Very small engines - a practical thread

Sac Arrow

Sac Arrow

Touchdown! Greaser!
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Snorting his way across the USA
Okay, so, the premise is this - you are stuck in the Yukon wilderness with some stuff, your cell phone, perhaps your laptop, and of course survival gear to include lots of .22 LR ammo and some fishing gear and warm sleeping bags and parkas and such.

We all know that you could be drifting in the middle of the Pacific Ocean, thousands of miles away from any shore and hundreds of miles away from any shipping lane and your death is certain but one thing is constant - you can still post to Facebook and your favorite aviation message boards. It's funny how that works out but it seems to.

Tiny engines are fun. Bigger engines are more fun. But we know that the tiny RC airplane engines don't suck up much fuel, are noisy, don't last very long, but, if you ran through the numbers, they aren't very fuel efficient at all and they wear out quickly.

The smallest Honda generator is a lawnmower with a generator attached. That is overkill for my mission. I want something a lot smaller. A lot lighter. But that will have the reliability of the lawn mower Honda (or Briggs or Tecumseh) that will drive a small alternator so I can keep my low wattage devices operable for an extended period of time.

Little two stroke engines are horribly inefficient and noisy and break after not very long. Big two stroke diesels like you find in big massive ships are efficient and reliable and that is why you find them in big massive ships, as opposed to steam turbines and four stroke piston diesels. You can find hobby four stroke engines of very small size but they still are not made for extended service.

Is it POSSIBLE to have a small, Cox .049 or maybe a little larger IC engine, in a reliable, efficient package that can make a five gallon gas can last for six months of iphone recharging?

@Ted ?

Am I on to something?
 
One factor working strongly against you is the surface to volume ratio of the cylinders - volume scales with length cubed, but area with length squared - so you get a lot more surface per unit volume which results in a lot of heat loss and inefficiency.
Could they be reliable? Probably - assuming you are willing to give up some performance.

I like the steam engine idea. https://www.pmmodelengines.com/shop/steam/steam-engines/steam-engine-4/ 1/4 horsepower. But it would take a pretty big boiler. Then again, you need heat, so combine the two?

Or, https://www.pmmodelengines.com/shop/gas/gas-engines/air-cooled-red-wing-motor/ probably more reliable than a fast running model airplane engine.
 
Remember the laws of energy....and work. 5 gallons of gas will only do so much.

I'd second the wood steam engine idea. ;)
 
I have always wanted an excuse to buy one of these, and as much as I love internal combustion engines would probably pick something with minimal moving parts for reliability: https://www.bioliteenergy.com/products/campstove-2-plus

Basically a small fire driving a thermoelectric device that is both powering fans to fan the fire/cold side of the thermoelectric device and supply power to charge devices.
 
Matthew Johnson said:
I have always wanted an excuse to buy one of these, and as much as I love internal combustion engines would probably pick something with minimal moving parts for reliability: https://www.bioliteenergy.com/products/campstove-2-plus

Basically a small fire driving a thermoelectric device that is both powering fans to fan the fire/cold side of the thermoelectric device and supply power to charge devices.
Click to expand...
Ohhh, nice. Combine that with an electric firestarter and you're golden as long as you can find material to burn.
 
There are times and places for different tools. Sac, this is not a time and a place for a gasoline engine. There, I said it. Send out the search party for the real The Ted.

@Capt. Geoffrey Thorpe hit on a big part of it. Physics makes it really hard for super tiny engines to be efficient due to heat transfer/loss. Gasoline will burn at (roughly) the same speed/flame front propagation regardless of engine size, but a tiny engine will have a much larger area relative to its displacement for heat transfer. I agree that they could be made reliable, but you'll give up some performance with that. And no matter what, they are just going to have a bad BSFC. They probably will still need to run at higher RPM (again, physics).

Pretty much all engines have limits below which you can't really get them efficient. Turbine engines are a good example of that, there's a reason why a small PT-6/TPE-331/RR250 is basically as small as it gets. And there's a reason why piston engines for which efficiency matters most tend to run really big cylinders.

The right solution to this is to have a small solar panel with you to charge your phone so you can post to Facebook and POA. Then you won't have to worry about running out of gas or what happens when you get water in the oil.
 
Capt. Geoffrey Thorpe said:
Solar panels suck when you are far enough north to not see the sun for a month or six.
Click to expand...

At which point a gasoline engine might make more sense. But I think Sac is stuck in a pleasant part of the Pacific so that won't be an issue for him. He wouldn't let himself end up shipwrecked in the arctic, not his style.
 
Sorry, Sac, I can't give you justification for that relating to your desire to have one of those engines in your "When I get stranded in the Pacific" tool kit. But the good news is that a solar panel is way cheaper than that engine anyway, and a better idea.
 
Matthew Johnson said:
I have always wanted an excuse to buy one of these, and as much as I love internal combustion engines would probably pick something with minimal moving parts for reliability: https://www.bioliteenergy.com/products/campstove-2-plus

Basically a small fire driving a thermoelectric device that is both powering fans to fan the fire/cold side of the thermoelectric device and supply power to charge devices.
Click to expand...
Tried that on more than one trip to Botswana. Those little things work beautifully and all you need is some scrap wood collected from the ground.
 
In Alaska, it may be better just to have a water wheel generator and place it next to a stream/river with sufficient flow. Or a windmill. Fewer moving parts than a tiny engine and probably easier than toting around fuel AND the engine.
 
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Checkout_my_Six said:
Remember the laws of energy....and work. 5 gallons of gas will only do so much.
Click to expand...

Five gallons of gas is about 30lbs. A normal four stroke engine uses about 0.5lbs/hp-hr so 5 gallons will get you 60hp-hrs of energy. Charging a cell phone uses a few kW-hrs per year according to these guys:

https://news.energysage.com/how-many-watts-does-a-phone-charger-use/#:~:text=Generally, phone chargers use about,to a 120-volt outlet .

60hp-hrs is about 50kW-hrs so it seems like Sac's idea is within the realm of reality, even allowing for reduced efficiency of a very small engine. I'd be concerned with cell phone coverage in the Yukon. Perhaps a satellite phone? However I have no idea whether satellite phones do internet.
 
flyingbrit said:
A normal four stroke engine uses about 0.5lbs/hp-hr
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Well, hold on. There are a whole lot of things that impact that, and part of the point above is that this isn't going to have 0.50 lb/hp-hr (which, BTW, is the BSFC that most Lycomings are rated at for best power). If you're at a best economy mixture (which is what you'd want) you're starting to talk about more in the 0.35-0.45 depending.

The most inefficient Lycoming I'm aware of is a 380 HP IGSO-540, at an 0.86 lb/hp-hr BSFC at rated power. I've never done runs on engines that small, but BSFCs of around 1 wouldn't surprise me.

Ok, done with unrequested technical data, carry on.
 
A small inverter generator is about 30lbs and shows fuel of about 0.1GPH at 50%(0.55 gallon tank, 6.3 hours at 50%). Which may be the minimum so 50 days at 1 hour per day of charging. Hook that to a Lithium pack for banking power for later.
 
Matthew Johnson said:
I have always wanted an excuse to buy one of these, and as much as I love internal combustion engines would probably pick something with minimal moving parts for reliability: https://www.bioliteenergy.com/products/campstove-2-plus

Basically a small fire driving a thermoelectric device that is both powering fans to fan the fire/cold side of the thermoelectric device and supply power to charge devices.
Click to expand...
That's pretty cool... IF the 3W of power it provides is continuous, and not just the battery output after the fire has charged it for a zillion hours. The website doesn't say. I have a "solar" USB battery pack... it works like a normal USB battery that you charge at home; if you wanted to charge it with only solar it would take about a week if constant sunlight. I bought it because it was no more expensive than other battery packs of the same size.

When my son in law did his cross country bicycle trip, he used a folding solar panel to charge his stuff with good success.
 
Dana said:
When my son in law did his cross country bicycle trip, he used a folding solar panel to charge his stuff with good success.
Click to expand...

It really doesn’t take much solar to power a lot of stuff. So long as we don’t have any HVAC needs, my 1200W solar setup will power everything we need in the RV.
 
Sac Arrow said:
We all know that you could be drifting in the middle of the Pacific Ocean, thousands of miles away from any shore and hundreds of miles away from any shipping lane...

Is it POSSIBLE to have a small, Cox .049...
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Properly tuned and unmuffled? Someone thousands of miles away will hear you and come to your rescue...or at least show up to tell you to shut it down.

Nauga,
and the Tee Dee screeeeeeech.
 
I think the russians did something like this. A direct thermo-electric generator run from a kerosene lamp. I think it was a bunch of thermocouples wired in series around the top hat of a kero heater, to run a small radio. There should be a more efficient way to do that now.

If that doesn't work, I'd go with wood/twig powered steam, as MS suggested in 2nd post. There seem to be a bunch of people making little steam engines, and making an alternator out of an RC brushless outrunner motor shouldn't be too tough.

Update: I didn't imagine it. Link - http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm

Enough juice from a kerosene lantern to run a tube radio.
 
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nauga said:
Properly tuned and unmuffled? Someone thousands of miles away will hear you and come to your rescue...or at least show up to tell you to shut it down.

Nauga,
and the Tee Dee screeeeeeech.
Click to expand...
Is this technique more or less effective than putting a large splash of gin in your martini?

John
Who is a wealth of old joke punchlines...
 
A decent chainsaw could drive an alternator and cut firewood. some even have small alternators built in to power heated grips. That would be enough power to keep devices charged without even having to rev up the engine much, probably just tweak up the idle a hair. and it has very few moving parts compared to its 4-stroke counterparts. I've run Stihl saws as old as I am which have had zero maintenance aside from a spark plug now and then.

The thermocouple on a kerosene lantern sounds like a great idea too.
 
drummer4468 said:
A decent chainsaw could drive an alternator and cut firewood. some even have small alternators built in to power heated grips. That would be enough power to keep devices charged without even having to rev up the engine much, probably just tweak up the idle a hair. and it has very few moving parts compared to its 4-stroke counterparts. I've run Stihl saws as old as I am which have had zero maintenance aside from a spark plug now and then.

The thermocouple on a kerosene lantern sounds like a great idea too.
Click to expand...

A chainsaw engine is a larger and has more fuel consumption than I had envisioned in my original post. I viewed something like a small, indestructible IC piston engine that will run forever with little maintenance, with low specific power output.

But, in an attempt to reel the Sac back in to reality, @Ted and @Capt. Geoffrey Thorpe noted that small size IC piston engines are inefficient. I understand that, I get it, (and I know that.) As a practical matter, any fuel for an IC engine has to be toted in, and in terms of power, a hand crank or solar solution would be more practical as it doesn't run out of fuel (if you don't.) The mechanical gadgetry side of me likes the hand crank option, but the lazy side that would prefer to be directing manual efforts in to tree sap hooch fermentation and preparing salted elk for winter storage (oh wait, I got shipwrecked in a tropical paradise.) Okay I guess I'm diving for fish and lobster and maybe I'll spear an occasional pig. All of those make great fodder for gratuitous posting on Facebook or POA. Especially the pig roasting on a handmade spit over firewood harvested from mangrove trees.
 
So I'll ask this - do you want to built a generator connected to a small IC engine, or do you want to build a small electrical power source that will run from simple to find fuel? Because I get just wanting to build something around a little engine, but thermoelectric or steam might be easier and more efficient.
 
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