roxxy

Hi there. I am currently doing a research on the Wankel's rotary engine and I wonder if any of you could help me out a bit. Move this post to the appropriate section if it's missplaces if you wish.

First of all, sorry for my bad english.

The things I would like to know are quite technical (based on an RX7, I dont know if the rotors are the same within the generations):

- The Width of the rotor, the height, the weight.
- Where is the precise placement of the 2 sparkplugs?
- Width of the internal gearing in a rotor of a RX7 (chose a gen, I have to make an example to calculations with the datas)
- The Width of the base of each dent on that gear
- # of dents
- Width of the gearing on the shaft
- Width of its dents
- # of dents
- In which material these 2 gears are made of
- Material used in the latest rx-7 or rx-8 for the rotor, chamber?
- The diameter of both gears.
- PSI boost of a twin turbo (stock)
- The compression ratio (10.0:1 ?)
- Information on the emissions of the exhaust cycle (% of fuel unburned, etc)

Also, If any of you has some idea of points on the rotary engine that makes it less fuel efficient than a typical 4-stroke engine, please let me know about it.

Also, if you have some technical sites talking about the pieces of rotary engines, let me know about it also.

Thanks ALOT.

PS: You can answer to just what you know.

kmaot

You can start here:

Link

but I don't think it really covers off your questions...

No7Yet

You've asked a lot, roxxy. I would suggest that you start by searching for SAE papers (http://www.sae.org). They're the authoritative source for such technical information.

Brandon
BR7 Racing

roxxy

Actually I'm doing a school research and I cant effort to buy these papers.

As for the rotaryengineillustrated.com , I already knew this web site, thanks anyways.

No7Yet

No worries. I'll give it my best shot!

RX-7s were sold from 1979-1995 in the USA. From 1979 to 1985, they all came with 1.15L engines (the 12A), except for a special model in 1984 and 1985, which had an optional 1.3L motor (the 13B). From 1986-1995, all RX-7s came with a 13B.

The 12A rotor width is 70mm. The 13B rotor width is 80mm. Rotors are a roughly equilaterally triangular shape, and have a generating radius of 105mm (according to Mazda). If you need the specific parametric equations which define the shape, I can post them.

Rotor weights and compression ratio can be found at: http://www.mazdatrix.com/faq/rotorwgt.htm

It depends on the year and engine. The only hard numbers I have are for the pre-89 12A. In this motor, the leading plug is 30mm and and the trailing plug is 18mm from the minor axis. In the post-89 13B, the leading plug was moved closer to the minor axis.

Sorry, I don't know.

The gearing is on the load side of the rotor (rotor gears), and on the side housing (stationary gears). The eccentric shaft, much like a piston motor's crank, has no gearing, but is rotated by force exerted on its lobes.

Sorry, dunno.

The rotor and stationary gears are made of stainless steel which I believe it milled. The rotor gears are held by either 9 (pre-86) or 12 (86 and newer) rotaries. The stationary gears are pressed into and bolted to the side housing.

While I can't say what the RENESIS is made of, all RX-7 motors have been made of cast iron (side housings), mostly-cast T6 aluminum with a chrome wear-surface coating, and cast iron rotors.

Sorry, dunno.

The FD boost pattern is 10 psi on the primary turbo, 8 psi during the transition, and 10 psi when on both turbos.

See above link.

Sorry, dunno.

For the last bit of stuff, SAE'd be the place to turn!

Brandon
BR7 Racing

No7Yet

<-- dum

roxxy

Wow thanks alot for your answers.

So In resume, the secondary gear is not making the shaft turn but its to maintain the epicycloid movement of the rotor? And the eccentric lobe on the shaft is the thing that is pushed by the inside of the rotor?

If so, could you tell me the height of that excentric lobe? Starting from the middle of the shaft? Or some other information on it?

Thanks alot

No7Yet

Yes, that's exactly right.

On a related note, it's the gearing ratio between the stationary gear and the rotor gear which defines the shape of the epitrochoid housing - with a k component of 4, for example, you end up with a 4-pointed rotor and a 3-"pointed" housing shape.

I don't have a motor pulled apart near me, sorry. There's no hard rule for the eccentric shaft lobe eccentricity, though - it is controlled by a few design considerations. If I get an e-shaft and a rotor in my hand in the next few days, I'll take some measurements for you.

Brandon
BR7 Racing

No7Yet

Wanted to clarify that... it should have read:

The rotor and stationary gears are made of stainless steel which I believe is milled. The rotor gears are held by either 9 (pre-86) or 12 (86 and newer) spring pins, which reduce gear loading. The stationary gears are pressed into and bolted to the side housing.

Brandon
BR7 Racing

roxxy

Thanks alot for the time you spend answering me!!! It will help me alot!!! You cant imagine how hard this information is to get on the net or in books.

I'd like to know something. Does the rotor make 1 rotation in the same time as the shaft does? I've read that it does not due to the ratio of the gearings but since the secondary gearing does not move, I'd need some clarifications.

Sorry about asking so many newbie questions.

No7Yet

No worries about the questions. I actually enjoy answering them.

The rotors revolve at 1/3 the speed of the eccentric shaft due to the gearing and it's planetary motion. The rotor gear engages and moves around the stationary gear. HowStuffWorks and RotaryEngineIllustrated have some videos which might help understand the motion.

Where are you, roxxy? I might be able to find someone with a torn-down rotary near you - nothing will help you understand the rotary better than seeing one work in person!

Brandon
BR7 Racing

Evil Aviator

The shaft makes 3 rotations for each rotation of the rotor due to the gearing as you mentioned. The tachometer shows the shaft speed, which is 3 times that of the rotors.

This SAE paper compares two different types of turbocharged rotary engines.
http://www.mindspring.com/~pko/13BTvs13BREW.html

Although this 4-rotor engine has quite a few differences from a regular street engine, there is a lot of technical information on this web page that may help.
http://www.mymazdarotary.com/mazda_r...paper_html.htm

More good technical information.
http://personal.riverusers.com/~yawpower/techindx.html

An affordable model of the 12A rotary engine is available online and at many hobby shops.
http://www.hobbysurplus.com/enginemodels.asp#rot

roxxy

Actually I live in Canada and I asked every mechanics place to call me if they get a rotary in their garage. You much know that RX-7's is hard as hell to find here. I think that it does not meet our emission restrictions.

I figured out this engine works, tks .

KevinK2

The rotary has more exposed suraces during compression/power/exhaust cycles. More surface means more heat loss the block ***'y. Here's a rough comparo I did:

thermal inefficiency

comparo with '2.6L' 944 4 cyl. I assumed spherical comb'n chamber, enlarged for same FD 9.0 compr ratio. adjusted bore and stroke from oem 2.5L, to get 2.6L with same bore/stroke ratio.

for FD rotor, R=105mm, and w=80mm. 40 cu-in face displacement. Determined contour radius is 7.67", and found larger radius for 5 cu-in chamber, then radius for 40 cu in displacement from there. also checked using flat chamber assumption ... about same results. I think the approximation of the chamber in the housing as a constant radius should be close enough for a comparo. Here are calc'd heat exchange areas, in sq inches:

944 ___ FD __ % more FD

Total @TDC

26.9 __ 51.0 __ 90%

Total @BDC

66.8 __ 86.1 __ 29%

NEW area @ BDC

39.9 __ 61.5 __ 54%

When things are the hottest near TDC, the area issue is the worst. Also a time factor. The rotary stroke is during 3/4 crank rev. while 944 is only 1/2 rev. The rotary will allow more time for heat exchange, unless typical rpms are 50% higher.

The 944 is a convenient comparo, as it fires 2 pistons per rev, and the rx7s fire 2 rotor faces per crank rev.

roxxy

That looks nice KevinK2. But being french, I dont know what "FD" is. Could you please tell me the diameter of the pistons of that 2.6L engine? Why do you say that the "total area" is not the same at BDC or TDC?

Thanks alot