High compression on low octane
 

It's been a while but this seems to be the place to ask "dumb ass questions" per FB K series groups.

I have a K swapped Insight with the goal of power AND economy, I've had a K20a3 with 11.5: compression and 5psi of boost, 3.4 final drive and while its a blast to drive I average 30mpg with 40mpg being my tank record. Meh

I now have a K24a4 on the stand and will be swapping it in next year. No turbo, well muffled. Stock compression is 9.7:1 and made for 87 octane.

I'm interested in running higher compression on 87. TSX engine is 10.5:1 which seems possible. what about higher?

My thought are that the car is almost half the weight of the original Element/Accords the engine came from so the load will be less.

My other idea is to add EGR to the system and control it with Kpro or maybe another means.

Also FWIW I fully expect less power than my current setup and I'm cool with that, I have other cars for that.

The original Insight engine was 10.8:1 and only required 87 octane. But I don't know how that translates to a K-series.

I've driven a manual K24 CR-V and really enjoyed the engine. It's gotta be awesome in a lighter car! Cheap and torquey! But I think I'll be sticking with the 64 MPG 3-cyl.

The engine in my previous GMC Canyon had, if I recall correctly, 10:1 or 10.5:1 compression. It ran well on 87 octane. The best ambient temperature for gas mileage was about 70 deg F. It lost about 1 MPG per 10 deg F at lower temperatures. The mileage did not improve at higher temperatures. I think that the knock sensor was retarding ignition timing at temperatures above 70 deg F.

I saw timing as retarded as 2 deg after TDC at high manifold pressure and low RPM, and as advanced as 45 deg BTDC at low manifold pressure and higher RPM. That engine would slowly and smoothly accelerate from 21 MPH in fifth gear, which was about 600 RPM.

Your higher compression should be possible. Pay careful attention to ignition timing vs RPM, intake air temperature, engine temperature, and manifold pressure to prevent detonation. You may need a knock sensor to get your timing fully dialed in. I would not be surprised if getting smooth running at low RPM required ignition timing a few degrees ATDC at higher manifold pressures.

If you are happy with less power, try a camshaft with delayed intake valve closing to get some Atkinson cycle effect.

BYD serial hybrids with direct top gear have an ICE running 16 to 1 compression,
I posted about it here"
https://ecomodder.com/forum/showthre...6-a-41587.html

The only other place I have seen talk of successfully increased compression without ping is here:
https://turbobricks.com/index.php?th...y-tried.66779/

I would say low hanging fruit is you want your intake charge as cool as you can get it.
In a dry climate; using an Ultrasonic Mist Maker (or Pond Mister) or 10 to produce max mist for per 'space required' for evaporation in the intake may work.

https://www.youtube.com/watch?v=jekXeBRZnGY

I tuned a few high compression K24's to run on 87, but it absolutely guts their low end torque, and they're very temperature sensitive. Best I can tell, OEMs get away with high compression on regular (without resorting to Atkinson cycle) by having very sophisticated knock detection, and very high resolution ignition tables. The ND Miata knock control is done via ionization detection through the spark plugs, and ignition control down to a tenth of a degree, just as an example.

There's very little downside if you're keeping revs up. Most of the ignition advance is lost below 2500rpm.

"...The Skyactiv-G[7] is a family of direct injection petrol engines. The engine compression ratio is increased to 14.0:1. To reduce the risk of engine knock at high compression, residual gas is reduced by using 4-2-1 engine exhaust systems..."
https://en.wikipedia.org/wiki/Skyactiv

Tuned length 4-2-1 exhaust system calculators are available online.
NB that the ...-1 pipe length and diameter is also important.
You can fool the exhaust into thinking it's exhausting into the atmosphere with David Vizard's Pressure Wave Termination Box, discussed in my other posts here.

Videos of the design how and why are available on his Youtube channel.
Videos of systems built by enthusiasts too.

There isn't really a magic bullet to solving the compression / knock issue. Adding a point of compression gives a few percent thermal efficiency, but unless you can run Atkinson cycle, you then lose that efficiency through retarding ignition timing, or you lose the monetary gains through high octane fuel. Turbos are just another way to get more compression, and come with the same set of issues. There are combustion chamber tricks, such as Logic's quoted tuned headers, changes to piston design or valve timing or combustion chamber shape, but these are largely outside of our control as lay people.

I'd wager the best engine swap might be one of the Toyota Dynamic Force engines. Honda never mated their highest efficiency engines to a manual transmission; the L series in Honda's hybrids were 13.5:1 CR in the automatics, but only 11:1 in the manuals. Mazda did Atkinson Cycle + manuals right, but due to cheaping out on materials, their efficiency is only mid 30's %, similar to the non-Atkinson Honda engines. A Toyota 3- or 4-pot Dynamic Force engine can reach 40-41%, they have manual transmissions available, and make decent power. Nobody else, other than perhaps Mercedes, seems to be building maximum efficiency gasoline engines.

This is an interesting read once you get into it: :)
https://turbobricks.com/index.php?th...y-tried.66779/
All sorts of testing and reporting back by engine builders.

Headers... Id just take it to someone reputable and ask for the equal length system and a pressure wave terminator. Plans in hand.
If I could afford it.. :)

I had this in a tab:
https://www.youtube.com/watch?v=5nKDNrUz5to

Cams: Same story.
If I could afford it! :)

Fuel and spark:
There I'm light.
pgfpro will know for sure. And about most else here.

And don't forget the water mist. As long as the vehicle is in a dry climate it will help.
I fill the house cooler up daily already. It's quite affordable.. :)

Shot for the engine info. Interesting! :)

That 16-17 to 1 BYD engine; I'd love to see stripped down.
What do you think we'd find?
Sodium-filled engine valves? :D

lot of swirl and quench, retard the cam

You know... I posted the video above as it's David Vizard.
But never watched it.
http://www.youtube.com/watch?v=jextyKc2UN4
David: Old and forgetting place names n stuff but he knows his s***! :)
'if you've got everything else (water injection included) right...'
"...We ran as much as 45 pounds of boost on 87 octane fuel.."

"...you got a 1 liter engine...with suitable water injection...?... the old 3 cyl chevy..??...a 100mpg vehicle..."
:eek: (eek? where's surprised? :) )

'inject fuel (and water) every 2nd stroke... every other stroke just inject water...'
a steam stroke... the droplet size is an important factor...'

Another person who doesn't follow your reporting?

I've got a Chevy 3-cylinder, but I don't know that I could manage the droplet size.

:o Ye... his videos are VERY long winded
I much prefer his books and written articles.`

Yes; he carries on about droplet size and getting the left over (unevaporated) droplet to turn to steam at just the right time.
But not much practical ; How To!

Even Aquamist's forum doesn't seem to have much droplet size info.
https://www.aquamist.co.uk/forum2/vbulletin/

The big Take Away here is that the correct amount of water injection with fuel and spark adjusted for it, allows much higher compression and the fuel savings that come with that.

From there one might play with different nozzles and pressures to try tweak droplet size.

I thought that was half of it. The remainder being the steam power power stroke.

What do you think are the proportions contributed?

The more I think about it, the more I think David passed from the realm of his experience into speculation at this point of his video.

Lets say we suck water mist only into a cold (room temp) engine.
The intake valves close and the compression stroke starts.
The increasing pressure increases the temperature of the mixture, where the heated air heats the water droplets, but it also increases the boiling point of the droplets.
So at what point, if ever, do the water droplets turn to steam?

This is the point at which I think David moves from experience into speculation...

If there's also fuel injected and a power stroke the pressure continues to climb past TDC, due to a dramatic increase in temperature. So at what point in the power stroke do the droplets turn to steam?

Then there's heat in the surrounding combustion chamber being absorbed where pressure would increase the rate of absorption, except there's a decreasing delta T...

Then there's evaporation occurring during this process....

Where (and when) do you want to inject the water?
Different places have different effects. Especially if direct injecting.

So...just how far down this rabbit hole of thermodynamic etc maths do you want to go!? :)
At some point, after much equation-ing, even the scientists say "Uck Fit! Lets just inject the damn mist (based on educated guesses) and see whatTF happens!?"

https://sci-hub.ru/https://www.scien...96890419300883

Also NB that Boric Acid is synergistic with water injection..!