4-Cycle More Efficient?

I'd say a two-stroke diesel, or a 4-cycle converted to ignition would be more optimal with the ultimate range coming from the 4c conversion. IIRC a transatlantic crossing was accomplished using an Enya(?) 1.20 4C converted to gasoline.

The two stroke diesel may run at less peak horsepower than the same basic engine on glow, but runs significantly longer on a given volume of fuel due to the different fuel air ratio requiements. It will also turn more prop without baking to death and thus efficiency gains help offset 2C mileage issues.

For range versus volume of fuel, you want gasoline or diesel fuel (if these are options for you) versus methanol and especially versus methanol plus nitromethane. If you were looking to gain the best range on 2 stroke glow, use a motor that will run on FAI or very low nitro fuel.

Mike D.

In my opinion (not worth much) the two stroke puts much unburned fuel out the exhaust. This is part of the reason motorcycle manufacturers gave up years ago on 2 stroke street bikes rather than try to find ways to make them comply with looming enviromental regulations (unburned hydrocarbons). Same reason you will start to see them disappear on snowmobiles and watercraft.

In duration per cc of fuel, any methanol engine will be at a distinct disadvantage to a similar gasoline engine. Gasoline simply has much more energy per cc.

Back in the eighties, Maynard Hill, multiple FAI world record holder set out to determine the absolute most efficient set up. The FAI at the time had a model aircraft engine displacement limit of 10 cc (.61 ci). Mr. Hill published a paper summarizing these studies with the American Institute of Aeronautics and Astronautics (you may want to look it up). He found that an 10 cc 4 stroke cycle model airplane engine with electronic ignition running on an exotic blend including gasoline, isobutane and synthetic oil was the optimum powerplant for his world record duration and distance pursuits.

Trying to calculate which would fly FARTHER on a given amount of fuel in the .61 to 1.2 cubic inch class engine....

Let's say the plane weighs about X lbs, and it carries Y c.c. of fuel, Which would carry it farther, a 2C or 4C engine?

Consider.... A 4C has to waste energy on an exhaust stroke. A 4C has less power than a 2C of the same displacement. A 2C blows a lot of unburned fuel out the exhaust. A 2C diesel is supposedly runs longer than a glow engine, but is that at reduce power production?

So, if the goal is to get the most range per unit of fuel, is a 2C or 4C better?

H.J.

4C almost always since the exhaust stroke that clears burnt gases is not the same as the inlet stroke that ingests new ones. All 2 strokes - except DI diesels - tend to throw unburnt fuel down the exhaust system.

Yes, I think it does actually. Methanol is CH3OH from memory. Diesel is mainly longre chain carbon strings - CnH2nH2 if you like.

I think the higher ratio of carbon to hydrogen plus the lack of the oxygen molecule means you get more bang per oz.

Formula one cars, tho now limited to a single fuel, of alleged restricted octane rating, at one time were using carbon ring compounds, that have even more carbon per molecule than straight chains - i.e. Benzene is C6H6 from memory. This got more power from the restricted tanks, espceially with turbochargers. It was also very carcinogenic and nasty stuff.

Go for carbon rings for the most bang per oz, but you need to design the engine to take it.

Its called direct injection, and most full size diesels do it. Well most big ones anyway.

4-stroke gas engine like Ryobi!, or 4-stroke diesel conversion engine, if you have the skills. The mark II gas 1.60 MVVS with the 7mm carb is the most fuel efficient off the shelf airplane engine for the power I have ever tested, save for the Honda 4-stroke moped engine.

My idea: Troll ??

I would use a 1.2 4-stroke, add ignition system, lower compression ratio, and recalibrate carburator for gas ( or benzene if your careful about handling cancer agents).

Ray Shearer

There is probably to many variables involved.

But from what I've read the 2C Diesel should often win the contest. A diesel should have both better fuel economy and better torque. But not necessarily better horsepower.

I think Moki produces a .60 or large engine specifically designed to run on diesel.

Another option which should yield good results if modified correctly would be to convert a glow 4 stroke engine to spark ignition and burn a gas/oil mixture.

Note: RC Diesel engines do not burn diesel fuel, they burn a Kerosene/Ether/Oil mixture. They are compression engines like diesels.

| Note: RC Diesel engines do not burn diesel fuel, they burn a | Kerosene/Ether/Oil mixture.

Yes.

| They are compression engines like diesels.

Of course, so are your `standard' R/C 2 and 4 stroke engines :)

| >| They are compression engines like diesels. | >

| >Of course, so are your `standard' R/C 2 and 4 stroke engines :) | | Not entirely true. Our "standard" "glow" engines get a LOT of help | from the glow plug, and catalytic action of the platinum acting on | the methanol. If they were true compression ignition engines, the | glow plug would not be required.

Even `diesel' engines often have glow plugs. My Rabbit Diesel, for example.

The glow plug just helps it along. Give the engine more compression, and it wouldn't even be needed.

SOME, but not ALL true compression ignition engines have glow plugs for cold starts, They do NOT come into play during "normal " operation. And there are a great many direct injection compression ignition engines that have no glow plugs at all.

I SERIOUSLY doubt that trying to run on methanol without a glow plug would be very successful, but I could be wrong

ex diesel mechanic bob

I have had glow engines start without the battery applied to the glow plug several times in my life, so I know that we are on the edge with this compression ignition thing.

It is a most unpleasant surprise when you are not expecting it.

Snarf

I'll take your word for it. I don't play with things like ether, got WAY too familiar with it's properties back when I was doing service calls to help people get their engines started in cold weather. I usually got the call AFTER the engine was well charged with ether, and the starting batteries thoroughly depleted.

Adding ether to the methanol introduces another ignition source though, so we have changed the parameters of the situation.

"Normal" glow fuel mixtures would not do well without the glow plug or a platinum element even with higher than usual compression ratios.

bob

Bob, You are talking full size engines with ignitions I suppose? The model diesel is a different engine alltogether.], and has no fuel injectors. A model glow engine will not run without the glow plug, unless it has a spark plug

The glow element will stay red hot if methanol vapour is present, so under the right conditions, the glow engine will start again, even without battery assistance. I have seen it happen only once, but it scared hell out of the guy it happened to. He is much more respectful of glow engines now.

that's EXACTLY what I was saying in the first place ;-)

A glow engine is NOT a compression ignition engine

bob

Well, it's (only) a question of word definitions. I was interviewed for a job at Ricardos (UK automotive consultancy firm) once and woing to my modelling background this very question came up. My interviewer gave the opinion that both model glow and whet we call "diesel" engines were in fact compression ignition engines. I can't remember what an engine had to have to be called a diesel, but ours didn't :-)

Anyway, I don't much care what name a thing is called by so I'll duck out again.