Posted by Power on June 17, 1998 at 01:19:48:
I've been out for a while...but something has bugging me for a while...
The prevailing knowledge is that once the intake charge reaches mach speed through the restrictor..no more power can be made. Hence the only option is to build torque monsters like the WRC cars which build 36psi at like 2000rpm and then taper off towards their "300hp" max.
1st EXACTLY why can no more power be made when the intake charge reaches mach speed? is it because a) the flow becomes chaotic b) no more air can flow through the restrictor than flows at mach, or c) both. b would obviously most likely stem from a, but not neccesarily.
Now I have absolutely no idea how a scramjet works....but it works....is there no way to apply similar principles to an internal combustion engine?...or does a scramjet slow the incoming air to below mach by using some sort of a tapered intake?...
Posted by T.O.O. on June 17, 1998 at 19:15:22:
In Reply to: T.O.O. Intake velocity..... posted by body on June 17, 1998 at 01:19:48:
The shape of the orifice or entry to a conduit will usually dictate
the volume and velocities. In certain areas air, due to it's unique qualities
as an elastic and compressable fluid, will stack up and create whats known
as "saturation". Once a conduit is "saturated" you can continue to use
more energy to push or pull the air, but the amount of additional flow
will deminish, as separation and shear have caused too much turbulence.
Aero folks have tried for years to design shapes which permit laminar flow at subsonic speeds and then maintain the "smooth" flow in transonic speeds and ultimately well past mach 1. We can achieve this with aircraft wings if enough tiny holes allow pressure balancing between the upper surface and lower surface. Manufacturing technology that is now allowing us to construct side pods with the coolant actually running through the carbon skin...the skin is the radiator, will allow the next generation of high performance aircraft to use such technologies. The JSF and hiper- cruise programs are the canditates.
The basic problem is how to create a shape or conduit where the flow will be happy subsonic and supersonic, and it can't be done without shape changes(moving surfaces).
So we have a choice: go for max. flow subsonic and suffer separation above mach 1, or the opposite. As the rev. band on WRC cars needs to be fairly wide, and there is usually an rpm limit by rule, it makes more sense to go for max. torque and gear the car accordingly. If you have enough mid range, gear the car to run in that band, and recalibrate your tach. so others will think you're deep geared, and watch them blow their high revers, while you're still running an rpm/hour pace which will allow a finish.
On the inlet side, unless you're using sonic shock to atomize fuel, if the main flow goes over mach 1, the fuel will separate and the quality of the burn will be suffering.
As far as ram and scram jet technology, each uses ram air to produce the compression necessary for combustion, but the air entering the ram jet is slowed to subsonic velocities, and HC type fuels are typically used. The fuel is sprayed into the burner section and burn takes place befroe exiting the nozzle. Assuming you can achieve mach 4 -6, you can then enter the "scram jet" arena, and properly the scram can provide power through mach 20. Now the burn speed in scram is supersonic, unlike the ram jet, and that presents some problems with areas, boundaries, and point of fuel injection. If the fuel is injected at the same place as for ram jet operation, the burn would take place after exiting the nozzle, so the solution has been to use hydrogen and in some programs air itself. The rate of burn with hydrogen is much faster than HC fuels, so the burn is contained and the result is thrust on nozzle exit.
The current group of craft designed to use this power use ram to accelerate to mach 4-6, and then the engine "converts" to supersonic burn and scram. The reason for using this method is that were you to use two separate engines, the drag penalty for each, regardless of ram or scram is so high that performance objectives can not be met.
We have had a close working relationship with General Dynamics and now Lockheed Martin for over 20 years. We've designed and fabricated many inlet and exh. ducts over the years, and as the defense industry has scaled down, we have been used more, and more frequently. We have one of the only test facilities that will allow testing at speeds above mach 8. Now we can't test full scale at those speeds, but so far there's not a tunnel in existance that can test full scale above mach 8.
I've said before that our work is quite diverse, with auto , aerospace, and medical testing and product production. As all of us still think of auto related programs as "favored", I can assure you that on many of these formerly black programs, we're always trying to figure out how to translate this new technology to cars, and you can already see it in our porting and combustion "space" non detonating chambers, which opened a back door into pulse detonation for us. Of course, we didn't tell the engineers that our PD knowledge came from racing engine we'd designed and rejected. This is one of those somewhat rare instances where the data from a "bum" test, was just what another customer wanted!
I hope that I haven't rambled to the extint that I didn't properly address your questions.
Posted by Power on June 21, 1998 at 15:36:53:
I forgot to thank you for your response to my previous question, so thank you. I still have a few questions. Would it not make more sense to design an engine to function with the intake velocity past mach? Is this what you pulse detonation engine did? Why was it innefective? I would think that if you were building an engine where intake restrictors were a requirement, designing an engine to reach mach 1 at the intake at around 3000 rpm and work effectively past that point would be the ideal. Is it simply to difficult to design an orrifice where the intake will flow effectively at mach? I might have misread your post, but you seemed to state that it can be done.
Your post to Frank was pretty informative. Who is the Japanese manufacturer who build's your cranks? Is it a manufacturer that we would be familiar with?
NITRO mentioned that some of your cars will be going down to Ennis. Will this be open to the public, or are you renting the track? I know that there are at least ten of us on this board that would love to show up if possible. Every day I get more anxious for more power out of the Type R.
JUN makes a 10.4 lb. chromoly flywheel for the B-series engines. Do you recomend keeping the stock flywheel or should I indulge myself? With your SC kit I would'nt think that a lightened flywheel should hurt me off the line. Drag racing the R would be more out of curiosity than competition anyway.
Do you have any experience with the Ohlins set-up for the Type R? Damn expensive, but I'm planning on running this car at Limerock, Louden, and a couple of local paved hillclimbs.
Posted by T.O.O. on June 21, 1998 at 21:22:17:
In Reply to: T.O.O. more Q's on intake velocity, Ennis, etc. posted by body on June 21, 1998 at 15:36:53:
Let's begin with the R Type. I do not have any knowledge of the Ohlins
set-up. Remember, these cars are new to me, as are all the Asian (street)
cars, relatively speaking.
I'd recomend any good light weight flywheel for the R. Personally, I'd probably go aluminum (not taking price into account) because the steel friction plate can be replaced if and when it becomes "used up", and you then have a new flywheel. Ont other thing, the sanctioning bodies are currently working on some SFI specs that components must meet if you're going to ever run the car at an NHRA affiliated track. Perhaps JUN will submit for approval. I can tell you this. The way that group works is less than ethical. One of our vendors makes scattershields for power glide drag race competition. They finally submitted three, and they all failed. The owner said they'd improve things and be back with an improved model. He purchased two approved units from a large aftermarket company (that does a lot of advertising in related publications), he then stripped them, powder painted them and put his logo on and submitted them....they both failed!! Each time you submit for testing it costs a lot. He finally bought some space in the National Dragster, and shortly after, he sent one of each brand in and both passed. It's a wonderful world.
If the weather doesn't cool off some I'm personally going to think twice prior to heading down there. When the T.H. Index is 116 in the shade, the news tells people that suffer from heart , respiratory, or any other cronic illness to stay inside. All I can say right now is that I'm glad I have AC in my drivers, because all of the above conditions apply to me. The young "wonderboys" who keep thingsa rolling are bitching about the heat as well. We'll see what's coming, and I'll let you know. If this keeps up, we'll be looking to come out to the coast with the cars.
The problem with restrictors is that the rules generally define the shape of the orifice, and in most cases, it's a square edged piece. It thakes considerable work or energy to accelerate air to and beyond mach 1. The amount of energy the engine would use to suck hard enough to achieve those velocities would be so much that I don't think there'd be much power left to use on the track. This gets into that pumping loss area that I often speak of when we get on turbo and intercooler issues, the more turns, the passage through the core, and the overall length of the tubing eat into your potential boost energy. That's one reason the little Eaton is so nice...it's so direct that the increase in air temp is negated by the improved pumping efficiency.
We're still working with pulse detonation and timed pulse ignition. Those programs are too promising to stop on, especially as some really crack propulsion folks are currently on the market....the problem there is to get them to think and understand "real world".
The scram isn't a separate engine from the ram because the drag penalty would be so high trying to accelerate to mach 4-6, that you'd never make it, and there's been a lot of money spent on that program a couple of administrations ago, and there's a little now..not nearly enough though.
I'm simply saying that if we could overcome the work necessary to achieve mach 1, and still come out on the positive side, we'd do it. Even shapes that are more conducive to making air converge are limited in ability due to the air density at or slightly above sea level. That's why there's only been one airplane in history that could fly sustained speeds over mach 1, and that's the F-111. It's max. speed at sea level was mach 1.35, and at high altitude it was capable of mach 2.7, which made it second in max. high altitude speed to only one air plane, the SR-71.
I can tell you this. My father was chief engineer on that program and the B-32, B-36, and the B-58, with the F-16 also in the early 70's. But the F-111's structure was milled from solid billit, and the air flow into the inlets was a challenge. The airplane also had to be insulated from the heat generated from those speeds, and they frequently came back from flights with almost all the paint burned off. The reason the air craft was built like a "tank" was because the max."Q" or stress was enormous at low altitudes. The reason most other aircraft can't fly those velocities is that they don't have the power, and structurally , they'd likely come apart.
Forgive the rambling, but I do have access to many people who have been dealing with high velocities for a long time now, and there've been many occasions where I beat them on project performance, primarily because, I didn't know that you couldn't do this or that. We will keep after it, because it's providing knowledge, and we need that, as "a little knowledge is a dangerous thing", or so they tell me.............................T.O.O. ...............................