Tuning for water injection: fuel, ignition, and EGT

[Richard L]

Thank you guys for chiming in.

I often wonder how difficult is to to tune to towards MBT with different burn rate, bore/stroke and combustion chamber design. For day to day and non-crucial tune (based on a square bore/stroke ratio), I think I would work on pump fuel plus 50:50 methanol/water and try to get the best possible outcome, because all the ingredients are easily available. This is what we have been trying to do all along.

I am hoping to find a way improve the flame speed on 50:50 mix and gain MBT without over-advancing the engine, do you think a small percentage of nitromethane will alter the flame speed in the right direction?

[hotrod]

The best way to safely tune for MBT (minimum best torque timing) is to find max power and then back off timing until you see a 1% power drop. That will ensure your on the safe side of the "Hump". (or an aproximate equivalent is find knock then back off 2 - 3 degrees)

There is very little change in power for the timing that brackets max power and a timing spread of maybe 8 degrees from too advanced to too late timing. Very hard for even the big guys with the expensive toys to find the absolute peak.

As far as the nitromethane I'm not sure I understand it burns quite slowly but can't say for sure. I know propylene oxide will speed it up --- but unfortuantely is sometimes speeds up combustion when the car is not even running ---- makes things go boom and people drive over their crankshafts.

The ideal timing will only change slowly with boost, so you could safely find best timing at a moderate boost level and then gradually pull back timing as you add boost.

Larry

[JohnA]

Just a quick note about NACA and SAE papers:

They are usually based on engines with combustion chambers inferior to those we use, so their AFRs might have to be richer just to catch up because of poor atomisation (usually they have no squish, swirl or tumble, hell not even fuel injection often)

Then we have the fuels themselves, they can vary a lot. Even recent SAE papers are based on test engines that would mimic model "T" quite well :lol: and fuels used could be worse than those found in the backstreets of Delhi in plastic containers. That is how you get the range of 80 to 100RON, while we'd be more interested in 95 to 115RON :wink:
The range is still 20RON but I'd bet that the flamefront would move differently.

[Richard L]

I am trying to clarify between knock threshold and MBT.

Tuning these days, knock threshold arrives much early before reaching MBT, it appears that no one are too concerned about MBT. I wonder if it matters or not whether if MBT is the main aim anymore?

The general road car tuning strategy seemed to be accepted as follows:

Run as much boost until the flow linit of the turbo is reached, dumping as much fuel as possible until egt is below 900C. Wind on as much ignition retard as possible until knock disappears.

I was wondering if this common method can be improved? with or without water injection.

[hotrod]

I agree I think trying to run ideal ignition timing is not as popular as it was in the past. I still think you should try to stay as close to ideal timing as possible.

Food for thought, the aircraft folks probably have done more testing and development on high performance piston engine in high load environments than all the automotive folks combined.

Many of them have timing fixed near ideal timing for max power. The way they handle max power for take off is they richen the mixture until the engine runs rough and then crank up the boost to the maximum recommended manifold pressure ( just short of det).

I think we should look more at managing boost pressure curves and less with playing games with the ignition timing.

I think the issue is it is much easier from a control system point of view to solve problems by pushing the timing values all over the map. It is much more difficlult to get fast acting stable boost control with enough head room so you can reach knock limited performance at high rpm with boost rather than ignition timing.

Most street turbos simply can't deliver knock limited boost at high rpm.

So they fake it by jacking in a lot of ignition advance, and create an electronic variable compression ratio by lighting the fire a bit early. It works to a point, but in theory it should not produce as much power as maintaining ideal timing and running the boost necessary to reach the knock limit.

Larry

[HOODEY]

The main subject in these threads is Detonation. There is the assumption that It can be detected.

How do you all guys go about detecting detonation????

[hotrod]

In real time -- the modern ECU's monitor for knock at least through the moderate RPM ranges. The Subaru ECU quits listening for knock at about 5700 rpm or so, as do many others becasue it is too hard the distinguish det from normal engine noise at high rpm, and engines are much less likely to have serious detonation at high engine rpms.

For after market solutions the "knock Link" is pretty popular. It is a add on knock detector with adjustable sensitivity. If set up right is appears to be quite effective.

In some cases -- especially on NA cars you can hear the detonation due to the characteristic knocking sound or sharp pinging sound.

After the fact, reading your spark plugs is still the final word on if you are experiencing detonation. Detonation causes some characteristic changes in the sparkplug appearence. In mild cases you get what is often called "salt and pepper " on the plugs. Small dark specks on the insulators (the pepper) are carbon blown off the inside of the combustion chamber. This appears first, then you get very small balls of aluminum that are so small you need a 10x magnifier to reliably see them. This is the "salt". It looks like white "dust" all over the spark plug electrodes to a casual observer. On close examination under magnification they are nearly perfect, brilliant silver colored balls of aluminum stuck to the spark plug electrode.

When you see these its time to back off, because they are bits of aluminum blown off your piston crown and combustion chamber.

The next steps are the plug it self begins to show the beating it is taking. The insulators can crack, the electrodes begin to get an "abraded" appearence -- all the sharp corners look like they have been chewed off by a very small animal.

Next sign is usually lots of smoke out the tail pipe as you hole a piston or break a ring.

Larry

[Richard L]

Originally Posted by hotrod

.... As far as the nitromethane I'm not sure I understand it burns quite slowly but can't say for sure. I know propylene oxide will speed it up --- but unfortuantely is sometimes speeds up combustion when the car is not even running ---- makes things go boom and people drive over their crankshafts....

Larry

Propylene oxide:
C3H6O -soluble in water and methanol

Nitromethane:
CH3NO2 -soluble in methanol

Will look into it.

[HOODEY]

With the Knock Link how do you set the sensitivity. Two little sensitivity will make the unit appear not to detect knock...Too much will make it seem as if there is knock when there is none...

[hotrod]

VERY BIG CAUTION with Propylene oxide: it was banned in NHRA due to some serious accidents as I recall.

It is a suspected carcinogen, it is not compatible with copper and there are cautions against mixing with more than 2% water.

Propylene oxide reacts with water to produce propylene
glycol, dipropylene glycol, tripropylene glycol and higher molecular weight polyglycols.

Hazardous Polymerization: Will occur. May polymerize violently, especially
in the presence of aqueous sodium hydroxide, chlorine, ammonia, strong
oxidants, and acids. If polymerization takes place in container, there may be heat and a violent rupture of container. Hazardous polymerization can occur when in contact with highly active catalytic surfaces such as anhydrous chlorides of iron, tin, and aluminum; alkali metal hydroxides; and peroxides of iron and aluminum.

Violently reacts with acetylide-forming metals such as copper or copper alloys.
Conditions to avoid: Ignition sources, temperatures above 50?C or 122?F,
confined spaces

In bulk form it may explosively polymerize, and has a very low boiling point ( 93 deg F. ) which can lead to high pressures in containers, and unitended exposure to vapors.

http://www.bndrc.com/pdf/Pro-Oxide.pdf
http://www.scottecatalog.com/msds.ns...5?OpenDocument


Don't even think of messing with this stuff, it kills people!!


Larry