max compreesion water injection

[SMOKEY44211]

Trying to get some info. Normally aspirated 87 octane gasoline fueled engine 2 valve wedge chamber dedicted pure water injection. What is the upper limit mechanical compression ratio before detonation threshold. There's a lot been written for artificial aspirated aplications. Blair and Heywood cite some examples but don't seem offer any limit. Vizard reports 18:1 kerosene fueled lab engine. The consenses is that it works but I haven't been able to get my eyes on anything that suggests what # would be optimum. ------Phil

 

[patprimmer]

There are two many variables to give a specific number including, but not limited to:-
Deck clearance.
Chamber shape.
Chamber, valve and plug finish re surface and sharp edges.
Water circulation and temperature.
Piston top geometry and finish.
Cylinder head material.
Head gaskt fit.
Inlet valve closing pont.
Ignition timing.
VE
Exhaust back pressure and scavenging.
EGR
Valve material.
Oil temperatue.
Valve seat geometry.
Valve spring seat ressure.
Valve fit in guide.
Valve stem seal.
Ring seal.
Oil consumption.
A:F ratio.
Air and fuel distribution.
Air fuel mixture quality.



Regards

eng-tips, by professional engineers for professional engineers
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[ca2sbl]

smokey44211:

Look at this page:

http://www.rbracing-rsr.com/waterinjection.html

Have fun,

Russ

 

[SMOKEY44211]

Pat I agree with you about the variables described. However if you look at the published cr ratio from the major automobile manufacturers designed for 87 octane fuel they all fall within half a point of 9:1. I failed to mention Ricardo because most of his research was with fairly low octane fuel. I have a four cyl. engine, iron block, aluminum 2 valve wedge chamber head. Ceramic coating on piston head, combustion chamber and valves. Cr is at 16:1 with a full time water injection system. Haven't run it on the dyno yet. I figured I'd check here as I suspect there is a higher optimum #. This is my first venture with this type of configuration so I don't have any data base or experience to draw from. I'll post results when they become available.------Phil

 

[patprimmer]

All my qualifiers not withstanding, 16:1 on 87 octane plus water injection sounds much to high to me. My thinking would be 12 or 13:1 CR tops.

Can you start your tests with say 100 octane and see how much water you need and what park advance you can tolerate. That might save an engine and indicate if you can push further with the low octane.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[Lou Scannon]

Smokey44211 , do you have analysis or data showing the advantage of 16:1 or higher compression versus a lower compression ratio?

 

[patprimmer]

Opps

Park advance should obviously be Spark advance. I hate this keyboard.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[GregLocock]

I'd thought the automotive diesel boys were tending to /reduce/ CR so far as they could these days, chasing real-world efficiency.




Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[adrag]

I thought that was for nvh reduction purposes. Reducing CR quiets the engine at idle quite a bit. Then higher boost pressures are run to bring the dynamic CR back up.

Alin

 

[dgallup]

I think there are two reasons the static CR on high speed diesels is coming down: NOx reduction & an increase in turbo boost pressure.

 

[curtis74]

Quote: "Pat I agree with you about the variables described. However if you look at the published cr ratio from the major automobile manufacturers designed for 87 octane fuel they all fall within half a point of 9:1."

Don't use manufacturer's published recommendations for anything but toilet paper.

Take for instance a traditional small block chevy, flat-top pistons, large-chamber smog heads, 8.5:1. You can run 87 octane all day every day. Swap to modern Vortec heads with smaller chambers, 9.5:1 compression, and still you can run 87 octane all day every day. The simple re-design of the chamber shape makes flame speeds much faster and you can use much less total ignition.

Factor in head alloy, piston configuration, EFI or carb, or any of the factors listed in patprimmer's post and the possibilities are endless. I recall reading an article about a high school shop class that built a chevy 502 with 12.5:1 compression, a 16:1 A/F ratio, and ran 87 octane with no detonation. It was all using a careful manipulation of the factors listed in patprimmer's post.

Sorry to be so vague, but there are just so many factors invovled that its hard to pinpoint. Give two builders the exact same set of parts and they will build two engines that have different detonation thresholds; cam ICL, ignition timing, quench height from the machine work involved, radiator efficiency... too much to predict

 

[dicer]

18:1 on Kerosene? Maybe with timed injection. Kerosene has a very low octane rating, and would knock up a storm way before low grade pump gasoline will.