Automotive History: Ultrasonic Fuel Systems We Could’ve Had

Ultrasonic humidifiers—hang on; I promise relevance—were all the rage in the ’80s. These were great; they made cool fog which humidified the entire space, a giant advance over the boiler types which spewed hot steam and drops of hot water; soaked down the everything in their close vicinity, and made slurp-glurk-whistle-gurgle-flup-flup-flup noises all night, worthy of Don Martin. When I was nine or 10 I had an ultrasonic humidifier in my bedroom up there in the dry suburbs of Denver—a Samsung HU-701A, the one shown; described, and priced (yee! $252 today) in the upper right corner of this April 1985 Popular Science showcase:

Geeky gradeschooler me, I took to playing with it. Next to the water tank was the vapourising chamber and distribution tower. I couldn’t find any pics of a 701A, so this very similar model from a year or two later will stand in:

There was a float switch to cut off the ultrasonic nebuliser if the water ran out, but no interlock to stop the music if the chamber weren’t installed. I discovered a finger could be kept right atop the ultrasonically-energised water stream only very briefly before it started hurting, though I couldn’t figure out what was happening to cause the pain. I got a clue when I immersed my eyeglasses just below the surface of the water pool, with the lens right above the nebuliser: when I removed them after a few seconds, there was a melt-distorted area about a centimetre in diameter. Oops! The lens was ruined; I don’t recall what fib I came up with for my mother about it.

About 15 years earlier, many states away in Florida, a couple of electrical engineers had got to playin’ around with ultrasonics as well, but they were less interested in high-tech finger-cookery or spectacles-melting, and more interested in lowering auto exhaust emissions. This is from the March 1973 issue of Popular Science:

They bought a Slant-6 ’72 Duster and retrofitted it with an ultrasonic fuel system of their own design and build. That’s way cool, even if PopSci’s artist misdrew the car as a ’72 Demon. The chart shows the vastly sweeter breath of the ultrasonic-equipped car, which—compared to the same vehicle with its production Holley 1920 carpotato—put out less than 18 per cent of the carbon monoxide; less than 8 per cent of the unburnt hydrocarbons, and between 8 and 43 per cent of the NOx; that’s massively cleaner.

The chart provides context of ’75 and ’76 US Federal emissions standards as well as other low-emission try-outs: Chev 327 V8s fuelled by propane and by natural gas; a turbine engine, an experimental Mazda Wankel, and a simulated sky-pie Stirling engine. More, the car gave much better gasoline economy with the ultrasonic system, at a time when cleaner exhaust usually meant more fuel consumption.

The emissions reductions were confirmed in rigorous US DOT testing (section 1-12 of the linked document), but not the fuel economy benefits. The DOT’s testing contractors found the Duster’s original carburetor faulty, so they installed a new one for the baseline tests. The emissions benefits stayed, but the new carb did more or less as well as the ultrasonic setup for fuel consumption.

The results are particularly impressive for having been achieved without the feedback (closed-loop) mixture control made possible by the exhaust gas oxygen sensor Bosch was to release a few years later. They’d’ve gone together like water and melon.

Not a word in the whole article about how the car was to drive. But given just exactly what this system did, it would pretty much unavoidably improve performance and driveability compared to a carburetor’s sloppy, halfassed work (hey, just like Jan Norbye’s usual and customary reporting!).

Here we see the car was in fact a Duster and not a Demon. The car had A/C, which makes sense in Florida, and just look how completely the controllers hogged up all the space below the Duster’s under-dash A/C outlet and that funkatronically plaid seat vinyl. Even manufactured computers were great big things at that time, let alone hand-built prototypes like these.

How did the system work? An electronic computer balances engine load (as sensed by intake-manifold vacuum); engine speed (sensed by distributor shaft RPM), and ambient temperature. The computer translates this information into variable fuel pulses, which are then directed to the active surface of a sonic reactor unit […which…] faces two fuel injectors. So they were shooting gasoline at an ultrasonic nebuliser to create a fuel fog much finer and more uniform than the assorted-size, chunk-style droplets from a carburetor.

Leave out the ultrasonic nebuliser, and that’s an identical description of a speed-density throttle body fuel injection system as factory-fitted to zillions of American cars in the 1980s and into the ’90s. But the ultrasonic bit really did the heavy lifting on this one; the output from a throttle body injector is visibly more like a lawn sprinkler’s spray than a humidifier’s fog; better than a carburetor, but nowhere near this much better, as admitted with inadvertent prescience in that first paragraph touting ultrasonic fuel induction as a better method than cleaning up dirty exhaust.

I confirmed my hunch on that by checking the combined, new-scale fuel economy differences of carbureted versus TBI versions of a few different models—’85 versus ’87 Aries 2.2/auto (carb ’85 4.5 per cent better) and ’88 versus ’89 Caprice 305/auto (TBI ’89 5.8 per cent better). Yep, fuel economy improvement with TBI was trivial at best; not close to the ultrasonic’s improvement.

A fuel fog like this what the ultrasonic setup provided does not tend to condense and puddle in the manifold anywhere near so much as a coarser mist. That would put it much closer to one of the big reasons why a dry-manifold system (port fuel injection) works so much better than a wet-manifold system (TBI or carburetor): the intended amount of fuel reaches every cylinder, always.

I really think it was probably feasible—at least very ripe for further development. The results shout loudly, and computers and components were rapidly shrinking and improving at the time, too. The ultrasonic nebuliser and its driver in that 1985 humidifier were altogether a hold-in-the-hand collection of parts.

But instead, automakers stuck with carburetors long past their use-by date, and cleaned up the exhaust with catalytic converters. I doubt it’s because of a flaw in the ultrasonic concept; I have an easier time thinking they saw a flaw in where the idea hadn’t come from. Mind, I don’t claim ultrasonic induction would’ve made catalytic converters unnecessary—maybe or not, but cleaner exhaust in = cleaner exhaust out and much longer cat life.

Also mentioned in the article is that retrofitment to existing vehicles would be easy, and that’s probably right. Looks like they used an electric fuel pump; those were readily available at the time, and the rest of it would just be replacing the carburetor by an appropriately-configured throttle body-injectors-ultrasonics assembly, putting the control box somewhere, and wiring it all up. Easier; safer, and surely more effective than trying to retrofit a catalytic converter—though here again, the ultrasonics would’ve greatly facilitated cat retrofitment.

Here we get a look at the hardware, and although the artist didn’t quite completely grasp the point—they drew a choke plate; none would be needed, and there’s no choke on the actual car—it does show how the injected fuel would hit the ultrasonic plate. The underhood photo shows a stock ’72 Slant-6 air cleaner sitting in its factory-intended location, which implies even this handbuilt prototype with big, klunky components available at that time fit within the original packaging and allowed the hood to close.

This final page talks about work being done on the subject by others. Dr. Thatcher received about eight patents in the field. None of this stuff was ever commercialised, as far as I know. That’s a shame; this looks like it was a really good idea. Perhaps it’s a pity Thatcher didn’t work for Carter or Holley or Stromberg or one of the automakers.