I think that you should google it...
http://neubranderinc.com/blog/2007/0...soline-busted/

 

Heck no!!! My car ain't no experimental machine. If i did that and damage my engine, then it's all over and my warranty will be voided.

 

Other than a reference to Mythbusters this looks like more tests have shown positive results in MPG than not.

Apparently this is an older idea. Thanks anyhow for the info.

The plastic, paint and rubber solvent action would stop me from trying it!!

 

I use a gallon of xylene in my tank pretty regularly. It wont hurt anything and it has a native octane of 117.
It does actually increase the fuel economy slightly (in my case, about 10%), but it is typically up to $18 a gallon, so it isn't financially viable as a "mileage extender".
I just use it as knock-suppressant.

 

Great thread. A few comments...

The combustion chamber is not an area of flow. It's a chamber. Furthermore, with the velocity of air/fuel mixture entering the combustion chamber, there's no possible way that the flow is laminar. Additionally, turbulent flow is much better than laminar flow for even heat transfer (I spent a year and a half learning heat transfer and fluid dynamics and another 3 years operating a nuclear propulsion plant on a submarine). I'm not sure where you got this information, but it's obviously wrong.

The danger of knock is the pressure waves it causes as localized "explosions" occur randomly, often near the boundary edges of the combustion chamber.

A J&S Safeguard would solve this, although it's probably overkill for a non-turbo rotary. However, it's probably the best form of knock control on the market (it can even retard individual cylinders). I'm not sure how much use they've seen on rotaries, but I know they'll work.

That's not knock, that's normal. Every modern engine ignites the mixture before TDC. It's called advanced timing.

Detonation is most common at lower rpms under heavy load. The key to minimizing it is through good combustion chamber design, with quench pads that will squish the air/fuel mixture towards the center of the chamber, and keep it away from the edges. Actual mixing of the air and fuel is another factor. Not only does a better mixture promote even burning, but it will also result in less deposits built up in the combustion chamber, which tend to accumulate at the edges and heat up, causing the aforementioned localized "explosions".

It'd be interesting to use a Safeguard on an RX8 to see exactly how much more detonation occurs using 87 octane (AKI) over 93. I doubt it's a significant amount (at least on a stock vehicle), but the Safeguard is sensitive enough that even a miniscule amount would be noticeable.

 

The J&S is useless on the Renesis, boosted or not.

Detonation is most common at the torque peak, not low RPMs.

"Flow" in the combustion chamber is actually an issue in a rotary motor since the actual combustion chamber is always moving.

Welcome to the forum. Read the thread before you comment. Thanks.

 

Why's that? I'm curious, just because I've heard of it being used on older rotary applications.

No. It has nothing to do with peak torque, and everything to do with how slowly the engine is turning.

Flow is throughput. Moving a chamber around is not throughput.

Obviously I did (notice how I quoted other posts).

 

Because the mic can't discern actual knocking events from background noise and normal combustion fast enough to affect the timing in a meaningful way.
By the time a detonation event has occurred, it is already catastrophic.
Furthermore, the Renesis does not respond to timing retard in the same way as piston motors. If you could detect incipient knock and you responded with a few degrees of retard, you will actually trigger a knock event.


The chamber is moving (same explanation for your other misunderstanding below) - flame speed as a function of combustion cycle time is less important at the slow end than the fast end, especially when pressure rise time is fairly long.
Knock only matters in this motor (and is most likely to occur) when the Ve of the motor is maximum.

Throughput on this motor is a direct function of chamber forward velocity.

No, you read up to the point where you felt like commenting and not up to the point where the salient points were already addressed and dismissed.

 

Uh, knock sensor placement would determine how easy it is to discern knock from background noise. Regardless, the J&S is configurable and quite capable of adapting to various engines as well as any other knock sensor could, and is even capable of multi-sensor setups.

We're talking detonation here, not preignition. Detonation is rarely catastrophic unless it's occurring in large amounts. The J&S sensor is sensitive enough to retard individual cylinders the moment knock is detected.

That's what I'm trying to explain to you: it's NOT flame speed, it's the speed at which the combustion chamber is expanding.

Forward velocity? The chamber is rotating! You're not making any sense.

Well, I'm fairly sure I'm capable of controlling my own body, and I definitely remember reading the whole thread. So since you're not an internet mindreader, I'm just going to have to assume that my memory serves me correctly. I'm not sure what your problem is, I was simply trying to add to the discussion. I freely admit that most of my experience is with piston engines. However, most of what I said applies to the rotary, too. I simply wanted to correct a few glaring pieces of misinformation that I saw here.

 

I am quite aware of what the J&S is capable of. I've used that device many times over the past 15 years.
It doesn't work effectively on the Renesis.


"Pre-ignition" is detonation (though not the converse).
The first detectable detonation event in this application is usually its last and, as noted above, retarding the timing will not quench the next detonation event in the Renesis.


Then you don't know what you are talking about if that is your explanation.


In which direction is the chamber rotating?

Well, I'm afraid that adding to that misinformation is not an effective way of dispelling it.

 

speaking of which, the usual over the counter xylene is only 107 or so, 117 is reserved for a highly purified specific isomer of xylene

 

Two of the four isomers (108-38-3 and 106-42-3) have roughly the same motor octane number. That is the para and meta variants. Its around 126. Ortho-xylene (95-47-6) is around 102.
None is more "pure", they are just different isomers.
Off-the-shelf xylene (1330-20-7) is a blend of all three. The net (mean) octane is 117.

You might be thinking of toluene.

 

You've got considerable tuning issues if you're encountering combustion prior to the spark plug igniting. There's a considerable difference between that (and how it occurs) and typical detonation events.

I think you're the one who doesn't know what I'm talking about. The combustion chamber expands at a speed that is directly proportional to rpm. At lower rpms, the chamber is expanding slower. That leaves more time for pressure to build up in the chamber and create the conditions for detonation to occur.

That's not a direction. What is the direction of a circle's tangent? It would depend on where that tangent lies.

 

True and true.
Unfortunately, on the Renesis, it just doesn't matter. You cannot effectively alter ignition timing to quench detonation after a detectable event has occurred, regardless of the source.

Perhaps. But if it is this:

...then, again - you don't know what you are talking about. In the Renesis, abnormal flame front speed is only an issue at high engine Ve. Because the forward velocity of the combustion chamber is relatively high - even at low RPMs - and charge density is so low, "abnormal" combustion is, in fact, created intentionally by the trailing ignition.

In which direction is the chamber rotating?

 

rarson--you seem like a thinking kind of guy and thats good. I think too much sometimes.
Experience with recips does give you some basic knowledge of the rotary workings, but there are some very significate differences. Keep that in mind?
For example in a recip engine you do not have leakage of gases between the combustion chambers ( unless you have something very wrong!), and certainly you dont have 2 sparkplugs that fire at different times on the same combustion event during all rpms.
Just food for thought--ok?

Moving combustion chamber?? You lost me there! Combustion chamber doesnt move--its in the same place for every rotor face (hopefully). Combustion chambers only expand and contract--they do not move positionally---????

 

Uh, its called EGR. All piston motors have some form of EGR.
Rotary motors don't particularly need it because they are poorly sealed engines by design.

You really don't understand how the rotary works, do you?

 

I'd like to know how octane works in an RX-8. I heard no knocking in mine, and with previous engines, i would lower the octane. I didn't in this car, but always heard in a regular car the wasted octane would lead to more carbon.

 

Negative---egr is nothing like that. Slow your reading down.

Yes, i understand that a combustion chamber does not change position. What is inside the combustion chamber, changes positions and there are different designs and different styles of combustion chamber but the location of the chamber itself is basically the same--rotation after rotation. The shape changes, the volume changes, the colors change, the smells change, the composition of the surface changes and the temperature changes, but the position remains the same. If yours doesnt then you are a better turner than I thought!
Maybe you need to reboot?

 

Are you smoking crack?!?

The very nature of the rotary motor is that the combustion chamber is in constant motion. The intake charge is on a constant ride.

I can't believe I'm actually having to explain this to you.

 

This is for you:

http://www.youtube.com/watch?v=OuId4nuxXaM

 

And, for the sake of posterity, I am going to block off one of your possible back-pedaling possibilities: That combustion occurs in the same position inside the housing.
First of all, it doesn't - it moves forward and back based on ignition timing and load.
Second, that is the combustion phase of the combustion cycle. The chamber, however, moves with the charge.

It is completely unlike a piston motor where the combustion chamber is immobile and the charge sweeps in and out of it.

 

You do not have this in the rotary motor either. Each rotor is like a separate piston. But what you were thinking of (undoubtedly) is the "leakage" of gas from one combustion chamber to the next on the same rotor. This is functional EGR and it is accomplished on a piston motor through an external valve and, to some extent, through cam timing overlap.

 

Haha, MM pwns.

 

We are not speaking apples to apples obviously.
Chamber is defined "as an in closed space"
This chamber space inside the rotary engine never moves. It changes shape, yes. But the chamber itself does not move.
Take a snapshot of where the rotor is at a point in time. Mark it's spot. Now do one complete rotation of the E-shaft--no more, no less. The chamber will be in the same exact spot it was as before.
Now the combustion event INSIDE the chamber CAN occur in different areas of the combustion chamber according to what the engine has been directed to do, but the chamber itself is always available at the same spot.
It is the same for recip engines. Recips have a different shape for the combustion chamber but the combustion chamber itself uses the the same mechanical principle. All it is, is an available space for an combustion event.

The leakage between apex seals ( of course it is face to face---duhhhh) is not by design like an egr system. Jeez Jeff.
I would much prefer to have a totally sealed engine, but that has not been obtained as of yet. Rotary or recip.
Mazda acknowledges "spitback", Racing beat speaks about the small amount of combustion gas that gets by the seals, chatter marks etc-----oh wait a minute---you are in one of those debating modes.......nevermind.
OD

 

You are highly confused and, as I pointed out 3 posts up, I'm not allowing you to back-peddle with this sort of drivel. You got it wrong - terribly wrong - and you should probably sit down, shut up and listen for a change.

Rinse. Repeat.