Engine technology thread.

[Dimman]

Originally Posted by serialk11r

Uh no...ignition is supposed to happen at maximum compression. The temperature is higher after ignition than before, otherwise your engine wouldn't make power.

Hmmm, can't help you with the chemistry I guess. I just know for peak power you want your AFR to be in the low-mid 12:1s and high 11:1s for a bit of a safety margin with boosted cars. And stoich is 14.3:1, which is okay for cruise and low load, but can blow up a boosted motor under load.

[1660]

The answer has to do with efficiency. A lean burn is most efficient and consumes a boundary layer between the flame and metal, increasing the temperature of the metal. The hotter metal also act to increase efficiency by promoting the combustion of the protective boundary layer and raising the temperature even more.

Running richer preserves the boundary layer and reduces metal temperature.

[serialk11r]

Hmmm so stoichiometric definitely burns hotter than rich, that's clear. So it's down to why lean is hotter than rich.

So a rich mix will produce the same heat as stoichiometric, but the extra fuel will both cool and increase heat capacity, thus lower temperatures but same pressure (hmmm this is a rather big waste of fuel :O). So if it's quite rich then I can see the temperature going down a lot. A lean mix produces less heat but hmmm I can't see it being higher than stoichiometric, but the temperature would drop less for each increase in A/F ratio than it would drop if you were decreasing A/F by the same amount, since liquid fuel has a very high heat capacity compared to air. Does this sound right to people who actually tune cars?

@1660 I think theoretically you always want stoichiometric because the extra air doesn't do anything, but in real world situations burning lean is an easy way to reduce fuel consumption since other methods of limiting torque output generally sap a lot of energy. However if the engine is built with intake duration reduction or something that accomplishes that and it can expand the exhaust to near atmospheric pressure, you definitely do not want lean.

[1660]

You're one tracked mind, so you really don't see the point. Higher temperature create engine problems like burnt valves. That's why they used EGR, exhaust gas recirculation, etc. to reduce combustion temperature.

[serialk11r]

Higher temperature = more power/efficiency in general, it's just the engineering limitations that create the need for those. I don't think EGR is relevant in this discussion.

What I was discussion was theoretical efficiency, which you don't seem to be catching on to. If you are running 100% intake duration then lean burning is more efficient since it reduces wasted pressure, but that's not really the point. A lean charge will theoretically never be as efficient as reduced amount of stoichiometric charge. There is no way a lean charge can burn hotter than a stoichiometric charge, since there is simply less energy released.

And maybe if you're going to try to throw something like the first sentence, you should use correct grammar. I was just pointing out a fact.

[WingsofWar]

i tune by EGTs on my rx7

AFRs are unreliable when it comes to a rotary, or any super high performance endurance engine for that matter.

Some veteran tuners told me once..reason why lean mixtures burn hotter is amount of oxygen present in the gasses after powerstroke. The more oxygen the more superheated the gasses get, and raises internal pressure..which damages seals, bearing, internals. Correct me if im wrong, but knowing that saved me from blowing up my current setup and running good power for a long time.

A stoich mixtures in my rotary shoots my EGT warning lights up the roof, and while i probably gain some power with a leaner mix..im also damaging my engine. Iv already blown 2 engines already tuning with AFRs only. Last time i check my AFR conversion tables I was at a happy average of high 10 AFR.

Tuning with EGT + AIT is the best tuning option because you can convert to EGT temps to AFRs and monitor before,during,and after...engine dynamic performance.

[Dimman]

Originally Posted by WingsofWar

i tune by EGTs on my rx7

AFRs are unreliable when it comes to a rotary, or any super high performance endurance engine for that matter.

Some veteran tuners told me once..reason why lean mixtures burn hotter is amount of oxygen present in the gasses after powerstroke. The more oxygen the more superheated the gasses get, and raises internal pressure..which damages seals, bearing, internals. Correct me if im wrong, but knowing that saved me from blowing up my current setup and running good power for a long time.

A stoich mixtures in my rotary shoots my EGT warning lights up the roof, and while i probably gain some power with a leaner mix..im also damaging my engine. Iv already blown 2 engines already tuning with AFRs only. Last time i check my AFR conversion tables I was at a happy average of high 10 AFR.

Tuning with EGT + AIT is the best tuning option because you can convert to EGT temps to AFRs and monitor before,during,and after...engine dynamic performance.

It's a rotary. Just driving it damages the engine.






heh...

[bigbcraig]

Oh be nice. Have you ever driven a rotary? After driving an RX-8 for one day I had buyer's remorse for months about my WRX.

I don't care if you need to tear apart a bone stock one down to its rotating assembly every 60,000mi to replace the apex seals. They feel like no other.

... and boxers are supposed to be smooth

/iswearimnotafanboy

[Exage]

I can't recall the last time I saw a R3 on the street... You have to be a true rotary-head (perhaps a bit insane as well) to order a new one here considering the price is on par with WRX STI and EVO X.

I was mulling over on used RX-8s when I came time to replace my first car. They were a couple grand more then I wanted to spend at the time so I didn't (among a couple other reasons).

The auto magazines were going off last week about the possibility of the 16X featuring laser ignition instead of spark plugs.

[WingsofWar]

Originally Posted by Exage

I can't recall the last time I saw a R3 on the street... You have to be a true rotary-head (perhaps a bit insane as well) to order a new one here considering the price is on par with WRX STI and EVO X.

I was mulling over on used RX-8s when I came time to replace my first car. They were a couple grand more then I wanted to spend at the time so I didn't (among a couple other reasons).

The auto magazines were going off last week about the possibility of the 16X featuring laser ignition instead of spark plugs.

Mazda is looking at the technology of laser ignition, but they are probably not going to pull the trigger on it just yet. For obvious reasons, says a source I cant disclose.

While i agree that the WRX STI and EVOX are overall better cars than the rx8, especially at the price point. The RX series FC/FD and the rx8, SE....gives me a completely different driving experience than any sports car iv ever driven. I almost feel like my entire soul is being sucked into high heaven..and even if i was going slower than any other cars..i wouldn't know it, because i'm just in a entirely different sort of world behind the wheel of a rotary car.

Am i a fan of a rotary engine? yes! Is it a good engine? compared to a piston engine no...

But you sir are a smart man for not buying an rx8. Sometimes my friends ask me about buying an rx8..and i always recommend no. But if they go ahead and buy one despite my recommendations..massive kudos!

[Exage]

I can see problems that would plague Mazda trying to implement laser ignition at this time. I'm sure we'll see it sooner then later though due to the cut throat emissions standards that continue to be implemented.

The RX-8 will always have a place in automotive history. I thought it was a very interesting take by Mazda and a fantastic car at introduction. I do hope it's replaced with a more direct successor to the RX-7.

I unfortunately have yet to drive a RX. I can related to the power delivery, but not the weight and it's distribution coupled with smoothness of the engine. I should really engage in more test drives... Also, much respect for keeping a FC on the road. I'm sure she's a great example!

[Dimman]

Rotaries feel and sound weird. It ain't natural dang it!

My rotary distrust comes from a former co-worker who was a rotor head. He would talk about all the wonderful properties of the 12A and 13B. But he was ALWAYS working on them. I've handled pretty much all the moving parts of a rotary that he has brought in at one time or another (not that that's a lot of parts, btw...).

I envy their weight and packaging, though.

As for the 16X, laser ignition sounds like it's still very experimental.

[Dimman]

I've been thinking about cams lately. Lift, duration, overlap, intake velocity, scavenging, etc...

Anyone want to expand on these?

[Snaps]

^ I would love to, but I don't have the knowledge...At most mine is basic:

Lift: How far the cam lobe moves the valve - higher lift = more area around the valve for the air/fuel mixture to flow = more power in most cases. Too much lift can turn a non-interference engine into an interference engine, which is generally bad.

Duration: How long the valve is held open (measured in degrees), larger duration = longer time for air/fuel mixture to fully fill the combustion chamber. In reality, there is an optimum duration for each engine dependant on how much the head flows, the displacement of the engine, etc. If the piston begins to travel toward TDC and there is less pressure in the cylinder (compared to the pressure in the intake ports), the valve should stay open until the point where there is no difference in pressure. However, this is limited by the movement of the piston -If the piston gets to TDC (combustion stroke) then the intake valve needs to be closed before the spark plug fires.

Overlap: The amount of time the intake and exhaust valves are open at the same moment, don't know too much about the benefits of increasing/decreasing this, so I'll leave that to someone else

Intake velocity: A higher Intake velocity means more air flow into the cylinder when the intake valve is open, this obviously means more fuel can be used, and more torque can be achieved. A high intake velocity at low rpm is achieved by using smaller intake ports, this means the air travels faster into the cylinder compared to an engine with larger intake ports. However, by having smaller intake ports, you 'choke' the engine at higher rpm where the engine needs to flow much more air. Small intake ports are more generally used in Family sedans, V8's, etc. where the aim is to achieve a higher torque for the type of car (i.e. family sedan is likely to be driven around town a lot, it is more efficient to have more torque in the lower rpm ranges).

Larger intake ports cause a slower Intake velocity at lower rpm, which causes less torque, but these engines usually create more torque in higher rpm's (as this is when the Intake velocity is high, and the engine is not being choked by small intake ports), because of the higher rpm, the engine creates more power with the available torque (Power = [Torque x RPM]/5252, increasing rpm while maintaining torque will result in a higher power). Engines with larger ports are generally used in racing, where the rpm's are always kept high, and the larger ports create the same torque at those higher rpm's.