 rpm. The dome volume on that low stroke get really high and really tumble killer like. Therefore the squish design is very important as well as the chamber design to get the burn duration as far as possible down in duration numbers. I still need 130+ Nm/liter@10,000 rpm, means friction and combustion are my focuses.
DAMPFHAMMER engine:
2000 ccm, Honda K20 NA engine
4000 rpm bandwidth of at least 192 ftlb
310 hp@8200 rpm
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