Mazda stops making Wankels

The Rotary Engine is DEAD.

Remember this commercial for Wankel from the 1970s: https://www.youtube.com/watch?v=oHzeGEHWMjo - I sure do.

We had a cat at the time we named Mazda because he purred so much.

I loved my '91 RX-7, but that article is from 2012

It’s a shame, really it is. In the world it was originally introduced to, it was a wonder of science. Fewer moving parts, no valves at all, beautiful power curves, etc. The wipers, or “apex seals”, had to be replaced every 30K or so, but the whole mill was so simple that it took a fraction of the time required for a ring job for a piston engine. If the builder wanted more power, he could stack on another rotor.

Gas was cheap, and clean air standards hadn’t tightened yet. Everything was jake. If I remember right, the killing blow was the new EPA reg that said the engine had to meet specs for 50 K miles without major repairs. The Wankel of the time could meet the spec, but when the seals wore, it smoked too much.

Alas.

So sad. My first car was an 86 rx-7. Sure enough, I blew the seals on it at like 85k miles. Also, was doing 90 in third gear while merging onto the freeway after a shitty day at work.

Jerks

I was under the impression that Mazda was planning to develop a new rotary engine and start using it again in a new version of the RX-8 or the like.

A guy who has ideas to improve wankel shortcomings.


And a 12 rotor wankel:eek:
https://www.youtube.com/watch?v=Q2IFWveYBRs

Huh. I thought that was just snow on your mustache.

The rotary engine was nice but intrinsically flawed. They typically lose compression around 60-80,000 miles. I bought an RX-8 brand new the first year they came out in 2004. Now I knew you had to baby these cars and I did, making my original wankel make it to nearly 120,000 miles (yay?) before needing to replace it. My rebuilt “new” engine, which cost me over $6000, lost compression after a paltry 60-some thousand miles.

Though not as cheap as it is today.

One of my best friends from high school was one smart kid–we are talking a 4-year everything paid ride at MIT smart. He told me that his greatest joy was when he was registering his car with a Wankel engine at the Department of Motor Vehicles, the clerk got a “blue screen of death” look in his eyes when he answered “Zero” to the number of cylinders…

From what I know about that type of engine is that by design limitations they burn oil and tend to have incomplete combustion on top of that, so they can’t get past current emission standards.

Compared to a conventional piston engine, the combustion chambers of a Wankel engine have a high surface-area-to-volume ratio. This has a couple of important consequences:

[ul][li]The flame front can’t reach all the way to the walls of the combustion chamber, leaving a thin layer of unburned mixture (see flame arrester for explanation of this phenomenon). This is true for conventional piston engines as well, but the relatively larger surface area of the Wankel combustion chamber results in higher emissions of unburned hydrocarbons. You can fight this with a bigger catalytic converter, but at some point the expense/packaging requirements get to be just too much.[/li]High surface area also means relatively high heat loss; a larger portion of the heat of combustion gets dumped into the engine block (and ultimately the radiator) instead of being converted to mechanical work. This means crappy efficiency/MPG. Unlike the unburned-HC problem, there’s not a lot you can do about this.[/ul] So it ends up being a double-whammy: compared to a conventional piston engine, a Wankel needs to burn more fuel to get down the highway, and it makes more emissions per unit of fuel burned.

So, where do the Wankel wankers go now?

We’re back to Otto cycle pistons now; I guess the Wankel wankers are now Otto-eroticists.

[quote=“Machine_Elf, post:15, topic:744429”]

Compared to a conventional piston engine, the combustion chambers of a Wankel engine have a high surface-area-to-volume ratio. This has a couple of important consequences:

[ul][li]The flame front can’t reach all the way to the walls of the combustion chamber, leaving a thin layer of unburned mixture (see flame arrester for explanation of this phenomenon). This is true for conventional piston engines as well, but the relatively larger surface area of the Wankel combustion chamber results in higher emissions of unburned hydrocarbons. You can fight this with a bigger catalytic converter, but at some point the expense/packaging requirements get to be just too much.[/li][li]High surface area also means relatively high heat loss; a larger portion of the heat of combustion gets dumped into the engine block (and ultimately the radiator) instead of being converted to mechanical work. This means crappy efficiency/MPG. Unlike the unburned-HC problem, there’s not a lot you can do about this.[/ul] So it ends up being a double-whammy: compared to a conventional piston engine, a Wankel needs to burn more fuel to get down the highway, and it makes more emissions per unit of fuel burned.[/li][/QUOTE]

Couldn’t they just make the combustion chambers smaller and put in some more of them?

Once on “To Tell the Truth” in the 1970s the contestants were women who had. . . something to do with automobiles. Don’t recall exactly what. Anyway, Nipsey Russell asked one contestant, “Are you familiar with a Wankel engine?”
She thought somewhat wistfully, and said, “I haven’t heard of one of those in a long, long, time.”

Nipsey did not vote for her.

If you take a given 3D shape and make it smaller you actually increase the surface-area-to volume ratio.

Take a sphere, for example: SA/V = (4pir[sup]2[/sup])/(4/3 * pi * r[sup]3[/sup])

The ratio scales with 1/r; make r smaller, SA/V gets bigger.

Take a cube: SA/V = (6 * L[sup]2[/sup]/L[sup]3[/sup]

Again, SA/V is proportional to 1/L.

The V-10 and V-12 piston engines you see in supercars are smooth, high-revving and low-inertia, but they sacrifice efficiency to obtain those characteristics. There’s a reason econoboxes are powered by 4-bangers.

Same is true for the geometry of the Wankel’s combustion chamber: one giant rotor would be more efficient than a multi-rotor engine. To the extent that multi-rotor Wankel engines were produced, it was generally for higher performance cars that needed more power, but still wanted smooth power output and may have had to deal with under-hood packaging constraints. Taken to the extreme, four-rotor engines were produced for racing teams.