Most efficient piston type engine? 3

[enginesrus]

The first engine that comes to mind is the Wartsila (formerly Sulzer) 2 stroke ship engine, Mercedes is suppose to have a 50% efficient F1 racing engine.
Nissan is suppose to have a 50% engine, even Fairbanks Morse, as well as Achates.
So what is the latest news on high efficiency?

 

[gruntguru]

All the F1 engines are now greater than 50% TE and at best are probably more more efficient than the Wartsila. Mercedes were claiming 50%+ seven or eight years ago and all the engines have improved significantly since then. Pat Symonds lecture doesn't give a number for TE but includes a lot of fascinating insights.
Link

je suis charlie

 

[CWB1]

Large stationaries are advertising upper 40s while meeting emissions, but operating points well over 60% are achievable. Anything that has to pull the entire lug curve will always be lousy for efficiency compared to modern high-speed stationaries optimized for an operating point, 2-stroke low-speed beasts notwithstanding.

 

[TugboatEng]

Large stationaries are the low speed and very large medium speed engines. On they're own they're only approaching 50%. The slow speed can get above 50% in shipboard applications where the have lots of cogeneration loads. High speed engines mostly have not made it to 40% yet.

Note that I am working off antiquated but accepted definitions. Low speed < 250rpm < medium speed < 900rpm < high speed.

 

[gruntguru]

Pretty sure the best Wartsila has circa 52% TE - shaft power only.

je suis charlie

 

[Factoter]

The various Scandinavian Hot Bulb engines ran in the most effective way, and in reality what is most efficient is what is most effective. That being said Volkswagen drove a hybrid Golf prototype across the USA and claimed 500mpg, somehow they built a steam boiler into the exhaust system, and injected SC steam into the combustion chamber. Definitely a one-off.

 

[Factoter]

Can’t find the link to VW Golf, did anyone else see this news story? —-think it was ~2015. Apparently this is an over unity result . . . series hybrid hydraulics vehicle might achieve over %50 equivalent TE, with gas engines, IDK.

 

[TugboatEng]

It might be hard to find because your MPG is so far off.

https://www.motortrend.com/news/a-volkswagen-golf-tdi-drove-through-48-states-and-averaged-81-mpg/

The year was right.

 

[BrianPetersen]

Also, that was a production vehicle (and one whose technology was later to be implicated in the "dieselgate" scandal). That sort of low fuel consumption isn't due to any revolutionary technology, more due to simply driving slowly and steadily so as to be as efficient as possible.

There was no "steam boiler" in the exhaust system of that vehicle (I believe it was BMW who did that experiment). Although it wasn't specified, the car would have used either the 6-speed manual or 6-speed dual-clutch automatic, in both cases having fully mechanical transmission to the wheels. No "series hybrid hydraulics" ... that's less efficient than electric+battery, and if you're doing steady speeds, that's less efficient than gears and shafts.

 

[BrianPetersen]

Wikipedia has an article about the Turbosteamer with links to further information.

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

Does not appear to be worth the aggravation.

 

[Factoter]

Thanks for the responses. Turbosteamers and hybrids, oh dear. In terms of maximum preservation of thermal angst, Top Fuel dragsters must be the winner each and every time, those phonons are all cleanly morphed into earth shaking euphoria. Perfect unity mach8ne!

 

[TugboatEng]

The valve springs of a top fuel engine are the most fascinating part to me. It seems like it should be the lowest stressed part for such a few cycles of fatigue yet they get some of the most attention including polishing of the wire. I don't think even NASCAR does that. There must be a reason but it's super secret.

 

[Factoter]

Is it easier to finish Ti alloy?— must admit that these springs exist is news to me. With no traditional coolant system and valves never closing, all the heat goes into the guide and springs, so maybe Ti is getting near critical temps?
For giggles I calculated TE of a top fuel dragster at 0.007929%, beat that!

 

[gruntguru]

What - you didn't add the shredding of rubber and clutch discs into your useful energy output?

je suis charlie

 

[BrianGar]

https://www.youtube.com/watch?v=mUq-K9jcaB8

Brian,

 

[Factoter]

Here’s the very poor wikipedia link to this unusual combustion: ddt

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

18:1 mechanical CR, boost up to 5.5 bar, lambda over 1.3 and fuel with no aromatics.
I’m assuming the Detonation is preferably at peak RPM when piston speed is greatest, and special cooling squirter to prevent meltdown of pistons, although how they still don’t melt? Diamonds?
IDK.
—To draw from the earlier Achates Thread:—-Is this suited to opposed pistons, as Tug mentioned, there’s a 2x expansion, so better suited to a faster combustion? The above video makes me think that the Achates OP is a detonation diesel, based on the timeframe, I know that a number have been said to exist. Could this be one? Any opinions?

 

[BrianPetersen]

The video above is surely just the tip of the iceberg, the small part of development that they feel they don't need to keep secret.

Ever-so-slightly-educated guesswork follows. (Purely mine.)
They're running on the verge of detonation, but still keeping rate of combustion finite so that it is a progressive almost-self-ignition and not a simultaneous ignition everywhere in the combustion chamber.
They're not relying on in-cylinder charge motion as much as conventional production engines do - they're getting the speed of combustion via the plasma-jet ignition and the almost-but-not-quite detonation. The flat-pancake shape of a F1 cylinder (due to the extreme bore/stroke ratio) doesn't lend itself to tumble charge motion that is typical of production 4-valve-per-cylinder engines.
Completing combustion very quickly, in a small number of crank degrees and while the compression is high, cuts down on the time available for heat transfer to the pistons.
The big bumpy cams necessary for high-RPM peak power leads to lower dynamic compression ratio at lower revs, so detonation at lower revs probably isn't as much of a problem - the effective compression ratio will be lower because the volumetric efficiency is lower. These engines will not have friendly, smooth, daily-driver-suitable torque curves.
Running high lambda keeps peak combustion temperature down.
They're probably doing some in-cylinder stratified-charge trickery to keep the mixture next to the piston as high lambda (lean) as possible to act as an insulating layer.
High lambda (high dilution) plus completing combustion very quickly so that the burned charge is more fully expanded, cuts down on exhaust-gas temperature.
Cutting down on heat transfer to the pistons (and head) is an important bit of improving engine efficiency.

A nuisance with Achates is that you can't put the injector and spark plug in the center of the chamber, because there's a piston there instead of a cylinder head. Not saying it can't be done, but it would need a re-think of the combustion process.

 

[Factoter]

BP. Good insights, and thanks for the ‘guesswork’.

—-One tiny morsel from this presentation, is that MGU machine can directly power the crankshaft, if the batteries are at capacity. The fuzzy diagrams show a ‘blackbox’ so guessing what this means, or that I interpreted it correctly. But sounded like indirect coupling of turbo to crank,
—-Regarding the lambdas: 1.3 varying up to 1.5, and potential for 2.0. I have no knowledge of combustion properties at these temps and pressures, or these fuels. 1.3 is uncommonly lean.

 

[BrianPetersen]

Yes, they're recovering some output power from the exhaust turbine under some conditions.

Lambda 1.3 or thereabouts is probably the average for the whole chamber. If they're doing what I suspect - using direct-injection to deliver a shot of fuel through the last half-or-thereabouts of the intake stroke and first part of the compression stroke - my suspicion is that via clever injection timing and nozzle aiming, the top (let's say) half of the cylinder will be as close to lambda 1.0 as they can get (a bit of this is what works its way into the "prechamber" and the rest of it is next to the cylinder head) and the bottom (let's say) half of the cylinder will be way, way lean. Inevitably there will be mixing but this way the top part of the charge (starting at the spark plug / prechamber) can burn quickly and work its way down through the more dilute charge closer to the piston, with the last bit of boundary layer next to the piston acting as insulation for at least the first part of the combustion process.

Spark plugs don't like igniting mixtures leaner than roughly lambda 1.2 under normal conditions, and in a conventional engine, power loss starts getting out-of-proportion due to slow and incomplete combustion short of that. But, heating that mixture close to its self-ignition temperature via higher compression helps combustion along.

 

[gruntguru]

- Detonation melts pistons not because the gas temp is higher but because thermal protection provided by the boundary layer is scoured by shock waves. So yes they are not running in detonation.
- They are almost certainly achieving a form of HCCI (or SAHCCI) at some operating points and in some portion of the chamber.
- Bore is 80mm and stroke is 53mm. Not as oversquare as earlier F1 engines.
- Inlet cam is very short duration to produce EIVC Miller cycle. This will not reduce dynamic compression at low rpm as much as LIVC.
- The spark plug sits in the pre-chamber environment which will be at lambda 1.0 or richer.


je suis charlie