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Modern MBTs pros and cons of diesel and gas turbine engines?


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Ikanator #21 Posted Dec 03 2016 - 13:47

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View Postcollimatrix, on Dec 01 2016 - 04:26, said:

 

You're right about the filters, although according to Ogorkiewicz the airflow for a turbine and a diesel of equal output is comparable.  I think the difference is that most of the air for a diesel is air that's getting pulled around the radiators, while all the air for the turbine is going through the engine, so it has to be filtered.

 

On the other hand, turbines have no radiators to maintain.

 

 

I've actually heard that an Abrams stands out less on thermals than a Leo 2.  I know, I was pretty surprised too.  The reason is that the diesel puts out a cloud of fine particulate that scatters the IR emissions, and rises above the tank and is thus obvious from a long ways off.  Turbines (or at least the AGT-1500) apparently don't do this.

 

 

There was even a modified version of the AGT-1500 that had some new parts swapped in that had significantly better idle efficiency and time between overhauls.

 

The AGT-1500 simply isn't remotely representative of what mrn turbines are capable of.

 

The air flow through a diesel engine's radiator isn't the only air flow a diesel needs. There is also an air flow through the engine itself. If there is no air entering the cylinders when the pistons move down on their intake strokes the engine will not run. And if that air is not filtered then sand, dust, grit, etc. will damage the engine and greatly reduce its use life.

 

While I suspect that a diesel might be less adversely affected by dirty air getting inside it than a turbine, that is only a guess on my part. The traditional analysis is that diesels are more fuel efficient and turbines produce much more horsepower per weight of engine. Though I am not familiar with all the latest advances in turbine technology and I have seen other posters argue that fuel efficiency between the two engines may now be comparable.



collimatrix #22 Posted Feb 18 2017 - 23:08

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The air that the diesel engine actually consumes; i.e. the air that's going into the cylinders to burn the fuel is a pretty small amount compared to the air that is used to cool the engine.  Per Ogorkiewicz, the amount of air that's consumed by a diesel plus the amount of air that's used to cool the diesel is about the same as the amount of air that the turbine actually uses to compress and burn fuel for the same horsepower.

 

So for a given horsepower a diesel powered tank and a turbine powered tank will need about the same size grilles to let in air.  However, for the diesel relatively little of that air is actually going into the engine, so only a small percentage of that airflow needs to be well-filtered of dust.  For the turbine, all of the air is going into the engine, so all of it needs to be well-filtered if the engine is to last.  So, for a given horsepower, air filters need to be much bigger for turbine powered tanks.  Neither engine type will be happy if it gets a bunch of dirt in it.

 

Diesels are still more efficient than turbines.  Since the engines of the Leo 2 and Abrams were developed, diesels have gotten somewhat better while turbines have gotten a lot better.  My prediction is that turbines will eventually overtake diesels for efficiency because they have more growth potential.  Diesels practically can't exceed a certain compression ratio or they get diesel knock and piston head damage.  It's a similar problem to why gasoline engines have such low compression ratios, although for diesels the problems start to happen at a much higher compression ratio, and thus diesels are more efficient than Otto cycle engines.  Turbines are limited in their overall pressure ratio and turbine inlet temperature only by materials limits.  The materials get a little better every year.






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