Advice About Ethanol in an RC Nitro Engine
 

Hi there!

I'm a (total) beginner looking for some advice about using ethanol in a nitro engine, So a little background info:

There's a group project I'm doing where we test the efficiency of various methods of propulsion in RC cars. So my task is to look into using biofuels (in this case alcohols).
This of course includes methanol, but I'm quite interested in using ethanol. I intend on using a 2-stroke nitro RC engine, 0% nitro, 15-18% Klotz Benol castor oil and ethanol. However my biggest concern is whether or not theg glow plug can remain hot enough with ethanol. What do you guys think? Are there any other things that I should be concerned about??

If it helps:
- The engine won't be running at full throttle (or at least for very long)
- The engine will likely be running for a somewhat prolonged period of time (although if we design the experiment, the engine will only be running for a short period of time for each reading)
- There will be no long term use of the engine

Excuse my lack of knowledge and any responses are greatly appreciated :)

Thanks, P0tatoPatato

You can always wire the glow plug to always have voltage on it, that way you're not relying on combustion to keep it hot.

I have no experience with ethanol so can't give specifics but I can think of two problems you could run into

1. Getting the right compression ratio / head shimming. I have no idea where to even start with that.

2. Ethanol has a less pronounced cooling effect. This could lead to temp problems and vapor locking though if you are not running wide open, that might not be as much of an issue. Could also cause pre-ignition problems but that goes back to the first problem.

wont that Pre-ignite the incomming mixture, and therefore not allow decent cycling?

Dig around on some of the RC aircraft forums and search for "FAI fuel", which is just 80% Methanol and 20% castor oil. You should be able to get a good idea of what it takes to make it work.

Sounds like a good idea. Will do.

No, airplanes use glow plug heaters to keep the plug lit at low throttle to prevent stalling during landings.

Straight alcohol with no nitro content will have a hard time idling. Keep that in mind with your testing.

From what I was told is that Ethanol has a higher burning energy than Methanol, With that knowledge it is clear you need to adapt the ignition timing (glow plug number and/or head clearance) to make it work. Once I did run an Ethanol based fuel w/o adapting the compression and the idle was unreliable. I do believe those high energy fuels like the Runnertime Ultra (16% but needs headclearance of 25%) are based on Ethanol.

Better to ask on RCGroups. The airplane guys spend alot of time messing with different fuel combos.

Good to know, thanks Rick, learned something new.

I'm actually in the process of switching a four-stroke glow motor over to ignition. All the power of nitromethane, with added fuel efficiency, less oil mess, and more reliability.

The engine will be a little harder to start on the no nitro mix and wont idle as nice as even a low nitro fuel like 5% without changes to the combustion chamber shape and a hot glow plug. You could always prime the engine prior to starting with a few drops on nitro based fuel through the venturi of the carb, and speed the idle up a little more than usual. If you run a hot plug you shouldnt need to keep a glow driver on it when running. Hotter plugs are more fragile though, thinner element wire.

(For the record, I used a 15% BeNol / 85% methanol mix to after-run my high nitro marine engines to burn out any residual nitromethane prior to oiling. They can be harder to start on this mix, but they are set up for lots of nitro and run cold plugs.)

If the carb was tuned for different fuel previously, it will more than likely be out of tune for the new mix. Particularly if nitro was involved.

For racing, this can be a problem but for this experiment, it will be fine. Many models use a constant power source on the igniter for ease of running. A glow engine (or diesel), in many forms can run on virtually any fuel. We used to say the can run on "rat farts". Since he will have control over AF ratios via the carburetor and not seeking high RPM, detonation is not likely. I'd say get an inexpensive engine and try things out.

This was already done 80 years ago. RC nitro engines were invented in post-WW2 Europe, which didn't have a lot of resources to spare for hobbyist activities. Nitro engines run on methanol, which is already a biofuel made from fermented cellulose, and lubricated with castor oil, which is also sourced from plants. If you want to get rid of the nitromethane content in commercial nitro fuel to make it 100% plant-sourced, you can do that, you just need to modify the engine to run higher compression.