making a 2stroke petrol engine.

Started by Rajesh14305, March 01, 2014, 08:49:32 PM

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Rajesh14305

My two friends (mech engg) and me are planning to make a 2stroke petrol engine. We have done all the drawings and.planning. now the problem is we dont know how to contol the spark plug timings. Wheather we should use a glow plug for it or not.

K K Iyer

@rajesh14305
Why don't you know?
How to control the spark plug has been in the public domain for 100 years.
Got to read up man, not just ask.
Please think of the possible consequences of using a glow plug in a petrol engine.
I presume your friends are not trying to invent something new.
If they are only trying to see if they can build a 2 stroke engine that can run, there are plenty of samples to copy for a start.

Please don't mind my comments, but questions like this scare me.
How can the planning and drawings be complete without deciding whether glow or ignition?
You didn't even say whether:
Capacity is 5cc or 500cc.
What's the compression ratio?
What's the induction method?
Single cylinder or multi?
Crankcase cast or machined?
Ringed or not?
Contact breaker or electronic ignition?
Carburettor or fuel injection?

Anyone who has tackled such issues would already have decided on glow or ignition.
If glow or ignition, and ignition timing issues are yet to be tackled, i fear there may be many other basic issues still to be tackled.

As i've said earlier on this forum,
1. We need to be clear about our objective
2. Don't have to reinvent the wheel

You may have seen on youtube the kind of fantastic multi cylinder miniature engines people have built.

As a college engineering project, a small 2 stroke is worth building.
And all the data required for that has been available for years.

Wish you and your friends good luck and success with the project.
Regards.



Rajesh14305

#2
Ok they are trying to make a 35 cc ic engine. As u asked .they r going to cast the crank case.it is fuel injected system.and it is a one cyllinder engine. It is electronic ignition system.yes it is ringed.

saikat

Rajesh - if it is electronic - why you are asking how to control the
spark timing ? - are you going to make the electronic ignition unit as well ?

generally - on electronic ignition units - spark timing is controlled by a hall effect sensor used
to sense crank position and piston TDC.

What king of mech engg ?? if they do not know this ??


praveen

whole world knows Ignition (Spark) occurs at the end of "Compression Stroke". I wonder why mechanical engineers designing engine without knowing basics! :headscratch:
Anyways all the best for your engine build!
@Iyer sir , good set of questions!!!! {:)}
To increase thrust you need more  money! But to reduce weight you  need nothing!

Rajesh14305

#5
Thank u all for telling like this.sir they are reading in 1st year mech .we always want to build something that costs more as we dont have such budget to buy that thing.thats why we thought of build engine. Again if were in 4th year we would nt ask help from u.ok.agin we know that spark  happen in compression stroke. Our problem was when air fuel mix is  compressed if spark happen(we dont have a sensor-a sensor in luna kinetic engine :giggle:) before complete compression what happen. And what will happen if  we use glow plug.don't think that we are going to build a engine without having  zero knowledge about it .knowledge should be shared .if some one asking for  knowledge and u have it.you should nt tell him that oh you dont knw this little thing.but u should tell him how the path

saikat

Well said Rajesh - I think we got carried away in our
arrogance.

I have some knowledge in these matters -  I will help out
and answer - if you have any specific queries.

K K Iyer

Fine examples of how a civilised conversation should take place. (Reply 5&6)
What a contrast from from yesterday, when the first thing i saw was a post insulting rcpilotacro.
@saikat sir,
Your observation applies to me too!
@rajesh14305
Ideally ignition should take place just as the piston is passing TDC.
However, it takes a little time for the flame front to travel from the spark plug to the piston crown to ignite the entire fuel/air mixture.
Hence ignition has to a little before TDC (BTDC).
If it is early, the piston gets a kick before the compression stroke is completed (knocking)
If too early, the engine will start/run backwards.
If too late, unburned fuel goes out through the exhaust.

In 1971-72, used to time my Royal Enfield Ensign (150cc, 1956) by removing the plug, inserting a jhadoo teeli to feel when the piston was at TDC, then turning the crank back till it was 1/16th inch BTDC. In that position, used to set the contact breaker to open...
...which suddenly broke the current to the LT side of the ignition coil, which fired the HT side...
...which gave us a shock while holding the black cable near the cylinder head to check if it sparks...
(No sensors then in Enfield, Jawa, Vespa, Lambretta, Fiat, Ambassador...)

Later in my Maruti Van (1985), used a homemade cardboard dial to set the dwell, lacking a strobe...

Leaving it there for Saikat sir to take it forward, including what will happen if you use a continuously burning glow plug etc.

Some other members may be able to guide on metallurgy...
Got to stop before i get too carried away.
Regards.

K K Iyer