Most efficient piston type engine? 2

[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?

 

[BrianPetersen]

Yes, and the pre-chamber environment is lambda 1.0-ish because the vicinity of the combustion chamber outside the pre-chamber is lambda 1.0-ish, at least for the part of the compression stroke up to the point of ignition (which is only a few degrees before TDC). There's no dedicated injector for the pre-chamber because the rules only allow one injector per cylinder - so they have to be doing it via stratified charge through injection timing and nozzle-aiming trickery.

 

[TugboatEng]

If the rule makers were using the unlimited budget of F1 to develop new engine technology for the rest of us the single injector rule was a smart trick to make the technology more applicable to on the road use. Directing charge into pre-chambers is nothing new.

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.

 

[gruntguru]

Peak piston speed ~40 m/s
Speed of sound (detonation front) ~1000 m/s

je suis charlie

 

[gruntguru]

B.P.
Yes, duration and timing of (a late) injection pulse would be critical to get Lambda 1 in the pre-chamber.

je suis charlie

 

[TugboatEng]

The piston may need only establish some distance. The key may not be to outrun the shockwave all together but to meet it at a lower energy level. Where was that Yamaha link again? They were pioneers on this type of stuff.

 

[Factoter]

Here is spark ignition side by side with an hcci, c.2007

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

Here is readable summary of these technologies:

https://www.ni.com/en-us/innovation...ontrol-low-temperature-combustion-engine.html

Have thought hcci to be a detonation combustion, although have never seen it called this, I am looking for arguments that it’s not.

 

[Factoter]

High efficiency dilute gasoline engine at Southwest research institute:

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?

 

[BrianPetersen]

I think "pre-competitive" means research-stage, before individual companies start doing their own variations and calibrations on it (i.e. in competition with each other and with other technologies).

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.

 

[gruntguru]

HCCI is combustion propagated by flame front(s) at multiple locations simultaneously.

Detonation is combustion propagated at much higher speed - usually sonic velocity via a shock wave.

je suis charlie

 

[Factoter]

http://www.epi-eng.com/piston_engine_technology/detonation_and_pre-ignition.html

“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...school/lecture-notes/2017_Ju_All_combined.pdf

—-hedge engines, dilution is of oxygen radicals via egr. (Not of the fuel air ratios)

 

[Factoter]

This has pictures of ceramic coated pistons:

https://www.wireilla.com/engg/ijmech/papers/5216ijmech01.pdf

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.

 

[TugboatEng]

GM used ceramic barrier coatings on the pistons of their turbocharged 6.5L diesel engines made from 1993-2000. Most manufacturers seem to be diverging from that practice and adopting steel pistons. Everybody seems to have gone to Mahle Monotherm pistons.

 

[BrianPetersen]

Bear in mind that the Formula 1 situation is extremely optimised for full-load operation high in the RPM range, and its operation is extremely contingent upon fuel chemistry. Those engines are not designed for efficient part-load operation (typical of daily-drivers), or smooth idling with impeccable low-speed driveability, or compliance with Euro 6 or US EPA Tier III emission standards, or cold-starting in -30 C, or driving 10,000+ km between engine oil changes, etc.

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.

 

[TugboatEng]

Here is the GM 6.5 example. An interesting detail, the piston is not part of the combustion chamber. This engine has pre-chambers.

 

[BrianPetersen]

Diesel engines aren't subject to the detonation and pre-ignition constraints, so if there's an application for thermal barrier coatings or less thermally conductive materials (e.g. steel pistons), it's there. And they don't rev high, so if the piston is a bit heavier because it's made of steel, no big deal in that application.

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.

 

[TugboatEng]

I wouldn't say the pre-chamber has gone the way of the dodo. We were just taking about F1 using a pre-chamber. Also, many industrial diesel engines have spark ignition gas options now which use pre-chamber. The PC is dead for diesel but it's becoming relevant for every other fuel.

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.

 

[BrianPetersen]

not really on topic of thread title but on topic of GM 6.2/6.5 and automatic transmissions ...

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 ...

 

[TugboatEng]

Your story rings true. There is a vacuum pump and modulator to simulate a carburetor on my truck as well. I have the TH400 transmission. I had a hard time finding a modulator so I had to drive for quite some time with full throttle shifts only. Part throttle shifts were hard and nearly smack your head on the back window. I trained myself to floor it at the shift points to prevent that.

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.

 

[Factoter]

Recently was looking at a non-compliance 6.5 in CA, original owner gifted this gmc3500 rather than attempting to sell out of state. Needed plugs and radiator cap, and looked like it never had any maintenance in 20 years, but loads of truck for the money. It’s probably in Mexico now.

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_Temperature_Combustion.pdf

“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)

 

[SwinnyGG]

Therefore "detonation" is not the proper term.

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'.

Detonation is not correct term, but knock is, for HCCI.

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.