“And that’s with better performance,” he added. “The modern diesel has greater torque in it than the turbine does. And you’ve got a couple of other things going for you as well. First, we’ve changed the nuclear, biological and chemical protection system, so it doesn’t operate off of the engine. On the turbine it operated off of ‘bleed air,’ so you had performance degradation on the turbine when the NBC system was on – and it’s on quite a bit. So that helps. Then, at idle, this [diesel] vehicle uses less fuel than if you put an under armor auxiliary power unit in there. And it’s quiet – it’s very quiet. The heat that comes out the back of the engine is 300 percent less than what was coming out of the back of the turbine. So there’s a significant reduction in heat signature and you can actually stand behind the tank now – when it’s running – and have a conversation.”
I looked up whether Cummins provided the engine for the Abrams tank, and discovered that it uses a gas turbine, not a diesel. I was gob-smacked. My engineering spider senses were tingling. On a checklist comparing a gas turbine against a diesel, in a tank, I can imagine that there are a lot of bullet points that I don’t even have a clue about, so I was willing to give the decision by the Pentagon the benefit of the doubt. However, the very next article on the search results was this one, showing a lot of compelling reasons to switch out the turbine for a diesel, and this made me feel justified in my feelings. Again, though, I am open to the possibility that other, valid constraints may still dictate this solution. Maybe it’s a mass/acceleration, or a moment-of-inertia/maneuverability thing? I don’t know, but the idea of the engineering tradeoff conversation on this topic fascinates me.