Fuel for 2 stroke engine

[minh-thanh]

Hi All
I'm trying to run my 2-stroke engine with gasoline and oil 2-stroke ( 4% ), it's hard to run at low speed and it doesn't run "smoothly" ,so is there any way to fix it?



It runs well with nitro fuel

 

[rweber]

Hi,

gasoline is not as ignitable as methanol. This means you need good compression, and what's more important, good mixture preparation. Possibly, you can improve the carburetor so that it does a better spray of the gas-air mixture.

 

[WOB]

There is something wrong with the fuel system. Those air bubbles going back up the fuel line to the tank indicates there is something wrong with the carb/needle-valve. There should be no air bubbles in the fuel line. Is the jet oriented properly in the air stream and is there a low pressure zone( venturi) at the jet's location?

WOB

 

[minh-thanh]

Thanks rweber, WOB !

There is something wrong with the fuel system. Those air bubbles going back up the fuel line to the tank indicates there is something wrong with the carb/needle-valve. There should be no air bubbles in the fuel line.
WOB

with air bubbles: it usually happens when I run the engine long and it heats up, it also happens with nitro fuel, I try to reduce it by putting the fuel tank about 10 mm higher than the carburetor

Is the jet oriented properly in the air stream and is there a low pressure zone( venturi) at the jet's location?
WOB

Yes, it is in the right position
I plan to change oil 2 stroke , I'm using this, it's cheap.

I intend to use oil Castrol .. hope to improve

 

[WOB]

There should be no bubbles in the fuel line! Every bubble that enters the line has to enter thru the jet which means fuel metering has to stop momentarily to allow the air in. There is no way to get a smooth run in that case. Is the fuel tank vented? There has to be a pressure differential to force the bubbles into the line and upstream into the tank against the fuel flow. I do not believe the oil is a factor.

WOB

 

[rweber]

It looks to me like the bubbles are coming out of the carburettor. Gasoline does not cool as much as Methanol. Did you check the temperature of the carburettor? Maybe the gas is cooking?

 

[Mechanicboy]

Gasoline has an initial boiling point at atmospheric pressure of about 35 °C (95 °F) and a final boiling point of about 200 °C (395 °F). methanol (CH3OH) has aboiling point of 65 °C.

But the boiling point is not generally problem if the fuel hose is not near the engine and the carburator is insulated from the engine with the non leading material to example use heat resistant plastic part between the engine if there is hottest part where the carburator is mounted on.
And there is cooling effect in the spraybar due venturi effect.
If there is air bubles, there can be air leakage in the fuel needle since the oil is not thick to keep needle and spraybar sealed from air leakage.
Model engine fuel has "fatty oil" to keep fuel needle and spraybar "tight" against air leakage.
Use fine treaded fuel needle and tight tolerance between needle and spraybar to preventing air leakage.

The oil mix in the model engine without piston ring when the gasoline is used, add more oil SAE 70, in case not available, use SAE 20W-50 or similiar (not 2 stroke engine oil for gasoline engine with piston ring). 3 parts gasoline and 1 part oil.

 

[bluejets]

Looks like it's getting stinking hot ....!!

 

[Mechanicboy]

Looks like it's getting stinking hot ....!!

Read chapter 15, page 102 about fuel/oil mix for model gas engine in this link.

https://rclibrary.co.uk/files_titles/1996/Engine_Encyclopedia_RonMoulton_partA.pdf

 

[WOB]

Looks like it's getting stinking hot ....!!

The reason it is getting hot is there is no forced airflow over the cylinder. This kind of engine usually has a propeller instead of a flywheel or a water cooled head[FONT=Georgia,"Times New Roman",Times,serif] [/FONT]if the flywheel is required.

WOB​

 

[minh-thanh]

Hi all !

Possibly, you can improve the carburetor so that it does a better spray of the gas-air mixture.

There is something wrong with the fuel system. Those air bubbles going back up the fuel line to the tank indicates there is something wrong with the carb/needle-valve. There should be no air bubbles in the fuel line.
WOB

There should be no bubbles in the fuel line! Every bubble that enters the line has to enter thru the jet which means fuel metering has to stop momentarily to allow the air in. There is no way to get a smooth run in that case. There has to be a pressure differential to force the bubbles into the line and upstream into the tank against the fuel flow. I do not believe the oil is a factor.

WOB

Maybe the gas is cooking?

Gasoline has an initial boiling point at atmospheric pressure of about 35 °C (95 °F) and a final boiling point of about 200 °C (395 °F). methanol (CH3OH) has aboiling point of 65 °C.
, in case not available, use SAE 20W-50

Looks like it's getting stinking hot ....!!

Today, I checked it again, I noticed that when the engine was running long and warming up, the carburetor was also quite hot.
So I decided to improve its temperature first :


and results :



Thank you for your comments !!!

 

[Mechanicboy]

Minh Thanh..

Can see there is not bubbles from carburator, also improved by insulated carburator from heat. And which fuel mix are you using to run gas engine?

 

[minh-thanh]

Mechanicboy !
Yesterday, I only had a little viscous 2 stroke. So today I use SAE 20W-50 as you said, the ratio is 1:20

 

[Mechanicboy]

Minh Thanh..

How it worked on your engine with this fuelmix? (I am deaf and can't listen the sound of your engine how it works in your movie, i am using feeling fingers to feel the engine is running with correct settings or not. Working as car mechanic since 1993)

 

[bluejets]

The reason it is getting hot is there is no forced airflow over the cylinder. This kind of engine usually has a propeller instead of a flywheel or a water cooled head[FONT=Georgia,"Times New Roman",Times,serif] [/FONT]if the flywheel is required.

WOB​

Exactly....but it doesn't help how it runs and that was my point.

 

[bluejets]

Hi all !









Today, I checked it again, I noticed that when the engine was running long and warming up, the carburetor was also quite hot.
So I decided to improve its temperature first :

View attachment 108341
and results :



Thank you for your comments !!!

Good job...sounds really great.

 

[minh-thanh]

Good job...sounds really great.

Thanks bluejets !

Minh Thanh..
I am deaf and can't listen the sound of your engine how it works in your movie, i am using feeling fingers to feel the engine is running with correct settings or not.

I'm sorry to hear about that !!
About the mix, I remember I read somewhere about being able to use SAE 20W-50 for a 2-stroke engine, as well as the same ratio as when using viscosity 2 stroke

And I have a question: can I use SAE 20W-50 as a lubricant for a 2-stroke engine ??

 

[bluejets]

And I have a question: can I use SAE 20W-50 as a lubricant for a 2-stroke engine ??

In small engines such as this, I'd tend to go towards Methanol and a mix of 20% castor oil ( Castrol M). 4 parts fuel and 1 part oil
Reason being it may use more fuel, BUT it keeps it cooler as the ignition temp is not as high as petrol.
That plus Castrol M has a large heat removal ability AND a much higher impact absorbing quality. ( big ends etc)
Methanol absorbs moisture so keep the can sealed when not using.

Minus side is one needs to give it some after run oil such as "after run oil" used by aeromodellers or just plain Machine oil.( works just as well)
Castor ( Castrol M ) tends to go gluey inside engines when left for long periods.

If this is ever the case, NEVER try to run the engine or pull it apart for that matter.
Simply remove the plug, warm the entire engine with a hair dryer, and when cool, fill with straight methanol and slosh it around and then dump it.
Engine will start to move a little, so add more methanol and turn ever so carefully back and forth until free again.

Don't really expect that you would need to go out and buy all this gear but perhaps if you know someone from an aeromodel club where you could "acquire ' a small amount to try.

Perhaps you should post your other poppet valve engine in the forum also, as i think most would like to see your achievement there as well.( saw it in youtube)
Cheers Jorgo

 

[Mechanicboy]

Castor oil is not mixable with gasoline. To mix into gasoline, add some percent of ether due chemical polarity then castor oil is mixable with gasoline.

Minh Thanh: And I have a question: can I use SAE 20W-50 as a lubricant for a 2-stroke engine ??

In old days the motor oil was used in model gas two stroke engine engines and model diesel engines without problem. I has used motor oil SAE 10W-40 and SAE 20W-50 in model diesel engine when i did not have castor oil available.

 

[Mechanicboy]

Bluejets: Don't really expect that you would need to go out and buy all this gear but perhaps if you know someone from an aeromodel club where you could "acquire ' a small amount to try.

I am model aero builder and flies own model airplanes..