Tag: Engineering

Today in Weird

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Source if the leak

The leak in the space station was some screw-up with a drill who tried to hide his mistake:

Last week, a pressure leak occurred on the International Space Station. It was slow and posed no immediate threat to the crew, with the atmosphere leaving the station at a rate such that depressurization of the station would have taken 14 days.

Eventually, US and Russian crew members traced the leak to a 2mm breach in the orbital module of the Soyuz MS-09 vehicle that had flown to the space station in June. The module had carried Russian cosmonaut Sergey Prokopyev, European Space Agency astronaut Alexander Gerst, and NASA’s Serena M. Auñón-Chancellor.

The crew on the station was in no danger, and, over the course of several hours, Russian engineers devised a fix that involved epoxy. A preliminary analysis concluded that the vehicle is safe for return to Earth (the orbital module detaches from the small Soyuz capsule before entry into Earth’s atmosphere).

The drama might have ended there, as it was initially presumed that the breach had been caused by a tiny bit of orbital debris. However, recent Russian news reports have shown that the problem was, in fact, a manufacturing defect. It remains unclear whether the hole was an accidental error or intentional. There is evidence that a technician saw the drilling mistake and covered the hole with glue, which prevented the problem from being detected during a vacuum test.

“We are able to narrow down the cause to a technological mistake of a technician. We can see the mark where the drill bit slid along the surface of the hull,” Dmitry Rogozin, head of the Russian space agency Roscosmos, told RIA Novosti. (A translation of the Russian articles in this story was provided to Ars by Robinson Mitchell). “We want to find out the full name of who is at fault—and we will.”

………

In this case, the technician used glue instead of epoxy. As the Soyuz hull is made from an aluminum alloy, it could have been properly repaired on Earth by welding, had the technician reported the mistake.

The Soyuz manufacturing issue represents another significant problem for the Russian space agency’s suppliers and its quality control processes. Already, the manufacturer of Proton rockets, Khrunichev, has had several serious problems that have led to launch failures. Rogozin was recently installed as the leader of Roscosmos to try to clean up corruption and address these kinds of issues.

Seriously, this sh%$ is rocket science, and everyone screws up.  You own it, and the Russians know how to use a TiG welder just as well as anyone else, and the fix along with post weld inspections, should not have taken more than a couple of hours.

Bondo is not an option in space.

This is Ingenious

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Comparison of various cycles


SPCCI Cycle


Pressure Profiles

Diesel engines have been getting a lot of bad news recently, but there is a another form of compression ignition that has been lurking in the laboratory for years.

A diesel compresses the air, and then squirts in fuel, which ignites in the hot air.

The other form of compression ignition compresses a fuel air mixture until it all ignites simultaneously.

Theoretically, this could result in superior fuel economy and low levels of pollution.

This is a tremendously difficult thing to do since things like this, since the line between ignition and nothing is a very fine line, and things like ambient temperature, barometric pressure, etc. can cause premature ignition, i.e. pinging, which hits the inside of an engine like a hammer.

Nissan has come up with an innovative way to fix the timing, they have added a spark assist so that they can control the timing.

As opposed to a conventional spark ignited engine, where the flame front progresses from the spark, in their “Skyactive X®” technology, and the initial local ignition kicks up the pressure and temperature enough for the compression ignition to kick in.

Mazda is now has a car with this technology on the road:

Despite rumors to the contrary, the internal combustion engine is far from dead. Recently we’ve seen several technological advances that will significantly boost the efficiency of gasoline-powered engines. One of these, first reported back in August 2017, is Mazda’s breakthrough with compression ignition. On Tuesday, Mazda invited us to its R&D facility in California to learn more about this clever new Skyactiv-X engine, but more importantly we actually got to drive it on the road.

The idea behind Skyactiv-X is to be able to run the engine with as lean a fuel-air mixture (known as λ) as possible. Because very lean combustion is cooler than a stoichiometric reaction (where λ=1 and there is exactly enough air to completely burn each molecule of fuel but no more), less energy is wasted as heat. What’s more, the exhaust gases contain fewer nasty nitrogen oxides, and the unused air gets put to work. It absorbs the combustion heat and then expands and pushes down on the piston. The result is a cleaner, more efficient, and more powerful engine. And Skyactiv-X uses a very lean mix: a λ up to 2.5.

………

This is known as homogeneous charge compression ignition, or HCCI, an idea that Kyle Niemeyer covered in depth for us back in 2012. HCCI has some other advantages, too. On top of burning cooler and with fewer pollutants, the combustion event happens faster, with a higher pressure peak, so you get more work out of the same energy. All of that sounds pretty wonderful, so you’re probably asking yourself why every gasoline engine on the road doesn’t just use HCCI.

Unfortunately, it has been one of those ideas that worked in the lab but couldn’t ever quite be translated into a production engine. The biggest problem has always been controlling exactly when during the engine cycle compression ignition occurred, something that you want as close to top-dead center as possible.

………

Obviously, this wasn’t without challenges. The fuel:air mix needs to be a little richer near the spark for it to ignite than you want it to be throughout the rest of the cylinder. These need to be distinct regions to avoid λ dropping to 2 or below (which won’t undergo compression ignition). That’s achieved by swirling the air inside the cylinder and generating a vortex effect, where the calm center has a low enough λ to ignite by spark, surrounded by a high λ region that then undergoes compression ignition.

Mazda’s next challenge was to prevent pre-ignition, or knock. Higher compression ratios increase the potential for knock, which is why higher compression ratio engines usually also require more expensive, higher octane fuel that is knock-resistant. Now, technically, compression ignition is knock, but if it occurs before you want it to—at top dead center—bad things can happen, because a combustion event will exert downward pressure on the piston as it’s moving up on a compression stroke.

The solution here was to use less time to heat the fuel:air mix. There’s a small initial injection of fuel at first, then the bulk of the fuel is introduced into the cylinder as late as possible during the compression stroke. This is done using multiple orifice injectors to increase atomization and mixing of fuel and air.

If all that wasn’t enough, there’s the added problem of keeping track of compression ignition. In the past, this has been one of the hardest problems for HCCI engines to solve. Ideally you want combustion to happen at the same point in the engine cycle each time—about four degrees after top dead center. But as ambient conditions change—a cold day in Denver versus a hot one in Houston—the time needed for the fireball to reach sufficient pressure also changes. So the engine ought to be able to change spark timing to keep the peak pressure at the right spot.

It’s basically an ingenious use of the stratified charge engine to create an HCCI engine.

Neat.

How Not to Design Reasonably

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One of the fails going around the internet is Juicero, which is selling a press to squeeze raw juices from its pouches into a cup.

This press recently had its price reduced to “only” $400, for a juicer.

What’s more reporters at Bloomberg discovered that you could get about the same amount of juice from the pouches using the Mark 1 human hand.

Not bad for a company that has raised $120 million in VC funding  ……… For a juice squeezer.

After all of this product designer Ben Einstein did a a disassembly and a deep dive, and  he found a ridiculously over-designed mess.

The short version is that there is a press using a custom motor and custom gear train, a half dozen machined aluminum parts which drives an aluminum plate against the pouch to uniformly apply pressure.

Einstein inventoried the following:

  • An extremely complex plastic molding, including co-molded parts.
  • A heavy custom machined aluminum frame.
  • A custom power supply.
  • Massive custom hinges on the door.
  • Custom sliders.
  • A very robust custom gearbox.  
  • Etc.

Looking at this problem, I immediately have a better way of doing things.

I could make a prototype using an off the shelf aquarium pump for less than $100 in in parts.  (It would work like the so called “Neat Squeeze” toothpaste tube), or do something similar with a store bought pasta maker retailing for $29.99.

That took me all of 15 minutes to think about it.

This is all of Silicon Valley dysfunction in a squeezable pouch.