Help me understand Fuel Burn
 

not a thred to bash or discuss how much gas the car uses. But to understand how it uses it. I have a question or two for those who know this motor because right now, there are things I don't understand.

A typical piston motor burns each cylinder once per "revolution", which is two piston throw's in a 4 stroke if I am not mistaken.. So the crank turns 360 degrees and you've got 6 total burns from your normal V-6. Am I correct so for?

With the Renesis, How many burns do you have per crank turn? Is that 6 as well?

Thank you

A "revolution" is just that- one revolution of the crankshaft. You mean an otto cycle (4-stroke) engine has one power stroke per piston per cycle- or two revolutions to one power stroke. I'll have to make an image of this later to actually figure it out, but I know offhand that rotor RPM is 1/3 of e-shaft rpm, so initially I'm guessing that a rotary has more power strokes per shaft revolution- 2 strokes/3 revs instead of 1 stroke/2 revs, if my math is right.

See... There's my confusion... Seems like each rotor turns multiple times per revolution of the crank, but how many combustions are there per crank revolution..??

other way around. the crank turns multiple times (3) for each full rotation of each rotor. When you are at 9000rpm readline, each rotor is spinning 3000rpm. But each 1 rotation of the crankshaft you will have 1 combustion event per rotor.

Now think about there being 2 spark plugs that each fire each time there is a combustion event - each e-shaft rotation and @ 9000rpm readline you are talking about 18,000 ignition events per minute per rotor.


From Paul Yaw (yawpower.com)


http://www.yawpower.com/dectech.html
http://www.yawpower.com/rotcyc.gif

http://auto.howstuffworks.com/rotary-engine.htm

http://www.rotaryengineillustrated.com/


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So with the rotary there are two combustions per revolution.

With the V6 there are 6 combustions per revolution.

We know what the volume of the combustion chamber is and we know what the range of accpetable mixture is, how does the renesis get even comparable fuel burn to a v-6? You'd think it would be much better.

No... in a V6, there are 3 combustions per revolution...

Remember, they're a 4 stroke engine, which mean on every fourth stroke, there's a combustion.

Nope, incorrect, a normal V6 or I6 will only have 3 combustions per revolution, not all 6.

i don't understand your question. reword please

I think what he's trying to say is why do rotaries eat gas like a V6.

Europeans consider the 8 as 2.6 liter because of the combustion chambers.

So think of it as a 2.6 Liter motor and that will explain the gas consumption.

Also, the car is tunned to run pig rich for emissions, which consumes alot of gas.

OK.. and they tend to run at higher RPM's as well.

I can see it I guess...

Poor fuel economy is because of the large surface area compared to chamber volume, and also that the four strokes occur in three different locations instead of a single cylinder.

That inlet/exhaust timing is via ports, rather than a cam which can be tweaked, is a factor.

FWIW, the firing frequency of a 2 rotor Wankel is the same as that of a 4 cylinder piston engine at the same rpm. We've had some amusing threads figuring that one out.

Ken

I think what seems confusing would be the confusion between rotor rotation and shaft rotation (RPM).

Every 1 ROTOR rotation there would be 3 combustion episodes, one for each side of the rotor.
But for each Rotor rotation there are 3 shaft rotations, hence 1 combustion episode per shaft rotation, per rotor.

Times 2 rotors = 2 combustion episodes per shaft rotation.

i thought we had a 2 stroke 4 cycle engine....

Nope. It's a 4 stroke. It has induction through ports and burns oil, like most 2 strokes, but it's a genuine suck-squish-bang-blow 4 stroker.

All part of the plan to further confuse the piston acolytes.

Ken

Wait wait so your saying my car doesn't have pistons?

Lots of good stuff about the differences between a rotary and reciprocating piston.

The simple side of all that was sort of added; pistons or rotor, the engine flows the same at any given RPM as any other typical 2600cc engine.

And yes, as was eluded to earlier, it is a bit richer then the distant cousin with pistons. Its a little more then that alone.

Piston engines are closer to a spherical shape in the combustion chamber which allows for much better control of detonation. To acheive the most power and efficiency a motor is tuned to the edge of detonation. Interesting thing is with all the extra parasitic loss of the valvetrain, a piston engine wastes more energy to turn over.

Rotary engines are far from spherical in the combustion chamber shape. While that adds more surface area to quench the air-fuel along the boundary edges the real issue is in the nature of combustion that leads to detonation.

To avoid detonation, two things are done; richer mixture and retarded ignition. Retarded ignition is why the Exhaust Gas Temp is so high, generally about 400° higher then a piston bouncer. That translates to about a 25% loss in efficiency. Typically with richer fuel mixtures another 10% loss is compounded. However, the reduced friction is a gain of about 10%, effectively negating the richer mixture loss.

If a higher octane fuel were available, maybe in the 140 range the timing could be advanced and the mixture leaned down to where a rotary is nearly competitive to a piston slapper. That is in effect the main reason Mazd played with the rotray on the hydrogen program; because it does deliver an equal level of efficiency with that fuel. Of course the drawback there is gasoline and most other liquid petroleum based fuels offer some lubrication qualities; not nearly as good as oil but certainly better then the water that comes from the by-product of burning hydrogen (or natural gas). So with those fuels the amount of oil injected increases substantially.

That kind of depends on whether you count the brakes... :)

Ken

2 "burns" per eccentric (crank) shaft revolution and airflow comparable to a 2.6L motor so it is most comparable to a 2.6L 4-cylinder in terms of airflow and combustion events.

i know their are 4 parts, but i thought rotaries did it in 2 strokes?

thats why we're consider 2.6 liter for sizing turbos and for classifying car class.

No...rotaries do all four strokes. 2-strokes only do squish-bang, with "blow-suck" taking place near BDC via pumping action through the crankcase. 2.6 (double the 1.3) because all four strokes for each chamber occur in a single rotor revolution.

Ken

Two Stroke

Aixro hasn't sold enough rotaries to do one for them yet. :icon_no2: