[stillsearching]

This is a topic potentially crossing a number of areas, but the 'mother' topic is what kind of effects an engine has when run at very low RPM's (lets say everything under 1800rpm at the absolute maximum, and mostly focusing on the 500-1200rpm range as a target for actual cruising) including potential engine damage ("lugging" is called bad, why? Can you modify around what makes it harmful to handle it?), efficiency benefits, problems from slow turning pistons making flamefronts not run well under load, etc. Both gas and diesel.

If you think about it, engine efficiency is nothing more than cubic inches of displacement times rpm per mile in a way. To get 30hp to cruise on you are pumping X amount of air normally (in gas/stoichometric engines, diesels are different) and it doesn't matter whether thats a 250cc motor at 14,000rpm or an 8 liter at idle. Using a smaller engine is not automatically more efficient, but when your air pump moves less air it uses less fuel (in gas engines), has less friction and other benefits. Lots has been done trying to put small engines in large cars, often with forced induction to make back up the power, sometimes with less than stellar results. I'd like to push things the other way - big engines turning ridiculously slowly and modified for slow running.

There's a couple reasons for this:
- one of them is actually exploring cheap alternative power stuff. You can get used car engines cheaper than you can get used garden tractor engines alot of the time, they are just ridiculously overpowered. The only choices are deactivating certain cylinders (something i'll explore in a separate topic) and turning the engine SLLOOOOOOWWW.
- long engine life is also a side benefit. The Lister 6hp diesels built since the early 1900's were known for running _50-100k hours_ before needing a rebuild. (6-12 years of nonstop 24/7 service, producing power, working in oilfields or whatever) Part of that was because they turned at 600rpm and were overbuilt so that a 6hp engine weighed more than a big block chevy. (something like 890lbs?)
- noise, i've always been annoyed by the BUUZZZZZZ of small engines at high rpm, whereas the slow putt-putt-putt-putt of some of those late 1800's and early 1900's engines is almost relaxing. For stationary quiet genset power and such it's alot easier to muffle.
- plus just plain other projects of interest where ultraoverdrives could make large engines (like in a hot rod) actually efficient, I just don't know of many people who have even TRIED to cruise under 1200rpm on the highway... I mean, what even happens?
- some fuels have a slower flame front more suited to slow turning engines (producer gas is I think one, whereas atomised gasoline burns fast by comparison, and some of the thicker straight vegetable oils run great in a 600rpm Lister but will screw up your Veedub apparently)


Now it's possible there are diminishing returns below a certain speed, otherwise like big truck engines would already be capable of lugging like this... yet certain much larger engines DO lug like this - train/rail stuff is like 800rpm if I remember whereas the bunker fuel used in container ships maybe runs 90rpm direct drive to the screws. And as they do so start quoting phenomenal efficiency numbers. (exceeding 50% in large ship diesels)

Now i'm not desiring to run dirty as hell bunker fuel, i'm not sure if it would work the same under road diesel in a large marine diesel or not, i'm just trying to increase efficiency by turning slower, or to find optimum efficiency rpm's for different types of fuels especially various alternative and natural fuels. Even if there is an efficiency loss turning slower than ideal, it may be worth doing so for economic reasons at times.

I'm a part of another project elsewhere on the web (related to/branched off from the global village construction set stuff, look it up the original on TEDtalks and such) trying to help mechanize the third world with better solutions, lower pollution than what they are forced to do now, using available local/renewable fuels, on a very low budget like in places where financing is not often available. A $200 junkyard diesel for a utility tractor which is only 80% as efficient (turning real slow to produce 30shp) as a $5000 industrial diesel turns into a form of self financing - you use the cheaper engine the first year, until you can afford to buy the more efficient industrial diesel. Or if the industrial diesel ever breaks since you probably cant afford to repair it til after harvest, you can use the $200 diesel to get in this year's harvest. Both are supported, run whatever engine you have available, modified to work as well as possible, while also having an ideal efficiency version as well.

Sooo.... yeah. Part of my volunteering was to find ways to find the "market-cheapest" engines and derate them down to the desired shaft powers (typically 18-50hp constant) with the best efficiency possible by turning slower or deactivating cylinders, while also being understressed. (a 6.2 GM diesel is preferred to a 1.0L lupo engine because the former will run for decades at 40shp but i'm not sure the lupo would, it's also available in junkyards and cheaper) Other projects aimed at generators or stationary would like to lower it to the 4-10shp level, with the smallest car engines turned as slow as possible, maybe with 1-2 cyls shut off but mostly just with low rpm mods if doable. New industrial diesels usually cost at least $2000 in that HP range, and new 3600rpm gasoline engines have too short of a lifespan running that fast.


So that's the why to try... can someone maybe an engineer or experimenter tell me why I can't do it, or maybe if someone else has tried and found problems?