glow plugs & fuel

[steve williams 3Participant @stevewilliams3]

[steve williams 3Participant @stevewilliams3]

Hi all

I am making a 3 cylinder radial engineof my own design to run on nitro which is going well the crankcase, cran,k con rod, pistons & barrels are all made including the timing gear & cams.

cananyone avise me as to which glow plugs & fuel to use. I understand that the plugs come in heat ratings & the fuel has varying nitro content. I have made a few engines now, steam & spark ignition petrol but not glow fuel.

my question is, what would be a good starting point i.e which plug & fuel to use.

the engine spec is .

3 cyl radial

4 stroke

around 66 cc

10:1 comp ratio

induction drawing through carb via crankcase.

any advise would be very welcome.

cheers steve

[nodakerParticipant @nodaker]

Steve,

 

I am located in the USA and am assuming you are located in GB.  I would suggest starting with a fuel made for 4 strokes with 5% nitro due to the high compression ratio you are proposing.  I don’t think you want to draw fuel through the crankcase as you are making a 4 stroke engine, not a 2 stroke engine.  Single cylinder 2 stroke engines can draw fuel air through the crankcase as the fuel air mixture is inducted into the crankcase via an inlet port in the crankshaft, a rear rotor valve or a piston port.  All of these methods provide a method of sealing the crankcase during the power stroke so the fuel air mixture is compressed in the crankcase prior to opening of the inlet ports near the bottom of the power stroke.  A multi cylinder 2 stroke engine complicates the induction method and requires an internal crankcase seal between cylinders and a separate induction system for each cylinder or a means of providing external pressurized fuel air mixture to the engine which really complicates things.

 

(Added later)

 

As far as glowplugs, any good 4 stroke glow plug should be adequate.  4 stroke glowplugs have a heavier glow element so it retains heat better.  In the US, Fox makes a popular 4 stroke glow plug.  OS also makes glow plugs.  I would suggest starting with a middle heat range plug.  You will know if the plug is too hot as the element will burn out  and a cold plug will foul with oil and carbon.  I would recommend provision of an “onboard” power supply set up so power is supplied to the plugs during engine idling so as to keep the plugs hot and prevent fouling.

 

(end addition)

You are proposing a 4 stroke radial engine.  I am having trouble visualizing a method of feeding the fuel air mixture through the crankcase due to the radial arrangement of the cylinders without an exterior pump (positive displacement air pump supercharger)as you will not be able to use the pistons as an air pump.  It seems a much simpler method of fuel air induction would be to route the fuel air mixture directly to the intake valve for each cylinder through use of either an intake manifold with one carbeurator  or a carbeurator for each cylinder as is currently done with modern 4 stroke model aircraft engines.   The latter method would certainly simplify setting fuel air mixtures.

 

As far as lubrication of the crankcase and rod end bearings, commercially produced 4 stroke model aircraft engines get their lubrication from blowby past the ring(s).   Without knowledge of your proposed bearings I would suggest a 4 stroke model aircraft fuel  with some castor oil for its added lubrication qualities.  As an alternative, a wet or dry sump might be utilized and a lubricating oil compatible with the 4 stroke fuel constituents (lube oil and methanol).

 

Your project really sounds interesting and I would request that you post some pictures of progress and project updates.  I am myself working on my machining skills so as to be able to make some single cylinder engines for play purposes and possible incorporation into flying models.  I have been flying RC aircraft since the early 1980’s.

 

Hope the above provides some useful information.

 

John

 

 

Edited By nodaker on 17/05/2010 23:06:35

[steve williams 3Participant @stevewilliams3]

Hi john

thanks for the information you gave me, I didn’t realise that there were 2 & 4 stroke fuels & plugs so thatis realy helpfull. I will make your sugestions a starting point & go from there.

as reguards to the induction method, I got the idea from an old war time aircraft engine maintenance manual. the inlet port islinked externaly through a pipe to the crank case so induction is drawn through the carb into the crankcase lubricating the crank, the mixture is then pulled up the pipe by the induction cycle of the piston. there may be a nead for some type of read valve between c/case & carb to accomodate any pressure pulsing back through the carb.

thanks again steve

[Ian S CParticipant @iansc]

The engine type you’r thinking of is the rotary engine in which the crankshaft is fixed to the aeroplane, while the rest of the engine, and propeller revolve, the intake valve in some of those engines was in the pistons,those engines had a problem in that a fuel/air mixture was in the crankcase, and sometimes ignighted there. Later engines had the two valves in the head. The reason for castor oil mix with the fuel was that the two did’nt mix, and the oil stuck to the mechanicals and was’nt washed off by the petrol. The fuel was drawn in by the centrifugal force of the rotating engine.Ian S C

[Ian S CParticipant @iansc]

Nice photos Steve,but nyloc nuts arn’t really the ones to use for cylinder base nuts,they don’t like too much heat, if you need to lock them lock wire is the way, if you use lock nuts on studs you just turn the studs into bolts. For hot parts on aircraft engines metal lock nuts are available. Ian S C

[steve williams 3Participant @stevewilliams3]

Hi Ian

thats a good point about the cylinder base nuts I will change them before I run it

(hopefully run it ).

cheers steve

[Ian S CParticipant @iansc]

You’ll run it, I’m keeping my fingers crossed for you, you’v got some nice looking work there-good luck Ian S C

Edited By Ian S C on 20/05/2010 12:07:45

[Clive FarrarParticipant @clivefarrar90441]

I suggest you go to a model aircraft shop and get some model technics Forula Irvine with 5 % nitro.

I run all ( 8 ) of my FS engines on it. There is a big range of 2 stoke plugs with diferent heat ranges, but not so for four strokes.

 

The best in my oppinion are OS “F” plugs  at abut £4.50 each.  

A good second best is Just engines own brand.

 

Look up just engines on the web and you will find lots of good info.

 

regards Clive

 

PS were did you get you plans from are there any links you can send me.

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