So, I'm just going to through some info out there to maybe, spark some intellectual conversation. I'm not sure too many people are aware of how scram and ram jet engines work or the priciples behind them, but basicly they are supersonic jet engines that have no moving parts, and in order to get them to perform they need to have moving air to start the process of your (suck,squish, bang, blow) actions of the typical turbine engine. I got to thinkin about moving air and the turbo inlet and intake systems and was thinking that some how the concepts could overlap, where as one could create a ram/scram intake set-up to possibly incease the presure to the turbo inlet. Scaled down of course.

Also, another recent, similar, example was where I read info about the newly discovered aerodynamic properties in Formula 1, where similar techniques were used to ad downforce and increase the propulsion on the car. I don't know, am I looney ? If so why?

 

The maximum speed for normal combustion is ~480mph (air flow through a jet engine). In a SCRAMjet, the air flow is at supersonic speeds, yet combustion can still be supported.

Trying to generate supersonic flow is near impossible with our sub-sonic cars. We'd need a system installed on the car to generate airflow at that speed (most likely at very low volume), then we'd need to slow it down before stuffing it into the engine so it could actually burn.

 

I suppose, I was looking for solutions, not obsticles, on how to encourage a thread where one could offer up ideas, where as to get an increase in performance outside the normal "good ole boy" tricks. ... some out of the box thinking I guess it's just ideas that might work, but with no solid base really. ...a rough draft if you will. Is this thing on?

Another idea I had floating around was to some how create a muti staged turbine section on the front of a turbo, where the air could become even more compressed than it currently is, kinda like the front section of a turbine housing. I just haven't figured out how to get the turbines wheels in between the stages to roatate in the opposite direction, unless you could use cylinders 1&2 for clockwise rotataion and maybe 3&4 for counter clockwise rotation. I don't know...

I think I should of named this the idea thread, or Crazy J's nonsense ramblings.

Maybe someone has a different idea, electronics, spark, thermal expansion theories, new aerodynamic ideas. New ideas are awesome. Brainstorm anyone?

 

Well if you get into the technical aspects of Ram and SCRAM Jets, it takes a lot of work to make them work. Like previously posted they take high speeds to get them going. For example the SR71 Blackbird is a Jet/RAM Jet airplane. The normal turbine jet gets it off the ground and up to speed. Then the RAM jet takes over once the correct speed is obtained.

Here is where the techincal stuff comes in. There are several sensors that constantly monitor pressure, air speed and other vital information. Then internal flaps within the engine constantly move increasing or decreasing the inlet size of the Air Intake, trying to keep a constant flow in the RAM jet. Its a fine balance to Air Speed because too little and it stalls. Too much and it will blow the combustion out (like boost blowing out spark). All these things must work together. IMO there is no way to feasibly apply this to a car. And even if you could, it would take a NASA budget to design and implement it.

Speaking as a Mechanical Engineer, it is a really cool concept and one that will take us further into space flight and advanced weapons.

 

mmm ... aerospace stuff .

Ram jets are very simple, you can actually build one in your garage. All you need is a constricting tube, a fuel injection port, and spark source (spark plug will do), and possibly a flame holder (mesh screen). The challenge is to get it into an environment where it will actually work. Ramjets work best at supersonic speed, ideally around Mach 1.5-2. The constriction in the tube acts like the compressor (slows the flow to subsonic speed while making it more dense), the fuel adds heat, and voila ... thrust! A scramjet is a "supersonic combusting ramjet" - same idea as the ramjet, just much higher speeds are supported. Makes it more attractive for very fast airplanes and supplemental thrust for space launch vehicles. One problem with using a ramjet type augmentation in a car is that it's principally a steady-state (constant flow) system, whereas the car is a pulsed detonation engine. The other is that the flow in the car's system just isn't fast enough.

The multi-stage compressor is another interesting technology. Actually I think that's been done on cars (large trucks?). It's essentially sequential turbo charging, but you need to add an intercooler between the stages, which makes it mechanically more complex than a jet-engine with a multistage compressor. The jet engine can take the heat, because it adds fuel after the final compression and jet fuel has very high octane rating (high auto-ignition temp), on cars you have to worry about knocking so you need the extra cooling. Some cars are starting to approach this setup though by injecting fuel straight into the cylinder after all (or part) of the compression stroke. I think it's called "direct port injection" or somthing like that, and requires insane high fuel pressure to work (if you are boosting 20 psi, and have 10:1 compression, you'd have to inject fuel at 200+ psi to force it into the cylinder).

I think there's also a shockwave compression setup that's been used (or at least proposed) for augmentation to boosted engines. This one actually benefits from the pulsed nature of the exhaust stream, but you're still heat limited.

It's all about finding clever ways of cooling the air-fuel mixture and keeping it from auto-igniting, then you have lots of options in compressing the snot out of it.

 

Jet fuel is kerosene and has an octane rating of about 30. In a jet engine, kind of like a diesel, the fuel is ignited right after injection; it's not sitting around in a hot, compressed atmosphere. Jet engines can take the heat (and need high temps for efficiency) because the turbine blades are made from really high-tech nickel super-alloys.

Dave

 

you're right, I was thinking of RP-1 ...

 

Jet engines also use bypass air to keep the flame from directly touching any surface (outside of the turbine blades).

 

wow, my head hurts from reading this thread lol

interesting read!

 

Fuel for a piston-engine powered aircraft (usually a high-octane gasoline known as Avgas) has a low flash point to improve its ignition characteristics. Turbine engines can operate with a wide range of fuels, and jet-aircraft engines typically use fuels with higher flash points, which are less flammable and therefore safer to transport and handle. The first jet fuels were based on kerosene or a gasoline-kerosene mix, and most jet fuels are still kerosene-based.

^^ from Wikipedia

 

nm

 

Whattt!! you can take the technicality

 

Sort of... I work for a large jet engine producer on these parts.

The "bypass air" that you are referring to only really bypasses the combustor. It still has to be high pressured so that it can be pumped out into the rest of the stream as cooling air. At this point, the "flame" is gone and all that remains is combustion products and REALLY hot air.

True "bypass" air is usually from the fan on jet engines, that never really cools anything. It is simply used to create thrust.

On the original topic, there is no way a ramjet, much less a SCRAMjet, could be put on our cars. We would have to be able to drive at supersonic speeds to take advantage of this concept. That would be really cool though!

Great topic for an aerospace engineer like myself. Thanks guys!

 

Thanks! That's what I meant to say.

In the F100 series (F-15s/16s) the high-pressure bypass air is also fed out along the walls of the cumbustion chamber.

 

some people put velocity stacks right at the mouth of a turbo. this causes air to compress just before it enters the compressor.