Most efficient piston type engine?
Most efficient piston type engine?
(OP)
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?
Nissan is suppose to have a 50% engine, even Fairbanks Morse, as well as Achates.
So what is the latest news on high efficiency?
RE: Most efficient piston type engine?
Link
je suis charlie
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
Note that I am working off antiquated but accepted definitions. Low speed < 250rpm < medium speed < 900rpm < high speed.
RE: Most efficient piston type engine?
je suis charlie
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
https://www.motortrend.com/news/a-volkswagen-golf-...
The year was right.
RE: Most efficient piston type engine?
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.
RE: Most efficient piston type engine?
Does not appear to be worth the aggravation.
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
For giggles I calculated TE of a top fuel dragster at 0.007929%, beat that!
RE: Most efficient piston type engine?
je suis charlie
RE: Most efficient piston type engine?
Brian,
RE: Most efficient piston type engine?
https://en.wikipedia.org/wiki/Deflagration_to_deto...
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?
RE: Most efficient piston type engine?
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.
RE: Most efficient piston type engine?
—-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.
RE: Most efficient piston type engine?
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.
RE: Most efficient piston type engine?
- 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
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
On the subject of detonation, I have heard NASCAR and motorcycle engine manufacturers utilizing their high piston speeds to outrun the shockwave from detonation. It was some years ago that I heard this and can't provide any sources.
RE: Most efficient piston type engine?
Speed of sound (detonation front) ~1000 m/s
je suis charlie
RE: Most efficient piston type engine?
Yes, duration and timing of (a late) injection pulse would be critical to get Lambda 1 in the pre-chamber.
je suis charlie
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
https://www.youtube.com/watch?v=oNCBbcINHuk
Here is readable summary of these technologies:
https://www.ni.com/en-us/innovations/white-papers/...
Have thought hcci to be a detonation combustion, although have never seen it called this, I am looking for arguments that it’s not.
RE: Most efficient piston type engine?
HEDGE is . . .”dedicated to the development of pre-competitive technologies that will be needed to cost-effectively achieve future emissions and fuel consumption requirements for world markets.”
Is pre-competition before or after F1?
RE: Most efficient piston type engine?
HCCI has been at a research stage for so long, and without resolution of some fundamental difficulties, that I have my doubts that it will ever get any closer to production than Mazda's Skyactiv-X system, which is spark-assisted and uses stratified charge to achieve fast but smooth (non-detonation) combustion.
Lean combustion is a non-starter for production applications for NOx reasons. It is not possible to get the NOx low enough merely via lean-burn to comply with current and foreseeable emission standards without aftertreatment, and NOx aftertreatment for lean-combustion applications involves SCR and AdBlue / DEF the same as diesels are using, and nobody wants that aggravation and expense.
RE: Most efficient piston type engine?
Detonation is combustion propagated at much higher speed - usually sonic velocity via a shock wave.
je suis charlie
RE: Most efficient piston type engine?
“Engines don’t ‘detonate’ ! 'Detonation' requires either a phase change as part of the exothermic event or a diverging nozzle. Auto-ignition ahead of the flame front in SI (spark-ignition) engines is sonic, not supersonic. Therefore "detonation" is not the proper term. Either "auto-ignition" or "knock" are correct descriptors, knock referring to the audible sound emitted from sound waves traversing the combustion chamber at less than sonic velocity."
—This above is a rewrite of the Allen Cline article on knock, that many are perhaps familiar with. The only adjustment is switching terms from ‘detonation’ to ‘auto-ignition’.
also, S.Onishi, c.1979, atac paper, refers to hcci as ‘abnormal combustion’
—Plasma assist comb., PAC, from the F1 vid., might be microwave assisted? Here are some images:
https://cefrc.princeton.edu/sites/g/files/toruqf10...
—-hedge engines, dilution is of oxygen radicals via egr. (Not of the fuel air ratios)
RE: Most efficient piston type engine?
There are some number of articles available that discuss various sintered ceramic coatings for hcci thermal control, and some others reporting material toughness young’s modulis and also ablation resistance of various compositions, But can’t find anything on how practical ‘thermal-barrier-coatings’ are for daily drivers, and what happens when it chunks off —it probably doesn’t. Either way, if spark plug is shrouded in a pre-chamber with injector, combustion chamber mechanical damage could be manageable with sustained knock.
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
Mazda's spark-assisted HCCI system is likely as close as such a system will get for a daily-driver application ... and it doesn't operate in SA-HCCI mode all the time ... and it doesn't appear to give a fantastic improvement in consumption over the regular Skyactiv-G engine, which is already pretty good ... but not earthshatteringly better than the consumption of a reasonably optimised normal port-injection variable-valve-timing four-banger. Friend of mind has a VW Golf with the 1.8 TSI four-banger, and it does pretty well in daily driving. Direct-injection, turbocharged-intercooled, VVT.
Auto engineers know about ceramic coatings. If the benefit exceeded the cost, they'd be in production - and there have been some. If they're not used in a particular application (most), at this point in time, it isn't because nobody thought of it before ... it's because someone looked at it and established that the benefit (if any) wasn't worth the cost. Keep in mind that a ceramic "thermal barrier" coating, or manufacturing parts from heat-resistant ceramics (been done), doesn't stop all heat transfer to and from the surface. If it slows heat transfer through the surface, thus leading to the surface temperature being higher, thus leading to the temperature of the charge being higher at the end of the compression stroke, thus increasing self-ignition (detonation) propensity, thus forcing the compression ratio to be dropped and/or ignition timing to be retarded ... was it worthwhile?
Cylinder heads are made of aluminium nowadays. Aluminium conducts heat quickly. Maybe that's by design ... to cut down on hot-spots that lead to pre-ignition or self-ignition (detonation). The aforementioned Formula 1 engines, the Golf 1.8 TSI engine, the Mazda Skyactiv-G or -X engines, all use aluminium cylinder heads. Changing to a less thermally conductive material, like cast iron ... isn't something that is a foreign concept to engine designers. They use aluminium because the benefits outweigh the costs.
This ain't simple ... and the engineers ain't stupid.
RE: Most efficient piston type engine?
Here is the GM 6.5 example. An interesting detail, the piston is not part of the combustion chamber. This engine has pre-chambers.
RE: Most efficient piston type engine?
Diesel engines with prechambers have gone the way of the dodo. Direct-injection engines are more efficient due to lower heat losses in the chamber. The old GM indirect-injection (prechamber) 6.5 was replaced with the direct-injection Duramax.
The prechambers in the F1 application are really small, a few percent of the total chamber volume, so the thermal losses aren't meaningful in the big picture ... benefit outweighs the cost.
RE: Most efficient piston type engine?
Pre-chamber diesel engines do have a big advantage, they have a wider power range do they run more like a gas engine. I recently blew the 6.2 diesel in my truck which is why I'm building that 6.5. I already committed to making room for a center mount turbo so I could easily fit a Duramax but the direct inject diesel engines don't have the RPM range to make a 3 speed automatic with 4.56 gears drivable. I would have had to make many more changes to accomodate the narrow DI powerband.
RE: Most efficient piston type engine?
Years back a roadracing buddy bought a used GM G-van cheap because it was a non-runner with a blown-up 6.2 non turbo. At the time of buying it, it had a (I think) THM350 installed in the vehicle, and I believe it came with a blown-up 700R4 loose in the back.
From what he could tell, the trans blew up first, and rather than repairing and upgrading the 700R4, the previous owner dropped in the 3-speed non-overdrive. What the previous owner didn't do, was figure out what to do with the THM350 vacuum modulator on this diesel engine, so they left it unconnected. This, of course, told the transmission to operate as if the engine were full throttle all the time, upshifts at whatever max upshift speed the valve body was calibrated for. That blew up the engine. At that point the previous owner determined that they were in over their head, and Jack bought the blown-up remnants.
He had the 6.2 and the 700R4 rebuilt with upgrades to beef up the transmission, and drove it for years afterward; we split a ride to Road America in that van.
Those were the days. Another racing buddy had a Ram van with a 225 slant six and single-barrel carb. Yet another had a Ford cube van with a 7.3 non-turbo; quite a rocketship (not). Yet another had a Ford cube van with a 460, which decided to quit running on the way back from Mid-Ohio due to a broken wire inside the distributor ... on the Ambassador bridge in Windsor in the queue for passport control. "Oh, this again. I know what's wrong." Nothing like attracting the attention of border patrol by opening a toolbox and working on your vehicle in the forecourt of passport control ...
RE: Most efficient piston type engine?
It's on topic though. My 1.25 ton truck with the 6.2 diesel, no overdrive, and 4.56 gears with 31 inch tires managed 18 mpg. It didn't really manage 65 mph but now with the 37 inch tires that won't be a problem. The fire ring on the head gasket fretted through the block and killed it. The 6.5 I bought to replace it bad the same problem which is why the top deck is so clean in the pick I posted.
The 6.5 has a turbo but also has different pre-chambers. I have no idea what the milage will be. Maybe I'll report back when it's done.
RE: Most efficient piston type engine?
Back to this detonation versus ‘knock, auto-ignition’ and hcci: have found a parsing of detonation into slow and fast, from the textbook ‘Combustion’, by Glassman & Yetter, which states: “ . . . it’s a common error to confuse explosion and detonation.” Which is self-ignition by thermal initiation, versus a shockwave propagation. Detonation is not correct term, but knock is, for HCCI.
Here is a 20pg oil industry paper which doesn’t beat about the hedge;)
https://www.npc.org/FTF_Topic_papers/6-Low_Tempera...
“LTC is in essence controlled knock” (page 18)
“ alphabet soup of acronyms . . . HCCI, PCI, PPCI, CAI, RCCI, etc. <used> to describe the different approaches <to> low temperature combustion (ltc) <which> signify the different ways researchers are choosing to establish and control the basic requirements for this “flameless” combustion. (not laminar deflagration)” (page 12)
RE: Most efficient piston type engine?
We're in the weeds here but.. yes it is. Detonation in an engine is dangerous to the engine because of the damage which can be done by the shock wave. The presence of that shock wave is what defines 'detonation'.
Stop it. 'Knock' is a colloquial term - coined because an engine that's undergoing detonation makes a noise that sounds like something is knocking on something else with a hammer. 'Knock' is not an engineering term.
When you hear an engine 'knocking' there absolutely is a supersonic shock front inside the cylinder which is slamming into the cylinder wall, piston, head, whatever and probably damaging them.
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
Diesel engines knock louder upon cold start because the ignition delay is longer.
Injection timing set too far advanced results in louder knock because (1) the temperature in cylinder is lower at the time of start-of-injection because the compression stroke isn't finished yet, (2) the longer ignition delay results in more fuel being in-cylinder and partially premixed by the time ignition happens. And yes, excessive ignition timing advance certainly can break stuff.
Newer modern-tech diesel engines are a lot quieter because the rate of injection is much more tightly controlled. It's not uncommon to split up the injection cycle into two parts - a small initial pulse that premixes and ignites followed by the main injection event that burns progressively.
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
The shock front is what separates normal combustion from detonation.
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
“<it> has one of the highest well-to-wheel efficiencies with light and heavy-duty DME-fuelled vehicle efficiencies as 19% and 22.5%, respectively”
DME is made from methane and syngas from biomass, and in terms of CO2, is possibly one of the cleanest fuels, by virtue of carbon neutrality. Here is a wheel-to-wheel comparison that shows how it can blast electric vehicles from contention: https://gmobility.eu/what-is-well-to-wheel/
RE: Most efficient piston type engine?
Any sort of combustion engine that burns "a fuel" (no matter what it is) with air, and farts out its products of combustion, is going to have to deal with NOx.
Meanwhile ... I'm 22 km from home with my EV parked outside. The low-charge-warning was on when I got here (having not bothered plugging in the last three days), but the GOM says I have plenty of charge left to get home, where I can plug it in.
RE: Most efficient piston type engine?
RE: Most efficient piston type engine?
I’ve seen mechanics do cold-starts, spraying abundant ether, total abandon, and also the reverse where mechanics act like it’s live grenade . Thanks for the word on this.
RE: Most efficient piston type engine?
For example, I had to start this engine that has been ingesting salt water. There was still residual water in the intake manifold so I had to use ether to get it going.
The owner warned me about breaking piston rings. They leased me a boat that didn't run. I was damn well going to make that engine start so I could start earning revenue again.
I really despise this series of engines.