You are currently viewing our forum as a guest, which gives you limited access
to view most discussions and access our other features. By joining our community, at no cost, you will have access to start new topics, reply to conversations, privately message other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join RX8Club.com today!
Way back when the 2 most common mazda wankels were the 12a and 13 b. I believe they also made a smaller than 12a engine for the r100 and of course we all know about the 3 rotor cosmo engine. The difference between the 12a and 13b is
the width of the rotors. fatter rotor, more displacement. does anyone know if the length of the rotor is equivalent to stroke in a piston engine? I'm sure there are computer models mazda has that can simulate any configuration. The renesis is just a very much improved 13b. Wonder if Mazda will give us a different engine. Wonder if
an engine with a longer "stroke" would produce more torque?Just some friday morning musings...
This ad is not displayed to registered and logged-in members. Register your free account today and become a member on RX8Club.com!
Way back when the 2 most common mazda wankels were the 12a and 13 b. I believe they also made a smaller than 12a engine for the r100 and of course we all know about the 3 rotor cosmo engine. The difference between the 12a and 13b is
the width of the rotors. fatter rotor, more displacement. does anyone know if the length of the rotor is equivalent to stroke in a piston engine? I'm sure there are computer models mazda has that can simulate any configuration. The renesis is just a very much improved 13b. Wonder if Mazda will give us a different engine. Wonder if
an engine with a longer "stroke" would produce more torque?Just some friday morning musings...
As rotors get bigger, rpms must be reduced because the combustion zone is in motion, and you are limited by how fast the flame-front of the combustion charge can move. As you increase rotor diameter the speed at which the rotor faces move relative to the housing at a given RPM, increases rapidly.
from Wiki:
Quote:
The largest Wankel engine was built by Ingersoll-Rand; available in 550 hp (410 kW) one rotor and 1100 hp (820 kW) two rotor versions, displacing 41 liters per rotor with a rotor approximately one meter in diameter, it was available between 1975 and 1985. It was derived from a previous, unsuccessful, Curtiss-Wright design, which failed because of a well-known problem with all internal combustion engines; the fixed speed at which the flame front travels limits the distance combustion can travel from the point of ignition in a given time, and thereby the maximum size of the cylinder or rotor chamber which can be used. This problem was solved by limiting the engine speed to only 1200 rpm and use of natural gas as fuel; this was particularly well chosen, as one of the major uses of the engine was to drive pumps on natural gas pipelines.
Nubo, Thanks for the wankel history! Zoom, 15b probably fatter rotor easiest to acomplish wouldn't you think? I'm still curious if increasing the diameter instead of width would be analagous to increasing the stroke hence more torque. What I'm wondering is if (hypothetically) 2 15b engines were developed one of them by increasing rotor width and the other by rotor diameter, would the second engine produce more torque than the first? I'll dig around and find the answer. Remember when GM was trying to develop the rotary and failed back in the 70's? Anyone know if they did it from scratch...or did they copy Mazda? Anyone know what was wrong with their engine? (other than having GM engineers at the helm )
Last edited by Wankel_lover; 09-01-2006 at 12:42 PM.
Way back when the 2 most common mazda wankels were the 12a and 13 b. I believe they also made a smaller than 12a engine for the r100 and of course we all know about the 3 rotor cosmo engine.
Flamefront propogation ranges between 1300 to 1800 feet per second in a piston motor depending on the fuel mixture, compression, and heat. Simply put, it's limited by the speed of sound although the fuel has some effect on velocity at the kernal boundary.
Large industrial diesels have the same problem but they tend to gain efficiency with larger scale - just can't turn as high of RPM.
Using side ports with wider rotors is similar to adding displacement without making the valves bigger. It will pump more just not proportionally to the displacement increase.
The real challenge for the rotory is to take more heat out of the combustion cycle. Too much heat is exhausted compared to a piston motor. Mazda found some good efficiency gains in extracting more energy from the heat by going with the side ports (sans peripheral port) and eliminating the intake-exhaust overlap.
I'm betting down the road they come out with a sequential chamber shutdown for cruising speeds.
I'll keep mine for at least 5 years and I'll bet the next generation is worth waiting for.
GM had a 6.4L 4 rotor engine in the early 70's... if they could have figured out the reliable solution to the seal issue like mazda eventually did, it would still be the most powerful stock rotary engine in a street car (420+ hp).
if you can't do the math, thats 1.6L PER ROTOR... flame front issues
The performance of the C 111 even with the three-rotor engine was convincing right from the start. In 1969, the Wankel engine developed 280 hp from 600 cubic centimeters of chamber volume per rotary piston and gave the car a top speed of 260 km/h; with this engine, the car accelerated from standstill to 100 km/h in five seconds. The C 111-II of 1970 was powered by a large four-rotor Wankel engine which developed 350 hp and gave the car a top speed of 300 km/h. The second C 111 accelerated from standstill to 100 km/h in highly respectable 4.8 seconds. While some of the engines in the C 111-I cars had still featured dual ignition which was difficult to adjust, the four-rotor engine was equipped with single ignition exclusively. Both engines were direct-injection units
....
In retrospect, Dr. Kurt Obländer, head of engine testing in the C 111 project, described the Wankel engine as follows: “Our four-rotor engine with gasoline injection represented the optimum of what could be reached with this engine concept. The multi-rotor design called for peripheral ports for the intake-air and exhaust-gas ducts. We were able to solve the difficult problems in engine cooling and engine mechanics by technical means. But the main problem of the concept, its low thermodynamic degree of efficiency, remained. Due to the elongated, not exactly compact combustion chambers, fuel economy was poor, resulting in high fuel consumption and unacceptably high pollutant emissions. These drawbacks were inherent in the design principle.”
Negative.
The side ports are already very close to the water jacket. If you enlarge the chamber, you need to enlarge the ports or it'll run out of air.
only if the engine is wider, but the engine can be bigger in all dimensions
)
Linear Mode
