Trying To Keep Up With Cycle World Readers

Lots of good questions are proposed, so I’m obliged to try to find answers.

Raccoon Mountain pumped-storage hydroelectric plant
Giant water battery: Raccoon Mountain pumped-storage hydroelectric plant located near Chattanooga, Tennessee, began operation in the 1970s, like Northfield Mountain Pumped Storage on the Connecticut River a few miles from Turners Falls dam.Tennessee Valley Authority

An objection to my recent “What If All Automobiles—Never Mind Motorcycles—Were Electric?” story was that large numbers of solar and wind farms could generate energy that was stored during the day for later use when it’s dark or the wind isn’t blowing. Reminds me of the classic GI remark that, “If we had some ham, we could have ham and eggs. If we had some eggs.”

During 2018, wind supplied 6.7 percent of US electricity and solar broke 1 percent for the first time for a total of 7.7 percent. That’s the ham, because it takes time to get site permits, find investment dollars, and build and put online such clean, renewable power.

The eggs are a means of affordably and, with acceptable efficiency, storing large amounts of electrical energy for later use. Taking a familiar example, Los Angeles has a yearly average power demand of roughly 3,000 megawatts (maw). If we plan to supply the great city with eight hours of stored energy, they’ll need something like 24,000 mWh of it (3,000 mW x 8 hours). No such storage system at present exists, but a great many possible chemistries have been proposed by which to build it. Remember the rule: Business does nothing for nothing. Investors want to know their money will earn a competitive return, as compared with, say, hedge funds.

For the homeowner, Elon Musk proposes we combine rooftop solar with Li-ion household batteries from his Gigafactory. Or we could, as others propose, use our millions of electric-car batteries as energy storage for the hours of darkness. If we had millions of electric cars.

Batteries aren’t the only means of power storage. Right near me is Northfield Mountain Pumped Storage, which uses four giant pumps to send water from the Connecticut River up 1,200 feet to a shallow lake. When that energy can be sold at a higher price than it was bought, they run the water back through huge downcomers to drive the pumps as generators. The owners collect the difference. Trouble is, geography (a river, a lake, a mountain) that permits construction of this kind of plant can be hard to find.

Desert stormer
Desert stormer: Honda built the two-stroke, 400cc, single-cylinder EXP-2 to reduce fuel consumption and pollution while maintaining a high performance level. Frenchman Jean Brucy was fifth in the 1995 Grenada-Dakar Rally on the prototype machine.Cycle World

The folks at Rocky Mountain Institute proposed many years ago that all south-facing roofed area in the US be covered with solar cells—we again invoke the TED Talking Tinker Bell to accomplish this praiseworthy goal—whose power would be used to electrolyze water into oxygen and hydrogen. The hydrogen could be stored in compressed form (liquefying is said to require at least 40 percent more energy than electrolysis, so forget that) for later use.

How would we use it?

1. We could fuel combustion engines with it. For example: the gas-turbine electricity-generating equipment now firing on natural gas, which supplied 34 percent of US electricity in 2018. Simple-cycle turbines operate at 25–35 percent efficiency, but the latest Europe-style combined-cycle units are just hitting 60 percent efficiency now. Auto and light truck engines run okay on hydrogen—maybe 25 percent efficiency—but with the usual problems of storage (even compressed hydrogen takes up a lot of space) and assuring leakage-free systems. Pass me that Teflon tape.

2. We could run our home-liberated hydrogen through fuel-cell systems to generate electricity at 50–60 percent efficiency to power households and transportation.

3. We could pipe some of our hydrogen to neighborhood compressor stations with large onsite storage tanks. The stored pressurized hydrogen would power everything during the hours of darkness or during peak demand; LA’s record peak is twice its annualized average power demand. As I’ve noted before, such storage tanks will be located in your backyard because my family won’t let me have them in my backyard.

Other readers were interested in how engineers measure the speed of combustion in running engines. Today they just screw a bunch of ionization gauges into the head in a variety of places; one setup I saw had 32 such probes. Then recorded data shows how long it took the flame to reach each of those points in the chamber. Make a map, do an animation.

Questions regarding the chemistry of preflame and hot-flame reactions have been answered by fast-acting timed sampling valves and later chemical analysis. There are endless SAE papers about all this, revealing the many chemical reaction pathways. MIT’s Sloan Lab constructed the Rapid Compression Machine to explore preflame reactions, and a DuPont researcher named Sturgis made pioneering understandings of preflame reactions that today have become the basis for HCCI combustion—Homogeneous Charge Compression Ignition. This is a sparkless combustion that operates with a premixed fuel/air charge (no direct fuel injection). Honda built an enduro bike, the two-stroke EXP-2 of 1995, that ran on HCCI everywhere except at idle/low throttle and on top-end in which conditions it needed spark assist. It was fascinating. Also Mazda’s HCCI engine. Remember what Dorothy Parker said: “Curiosity is the cure for boredom, and curiosity has no cure.”

Gigafactory 1
Automaker Tesla began constructing Gigafactory 1 in Sparks, Nevada, nearly six years ago. Once it is completed, the facility reportedly will be the largest building in the world and powered entirely by renewable energy sources.Tesla

More information can be gathered by tapping a high-pressure microphone into the combustion chamber and placing a rotary encoder on the crank, giving by easy computation a series of pressure-volume curves. This has revealed the problem of cycle-to-cycle variation in spark-ignition engines. Analyzing hundreds or thousands of such PV curves revealed that the best individual combustion events yielded as much as 20 percent greater peak pressure than the worst ones.

Why the variation? At the instant that the ignition spark occurs, the local “wind” of mixture turbulence varies moment to moment in direction and intensity. On one cycle, the flame kernel is swept in a favorable direction and is shredded such that light up is rapid. On the next cycle, the flame kernel may be blown in a less favorable direction, so peak pressure sags.

How do we know what’s up with the flame kernel? Our data system “knows” when the spark occurs, but our microphone shows us that no significant pressure rise occurs for several crank degrees. Why? The kernel is tiny and, in its first few doublings, remains tiny, reacting too little of the charge for the microphone to “see.” Our researchers are fussy, wanting to know the microphone’s threshold, its response time, everything about it. And it’s all there in the specs, which improve with every new generation of such microphones. Grad students are assigned to do the error propagation through the whole process so they can accurately assign a plus/minus to every measured variable.

But it’s all happening so fast! In a MotoGP engine at 18,000 rpm, combustion takes roughly one thousandth of a second. But in computer terms, this is forever. A 1-gHz processor can perform 1 million clock cycles during a single MotoGP combustion. Just imagine the data you want, and instrumentation engineers are standing by to devise how to get it for you.