cordius

Displacement as anyone can tell you gives more power. I have to wonder, would changing the rotor shape change this as well? Here's my thought: Carve out the rotors to add more space for air, thusly more injected fuel, which means more power during combustion. The only problem that I can think of would be that it would not compress enough during the compression part of the cycle. This could theoretically be solved via a turbocharger. This is a lot easier than using wider rotors because in theory the modification could be done without changing anything else, except possibly a larger turbo. Any thoughts?

rotarygod

iTrader: (1)

Displacement will determine torque potential which in turn mathematically determines horsepower potential. Stroke will determine where the torque peak occurs. Longer storke will peal lower and shorter stroke will peak higher. Rotor shape will determine efficiency within the given displacement. If you could find a way to make the engine more efficient through changing rotor shape then you could affect power but it's solely an efficiency issue. This is why piston engine designers work hard to alter piston shape, valve angles, profiles, etc. Mazda is working with a different rotor shape in the new 16X which is taller but narrower to try to get an efficiency boost. You are correct that a larger area for air is less compression ratio which brings up a whole new world of issues.

RacerXtreme7

iTrader: (2)

Your not adding dissplacement, all you did was change the static compression ratio. Dissplacement is how much the engine dissplaces, in other words, swept volume from top dead center to bottom dead center. The only way to add dissplacement is to make it BIGGER such as widening the rotors (like going from a 12a to 13b) or making every thing bigger (rotors, housings, E-shaft etc like the 16X).

~Mike..........

cordius

That's what I would figure, but in theory a strong enough supercharger/turbocharger would help with that, no?

Also forgive the horrible pictures

Joker1337

A supercharger would help, but it's not only the displacement that matters.

Displacement determines (from an engine operation standpoint) how much air / fuel mixture is available for the pressure changes that drive the engine. If you change the volume by enlarging the chamber like that, you will not only increase the volume, but also drastically decrease the pressure. In fact, since PV=nRT, the gains you get out of one will be more or less canceled out by the other.

Moreover, since the air / fuel mixture becomes more volatile as P and T go up and V goes down (since the compression stroke on an Otto cycle is not in fact adiabatic), the increase in V results in a decrease in volatility and accordingly a decrease in the specific energy that can be netted from each combustion.

Even worse, a rotary engine does not completely finish the fuel burn (even with a direct-fire improvement) with standard compressions. Increasing the distance that the fire wave must travel during the combustion would likely increase the time that the combustion takes.

Furthermore, those tangs on the end of the rotor you sketched will be subjected to extreme cyclic stresses from the pressure waves and stress concentrations. I would very much question their reliability and their ability to form seals through deflection.

Slapping a supercharger on top will help you boost pressure, but it won't help you with the other losses. And you can just slap a supercharger on the car in the first place and get pretty much the exact same output or better than you would with the changed rotors.

cordius

There's a lot there I did NOT understand lol.

laundryhamperman

iTrader: (3)

The main limiter on peak power in a pre-mixed spark ignition engine, rotary, piston or other is detonation. Increasing the compression ratio, or increasing inlet pressure with a turbo pushes the engines operation enviroment into the realm where detonation is likely.

Detonation occurs when the flame travelling through the fuel mixture fails to burn through the entire mixture, starting at the spark plug, and travelling to the extremities of the combustion chamber, before the pressure increases that the end gas, the air/fuel mix ahead of the flame front not yet burned, detonates spontaneously. So its really a race of the flame front to consume all the fuel mixture before the combustion chamber conditions are that when detonation occurs.

The design work in changing pistons and valve angles, is to make a condusive enviroment for the flame front to beat the timer before detonation occurs. Increasing the surface area give a larger area for heat from the mixture to be transferred out throught the chamber walls, which less heat will make a mixture less likely to detonate. Some designs are meant to make the distance the flame has to travel, shorter so it will finish the race faster.


What was already said is that what you've done is increase the volume of the chamber, but the displacement is not how big it is overall, but how much the volume changes.

In a rotary, this is affected by the amount of "throw" in the eccentric shaft. To increase the displacement, as was also mentioned, the e-shaft will have to be made with a bigger eccentric lobe for more throw. Also, the rotors and housings will have be made bigger to account for the increased distance the rotor will travel.

So what you have drawn, is the same size rotor, so it will have the same throw, and the same displacement, but the ratio of the max volume of the chamber to the min volume of the chamber will be smaller. For turbo engines, such as the 13bt, this technique is done, but not as radically as you have drawn. The compression ratio is reduced to i think 8.5:1. This will decrease efficiency, but this is done because you are pressurizing the inlet air via the turbo. So to counter the likelyhood of detonation from the increased density of air/fuel mix, the amount of compression the pre-compressed mixture has to go though in the engine is reduced, so the engine will not destroy it self pinging.

The net effect is that you make more power putting more fuel and air in from the turbo, than you lose power from the decrease in efficiency from the reduced engine compression ratio.

Monkman33

iTrader: (28)

I would think that the only thing accomplished by your drawing would be a lower compression ratio.

Since you didn't change the actual displacement, you just changed the overall chamber volume. The more overall chamber volume there is compared to a set displacement value... the lower the compression ratio will be.