The Long, Twisted And Slightly Ridiculous Story of Avgas Part 1

other than whining about five dollar gas prices when your car needs a fill up you don't really think about it right you just pull into the station swipe your card and get on with it if you're an airplane owner though you pay what couple bucks more a gallon between six and seven dollars a gallon now for ab gas but come on if you're smart about money you would known an airplane but increasingly a lot of owners are wondering if let it have gas 100 octane will be available in three years well i'm here to assure you that it will be and i say that with all the confidence of a dallas fan thinking the cowboys will ever be in a super bowl again the problem is this stuff this is the molecular map for a stupidly toxic material called tetraethyl lead nasty as it is it's a great octane booster for gasoline and although we stopped using it in cars 30 years ago we still use the hell out of it in aviation gasoline for reasons we'll get to but first the beginning with this guy well actually no before him this guy charles kettering but really this guy thomas midgley who worked for kettering with general motors after world war one kettering by the way started delco and invented the electric starter there were lots of car buyers then with a lot of money and they wanted not just cars but fast cars one thing preventing that was the low fuel octane like really low around 60 or less as a result engines of the day like this cadillac model 59 had low compression engines typically around four or five to one and even though it was a five liter 8 cylinder engine it produced a pathetically low 60 horsepower teasing more power out of it required raising the compression ratio but because the fuel was so crappy that produced detonation also called knocking or pinging and sometimes incorrectly pre-ignition detonation isn't much of a thing in mainstream cars anymore but when it was it was caused by the fuel charge burning explosively in the cylinder rather than as an evenly expanding flame front that turns the fuel's heat into pressure and then rotational force through the piston connecting rods and crankshaft if detonation gets bad enough it can do this or worse lot worse there are several ways to prevent detonation but step one is higher octane fuel which burns with an even flame front it's not more heat or power but more orderly combustion that's where midgley and kettering started and actually they started with aircraft engines during world war one like this 12-cylinder liberty engine which encountered detonation when flogged at high altitude thanks to the poor fuel of the day the liberty actually had the same displacement as the rolls-royce merlin but the merlin had up to five times more power high octane fuel is one reason plus a giant blower after world war one midgley careened somewhat haphazardly through various experiments eventually settling on a disciplined march through the periodic table looking for an octane booster he landed on lead specifically tetraethyllead this stuff is synthesized into a liquid from a sodium lead alloy fuel dose with tel was so miraculous at eliminating knock that general motors moved to corner the market by forming the ethel gasoline corporation with standard oil they branded the hell out of it by deliberately avoiding using lead in the name because even then the toxicity of lead was well established this launched the famous filler up with ethel ad campaign and growing up in the age of i love lucy i was in the first year of college before i figured out that ethel merch had nothing to do with gasoline sure go ahead and laugh at me now but when i was riding to school in my old man's 53 rocket 88 oldsmobile we didn't know something that midgley did he discovered that during combustion lead precipitated and left deposits in the cylinders that's a bad thing so he added ethylene dibromide to the blend which caused the lead to exit through the exhaust pipe as a gas eventually condensing to the solid as lead bromide thus spewing it all over the countryside where 1950s kids like me ate it with our dirt pies lead is known to cause all kinds of maladies including iq loss in kids which maybe accounts for my ethyl merch situation you're maybe wondering how i'd segue back into aviation so here goes with this guy that's fang pilot jimmy doolittle who worked for shell between the wars and convinced the company to develop and market high octane aviation gasoline which is the forerunner of what we burned a day although the modern version has a whole lot less tetraethyl lead doolittle got help from this guy edwin alderman senior that name may be familiar because his son was the second man to walk on the moon anyway high octane avgas came along in the nick of time and many consider it instrumental in the battle of britain in a great big rush in 1940 the u.s ships stocks of 100 octane to england and that gave the merlins and spitfires and hurricanes up to 30 percent more power with good detonation margins pretty nice to have when you've been jumped by a bf-109 a key development in the uk before the war was 1938 to be precise was called alkylation this allowed u.s refineries to produce a high-octane base stock to which tel could be added to drive up the octane alkylation almost tripled the volume of gasoline production and yet today we know this stuff as aviation alkalete it's the base stock of all aviation gasoline world war ii was the golden age of aviation gasoline there was a brief peak in the mid 1950s when piston airliners were still a thing but jets sent the avgas market downhill and it's been going that way ever since in 1945 we made 25 million gallons of bad gas a day now it's about a half a million gallons a day and maybe reaching a temporary plateau after years of decline fast forwarding through the 40s 50s 60s and my ethel merciers gets us to this picture that's smog in los angeles during the 1970s and it wasn't the only place that muck would be loaded with lead bromide residue so not even a year after the mega polluted cuyahoga river caught fire in cleveland if you remember that the environmental protection agency was established and shortly thereafter the clean air act emerged initially it did not directly regulate lead but it did set overall airborne emission levels which would be met in part by these gadgets catalytic converters lead residue kill the catalyst in these devices so the epa eventually ordered lower permissible lead levels and gasoline before banning it entirely in 1996 except there's an asterisk aviation was allowed special exception to continue using leaded fuels for safety reasons because no suitable octane enhancing substitute has been found and that's where we are today unfortunately as other industries have gotten rid of lead general aviation enjoys the dubious distinction of being the major lead polluter in the united states it generates stories like these not a good look by now the perceptive viewer would have two or three penetrating questions when lead went away in the mid-1970s refiners had to find octane replacements for cars eventually electronic engine controls ecu's lower the need for octane somewhat so why can't you just use car gas in your airplane you can use car gas in your airplane or as we call it mogas but not in all engines because it lacks octanes for engines like this you do have to buy a supplemental type certificate to use mogas but they're cheap mogas isn't necessarily however especially during the past few months and some owners don't think the price difference over avgas is worth the trouble which is one reason that only about 100 airports in the u.s have it another reason is that fuel suppliers often insist on supply contracts that exclude mogas or other fuel sources due to liability and fit for purpose concerns if avgas prices remain high maybe that'll change it hasn't yet there's another problem and that's ethanol which was mandated for refiners to appease the corn lobby this has negative impacts on gasoline pool vapor pressure and reduced overall gasoline supply but it resulted in refineries retooling to make lower gasoline octane since the ethanol was providing that quality ethanol nav gas is a non-starter because it's hydroscopic meaning it collects water this can cause phase separation exacerbated by temperature changes as we climb to altitude and while that's a pain in the ass in your lawnmower this is what happens in an airplane so alcohols haven't been favored as octane enhancers if you burn mow gas it has to be ethanol free e0 and refiners do make it mostly for the boat and recreational market it's quite the sport to say how dumb airplane engine designers are for not having developed engines that don't need 100 octane gas well first of all they have something like 125 000 airplanes in the us fleet have engines that don't need 100 octane fuel and this company swift has a 94 octane unleaded have gas you can buy all day for prices similar to 100 octane let it have gas but only at about 25 u.s public airports you want hardware we got hardware more than 20 years ago continental certified a couple of aircraft engines that essentially had automotive style ecu's or engine control units this tech had been developed during the 1990s by a startup called aerosands expressly looking forward to lead regulation that might eventually limit avgas octane the idea was to prevent knock on lower octane fuel through variable timing and pulse fuel injection they couldn't quite get it over the bridge however the high horsepower engines still require 100 octane gas that system now called continental power was also heavier more complex and expensive and it just didn't do much the market gave it a big yawn like comey tried a couple of times two most recently with this engine the teo 540 c1 or ie2 same idea that's automotive electronic technology applied to an old-school six-cylinder engine technam is using it in this airplane the p-2012 traveler still it requires 100 octane fuel because air cooling limitations make detonation possible in a portion of the operating envelope one other bit of hardware worth mentioning is water injection world war ii aircraft designers used it in some aircraft to quench detonation and boost power and even some jet engines had water injection although not for detonation control but to increase takeoff power and sure enough a company called airplanes offers their water injection impulse system for civil aircraft piston engines you can install one under stc in a limited range of airframes it works transparently by sensing temperature and pressure trends in the cylinders injecting water automatically into the induction system to tamp down detonation on lower octane fuels i phone the system it works great but at twelve thousand dollars it's not a cheap mod and since there's not a lot of mogas out there the payoff is questionable it would however make ul-94 suitable for high horsepower engines but however good or bad the adi idea is it just hasn't gained any market traction yet maybe someday so we're in cement overshoes still stuck needing 100 octane gasoline doesn't matter if it's leaded or unleaded a third of the engines in the fleet and these airplanes still need hundred octane gas and they consume two-thirds of that 200 million gallons a year we've known lead was threatened for what 45 years now so why don't we have an unleaded 100 octane have gas the biggest single driver is the asterisk for almost half a century general aviation has enjoyed dispensation from lead regulation till that changes nothing else is likely to either we'll explore the details in the second part of this video series i'll be right back

Channel: AVweb

Views: 231,947

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Id: 9F-WngVMJBQ

Length: 14min 23sec (863 seconds)

Published: Sat Aug 13 2022