RWagz

I thought it was just that rotaries are less tolerant of detonation?

rotarygod

Ever watched mythbusters? It had nothing to do with the paint!

rotarygod

Correct. They aren't any more likely to detonate than a piston engine is. The problem is that apex seals don't stand up to detonation in the same way that piston rings do.

kartweb

Paul,

I'll give you the simple side and if you're interested PM me.

Combustion chamber shape. The ideal shape is spherical - as there are two thermal sources one much faster then the other. Generally, the further apart the kernal is from the secondary propogation the greater the flamefront collision losses from the detonation effect as the timing differntial between the two sources allows the secondary propogation to grow in size.

Despite having two plugs (and therefore some detonation already designed in) the shape of a rotary combustion chamber creates longer distances for the thermal transfer sources.

Moreover a rotary aggrevates the shape challenge by rotating away from the kernal center. The longer "stroke" of the 16X will add to that challenge having a higher peripheral velocity.

Regarding the Hindenburg, one could speculate but read for yourself from wiki.

http://en.wikipedia.org/wiki/Hindenb...ster#Fuel_leak

My apologies for moving off center from the 16X Tech discussion however the use of hydrogen as a potential fuel source coupled with the detonation challenges that are left on the table to solve made it seem somewhat related.

rotarygod

Timing split plays a huge role in detonation resistance. That's why you increase split to decrease knock. If you pull them far enough apart, a rotary is no more likely to detonate than a piston engine. With split narrow, you are far more likely to.

Mazmart

iTrader: (12)

Appreciate it Kart. I'm aware of the ideal combustion shape and the rotary is probably the worst in a production vehicle by nature of the terrible area of flame propagation. The reason I asked is that rotaries were previously known (Pre Renesis) to be more resistant to detonation than their piston counterparts allowing the useage of relatively low octane fuels. I'm open to correction in an open forum on this.

Paul.

ASH8

^^ Yes Paul, this side of the world, early Rotaries were required to run "Standard" or the lowest octane fuels available.
Back then we had 2 choices, Standard or Super!

Super was the highest octane available.

Mazmart

iTrader: (12)

And Downing Atlanta (Our parent Company) ran Regular 87 from the pump rather than race fuel until they were forced to do otherwise by regulations.

Paul.

ASH8

^^^ Back then using Super Grade (High Octane) made little to no difference in performance or MPG.

In fact the use of Standard Grade was a real selling point as it was around 20% cheaper per gallon....for memory ?!?///?"!"!

rotary crazy

my race car makes less hp on premiun than it does on regular 87 octane, I still use it on track

kartweb

Earlier factory motors were pretty mild compared to the Renesis state of tune. Progressively Mazda continued to make mild gains with the NA motors reaching somewhere around 160 HP with higher compression rotors. But they still ran air pumps - and the only reason an air pump is added is to clean up an over rich condition, and most likely that was to help manage detonation. BTW most piston cars that ran air pumps did that more to manage NOx then detonation.

The Renesis is pretty much at the best state of tune Mazda could produce in numbers. Very little bolt on gains, but more important, Mazda wanted to provide both power and fuel mileage to the best of their ability.

IMO when comparing a piston motor to a rotary I look at both ends against the middle; The front end is fuel consumed, the back end is EGT, and the middle is power. A rotary takes more fuel and produces a higher EGT to produce the same power. Even though the Renesis has made some improvements it still requires an over rich condition almost certainly to inhibit detonation as the rotary is very kind with NOx emissions (even with high compression). Not to mention the EGT is at the edge of deadly to the cat in stock tune.

The 16X gives Mazda a "clean sheet of paper" approach. After over a century of reciprocating development, rotaries are still in their relative infancy. I think Mazda knows that there are still many subtle improvements that could fast forward the evolution of the rotary, particulary as new fuels may be introduced. Two of these "future" fuels ethanol and hydrogen both offer improved detonation resistance. Frankly is surprises me that Mazda isn't making the most of ethanol, but from a marketing standpoint that's not where the best bang for the avant guarde development buck is today.

T-von

Why is detonation in discussion here with the 16x? Detonation is more of a problem for boosted rotary's (not NA). A NA rotary is more likely to die from excessive carbon build up (compression loss) and over heating than from detonation. In 16 yrs I can't recall of any situation on a NA rotary street car that lost an apex seal due to detonation.

Renesis_8

probably beacause there is nothing more to discuss
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Easy vape

chetrickerman

ethanol blows ***. **** fuel, thats why mazda isnt looking into it, and rg along with a couple other people established that hydrogen sucks.

but kartweb, i completely agree with you on mazda's clean slate with the 16x. the rotary engine is still a baby, we do know a decent amount about it, but not even close to everything, or as much as we know about otto cycle engines

feelthesweetbea

1. why r the injectors located where they r and not closer to the plug, between plugs?

- The injector is located there for cost reasons... Mazda, through testing, found that the benefit of direct injection can be had at this location as well. With the way the air moves in a rotary, there is a counter clockwise vortex at the leading edge of the rotary face (Naturally aspirated... i know for sure... FI... not so sure). If fuel is injected into this vortex, it will remain there as the rotor begins its compression stroke and thus provide a leading edge stratified charge. The magnitude of this vortex depends on the geometry of the "tub" or recess on the rotor face. I haven't seen the engine in person (i hope to this weekend at the la auto show) but i bet that the tub is deeper on the leading edge side than the trailing edge side. Back to cost... it is cheaper to use low pressure fuel system than high pressure system, which would be necessary if the injector was located near the spark plugs. with the rotary... this is NOT necessary to obtain a stratified charge. Another check in the "Rotaries are more awesome than piston engines" list. (SAE Paper 930678 "An Experimental Investigation on Air-Fuel Mixture Formation inside a low-pressure direct injection stratified charge rotary engine" Y. Hasegawa and K. Yamaguchi, Mazda motor corp)

4. it appears as if the 16x dish on the rotor face is longer, how will this affect combustion?

-Thermal dissipation will be greater, however with the longer stroke i bet we will see a net gain in thermal efficiency.
-flame front will need to travel further along the surface (with direct injection strat charge, we may see an air-fuel mixture that will burn more on the leading edge anyway, thus reducing this detrimental effect?).


oh an my sig is wrong... i have a TII and a FD.

zoom44

hello feelthesweatbea- havent seen you in forever

arghx7

In terms of gas mileage, yes a rotary takes more fuel. But they do not necessarily run any richer than a piston engine under WOT (idle is another story). On my n/a 2nd gen I ran 13:1 across the board under WOT and I made 172 to the wheels, which is 50hp over stock in those cars. So what do you have to back up this claim? Stock the car is typically in the high 11's or so. How is this any richer than a piston engine typically runs? Manufacturers make cars run rich for safety.

And one of the main reasons why they run such high EGT's is that there is no valvetrain for the exhaust to go through to allow it to dissipate heat.

feelthesweetbea

hey, yah i generally just float around... not responding to much. i was on the board more before i bought my 2 rx-7's

Mazmart

iTrader: (12)

Although this isn't 16X specific, I just had to share the weird stuff I observed today: The new oil metering system on the 09s uses 2 metering pumps to supply the 6 nozzles and the metering pumps are on top of the motor. Truly interesting to say the least!

Paul.

Renesis_8

Nice!
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Effects Of Zoloft

zoom44

i have established that RG is wrong

kartweb

Very few people seem to understand detonation and considering the physics behind it, thats very understandable. Don't take that the wrong way its certainly not intended in any offensive manner.

Simply stated, the wankel has an inherent detonation problem due to the shape of the combustion chamber. There are three easy ways for the design engineers to deal with it;

1) Lower compression
2) Richer mixture
3) Retard the timing

In all cases they are at best a compromise so depending on what's needed is what's selected. Obviously compression tends to be static, but if they chose to (and they didn't) they could have added an EGR system to emulate lower compression at least to an extent.

That should answer why they run richer under some conditions.

Now regarding the lack of valvetrain, a 2 stroke also has no valvetrain. Look at any typical shifterkart and the EGT measured 6" from the piston runs about 1350° F at peak power. To extend the powerband on a 2 stroke the timing is retarded to put more heat in the pipe raising the temp and velocity, emulating a shorter pipe - extended 30 second bursts on a road course may see 1400° EGT - but at lower HP then it produces at 1350° at a lower RPM. Overrev.

Where all this applies to the 16X is the newer profile would appear to make the detonation probelm worse - but one has to believe that Mazda Engineering has figured something out that would make that a moot point. Could it be the direct injection system?

FloppinNachos

you blow ***. alcohol fuels run cooler have a higher octane and are oxygenated.

RWagz

...and produces about 37% less BTU (energy) versus gasoline (volume).

Razz1

I read the 09 version does too!