hey! thats cliffy's website! an engineering acquantice of mine!

 

we think alike, lol

 

Myths: Electric turbos and ram air.

This site covers our 2 current favorite topics, and backs it up with the math that I was too lazy to do..

 

A nozzle is just a small piece of pipe unless a fluid is being forced thru it. That takes pressure. At least it does here in Missouri.

There are no moving parts in a ram jet engine except, the ram jet engine's movement thru the air. Therefore a ram jet engine has virtually no thrust untill it achieves some velocity.,,,,,enough to form compression in what engineers call the "compression chamber"
A ram jet won't even start unless air is flowing thru it.
Air can be compressed by movement of the collector, or ram, thru the atmosphere

roadster with a stick

 

I recall that the air pressure in the small hole is less than than the air pressure on the incoming side although the velocity is higher. This is the venturi effect and is used in many things, carburetors, spray guns, etc. The air is coming through the hole to maintain equilibrium, nature likes things balanced. The temperature of the air will also change slightly, but return to normal when it regains its pressure. Properly done, significant temperature drops can be obtained.
We know that bends, obstructions, surface finish and diameters in pipes affects flow and pressure, the same principle applies in air and in water.
The ram jet example only goes to verify the statement in the original article that the ram effect only applies at supersonic speeds.

 

Nope!



The pressure at "1" is higher than at "2" because the fluid speed at "1" is lower than at "2".

Please, we are not proving the venturi principle here. One guy calls it a nozzle and soon we are discussing Spray guns and Carburetors.

We are not. Although the geometry and the physics are similar to our apparatus, Giovanni Batista did that work already.
We are talking about compressing air in a continuios flow by preventing the natural tendency of it to accelerate through a constricting inlet pipe.

Put another way, the air has energy applied to it by a mechanical movement, ie the tube moving thru it. As the tube constricts the air volume, the air will accelerate as the energy must dissapate or the air will have to compress. A condition it will resist as it wants to remain ambient or in stagnation.

Since more air is constantly available to enter the inlet orfice, the air has no choice but to compress unless the exit orfice allows it to exit and to do so at a higher velocity than the movement of the tube thru it. Venturi
This is all understandable and fairly agreed as understood here. The key to ram air apparatii is the application to the Throttle Body. So long as less air volume is consumed by the engine thru the TB than the ram orfice can collect, the incoming air has no way to dissapate the applied energy and must therefore compress.
Now we can argue about how usable that minute compression might be but we cannot deny that it compresses. Here then is latent energy which will dissapate by filling any void; read low pressure, read vacuum, area in the intake, TB or manifold. Thus meaning the downward movement of the piston, which draws in the air and normaly creates a lower pressure, AKA lower concentration of O2 laden gas (air), in the manifold, will have some compensation from the, albeit feebly, pressurized air supply.

To suggest it is useful may be a boast. But to suggest it dosen't exist ignores the simple physics.

Finally, the temperature of the air does not actually change in a venturi. The concentration of the BTU's, or calories of heat, simply increase and then decreases. This because the air compresses and then decompresses. Wa La!

Thanks for providing the proof there pal.

Ram jets do not need to operate at supersonic speeds. They are useful for missles at supersonic speeds, but seldom used for jet planes. I am guessing as I cannot recall a supersonic plane so equipped.


roadster with a stick

BTW water does not compress so it does not flow like gases do. Gases can decompress to fill a void. Or compress to flow through a small orfice. Water will "cavitate" or boil in a negative pressure area around a bend or exiting a narrowed fitting into a larger pipe. This uses a lot of energy and often makes plumbing noisy.

 

I know lol, I'm not denying that the air is pressurized, it is at 14.6 psia, or 0 psig. The concept of ram air is based on velocities... There is no mention of velocity in the ideal gas law, only pressure (F/A), volume(LWH), temperature, mass and a constant. A jet engine's thrust comes from flow of expanding exhaust gases through nozzle ... not intake air . A turbo/turbine creates pressure due to expanding exhaust gases.

 

A true ram jet has no turbines.
How does it get started?
Air must be moving through the chambers which are a venturi with fuel nozzles and a spark plug in the after chamber.
If the incoming air is not of a higher pressure than the ambient you don't get an engine providing thrust. You get a bomb.

A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of jet engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill.

AHEM!
roadster with a stick

 

AHEM lol

ramjet engine

Unfortunately there are two things that work against the ramjet:

1. Operating Speed
   Unlike pulsejets and jet-turbine engines, the ramjet will not operate unless it is moving through the air at a speed of at least 400 mph.
   If you attempt to start a ramjet while it's stationary or moving to slowly then it will give little or no thrust -- in fact you'll just get lazy, smokey flames billowing out both the intake and exhaust.
   This is because a ramjet relies on heating a fast-moving stream of cold air as it enters the engine and then expelling that air at a higher speed out the back. Unless the engine is moving rapidly through the air there's nothing for the burning fuel to heat.
2. Fuel Consumption
   As a general rule of thumb, the fuel-efficiency of an internal combustion engine is related to the compression ratio at which it operates. That is to say -- the more the air/fuel mixture is compressed before it is ignited then the more power you'll get from a given amount of fuel.
   Diesel engines have a compression ratio of about 20:1, most car engines operate at compression ratios as high as 11:1, a pulsejet runs at a compression ratio of less than 2:1 and ramjets are about the same at low speeds. As a result, the ramjet (like the pulsejet) is not a particularly fuel-efficient engine. What makes it worse is that since the ramjet needs to be operated at very high speed, it's going to have to burn a lot of fuel just to overcome the drag it creats at that speed.

Thrust is a function of expanding gases due to heat. There is no pressure gain until combustion occurs. Venturii do not create pressure, they modify airflow charicteristics. Nozzle flow is a function of mass/volume flow rate between 2 points, with 1 area larger than the other. The idea of ram air is not applicable at the speeds a car can reach... and the ramjet engine isn't useful in any automotive application

 

We are not talking about "Ram Jets" we are talking about "ram air". I used the ram jet to show a practical application of air compression by movement of a properly configured pipe through the atmosphere.

The same principles of ram air compression apply to ram air systems on automotive applications.

We are not talking about venturi as I have already explained. So other than the speed issue, which is significant to a practical application, most of the technical info you posted is useful but unrelated to this discussion.

roadster with a stick

BTW we will soon be talking about the flow of air thru the CAI and the manifold. So, tell me what you know about the flow and properties of collodial gases throught a dynamic vacuum manifold vrs a dynamic pressure manifold. And please, don't give us crap about what the word vacuum means.

 

I thought we were talking about ram air, which is a forward facing tube expected to create pressure or force more air into the intake path. Ok, a dynamic manifold would rely on intake velocity to change dynamic pressure, just like a big nozzle (using the n-word again) but would not be efficient at every engine speed/ load. That's why we have 2 different size intake runners, because there is only a small window where the effect will apply... It is more a matter of the aiflow needs of the engine than a forced induction effect due to ram air. Tuned intake manifolds are not ram air lol. I don't really see why a collodial gas would behave differently than say air, when compressed the amount of mass in the mixture would not change the mixture would just be denser at the point of exit... Where is sonoronos when you need him .
PS- this is shaping up to be a decent thread with some interesting concepts.. I'm willing to learn and bounce ideas off one another.. hell I'll even admit I'm wrong if needed, but I feel like the topic here is ram air.. I'm trying to isolate the ram air system from the rest of the intake system.

 

Ok, let me try this again lol.. The air is going to follow the path of least resistance from high pressure to low pressure we are on the same page with that. The air being pushed into the intake tube is going to fill the intake because the pressure is lower, as the engine is expelling pressure and drawing vacuum we can agree on that. When the air is stuffed in the tube at a pressure of 14.6 psia, the pressure of the air and the pressure in the tube are equal, and the air will begin to travel around the pipe because the pipe is full because it is easier for the air to do that than to compress all of the air in front of it. Ram air is more a matter of ideal location and constant intake tube filling.. not over-pressurization of the tube. The higher velocites will fill the tube quicker, getting the air to the chamber quicker.. more efficiently. When an engine is at high rpm, it needs a constant supply of air at a high velocity.. an intake inside the engine bay would just rob horsepower, rather than a ram air setup "making" power due to a forced induction effect.

 

The topic is about ram air. I believe I said that anumber of times.

But, 1) we must talk about the physics of it, hence the references to known science ad known applications and
2) we must talk about the entire intake system because this is a dynamic process. It does no occur, unrelated, in one specific point.

Unlike a super charger which can deliver compressed air with the vehicle at rest or Turbo supplied compressed air which is delivered with the engine ususally over 3K rpm's, the ram air involves the movement of the vehicle through the atmosphere. Since the process of the first two involves air flow pressure and properties beyond the throttle body, ram air discussion must do so as well.

Therefore we cannot limit our study to the inlet pipe and stop at the throttle body. After all, it is just a metering valve. The "work" happens in the cylinders.

And we cannot forget that, at best, the ram air will assist with any significance only with sufficient speed of the vehicle over the ground. So with the exception of the top fuel racers, funny cars, and the egos of some fartcanned Honda street racers, there is no reasonably useful assist for 1/4 mile times.

Ram scoops do look really cool though.


roadster with a stick

 

You have the physics right. And we agree on the process. And we agree on the objective, more air at higher speeds because the engine needs the volume.
Now, let us see how we can best enhance that with the application of geometry.
But first, we have people who insist that "air will not compress itself", therefore ram air doesn't work. Let's get into agreement that it does, how it does it, and why.

roadster with a stick

 

Sorry to break up the natural rhythm you two were developing, but I just wanted to say, this thread has really made me think

 

And did you come to any conclusions?

 

Please, don't get hurt doing that on my account. I don't carry insurance.

 

Im so glad my thread has become a debate... yay

 

I remember my 126 body Benzes had a windscreen trim that extended over the windshield about n inch off the glass. What this did was trapped the air flowing around the cabin and created a pressure bubble. When it rained, this pressure bubble force the water to stay in the path of the wiper blades giving the river a full clear windscreen. I always thought this to be a cool idea.

This pressure bubble was created by ram air compression. It worked at relatively low speeds, say 45 mph. I believe the basic dynamics would be essentially the same as what we are discussing.

I have no idea what inH2O pressure this was. But it was enough to exceed the incoming air stream coming over the hood of the sedan.

Curiously, 123 body diesel Benzes had ram scoops under the front headlights. Again to create higher pressures in the intake manifold and provide more HP at cruising speeds. These disappeared on the later Turbo'd models. Germans didn't put things on their cars for looks, only function. Sump'in was going on there.


roadster with a stick

 

I hate to bring this up again, but I'm not seeing a difference between ram air compression and flow through a nozzle. I can't find any information about ram air compression, but my thermodynamics textbook has alot of information on nozzles. If a nozzle has a big inlet and a little outlet (converging nozzle), it will increase air velocity at the expense of pressure.. If a nozzle has a little inlet and a big opening (diffuser) it will increase pressure at the expense of velocity. When I think ram air, I think of a large opening that gradually gets smaller..


Do you have any more info on ram air compression? I'm willing to learn, but I can't find anything.