Lets talk about diesels.

Discussion in 'Firewall Forward / Props / Fuel system' started by Terrh, Oct 17, 2019.

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  1. Oct 22, 2019 #21

    pictsidhe

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    Jet A is very low octane. You'd need a very low compression ratio. It's very close kin, kerosene, was once very commonly used in tractors.
    There are marine versions of numerous car engines. Such as the GM 4.3
     
  2. Oct 22, 2019 #22

    Terrh

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    the GM 4.3, 7.4 (454), 5.7/350, 240/260/300 6cyls are common marine engines, and are about 95% identical internally to their car/truck counterparts.

    The myth that auto engines can't handle aviation type demands is mostly that, a myth.


    Most diesels (excluding emissions systems) will run perfectly fine on 98%kero/2% oil or ATF. Most diesels will also run fine on a huge variety of other crap that I'd never dare fly with, but has been fun to experiment in trucks, such as filtered WMO (50/50 w/ diesel, and as much as 95%/5% gasoline in the summer), ATF, veggie oil, etc.

    I have no idea how to run kero in a gasoline engine successfully, but it probably can be done.

    Testing w/ an airboat or regular boat for a few hundred hours would seem wise.
     
  3. Oct 22, 2019 #23

    Rik-

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    What about.. The Audi inline 4 cyl diesel engine ? Seems to have the HP and the size down but as to weight?

    Sticking with Audi, they made a V12 diesel that has a weight of like 500 lbs but makes 500 hp too! There's actually a diesel company (cannot remember who) what was featured on AOPA a few years back with a V12 diesel for aircraft. Thought it had to be based off the same Audi Q7 V12 diesel engine that is used in Europe. I tried to by like a dozen of them from Audi but at the time they claimed they could not manufacture in excess of their own production needs. 40K Euros for an engine +
     
  4. Oct 23, 2019 #24

    cheapracer

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    Somewhere around 660lbs according to Audi.

    Your figures might be related to the LeMans race car's diesel V12 that was around 500lbs, but that's not the road car's engine.
     
  5. Oct 23, 2019 #25

    don january

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    I have a Thermo king 4 cyl Diesel engine from a cooling unit off a Semi trailer and weight to HP kills any Idea to mount to my single engine plane but sure would be nice I think if weight could be cut down to a third.
     
  6. Oct 23, 2019 #26

    Dan Thomas

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    Strength is the issue. GM tried that with their 350 back in the '70s and had huge warranty claims. They put diesel heads on a 350 gasoline engine, probably with a few other mods, and the bottom end couldn't take the pressures. Compression and combustion pressures are higher than with gasoline.
     
  7. Oct 23, 2019 #27

    Dan Thomas

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    In 2010-2011 I did some work on an SMA 230 hp diesel in a 182. It had maybe 200 hours on it and had numerous cracked components, leaking heads, a cracked propeller blade (MT composite) and so on. The heads are air AND oil cooled, and the oil gets to and from the head through passages in the walls of the cylinders. The cylinders and heads aren't a permanenty-assembled affair like Lyc or Continental, so there are head gaskets that start leaking the oil. There's a huge oil cooler on one side of the engine and a huge intercooler on the other side. Vibration was cracking them, too. Various mounting parts and struts and stuff were cracking. Induction stuff was cracking. SMA was good for all of it, but it highlights just how difficult it is to come up with something new and make any money at it. SMA is a big aerospace outfit, not a garage-based operation. They told us at the time that they'd spent a billion US dollars on the project, and had 50 (fifty!) engines flying worldwide. Going to take centuries to get any ROI at that rate.

    It was a four-banger, 15:1 compression. The FADEC wouldn't let you have control of the engine until it was warmed up enough to satisfy the computer, so it idled at a low speed that generated a lot of vibration, perhaps contributing to some of the cracking problems. And it had a ludicrous low-temperature limit for starting; IIRC it was around the freezing mark. So you don't go flying between October and March unless it's preheated? Very useful, that. In flight it has rather high low-temp limits as well.

    A 2010 video on the 182 diesel. An update of their experiences over the long term would be nice.
     
    cheapracer and Terrh like this.
  8. Oct 24, 2019 #28

    Terrh

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    The video says can't use it below -20 below 7500' and -40 between 7500 and 12500, with the winter kit. Without the limits are -5 and -10.

    I think air cooled diesels are maybe a non-starter, just because you lack the thermal mass to keep the engine hot while decending in cold weather.

    A billion dollars from a company I'd never heard of sounded ridiculous until I looked them up. I it's a pretty huge company, and a billion dollars over 20 years isn't even a fraction of 1% of their income, so that number sounds a little more reasonable.

    Still, If someone had a million dollars a year to throw at me, I'm sure I could figure out how to get a diesel flying in 5 years or less, or figure out why it can't be reasonably done ever. Nevermind 50 million a year.
     
  9. Oct 24, 2019 #29

    Hephaestus

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    The old bop 350 diesel while somewhat backwards compatible with the gasser - was clean sheet, and the block is substantially different than the gassers.

    The biggest issue was nobody taught people they required different maintenance and upkeep. I had many wonderful years behind the 4.3 diesel. It was an awesome engine if you kept it maintained and used fuel additives (seafoam) regularly. But i had a decade in an 82 6.2 diesel before ;) and i loved that engine most of all. (God it was cheap on fuel, no power... But beat the hell out of driving a civic)
     
  10. Oct 24, 2019 #30

    Rik-

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    This was their "Oldsmobile 350" that was a gutless pig. They ran, had some head gasket issues but they couldn't get out of their own way. Had one that would not climb the hills driving in Colorado. **** near stopped the car in the climb. Everyone jumped out and walked faster than the car would go.

    Chevy put them in the pickups. Would not pull their own weight. Had one of those too. Couldn't pull the airstream out of Monterey. Had to leave the Aistream, go the dealer, buy a new GAS truck and go back and get the aistream... I think GM just tried to rush something to market that was greatly under powered.
     
  11. Oct 24, 2019 #31

    cheapracer

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    There is a research engine kicking about that is basically a normal petrol engine, including spark plugs, but runs on pre-atomised diesel using a small supercharger type mechanism to mix air and diesel ready for injection, seemed a good thing, but like many good things you don't hear more about them ...

    I wonder if it maybe infringed Orbital's (read Evinrude 2 strokes) Patents.
     
  12. Oct 24, 2019 #32

    thjakits

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    Hi all again,
    ...there seem to be a few erroneous concepts around...

    - Diesel/Kerosine/Jet-A ....are all basically the same - differences are in definitions of the very specific: additive content, lubricant content, refining tolerances...
    - Any of the above do not list "octane" numbers, they do have a octane level of course, but that is quite useless
    - The above use a "cetane" rating, which for all purposes is a inverse to the octane rating...

    - A gasoline engine adapted to burn Diesel or Jet-A would be structurally just fine as long as cylinder pressure ratings are kept at the same level as the original gas engine. The idea is NOT to make it a "Diesel-engine" (by definition: selfignition by compression heating the environment), but to keep on using "gasoline-engine" ignition tech: Spark!
    As it is, even a compared to Diesel low compression ration in a gasoline engine woudl ignite a diesel charge - however in a rather unprecise and uncontrolled manner - just like or worse, when you use too low octane gasoline in your engine...

    The idea/concept is to use the comparatively low weight gasoline engine, and use gasoline and diesel tech to make that gasoline engine be happy with diesel/Jet-A...
    That means:
    - same compression ration as the original gasoline engine
    - provide it only with enough Diesel/Jet-A to not exceed the gasoline burn parameters
    - You cannot introduce the Diesel before the intented ignition, so you inject it just like in a Diesel engine.
    - Diesel injected in a gasoline engine will probably not always ignite correctly (because of the low compression ration), so we need to make sure ignition happens - spark!!
    Today technology is sufficiently advanced to time the needed events (fuel injection and spark) down to very precise rotation angles (crankshaft) ant about all useful rpm levels...
    Diesel injection technology is also far enough to provide a easily ignitable spray/mist.....

    AFAIK - NO one is trying to do a Low-Copression-Spark-Ignition-Diesel....
    Even the "low compression"-Skyactive-D is still around 1:14 and does NOT use Spark-Ignition...

    All Aviation Diesels under development or on the drawing board still use the Diesel-cycle (compression ignition).

    I believe, the main goal would be to be able to do away with Avgas and be able to use Jet-A.
    So - the goal would be to be able to use an engine as lightwight as present gasoline engines, but able to use Jet-A...

    I am sure someone tried this in the past - but probably problems like sparkplug fouling, diesel mist drop size, etc. prevented success. New Technology - time to revisit the concept!

    However - it seems huge steps are made in battery tech - I see the ICE becoming obsolete fast....
     
  13. Oct 24, 2019 #33

    TarDevil

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    OK, I'm the dumbest in this thread, so educate me.

    I drool over the concept of using diesel or JetA in aircraft for a variety of reasons, but if BFSC is not better in a spark ignition diesel (do we have an acronym for that yet??) would we not pay a weight penalty with the heavier fuels?

    I played around with a long range design years ago and was able to fund the extra weight employing diesels because of lower fuel burn.

    So, how does the SID (there's an acronym suggestion if one doesn't exist) compare in fuel efficiency?
     
  14. Oct 24, 2019 #34

    cheapracer

    cheapracer

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    This old one again..

    No, just no. Mega factories around the world have and are being built to service the lithium battery industry as we know it now.

    Think about it, there's probably a trillion+ dollars gone into/going into all those factories, does anyone consider that they didn't investigate every possibility of a "New, WOW!" battery coming before they made/making these investments.

    Occam's Razor, and simple logic tell us that now, batteries at 4 times the energy density are here to stay, and the magical cure is unknown for when, or if it will ever happen. Like so many great scientific discoveries, it will be completely accidental if ever at all, so at this time is completely unknown. WiFi, that you're likely using now, was an accidental discovery, as was penicillian, etc.

    PS:, I own about 30 Electric cars at any one time, and daily in a Tesla S, so I ain't anti-battery by a long way, new discoveries are very helpful to me ....
     
  15. Oct 24, 2019 #35

    cheapracer

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    The engine I mentioned 2 posts above is on the net somewhere, might even be on my computer.

    It was a flat twin if I remember correctly.
     
  16. Oct 24, 2019 #36

    Dan Thomas

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    Those are the ones. I remember friends getting so disgusted with them.
     
  17. Oct 25, 2019 #37

    sming

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    Was it a gasoline/diesel hybrid (RCCI) with 60% efficiency ?

    I've seen this one:
    https://www.sciencedirect.com/science/article/pii/S0360128514000288
    nice video :
    It's a monocylinder I believe.
     
  18. Oct 25, 2019 #38

    TiPi

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    look up "hirth heavy fuel engine", they have some of their 2-stroke petrol engines available with Jet A-1 or equivalent fuels for military applications. There are a few more engines for military use running on jet or diesel fuel but based on petrol engines. The injection system becomes quite complicated due to the need to atomise the heavier fuel fine enough (it doesn't vaporise) to start the combustion and maintain a controlled flame front (flame speed). And up goes the price. For the military, a single fuel fleet is worth more than the extra cost of some of the engines to run on that fuel.

    New 15hp UAV Engine from Hirth Motors
    The heavy fuel engine can be upgraded to Hirth’s iPower fuel injection technology which uses compression wave injection to enable spark ignition of heavy fuels. This variant meets NATO’s one-fuel policy to eliminate gasoline for safety and logistics reasons.

     

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    Last edited: Oct 25, 2019
  19. Oct 25, 2019 #39

    cheapracer

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    Nope, it was pure heavy fuel.
     
  20. Oct 25, 2019 #40

    PMD

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    It seems that there is still come confusion of just why diesel cycle (Compression Ignition = CI) is infinitely superior to aspirated charge (Spark Ignition = SI) engines for aviation, marine or heck ANY use.

    The number one issue is that SI engines (with a few rare exceptions) must aspirate their charge to have it dispersed within the combustion chamber when it is ignited by a spark (or, in far, far better designs, plasma from an igniter such as the aspirated charge compression ignition engines built by Mark Cherry at Smartplugs). ANY ICE is limited only by the amount of air and fuel you can stuff into the cylinder. Problem is, when you must aspirate a really bad fuel such as gasoline, it reaches a limit from the temperature and pressure while on compression stroke when instead of burning controlably from the point of spark igniting, the whole thing explodes at once (detonation). You can solve SOME of that problem by aspirating far higher octane fuels (such as ethanol, methanol, etc.) but even at the very extreme (fuel dragsters that make near 10,000 HP from less than 10 litres) spark plugs only get the engine working under very light loads. In that installation, they are totally destroyed the instant power goes up and the engine is once more a compression ignition (but in this case aspirated charge) diesel. Look at what happens at altitude with these engines. You need more air to burn the avgas, so you hang on forced induction (super or turbochargers). Problem is, you can now burn some more fuel to maintain power, but to do so, you flirt constantly with detonation, while the air availble to cool the engine is getting much less dense, so now you need to do something to limit detonation in the cylinder. The normal solution (look at Aerostar Lycs and P210 Conti) is to dump a bunch more gasoline into the aspirating airstream to cool not only the combustion chamber, but the whole bloody engine. Then comes the spark thing: as you get into lighter air, you get into poorer insulating air, so the magnetos (talking ox cart technology here - i.e.what most of us actually fly) start arcing all over the place so need to be pressurized or eliminated.

    Now, Dr. Diesel's CI engines (in long past referred to as "constant pressure" engines, due to how you CAN manage the BMEP curve) simply don't have any of these limits. The gasses coming into the cylinder contain no fuel, so the only thing that limits how much air you can jam in is your ability to deal with the heat and of course keep the whole thing together. Ignition happens when you inject fuel, and if you have enough strength and cooling, there is no limit until you literally fill the combustion chamber to hydro-locking levels (as IS the case with top fuel dragsters). So: in what technically sane world would you waste time building engines around a bad fuel and combustion concept when a much better one is right under your nose?

    The first successful aviation diesels were, IIRC, Packard radials, that set a mess of records in the '20s. The problem was that the materials and technologies of the day meant that injection pressures were too low to get really good atomisation, and lack of understanding of how dissolved air was knocked out of solution while supplying to injectors meant that timing was imprecise and not predictable, and the injected blobs of fuel might burn controllably on injection, or splat into the piston or cylinder only to explode with a big bang at the wrong time (the clatter and knock of old diesels that thus required HUGE amounts of cast iron to tolerate the shock wave and pressure spikes that could literally blow big chunks of cast iron off of the outside of the cylinder (cavitation).

    Even with all of those old-tech limits, Hugo Junkers (no slouch at this aviation engineering thing) built some incredibly successful diesel engines that used the 19 07 tech of opposed piston, uniflow 2 cycle to make some really nice engines. Now, you would ask where was the US in dealing with such nice tech? Well, if you take a ride in a submarine where performance, reliability, fire safety, energy density, smoothness, quiet, etc. are SUPER important (kind of like in airplanes) it will likely have an opposed piston diesel either as prime power or backup power - built from licenses by Fairbanks-Morse from Junkers patents and licenses.

    Today, we have a couple of huge advances that make aviation diesels inevitable. First, we have materials science that allows injector nozzles to live at 25,000 psi and up without eroding in a flash. THAT allows heavy fuel atomisation that dramatically improves cold starting and combustion efficiency. Second: we understand far better how to control timing, to the extent we can "rate shape" the injection events to first give a little pre-shot (into which the main injections can be fired at the resulting fireball that keeps fuel from reaching a quenching surface such as the piston crown). You will notice that modern automotive diesels are FAR lighter, cleaner and quieter than their predecessors (thanks to VW for starting down the road in 1978, and a pox on VW for screwing up royally a few years ago).

    On top of all of that, the diesel cycle of CI engines are extremely tolerant of fuel diversity (something that gasser SI engines really are NOT).

    What we need, though, is for someone to work with EXISTING mass market hardware to build small diesels for our relatively small power market. Small and very high performance (i.e. the whole power/weight issue - that automotive diesels do NOT cover well).

    BTW: from an earlier post about automotive engines no being in marine applications: take a look at the HUGE lineup of VWAG marine diesels - they are the full lineup of every automobile diesel they produce(d). Ditto, almost the entire world of stern drives are an auto gas or diesel on one side of the transom, and what is finally happening the outboard world sometimes uses auto engines plucked right out of a car (all gassers so far). In that world, there are now a few outboard diesels that are already on the market - i.e. VERY light, high performance diesels with almost identical use profile to aviation.
    https://boatdiesel.com/Engines/Volkswagen/Volkswagen.cfm
    https://www.mercurymarine.com/en/ca/engines/diesel/mercury-diesel/42l-tier-3/
    https://www.mercuryracing.com/wp-content/uploads/2015/05/2557_DieselOB_SS_NC1.pdf
     
    Last edited: Oct 25, 2019

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