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posted by martyb on Thursday July 26 2018, @06:55PM   Printer-friendly
from the opposition-is-growing-stronger dept.

Submitted via IRC for SoyCow1984

Horizontally-opposed engines are often referred to as “boxer” engines because the motion of the pistons sort of resembles a boxer, punching. Really, though, if any engine should be named for a boxer, it’s the other kind of opposed engine: the kind where the pistons actually “punch” right at each other. They’re called opposed-piston engines, and they’re fascinating.

Opposed-piston engines are not new at all; they’ve been around since the late 1800s, and even earlier in steam form. In fact, the famous Civil War ironclad USS Monitor used a variant of an opposed-piston engine known as a “vibrating lever” engine.

Essentially, an opposed-piston internal combustion engine is a two-stroke engine with no cylinder head, two separate crankshafts, onto which two sets of pistons are connected, with the pistons sharing one cylinder.

The pistons meet (well, nearly meet) at the center of the cylinder, the top dead center (TDC) for both pistons. ports on the sides of the cylinder let fuel/air in and exhaust out, and are exposed by the motion of the piston.

[...] What’s especially notable about the engines is that, in three-cylinder (remember, six-piston) form, the Achates Power vertically-oriented opposed-piston diesel engine shown in the video there managed to obtain thermal efficiencies in the high 40s/low 50s percent. Keep in mind that a conventional four-stroke diesel engine will only be about 35 percent thermally efficient, on average. That’s a big bump.

Source: https://jalopnik.com/its-time-to-learn-about-wonderful-and-weird-opposed-pis-1827804895


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  • (Score: 0) by Anonymous Coward on Thursday July 26 2018, @11:46PM (5 children)

    by Anonymous Coward on Thursday July 26 2018, @11:46PM (#713455)

    Most people were not paying attention.

    Sure, the required number went up... but you no longer really had to meet that number. There was a huge fuel economy bonus multiplier available, and all that was required was to make the fuel system tolerate a bit more ethanol in the fuel. (meaning it doesn't get corroded metal and crumbly rubber)

    Switching all fuel systems to earn the bonus would let a manufacturer meet CAFE rules with a lower number than before. Thanks Obama! Seriously I guess, because I like fuel systems that don't crumble and corrode.

  • (Score: 2) by JoeMerchant on Friday July 27 2018, @12:28AM (4 children)

    by JoeMerchant (3937) on Friday July 27 2018, @12:28AM (#713471)

    Our local station started carrying E50 or somesuch, at a considerable discount - like 2.09 when regular is selling for 2.69. Not sure what all kickbacks are in play with that, but if you live in your car it could make a difference.

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    • (Score: 2) by urza9814 on Friday July 27 2018, @01:43PM (3 children)

      by urza9814 (3954) on Friday July 27 2018, @01:43PM (#713662) Journal

      Our local station started carrying E50 or somesuch, at a considerable discount - like 2.09 when regular is selling for 2.69. Not sure what all kickbacks are in play with that, but if you live in your car it could make a difference.

      It's not cheaper because of kickbacks necessarily (although there's some farming subsidies at play I'm sure)...but when I've looked into this stuff in the past I found it was priced pretty comparable to its relative value compared to normal gasoline. I dunno about E50, but E85 can be expected to cause a decrease in fuel economy of up to 27%. 60 cents off of $2.69 is a 22% discount. So it could save you a bit of money if your car is properly tuned for it, but the savings aren't going to be huge. And you'll have to stop and refuel more often -- a full tank won't get your as far.

      • (Score: 2) by JoeMerchant on Friday July 27 2018, @02:38PM (2 children)

        by JoeMerchant (3937) on Friday July 27 2018, @02:38PM (#713688)

        While I agree that there is less energy content per gallon in ethanol than gasoline, it seems unlikely that substituting 15% of your gasoline with ethanol will decrease economy 27%.

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        • (Score: 2) by urza9814 on Friday July 27 2018, @03:41PM (1 child)

          by urza9814 (3954) on Friday July 27 2018, @03:41PM (#713712) Journal

          While I agree that there is less energy content per gallon in ethanol than gasoline, it seems unlikely that substituting 15% of your gasoline with ethanol will decrease economy 27%.

          Ah, sorry, perhaps I should have explained that a bit more...E85 isn't 15% ethanol, it's 85% ethanol. I haven't seen E50 and I couldn't easily find numbers for E50, but the US Dept. of Energy states that E85 will decrease your fuel efficiency by up to 27%: https://www.fueleconomy.gov/feg/ethanol.shtml [fueleconomy.gov]

          So E50 is about halfway between the standard E10 and that E85, so that could probably drop your fuel efficiency by close to 14%. With a given 22% savings on the price of it, it's still not a terrible deal if you're passing that gas station anyway, but it's not worth going too far out of your way for it. Although YMMV, quite literally...it's going to be a better deal for some vehicles than others.

          The root of my comment is that I own a "flex fuel" Pontiac G6 which is designed to be able to run on E85. A couple years back I was testing out some gas finder app and saw a place selling E85 for what *appeared* to be a great price just a few towns over, so I decided to look up efficiency numbers for my car specifically. I don't recall the exact details, but I do remember that the cost savings and the expected reduction in fuel economy were within one or two percentage points of each other. So I've never actually put E85 in my tank, because with those numbers it wouldn't have been worth going even a mile out of my way to find some.

          • (Score: 2) by JoeMerchant on Friday July 27 2018, @04:31PM

            by JoeMerchant (3937) on Friday July 27 2018, @04:31PM (#713737)

            O.K. - thanks - E85 was twisting my brain a bit... obviously.

            It may actually be E85 that they are selling at that super cheap pump - it's a weird station, different pumps sell different mixes all up and down the range - not just 4 or 5 choices at each pump, but actually different choices depending on which pump you pull up to.

            As far as energy density goes, diesel used to be the deal - up until the Gulf War II fuel price spikes, then they started actually charging for the value of it.

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