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Comment by madflame991 | Hacker News Reader

"The new engine will meld the best characteristics of gasoline and compression ignition engines with an innovative piston architecture refined by Achates Power that sets two pistons moving in opposition in one cylinder."

We already have this technology. Diesel engines ignite the fuel through compression. We also had the opposing pistons layout for a while (https://en.wikipedia.org/wiki/Opposed-piston_engine).

EDIT: we even have triangular-y shaped opposing engines (https://en.wikipedia.org/wiki/Napier_Deltic)

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That's what's puzzling. Opposed-piston Diesel engines have a long history. There are others now proposing them. Eco Motors [1] claimed they were going into production with one in 2014. Didn't happen. They might be a little better, but the claimed 50% improvement in fuel economy is a big jump.

These engines use valve ports, so piston motion produces the valve action. All the timing is set by the engine geometry. There are few variables adjustable at run time. This is also true of Wankel engines, which is why Wankels hit a wall - you can't tweak fuel injection timing or valve timing. In a Diesel, you can't even tweak the spark timing. Much of the improvement in IC engines has come from active control of fuel injection and spark, along with a few attempts at dynamically tweaking valve timing. These designs don't seem to be able to do that.

[1] http://ecomotors.com/video

Granted you're absolutely right, but the article does seem to acknowledge this:

"and allows the engine to run with diesel-like efficiency and power, while maintaining gasoline's emissions benefits."

Whether or not any of this is actually feasible is explored in elbigbad's sibling comment.

As an aside - I love the names of the Dark class of RN boats that used Deltic engines:

https://en.wikipedia.org/wiki/Dark-class_fast_patrol_boat

Dark Avenger probably being my favourite!

The Brits are just so much better at ship names than the US. We always name ours after places and politicians--boring! The Brits meanwhile have ships like Onslaught, Firedrake, Acheron, Invincible...

Well, possibly the most ominous one is "HMS Vengeance" - one of the UK's Trident missile subs.

Vengeance is fine for its deterrent use. I would be more worried about Victorious.

Or Terror, mind you - maybe that would be appropriate for a deterrent.

Hmm is this our "we have skulls on our hats, are we the bad guys?" moment...?

https://www.youtube.com/watch?v=hn1VxaMEjRU

The thing is, those skulls don't come from WWII, they originate with the napoleonic wars.

https://upload.wikimedia.org/wikipedia/commons/a/a6/John_Eve...

I agree completely. US Navy ship names are nothing short of horrible. They used to have some cool names back in WWII, like Wasp, Hornet, Enterprise, etc. They've kept Enterprise (there's a new Enterprise now planned to replace the now-decommissioned one). They had some cool submarine names way back too, like Nautilus, plus there used to be a bunch named after fish, which isn't too bad. But otherwise, over the last several decades, they just plain suck. The worst one ever is the carrier USS John C Stennis. WTF? They named a carrier after some dumb politician who was never even President, and all he did was get a lot of pork funding for military projects. He also got a Space Center named after him in Mississippi because he was good at this (and this was because he got the center placed there, even though there wasn't any really good logistical reason for it; they do NASA's rocket engine tests there. It's not anywhere near where the engines are actually launched from, it's just a pork project).

Yes, BMW is known for a similar design:

https://en.wikipedia.org/wiki/Flat_twin_engine

Not quite. The engine discussed in this article is almost the reverse of BMW's engine design. The crankshafts (where the rotational movement is transferred to the gear box) would be where the heads of the BMW engine are located. This means the explosion causing the rotational movement is at the centre of the engine, and keeps heat loss to a minimum. That's partly how they're going to get such high efficiency out of this design. The other way is the (I'm guessing) massive compression ratio they'll need to achieve for the auto-ignition of gasoline to occur.

What I think, and this is without being ICE engineer, is the same effect that helps Mazdas SkyActive engines achieve high efficiency, higher compression and longer exhaust cycle. That a two stroke achieves a high power output is not surprising, and is one of the main reason they're used, as the power to weight ratio is superior to 4 stoke.

To add to your comment, the SkyActiv engines are Atkinson-cycle engines, which improves efficiency by holding the intake valve during the beginning of the compression stroke, so that the exhaust compression ratio is greater than the intake compression ratio, extracting more work out of the exhaust gases. The disadvantage of this is that the engine has lower power density (it won't get the same HP/liter ratings that a similar Otto-cycle engine will). This can be made up for by adding an electric motor to make it a hybrid car, or by adding a supercharger (which makes it a Miller cycle engine).

2 strokes are terrible engines generally, because they have very high emissions, usually because they release unburned fuel in the exhaust.

This engine appears to burn gasoline rather than diesel fuel. I suspect the compression must be much higher to ignite gasoline than is required for diesel.

actually it's the opposite, you could run a diesel car on gasoline if you wanted (not wise as diesel fuel is actually used as a lubricant in high pressure fuel pumps)

Wouldn't you also get knocking?

Compression required to "diesel" petrol (gasoline) is lower, which is why some autos have the problem of continuing to run ("diesel") after the ignition (and spark) are shut off. Most now incorporate other controls and limiters, such as controlled fuel injection, to eliminate this.

Gasoline is comprised of a shorter set of hydrocarbons (mostly 6, 8, and 10 chain) than diesel (about 12-16 chain length, though 8-21 carbon are listed at Wikipedia). Volatility (and ignitability) increase with shorter chains -- methane (C2H6) and butane (C4H10) -- that is, two and four chain hydrocarbons -- are both gaseous at or near room temperature.

Longer chains still get you heavy fuel oils, tars, etc.

Longer chains still get you heavy fuel oils, tars, etc.

...and eventually that results in simple plastics like polyethylene, which is basically a very long chain hydrocarbon:

https://en.wikipedia.org/wiki/Polyethylene

Yep. I regret not having studied more chemistry in college. It's only started coming into context for me recently.

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