Lets talk about diesels.

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

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  1. Oct 25, 2019 #41

    TFF

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    In the US I don’t think a diesel will end up cheaper. Diesel is always more expensive in the US vs gas. It’s the kind of fuel we pump from the ground. Russian fuel has more diesel in the ground mix. Aviation gas is only more expensive right now because of the legacy lead. Only eight refineries can make aviation gas in the US out of 250. When they get rid of the lead and any local refinery can make airplane gas, it will be at least on par with Jet-A price wise. The general price advantage will go away then. Other parts of the world need diesel. Until the FAA allows retro into old airplanes, there will be no profit in a world of maybe 6000 new engines a year between Continental and Lycoming. They need 50,000 a year to pay for the tooling.
     
  2. Oct 25, 2019 #42

    thjakits

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    ...that's why I say - Gasoline engine compression ratios - spark ignition (to ensure ignition!!) - Diesel/Jet-A direct injection.
    That way you do not need the extra sturdiness/weight of the usual Diesel blocks and heads...

    Basically you use gasoline engine design and substitute diesel for gasoline, but still work it like gasoline. To make Jet-a/Diesel work like gasoline you need to inject it directly....

    Marine applications of Diesels: Look closer and carefully! NONE of the marine applications have the same power rating as the CAR-version of that engine. More like the same rating as a Diesel-generator pack withe the same engine....

    Mercury, Yamaha, etc.... may have come from a generic Car V8 or V6 or V4 design, but by now they have really nothing to do anymore with the car-versions!
    Try to install a car-crate-engine from your preferred brand in a speed boat!! Let's see how long that one lasts!
    There is a reason why a Mercury of the same power rating will cost you 2-3x more!!

    thjakits
     
  3. Oct 25, 2019 #43

    sming

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    Don't you think it's more a market thing than a technological thing ? I.e, boating (like aviation...) is small numbers and high end, so everything is expensive (like aviation...)
    There is obviously engineering in these engines, but not 2-3x more?
     
  4. Oct 26, 2019 #44

    Voidhawk9

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    Very common here, doesn't seem to be any problem at all.
     
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  5. Oct 26, 2019 #45

    Rik-

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    What does this mean? petroleum naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, liquefied petroleum gas, jet fuel and fuel oils all come from the same crude oil and are separated out in the distillation process called refining. It's basically a column still and the heat ranges is where they pull off each of the different substrates of oil.
     
  6. Oct 26, 2019 #46

    Rik-

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    I can tell you from 1st hand experience that it doesn't work worth a **** unless you change the bearing and ring clearances as the automotive engines are designed to run at what, 210 degres F, and a boat motor with a huge radiator (the water it's running in) won't see more than 140 degrees in temperature when your running it hard.

    The crank and rods seize.. Can be as quick as 15-20 minutes, or just far enough from the dock to make you go ****
     
  7. Oct 26, 2019 #47

    PMD

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    A few technical notes: Russian crude oil and US crude oil are not individual things. EACH reservoir is different from any other, and both countries have a broad range of crude oils. When one characterizes a reservoir, it is reported as an assay of what can be derived by simple distillation. That is important to refiners as it tells you what fractions will come from the PDU (Primary Distillation Unit) at the lowest cost. However, other than topping plants, no refinery is a simple distillation process. You can literally make any product in any proportion from any crude from a very complex (Nelson index around 15) by several steps such as cracking, alkylation, catalytic reforming, dimerization,vis breaking, hyrdogenation in many ways, etc. Refineries also remove impurities such as salt, heavy metals, sulphur, nitrogen, etc. Every process that you use will increase the cost of refining, so the holy grail is something that will produce your most needed products from atmospheric distillation, but as you can see, that is more of a dream these days than a reality. Avgas is actually pretty simple, but because it is such a small market, few are in it. Modern gasoline and diesel are extremely complex products that take a LOT of refining to meet current standards.

    Also, look at the link I posted for the Mercury 4.2 diesel. That engine is lifted straight out of a Euro VW/Audi and run at marine loads (i.e. nearly constant high power) using almost everything exactly as is in the car it came from. Many of the TDI VW diesels in their marine lineup are also run at near or full automotive power rating, except meant to be loaded constantly near full rating. Once more: straight out of the cars and trucks from which they come. Common as dirt.

    Modern diesels simply do NOT need to use any heavier components than their gasoline equivalent. Once more, read my explanation and you should be able to see why. Because that are NOT spark ignition, there is simply not very much to limit any given displacement from making any given power - unlike their highly compromised spark ignition equivalents.
     
  8. Oct 26, 2019 #48

    rv7charlie

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    thjakits,

    One of the two primary reasons diesels are typically more efficient than gas burners is the compression ratio itself. If you look at the most efficient of the modern gas burners in cars these days, their compression ratios are approaching diesel levels, in the 12-14/1 range, and their BSFC is pretty close, as well.

    On the subject of auto engines in boats, the Honda fours & V6s, in the 100-250 hp range, seem to transition directly into their outboards. When I was a kid, my uncle had in outdrive boat powered by an iron block 4cyl Chevy II (Nova) engine.
     
  9. Oct 26, 2019 #49

    cheapracer

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    Well Subaru, Honda and Mazda, the most recent examples of "modern" lightweight (yeah right ...) diesels make nonsense of your statement, even the Mazda at 14:1 compression..

    They are heavy, and nowhere near the weight of their petrol equivelants, period.

    3 major engine manufacturers that spend millions of man hours and dollars to use the least possible amount of materials that they can for big money savings.
     
  10. Oct 26, 2019 #50

    Dan Thomas

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    And I can tell you from experience that it works just fine. I overhauled a Chev 283, set all the clearances to book spec, and ran that thing hard in a boat for years without a hiccup. I put a gate valve in the water intake line and played with it to see what would happen if I got the temps well up or way down; made no difference except for fuel consumption, which went up some when the engine was cold.
     
  11. Oct 26, 2019 #51

    poormansairforce

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    ....which is why they have thermostats....
     
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  12. Oct 26, 2019 #52

    PMD

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    I can't speak for Japanese manufacturers, but I am intimately familiar with VWAG diesels. In the early IDI days, the 1.5 diesels shared most of the components with their gasser equivalent. Block castings just used a bit more wall thickness (remember, still old tech days) and of course heads were different, but about same weight. I doubt there was 20 lbs. difference in the engines. Today's direct injection engines from VWAG share more dimensions than hardware, but block castings are nearly idnentical withing engine families, gasser to diesel. The 4.2 Mercruiser is a good example. Of course, the real differnce is that current TDI have the power density to compare with SDI gassers, which the old stuff would NOT do. I will stand by my stataement (easily supported) that there is no good REASON for modern diesels to be any heavier, but I do recognize your concern (and it is what I have pointed out already about auto conversions and bespoke designs - they are too heavy.

    Stay tuned to this station and in not too distant future, I predict you will see a diesel that can challenge the Rotax 912/914 in power and weight. As well, one department of AVIC has a gear reduced 4 cyl opposed diesel that LOOKS like a bit bigger 914, but is reported to be about even up with Lyc 0-320 for weight and power.
     
  13. Oct 27, 2019 #53

    Rik-

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    The only marine engines with a water thermostat are the ones that are “freshwater” cooled meaning a closed cooling system which is predominantly a Volvo package. It’s not that common it adds weight and cost
     
  14. Oct 27, 2019 #54

    poormansairforce

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    Thats funny because my family has owned no less than 10 boats over 25 years and everyone of them had thermostats except my waverunner. Yes, they are 140°-160° stats but closed loop is becoming more common for fuel efficiency and the pressure and antifreeze keep the boiling away. I guess I thought you were implying that auto engines don't work because they are inferior.
     
  15. Oct 27, 2019 #55

    Rik-

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    No, it’s merely an engine building requirement that different between an automotive engine and a marine engine.

    Putting an engine into a boat that uses the lake, pond, river or ocean for cooling and the engines run cold as far as block temperatures vs an automotive temperature, the clearance of the bearings and pistons are different.

    Now one can probably run a low power setup ok if your not beating the **** out of it, but try this with the 500+ Hp motors and the fuse gets real short. My customers were buying the GM ZZ572 crate motors for like 10K and they were a disaster. Didn’t last 30 minutes in a 38’ V bottom. Of course a properly setup marine engine has a broader torque band than what is required in an automotive build.

    It’s just a different recipe and being cheap with a boat motor setup usually means your not boating much
     
  16. Oct 27, 2019 #56

    akwrencher

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    Sorry, but most of the above is utter nonsense. The only reason a marine engine would run colder than a car engine is a lower thermostat setting, and the only real reason for that is because many boats operate in salt water and higher temps cause more problems. Also, heat exchangers really are not uncommon, keeping the salt water out of the engine block. Not that 40 years of playing with boats would teach me much.......
     
  17. Oct 27, 2019 #57

    PMD

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    At one point in my life, I was a boat manufacturer, but airboats, so no direct experience with liquid-to-liquid cooling installations.

    I have fooled around the ZZ4 572 Chevies, but NOT in continued high load situations. I am aware of the use of LSx superchared Chevies in 7 marine outboards, but now I am REALLY curious about what is being done in cooling and/or internal dimensions for that service. Would also love to speak with Yamaha engineers about their 5.6 litre, 425 HP outboard on same topics.

    This is of interest to me, not only because of technical curiosity, but because I firmly believe the future of aviation diesels might be tied to the development of diesel outboards.
     
  18. Oct 27, 2019 #58

    dino

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    Raw water cooled boat thermostats open at around 170 F to reduce mineral deposits, Closed circuit cooled boats run at higher coolant temperatures which is good for fuel economy.
     
  19. Oct 27, 2019 #59

    Markproa

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    On the other hand my aircraft engine, a diesel Peugeot 1600, uses the same block as it's petrol version.
     
  20. Oct 27, 2019 #60

    cheapracer

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    The only relevant fact is what is weighs, installed and running, along with what power it's achieving.

    Most N/A 1.6 petrol engines do 110HP+ these days. To match that power, a 1.6 diesel will have turbo, intercooler, heavier internal bracing and heavier starter motor. Then there's the typically heavier diesel engine flywheel (and/or crankshaft) needed for torsional damping.

    So the diesel is considerably heavier in it's final configuration for a car fitment, starting out with the same blocks or not. What approach you have taken for it's aircraft application though, is unknown to me.
     

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