Combustion

The geometry of the combustion chamber has nothing to do with the air/fuel mix ratio. It can, however have something to do with the way the mix burns.

Check the spelling of Wankel.

Exactly. This is why some of the pistons tops have been modified to have better mix burn. In my case fuel will hit the air stream at a 90 deg. angle . How will that mix?

Wankle? I should know better , sorry.

That will depend on the relative velocities. As fuel velocities go from 0 to X*air you can move between dripping down the cylinder wall to spraying the other side of the cylinder. Then you have the issue of droplet size and spray pattern.

The questions lacks constraint.

Unless the fuel is being injected during air induction it will not hit the airstream at 90 deg - rather you will have a complex swirling within the combustion chamber which is dependent on the compression which is occurring and the geometry of the chamber.

If I remember correctly, corners are a cause for concern due to stagnation.

Some good thermodynamic CFD modelling may give you an idea of what is happening in the cylinder ...... but that is likely to be expensive!

How is the "air at 140psi" produced? On board air compressor? How much power will this consume? Will it require a storage tank for starting? How big?

Do you know what the internal pressure of, "equivalent piston at the top of compression" is? I don't.

Hi Lyn, The pressure of 140 psi is due to the compression of the air-fuel mixture when the equivalent piston is at the Top Dead Center of the compression stroke. Assuming 14.5 psi being atmospheric pressure, this amounts to a compression ratio(CR) of about 9.55:1 [ie. 140/14.5], assuming further that the engine is normally aspirated [ie not super/turbo charged]. Assuming no other modifications, only Hi-Octane petrol (about 98 Octane) will be stable enough to burn without any detonation. For example, kerosene engines will operate without detonation at a maximum CR of about 6.5:1 [ie about 90 psi. above which detonation can occur due to instability of kero]. LPG, on the other hand [Liquified Petroleum Gas] is extremely stable even at high CRs as is normal with diesel engines ie. about 20:1. Hope this has answered your question with the illustrations.

Pressure * Volume = number of molecules * Gas_constant * temp in K.

PV=nRT or P = (nRT)/V

n = (P*V)/(R*T)

Pfinal = (nRT)/(Vinitial-Vfinal)

T will change as the mix is compressed.

If you're planning to pull much horsepower via speed of operation, you might run into preignition problems with the far corners of the box combustion chamber. This has all been worked on for about 70 years, right up to yesterday.

I did not know that. Would you have other info about a rotary engine with a box combustion chamber, besides the Wankel. Better yet, would you know where I can find info about this possible problem. Appreciate any help.

You're talking about an air motor but making it the driver by introducing a fuel pump & injector.

Regarding the shape of the combustion chamber take a look at the NASCAR engine designs, For a two valve rule they seem to have perfected the shape for fast and complete burn. The rectangle chamber will leave some unburned fuel in the corners and depending on the location of the spark plug combustion may not give desired push during full burn. The ideal combustion chamber for gasoline is generally as small as you can go but still not shroud the valves for good air flow, the bigger the chamber the efficiency drops off both in burn quality and piston pressure. Also the sparkplug should be as close as possible to the exhaust valve or event. Mazda went to dual plugs on the Wankel's I worked on for more complete burn. Take a look at this site most intriguing design.. http://quasiturbine.promci.qc.ca/ETypeCombustion.htm

Sorry, this HTTP address doesn't get me anywhere in google,msn or yahoo

Try cutting & Pasting it worked for me at 6.37PM

Consider using a pre-combustion mixing chamber. To regsoft- I do not think you can model as an ideal gas, pressure to high. Use a correct z factor.

I was thinking the same thing about the z-factor.

After answering the OP with a quick reply, I started thinking. There is so much going on in the chamber in such a short period of time. Being able to accurately model what happens physically and chemically simultaneously has got to be incredibly complex.

IC engine technology is quite mature, so taking data and ideas from superior designs is a good place to start.

I don't know very much about this field; it never really seemed that interesting to me. Are there any designs that actually vaporize the fuel (no droplets) and mix with air before igniting?

Welcome to CR4!

Vapourizing the fuel prior to injection is counterproductive since the vapourized fuel then displaces air, reducing the possible charge and power, thus the prefered method is to introduce the fuel in liquid form but as widely dispersed as possible - maximum possible surface area to encourage complete combustion.

There is a second major drawback in vapourization of the fuel - explosion - either in the cylinder or in the intake manifold - both are VERY VERY bad for an IC engine. In the Cylinder the best scenario is a fast but controlled complete burn....

They should rename this site "CR4 - The Engineer's place to get your spelling corrected".

The short answer is "badly". The shape restrictions of a Wankel combustion chamber requires giving up some performance- power, speed, efficiency, lightness, pollution, wear.

You may find this man's work interesting. http://somender-singh.com/component/option,com_frontpage/Itemid,1/

Just ran across this and thought people here would be interested.

Improvement in simulating turbulent combustion speeds design

Multiscale complexity is common across all combustion applications-internal combustion engines, rockets, and industrial boilers-and can range from tens of meters to billionths of meters. New techniques being employed at supercomputers covers this huge scale range using fewer computer hours, and could benefit efficiency levels in the combustion industry. Read/Comment