The Oak Ridge study is here:
www.energy.gov...
(The first and second law energy balances are on page 20)
The NASA methanol steam reformer experiment is here: ntrs.nasa.gov/...
Modern petrol (gasoline - ‘Murica) engines are about 35 per cent efficient, and modern diesels are - maybe - early 40s.
That’s at about peak torque production. In normal road driving conditions - moderate loads and 2000rpm or something - they tend to be less thermodynamically efficient than that.
Modern diesels have higher compression, so they’re more efficient than petrols. Petrols can’t tolerate the higher compression because they’re knock-limited. That’s because the compression-ignition thing in a diesel is less about flame front propagation, and more about quasi-spontaneity.
It’s easier to understand efficiency using the first law of thermodynamics - which is about the conservation of energy. You can do a whole losses breakdown with the second law, too, but I fear the casualties we suffer will really mount up if we try that.
Oak Ridge National Laboratory in Tenessee did a breakdown on exactly the distribution of energy losses with a 1.9-litre GM diesel engine, back in 2011.
They are world-class brainiacs. (They did the second law version as well. Link in the description. Might need a pair of brown pants for that. #Deadpool.)
At normal roadgoing loads, out of 100 per cent of the energy in the fuel, about 26 per cent gets to the crank. And the rest is lost, which doesn’t sound real good. Three-quarters, just blown away.
We burn about 30 billion - with a ‘B’ - litres of petrol and diesel, here in Shitsville, annually. This means that more than 20 billion of that gets burned without serving a productive purpose. It doesn’t move anything.
Therefore, efficiency is perhaps the most important negative issue for the global dynamics of the human race. Certainly more people should think about it.
I’m gunna simplify Oak Ridge’s findings a bit, but here’s where they found the energy goes.
So here’s the basic problem, OK: We understand exactly where the losses occur. But there are immense practical barriers to reducing them.
The engine loses roughly the same amount of energy essentially through the radiator as it delivers to the crank for forward progress. This heat energy is just totally thrown away.
So just eliminate the cooling system, right? Retain the heat. That’s gunna push the piston down harder - because the gasses would be hotter and thus there would be more energetic expansion within the cylinder.
Thermal efficiency would skyrocket. For about 60 seconds. Then the elevated operating temperature would melt sundry vital components and destroy your engine. So there’s that.
Next, we’re losing quite a lot of energy out the exhaust manifold. Rapidly expanding, kinetically energetic gas is just being ejected. You can drive a turbocharger with that. In fact, the engine tested by Oak Ridge was turbocharged - so the efficiency increase from turbocharging (recovering some waste heat) is represented in those numbers already.
Turbos are good at repurposing energy that would otherwise be lost. And this is, of course, why there have never been more turbo cars on the market.
The third big loss category is pumping, friction and driving accessories (like the water pump): 21 per cent of energy is lost there. That’s quite significant, so reducing internal friction is a big deal for engine designers. But if you get too enthusiastic with that, engines start to misbehave.
And by ‘misbehave’ I mean they burn a lot of oil, or they start to wear out prematurely. And then there’s a customer backlash. Plenty of carmakers have had recent oil consumption backlashes - it’s because of engineering over-enthusiasm of the friction reduction front.
My challenge to you is: if you can make just a five per cent improvement to efficiency, you’ll be set for life. Carmakers will queue up to pay you those eight figures.
Before knocking on their door, I’d suggest you look at Mazda’s HCCI engine - homogenous charge compression ignition gasoline engine. Ultra-lean. Not knock-limited. Super high compression. Super complex, though. It’s rocket science.
Engineering tends to follow the path of least resistance. If there’s a simpler solution, they generally go with that. It’s cheaper. Easier to implement.
You now know exactly what you have to target: Do something smart with the waste heat. Smarter than NASA. Design a magic new material doesn’t need a cooling system (unfortunately, there are no new elements left to find…) Eliminate frictional losses. Eliminate inlet and exhaust valves, because driving them is a bastard for efficiency.
25 апр 2019
