This engine is nominally an 18cc two stroke diesel but it was more advanced than that, featuring a variable compression ratio designed to allow it to burn a variety of fuels. There is no ignition system or carburetor. Attached to the bottom bracket of a bicycle, the motor turned a roller which acted upon the rear tire allowing speeds of 15-20 mph.
Although it worked ok and ran fairly well, apparently the rider is required to be constantly adjusting the throttle and compression ratio in order to keep the engine running, according to this article online which explains much more about the unusual little beast.
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| thanks, Rolf! |
Jan 1985 The Classic Motor Cycle
Actually the variable compression ratio was not merely to accommodate a range of fuels but was essential to enable this engine to run at all, on anything. Since the engine is compression-ignited, and the fuel mixture is already in the cylinder during the compression stroke, the ignition timing is an accident of air temperature and cylinder temperature -- so to avoid preignition or failure to ignite at all, you have to tweak the compression to put combustion conditions near top dead center. See the linked article for all the fun and games you can have as you search for the optimum compression via one twist grip, at the same time as trying to optimize the throttle with the other.
ReplyDeleteWith the one a friend of mine bought (from a newspaper ad via a rendezvous in a designated parking lot, from which the seller swiftly disappeared) our experience was pretty much in line with the description in that article.
Thanks for the note! It's an unusual concept and surprising that it made it to production at all.
ReplyDeleteYou're welcome. The thing WAS fun to play with, being so outrageous a concept. Regarding the caption about only getting it to run on model-airplane fuel, we had no trouble with kerosene (to which I guess we must have added the recommended heavy dose of motor oil as upper-cylinder lubricant). But it sounded like a popcorn popper and smelled like a diesel truck. And the propulsion was of a magnitude that would interest only a cyclist utterly allergic to aerobic exercise -- a one- or two-percent grade would stall it out. I'm not sure why it was made with so tiny a displacement, except that with a fixed drive ratio, starting it by pedaling might have become difficult if it were bigger.
ReplyDeleteNow I want one!
ReplyDeleteHave a modern variant as a pattern if any one is interested in prototyping it.
ReplyDeleteHi Fire-Drop! I do R&D (shadetree) on ICE engines. Starting to specialize in ultra-efficient clean diesel engines, 4 cycle and 2cycle. I want to make multi-fuel generators and transportation options for underdeveloped countries and worldwide cheap transport. My email is corey@printingandsigns.net
ReplyDelete(initial 12/26/2020 commenter here) Well, someone did say something about high compression promoting more-nearly complete combustion, but as the linked "Progress is great" article noted, the combustion of the Lohmann is anything but. So if you get a miniature like the Lohmann to be "ultra-efficient and clean" (with its dauntingly high surface-to-volume ratio -- all that heat-sink metal within less than an inch of the fuel trying to burn) then I'll be very impressed. And I've never heard of a clean two-stroke, either -- the exhaust port opens too early, and also there's no way to close it before the intake port opens, so there's no way to keep some of the intake mixture from sneaking right on out. Two-stroke genuine diesels, with blowers on the intake-air ports, do much better because (1) there's no fuel in the intake air -- it gets injected near TDC instead; (2) there's no need to mix lube oil into the fuel because you aren't using the crankcase as a pump to charge the cylinder -- the crankcase keeps to itself and has motor oil in it; and (3) with no need to spill the exhaust pressure quite so thoroughly before the intake port opens (to avoid backflow into the only-weakly-pressurized crankcase), it's probably possible to place the exhaust ports lower and harvest more compression work before you dump the exhaust. Still, while two-strokes are great for power-to-weight ratio because of power strokes twice as frequent as in a four-stroke, it's hard to see how it can ever be a fuel-efficiency advantage to spill the exhaust (still with pressure in it) before the bottom of the power stroke.
ReplyDeleteA post by a second friend who later bought the Lohmann I've described, from my first friend who had it, can be found (currently) by googling "My lohmann engine; a tale of woe" or "My Lohmann engine no longer runs." (It was heavily damaged in a barn fire.) This was somewhere in the Puget Sound area; he'd bought it from my housemate in suburban Philadelphia, on a trip east in '81, and I visited him later that summer in Seattle to help him identify all its parts and install it on one of his bikes out there.
As you've probably found, Google brings up a number of posts on Lohmann engines.
(Correction: the linked article is at "Life in the Slow Lane" -- it's THIS thread, of course, which is named "Progress is Fine.")
ReplyDelete