Can Microturbine Exhaust Be Safely Cooled for Pedestrian Areas?

In summary, this air cooled diesel engine had three different gas flows going into a vertical stack in pipes. The exhaust went through the center, the engine cooling air went through the first annular space, and the engine room cooling air went through the second annular space. The first two were forced at high speed, but the third was drawn in by natural convection. During those last few feet, all three gas flows mixed together, coming out at a reasonably low temperature not to cause problems above.
  • #1
Jonsp
2
0
Hi guys, not sure if this is in the correct section but I'll go ahead anyway.

I'm working on an automotive design project. The car that I'm designing has twin micro jet turbines, like the Jaguar CX-75, to charge and power the electric motors propelling the car.

The problem that I'm trying to solve is that the heat exhausted from the turbines is incredibly hot and obviously isn't safe to shoot around in pedestrian areas. Apparently it can melt bumpers of vehicles behind and the tarmac below.

I'm wondering whether there would be a way to rapidly cool the air being exhausted to a heat which isn't capable of melting people. I don't know if it's even possible to cool air that quickly, but I'm stuck for ideas. Any help would be appreciated.

Thanks in advance.
 
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  • #2
Mix it with a huge volume of ambient air.
 
  • #3
How would I do that in the back of a car?
 
  • #4
I once had to do a design for a customer who wanted a large air-cooled turbocharged diesel mounted in the bilge of a wood boat, with a dry stack and no seawater cooling. We had to keep the temperatures in the engine room much lower than I at first thought possible. I found very excellent ideas on the Deutz website. I’ve since seen the same concepts applied to jet engine design. I would imagine that could be adapted for your design.

My time for writing right now is very limited. But if you like, we can talk more about this later. But I thought that this little tidbit might give your something to contemplate until then.
 
  • #5
Depending on the material of the body, you may want to consider sinking the heat to the body of the car as it will have a very large surface area.
 
  • #6
I rather like the idea of using the car body as a heat sink and a heat exchanger. My boat design did just about everything except that. If I had used a heat exchanger in the keel, then I guess that would have been similar.

This was an air cooled diesel engine with no water based coolant at all. It had fins on the cylinder jugs, much like an old VW bug engine. It also had a high capacity oil cooler for cooling the lower end. It had a shroud around the top end that served as an air duct to force the cooling air to where it would be most effective. The oil cooler was located inside that shroud. Cooling air was blown through the shroud by a powerful belt-driven ducted fan that looked sort of like the front end of a turbofan jet engine. All this was mounted inside of a small closed room.

I therefore had three different gas flows to deal with. From hottest to coolest, they were: the exhaust gas, the engine cooling air, and the air cooling the air space around the engine. Air to cool the engine room was drawn in through vents from the ambient sea air, without supplying another fan to drive it. The exhaust gas and the engine cooling air were forced flows, but the engine room cooling air was drawn in my natural convection.

For most of the duty cycle, the engine only supplied 50 hp or less; but it was rated at 120 hp for continuous operation with a 50,000 hour life. It could also supply as much as 400 hp for short durations, which was occasionally required by this duty cycle. The length of these high power time periods was limited only by my ability to get rid of the surplus heat, which the following design did very well.

Those three different gas flows went up a vertical stack in three different concentric pipes. The exhaust went through the center. The engine cooling air went through the first annular space, and the engine room cooling air went through the second annular space. The first two were forced at high speed, but the third was drawn in by natural convection. The momentum of the first two was sufficient to induce a momentum into the third because the first two were several feet shorter than the third. During those last several feet, all three gas flows mixed together, coming out at a reasonably low temperature not to cause problems above. That induced momentum was sufficient to draw fresh air into the engine room through the vents mentioned above. The customer retrofitted another device that provided supplemental cooling during his high power runs. It sprayed a water mist into the engine cooling air intake, which absorbed much heat. Similar water cooling was designed into some of the earlier jet engines, and has been used on some automotive engines as an aftermarket device.
 
  • #7
Well, you could always tow around a weenie-wagon and use your exhaust to cook the hotdogs for sale.
Pkruse, I love the approach that you took with the boat, but could it be miniaturized enough to fit in a car?
My first thought was to employ old-style suppressor technology, adapted to this purpose. Either a folded-path or conch-shell design, wrapped in baffles and absorbent materials such as brass or stainless steel mesh while still offering minimal back-pressure could be effective. Wrap-around tubes or even a surrounding jacket for liquid cooling would add to the efficiency.
That's all that I've got for now, but I can think on it some more.
 
  • #8
Rover produced a prototype gas turbine car in the 1950s (60s) it might be worth looking about to see how they got around the problem.
 
  • #9
In the gas turbine industry, a very hot exhaust is the first indicator that we have done a poor job of extracting the available energy, but somethimes cannot be avoided. Keep in mind that a simple diffuser will drop the temperature a great deal. As for fitting my boat ideas into a car, I can think of several ways of doing that. The same ideas have been put into aircraft engines.
 
  • #10
Pkruse said:
a very hot exhaust is the first indicator that we have done a poor job of extracting the available energy
Agreed. I assume, however, that such is an inherent problem with the engines involved. Hmmm... come to think of it, perhaps OP can find more efficient units to employ.
 
  • #11
That would normally mean increasing the number of turbine stages.
 
  • #12
Jobrag said:
Rover produced a prototype gas turbine car in the 1950s (60s)

There were some studies of gas turbine powered railway engines done in the UK in the 1960s or early 70s as well.

IIRC they came to nothing for a similar reason - what to do with the engine exhaust when traveling through tunnels.
 
  • #13
You could point the exhausts up.
 

1. What is a microturbine exhaust cooling system?

A microturbine exhaust cooling system is a type of technology that uses a combination of air and water to cool the exhaust gases produced by a microturbine. This helps to improve turbine efficiency and reduce emissions.

2. How does a microturbine exhaust cooling system work?

The system works by mixing cool water with the hot exhaust gases from the microturbine. The water absorbs the heat from the exhaust gases, which then cools the gases before they are released into the environment.

3. What are the benefits of using a microturbine exhaust cooling system?

There are several benefits to using this type of system. It can improve the overall efficiency of a microturbine, reduce harmful emissions, and extend the lifespan of the turbine. It can also help to reduce noise levels and improve the safety of the turbine.

4. Are there any potential drawbacks to using a microturbine exhaust cooling system?

One potential drawback is the added cost of installing and maintaining the system. It also requires a reliable source of cool water, which may not be readily available in some areas. Additionally, the system may not be as effective in extreme temperatures or high altitudes.

5. Is a microturbine exhaust cooling system suitable for all types of microturbines?

While most microturbines can benefit from an exhaust cooling system, it may not be suitable for all types. It is important to consult with a professional and consider the specific needs and capabilities of the microturbine before implementing this technology.

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