Erv187

do you think that if we increased the compression of our engines, would it work or would it run less efficient? say if we used 12.5:1 compression would that increase the torque a little?

rotarygod

You already have the highest compression rotors of any rotary. There actually isn't any more power to be had with any higher compression than it has now. Mazda did tests years ago to confirm this. You actually wouldn't make any more power at 11:1 than you would 9:1 and 12.5:1 would do nothing but make far less power and be more prone to detonation.

mikefrombarrie

So why is the renesis 10.0:1 then?

neit_jnf

higher compression increases the chances for detonation and the requirements for premium fuel...

very few gas powered cars (piston or rotor) have above 10 or 11:1. The only ones I've known that use 12.5:1 or even 14:1 are gasoline direct injection spark ignition

16:1 and above you go into diesel territory, the high temperatures reached by such high compression ignites the mixtures without a spark

higher compression on a rotary is more difficult to achieve than a piston because of the seal design, it would introduce too much blow by of compression been lost through them. The testing Mazda did proved this. To get higher compression the side as well as the apex seals would have to be redesigned.

There were prototypes of diesel powered rotaries that used special L-shaped side seals and twin-stage compression (a smaller rotor pre-compressed the charge before it entered a larger rotor to be further compressed). The L-shaped seals allowed for the higher pressures as these pressures actually forced the seals out of their grooves towards the side plates.

brillo

the limit's RG is referring to were discovered in the late 70's early 80's before the advent of good computer modeling and fuel control. I bet that when they were designing the Renesis about 8 years ago they found with more advanced computers they could squeeze a little more juice out at 10:1.

Higher compression does trend to lend it self towards more risk of detination, but again, our cars computers can do a much better job managing that risk than 25 years ago.

guy321

Actually, I think that RG was speaking about diminishing returns... Our engine at 10:1 or 1 is at it's most efficient and if you were to go higher it would be the EQUIVALENT of going back down to 9:1 in terms of power. ADDITIONALY you would be more prone to problems with the higher compression ratio.

Rasputin

The main objective in incresing compression ratios in production car is to increase part throttle fuel economy. And as there are no variable CR engines just yet (Miller / Atkinson-cycle engines excepted), the engine compression ratio remains a compromise between part throttle fuel economy and WOT knock limitations.

MrWigggles

I think you guys are all correct (except the original poster, sorry Erv.)

-Mr. Wigggles

pimp20g

my 02 celica GT-S was 11.5:1 and RSX Type S are 11:1

longpath

iTrader: (1)

Sorry to revive a long dead thread; but, since people here get so upset about asking questions without searching, I searched first and this came up, so it's either resurrect old threads and get grief for that or start a new thread and get accused of not searching.

So here's my understanding: Mazda chose the 10:1 compression in order to get the smallest possible combustion chamber so they could get the best idle emissions they could. They couldn't go higher, such as the 14:1 compression ration that the SKY-G engine uses, for whatever reason.

We know that the the 16X isn't hitting its emissions and fuel economy targets yet, or at least weren't recently enough that Mazda would be willing to make an announcement.

Higher static compression ratios wouldn't make more power and would require redesigns of the seals; but Mazda already figured out how to redesign the seals (the L shaped seals mentioned above); but, it would improve emissions and idle fuel consumption, which the Wankel has trouble with.

Higher static compression ratios do imply higher static expansion ratios, which leads to better off idle power, emissions, and fuel consumption.

So here's my question: Is there any fundamental reason that the Miller cycle couldn't be used in conjunction with the secondary and/or auxiliary intake ports to allow the compression ratio to be reduced from 3.5K-4K RPM on up to redline, while keeping the extra compression for better emissions, fuel economy, and low end, "off the line" grunt?

zoom44

only complexity

InZaneX3651

What would be a viable compression ratio for a potential SkyActiv SPCCI tech rotary? SPCCI of course needs a really high compression ratio (16:1) but what would be a viable option for SkyActiv rotaries aiming for better off the line response and better consumption? (assuming the L-shaped seals actually do their job) 12.5:1? 11:1?

TeamRX8

iTrader: (25)

the people who ask only demonstrate to establish their lack of rotary/wankel engine understanding and knowledge

^^not intended as criticism, it’s just the unadulterated truth.

because you have to understand how the forces of the combustion process are applied on the rotor and eccentric shaft to fully appreciate why the answers at the beginning of this thread are correct. It’s quite different than a reciprocating piston engine.
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InZaneX3651

Not to at all be rude but I feel like those who ask questions ask to confirm what they think is correct or to learn what actually is correct. From what I understand, upping the compression ratio further above 10:1 doesn’t increase power but does it help with fuel economy and efficiency like it does in piston engines? Not fully expecting a solid yes or no but an idea or a theory would be nice.

TeamRX8

iTrader: (25)

no, it does not.
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