Smallest most efficent gas/alcohol/deisel engine...
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Author:  Johnsinski [ April 6, 2022, 11:30 pm ]
Post subject:  Smallest most efficent gas/alcohol/deisel engine...

...that can make 20 hp, sustained.

I'm in need of 20 hp sustained.

Fuel source is not critical, but free vegetable oil would be nice, so that tends toward diesel I assume.

Mobility is not a huge concern, but volume and weight is.

Most efficient conversion from liquid fuel to mechanical flywheel type energy is what I'm after. Flywheel and or electrical storage may be used.

I'm thinking like a 10 horse briggs & stratton type motor, but with a turbo and built to be able to sustain 20 hp reliably (not stressing the engine). Warm up temps don't matter as it would be running long term.

Is there a gen-set out there already that could be super efficient and run on alcohol or bio diesel?

It could be scaled to a bigger system, but I want to try a small system right now.


Author:  Miatav8,MstrASE,A&P,F [ April 7, 2022, 6:14 am ]
Post subject:  Re: Smallest most efficent gas/alcohol/deisel engine...

Forced induction does not make higher output sustainable. The higher output is sustainable for a shorter period of time than the NA output. A larger NA that puts out the required hp would be more reliable.

A fuel cell is far more efficient than any ICE for producing electricity that can be used to turn a motor with a flywheel. The fuel is vapor from a tank of liquid hydrogen.

If you want an ICE, consider a lower tier (epa forced replacement) used kubota 1100-2500cc 3-4cyl engine from an 18 wheeler refrigeration unit.

Veg oil would need to be mixed with something else to burn better cold , preheated, or transitioned into a hot engine running off diesel then the diesel is shut off.

ICE needs a warm up time for longevity. An air-cooled engine could provide a shorter warmup and would weigh less.

One problem with using a gen powerful enough for peak loads is that ring loading becomes an issue if operated at much lower loads. For longevity, size for the constant load and unplug as needed to keep the amps within limits.

There needs to be a safety system to isolate the gen set from grid power so both are not connected. If the grid power comes back on and the sine waves are not synced and freq matched (they won't be), it's a short. There are closed transition switch systems for this purpose.

Author:  rx7locost [ April 7, 2022, 8:12 am ]
Post subject:  Re: Smallest most efficent gas/alcohol/deisel engine...

I am no expert. That said, I would think that a B&S 10HP and then turbo'ed is not an engine for longevity. They barely last 500 hours as NA. Then there is the issue of cooling. Doubling the HP would over-task the air cooling fins I think. Then comes the issue of lubricating the turbo. I guess some B&S type engines do have a real oil pump. For a constant RPM engine, it would be hard to beat a small NA diesel engine. It may not be the lightest setup though. Everything is a compromise. I think your goals are conflicting and only you can determine the best compromise.

Author:  Johnsinski [ April 7, 2022, 12:40 pm ]
Post subject:  Re: Smallest most efficent gas/alcohol/deisel engine...

You guys are just full of knowledge, that's exactly the advise I was looking for.

I would have never though of a refrigeration unit from a truck.

Trying to run a 10 hp motor at higher power non-stop sound's like a bad idea too. Thanks for checking me.

Now that I think about it, a turbo is not needed is it? If it's going to run at full throttle, it won't have the pumping losses of a throttle.

I would presume it would need to be recammed for some ideal lower RPM. What that RPM is, would be determine by the maximum efficiency of the engine selected.

Could it even be a modern 2 stroke of some sort? I say modern meaning direct injection and other things to reduce emissions. Which bring up a good point, it could have it's pipe tuned for that optimum RPM.

Preheating vegetable oil should not be a problem, nor preheating the whole system. It would run for hours or days at a time.

Author:  rx7locost [ April 7, 2022, 1:26 pm ]
Post subject:  Re: Smallest most efficent gas/alcohol/deisel engine...

Is this a generator project? If so, what kind of generator, a traditional or an inverter? What makes you think 20HP is your goal? HP is not flat across RPMs. Engines are rated HP at some RPM. Just a reminder that HP is equal to (torque * RPM) /5252. If you lower the RPM, the HP drops close to the same ratio. Are you looking for efficiency to reduce operating costs or to limit the heat generated by the engine? The lowest operating cost ICE would likely be Diesel, especially if you can use waste oil products for fuel. I hope you like the smell of French Frys and Chinese food. :mrgreen:

Take a look at this link to Jack's Kubota powered Locost trip for inspiration:


Author:  Warren Nethercote [ April 7, 2022, 6:01 pm ]
Post subject:  Re: Smallest most efficent gas/alcohol/deisel engine...

Ditto on the Kubota or similar. Long, long ago I was involved with automating lighthouses and we used air cooled Lister Diesels as gensets. Heavy but robust. The US Coast Guard ran a 'lifetime' test on one running continuously (yes, no oil change ...) but gave up at 15,000 hours. Won't satisfy light and compact, but light, compact and reliable?

Author:  Johnsinski [ April 7, 2022, 10:44 pm ]
Post subject:  Re: Smallest most efficent gas/alcohol/deisel engine...

Yes the concept is homestead electricity. So weight and volume are not really a concern, cost and efficiency are primary. Use of renewable liquid fuel is secondary, but free vegetable or waste oil sounds great. Weight and mobility are very low on the list.

If memory serves diesels were literally designed to run on peanut oil.

I pretty much pulled 20hp out of thin air. If I could average 2 hp (1500w) and be able to store 24 hours of that in a flywheel or battery that would be ideal. Used car "powerwall" batteries are cheap now. Inverter prices are coming down.

A small "30" size nitro methanol airplane engine makes 2 hp easy, but for how long? But maybe that's the solution, just replace the motor every month? They can be had for "free" if you know how to rebuild them. Gearing down would be an issue.

I will look at the Kubota diesels. I don't want to reinvent the wheel, so to speak.

Thanks again.

Author:  Warren Nethercote [ April 8, 2022, 6:37 pm ]
Post subject:  Re: Smallest most efficent gas/alcohol/deisel engine...

My 5kw Honda (admittedly gas) generator let's me keep my house running, albeit by turning off other things when I want to heat up the hot water tank. Princess Auto has a 12 kw (gas again) generator going on sale next week for around $2000CAD that would run my house without any management at all (beyond gas cans). You would need to source a Diesel gen set, but why wouldn't you buy off the shelf, or at least used with current prices? OK, you WANT to make it. :-)

Author:  crytes [ August 1, 2022, 11:39 pm ]
Post subject:  Re: Smallest most efficent gas/alcohol/deisel engine...

Look in the descriptions many of the green ones will be "multi-fuel" meaning they will run off of anything even close to diesel including vegetable oil, kerosene, or what they have probably lived on in military use jet fuel.

Author:  kabuku6 [ August 3, 2022, 7:01 am ]
Post subject:  Re: Smallest most efficent gas/alcohol/deisel engine...

Just an fyi, but if you're matching up a genset to a motor, the genset will dictate what RPM the motor runs at. North American electricity is 60hz, so our generators will usually run at 3600rpm for gas and 1800rpm for diesel.

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