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Study Notes 005
By William E. Steinman
Oxides of Nitrogen:
In looking at some of the problems with current automobile technology, exhaust emission poisoning of our atmosphere looms quite large. Some of the main ingredients of the smog in our urbane environment are the oxides of nitrogen. Automobiles create about half of all these oxides. Some of them, like nitrogen dioxide are quite deadly. In thinking of this previously, I conclude the people who are trying to solve this problem are going at it from the wrong end. They are trying to deal with a result rather than a cause.
If I was crapping black and I went to my doctor, I would not expect him to try to treat the crap. I would expect him to look at what I was putting into my system to cause black crap. ‘For crap sake,’ I thought. ‘If you don’t want oxides of nitrogen out of the engine, why the heck are you putting nitrogen in?’
Here is the deal. To burn gasoline in an engine, we put in gasoline and air. This mixture is ignited by a spark plug and burns to create the heat energy, which drives the piston to create motion. Everyone knows that. What many folks may not know is, it is the oxygen in the air that is necessary to the combustion. The nitrogen in the air is not necessary at all and about 80% of the air is nitrogen. Only about 20% is oxygen. So, if we do not want oxides of nitrogen from combustion, we should take the nitrogen out of the air before we put it into the engine.
While thinking about how to do that, I first though of using a centrifuge to separate N2 from O2. A look at the periodic table shows that oxygen is just a bit heavier than nitrogen. Since air is a mixture we should be able to separate it the same way we separate cream from milk. I also discovered there is a thing called a gas centrifuge. In fact, a gas centrifuge is used to separate the Isotope of Uranium 235 from the more common Uranium 238. U 235, of course, is the stuff that makes the big bang in the atomic bomb.
The question remains, is a centrifuge nitrogen separator technically feasible for automotive technology? We are talking about a lot of air per minute. Think it through. A 4-liter 4 cylinder engine running at 3000 rpm will suck about 6000 liters of air per minute. Each cylinder needs 2 revolutions to complete one cycle, but there are 4 of them. That ½ x 3000 x 4 = 6000. Since only 20% of that is oxygen, we will need to deliver .2 x 6000 = 1200 liters per minute. Please realize these are not scientific calculations. They are engineering approximations for strawman considerations. Additionally, the device must be easy to manufacture and inexpensive.
Okay, while I was considering the centrifuge, my old friend serendipity slapped me upside the head. I was visiting my sister who is suffering from a serious lung disorder called pulmonary fibrosis. This is a chronic disease with no known cure. It results in systematic oxygen starvation to the point where the patient requires constant oxygen therapy. Instead of breathing air with 20% oxygen, the patient breaths almost pure oxygen. This gives great relief to the patient and allows them to function much more effectively.
In my sister’s case, the oxygen is supplied by a device in her home called an oxygen concentrator. She has a long tube attached to this thing, which she drags around behind her whenever she moves about. It is a pain, but it beats heck out of not being able to function at all. It gives back some of the quality of life which most of us take for granted. I don’t anymore.
Well, how does the thing work? Actually, it works quite a bit like a water softener. It has two identical cylinders which are filled with a stuff called zeolite. I found the definition of zeolite in Microsoft’s Bookshelf.
zeolite (zê´e-lìt´) noun
Any one of a family of hydrous aluminum silicate minerals, whose molecules enclose cations of sodium, potassium, calcium, strontium, or barium, or a corresponding synthetic compound, used chiefly as molecular filters and ion-exchange agents.
The zeolite in the oxygen concentrator selectively absorbs the nitrogen in the air. The concentrator cycles between the two cylinders drawing air through one to produce concentrated oxygen while the other one dissipates its excess nitrogen into the surrounding air. The absorption and dissipation is controlled by air pressure. The property of this particular zeolite is to capture nitrogen under high pressure and release it under low pressure.
These concentrators offer an advantage over oxygen tanks of not being as dangerous. They are not as likely to explode. In addition, they do not cause the storage problems that oxygen tanks require. The big problem I see with these things for automotive nitrogen separation is the flow rate. It is typically 5 liters per minute. That’s quite enough for human comfort, but hardly up to the 1200 liters an auto engine would require. So, for now, these concentrators are just another line for research.
If we find a viable way of feeding an engine with pure
oxygen, what else will come of it? For sure, we will eliminate the oxides of
nitrogen, but what else will happen? I am sure a redesign of the intake ports,
jets, and manifold will be necessary. We should get a hotter and more efficient
burn. That could result I a dramatic increase in fuel efficiency. We may also
need a different fuel octane rating. I would not be a bit surprised to find
that a much smaller engine would be required to produce the same output torque.
These are possibilities that I present with no real analysis of the situation.
The redesign and analysis would require properly trained engine engineers.
It’s the kind of nitty-gritty problem that engineers are very good at.