Jan Ridders Pressure-controlled Two-stroke engine

Hi Jim,

A little thought have you tried the engine now you have modded it without the colourtune?

 

as If your colortune is like mine it needs an adaptor to fit into this sparkplug hole.

 

Introducing a lot more volume in the combustion chamber .. and it's self maybe making the low compression very marginal.

 

Jim

 

Terry - Thanks. One problem down, one to go. I will use a different browser next time.

 

Jim - A good thought. I don't have an adapter but the heads are so simple that I just made another one with 14mm spark plug hole. But the Colortune does introduce additional volume so I will change the heads and try it.

 

Jens - I will test for the "poof" when I have the head off. I get compression at the entrance to the expansion chamber but it will be interesting to see what happens at the cylinder.

 

Richard - You are a legend. Who would have thought of keeping the steaks cool until lunchtime with evaporating petrol and then just throwing a match in?

 

Overall, I am not sure how critical it is to have a perfect seal at the ball. Four stroke valves have to seal to stop them from being burnt by the hot gases but we don't have this problem here. And we have all had four strokes that continued running while waiting for us to do a valve job haven't we? A static test (by blowing into it) shows that the balls are seating very well. We just don't know if they are doing it at the right time.

 

Not beaten yet.

 

Jim

 

Hello all,

I think there is some confusion here !
In the article of Model Engineer no 4333 Aug/Sept 2008 my "Simple 2-stroke engine" and my "Pressure Controlled 2-stroke engine" were mixed up: in fact the subject was the "Pressure Controlled 2-stroke" (see pictures and drawing plan) but the text was mainly about the "Simple 2-stroke". The editor rectified that in some later issue of ME.
Now I recognize the same mix-up in this postings: on the (very nice) video with the Colortune spark plug I see the "Simple 2-stroke engine" and also the calculation about the engine's content from Richard and Terry are based on the "Simple 2-stroke" that has a piston diameter and stroke of 24mm: so 10.8 cc content indeed.
But I am constantly talking here about the "Pressure Controlled 2-stroke" (and I think James and John are doing it also) and that engine has a piston diameter and stroke of 18mm, so the content is about 4.5cc as I stated before.
So, the power of this engine is significantly lower than that of the "Simple 2-stroke" . If, additionally, some ignitions are missing (which can happen with 2-strokes) the power will decrease even more. Therefore I emphasize the importance of low frictions for at least keep the engine running. So please mount the spacers on the crank shaft (they where not on the ME plan I believe) to make the engine run "like driven by the wind" . You only can adjust the engine to its optimal performance once it keeps running more ore less well.

Friendly greetings from Holland,

Jan

Hello, here Jan again.

I read some concerns about the low temperature of the petrol in the carburetot tank. Due to the evaporation the temperature of the petrol will go down somewhat indeed ( the physics in Holland is the same as in the rest of the world, ha ha). This is one of the reasons that after some minutes of running the speed of the engine can go down a little. But if you then reduce the extra air at the outlet of the carburetor a little you will see the engine run faster again and the situaton will stabiilze because the temperature of the fuel will not decrease futher at some point.

Another reason why the speed of the engine will go down somewhat after some minutes is the evaporation of the most volatile component in the autocar petrol. But that will stabilize also after some minutes. You can eliminate this separtion effect by using Coleman Fuel since this has much less (different) carbon hydrogen components.
Friendly greetings from Holland,

Jan

PS. I will measure the temperature decrease of the fuel during the first minutes of running exactly one of these days, only for my (and your) curiosity.

Hi Jan,

 

I was not familiar with your models until I received your drawings for the 'Sabina' engine which is the subject of this thread (Pressure Controlled 2 Stroke). It was only when I got these plans that I saw it was a vertical cylinder engine and the one in the video is the horizontal 'Debbie, I found that very confusing.

 

It was only when I visited your lovely website that I saw the difference. My calculations were based on the measurements given in this thread which are those of the 'Debbie'. So I apologise for misleading anyone and thank you for your generosity in sending me the plans.

 

Best regards

 

Terry.

Hello Jan

You have cleared up a small mystery for me. Until the last day or so I wasn't aware that there was an alternative engine to 'Debbie' Simple Two Stroke (which is the engine I think I have built !). My friend Aussie Jim reffered to his 'Pressure Controlled Two-Stroke' that he calls 'Debra' as he felt this made it sound superior. I believe that both Jim's and my engines are both 'Debbie' Simple Two Strokes - am I correct ?

 

I am currently away on holiday at the moment so am unable to make further progress with my 'Debbie'. My engine spins freely almost to the same standard as yours - 5 revolutions with no compression from plug or chamber, 3 revolutions with just chamber and 1 to 2 revs with chamber and plug in place.

 

If my engine is not firing consistently on every revolution as Jim has discovered is the case with his, then surely this could be the reason for not running without assistance. Perhaps you may care to look at the short video of me attempting to start my engine. I appreciate that it may be very difficult to advise me from this alone but something may be obvious to you.

 

With thanks for your continued support on this perplexing issue.

 

John Somers

 

 

Confusion all round, and all my fault. Sorry about that. I had forgotten about the earlier 2008 article but I remembered reading John Woods Forum thread.

 

When I had problems, I simply tacked onto the thread without checking. For some reason, I just assumed that "Pressure-controlled", "Simple Two Stroke" and "Debbie" were alternative titles for the same thing.

 

In regard to the name, I didn't know that the Simple Two Stroke Engine was called Debbie until John Somers mentioned it. And mine is not called Debra to make it sound superior despite John's mischievous suggestion. After I made some small changes to Jan's design of Debbie, I felt that I had also to make a small change to the name.

 

Anyone seeing Jan's original and John's superb and beautiful copy would agree that if they were all real people, they would not have anything to do with my scruffy and very lower class Debra as shown in the Colortune videos.

 

If Debra runs, maybe I will tart it up. If it runs.

 

Jim

I have done some more work and here is the result:

 

Jim: I tested it again with the CM6 plug head and it made no difference.

 

Jens: With the head off, I get a very distinct "poof" from the transfer port. There is a general smell of Coleman fuel.

 

Jan: Your mention of two strokes misfiring led me to wonder if the cranking speed was too high for the (effective) throttle opening thus causing four-cycling like motorcycles do when the throttle is closed. After extensive tests, particularly at lower cranking speeds, I have concluded that this is not the cause of the problem.

 

To see if the ball valve really is the cause of the misfiring, I have replaced it with a poppet valve. I can see this valve operating. And it makes no difference. The valve and the tests are on YouTube and if TerryD's advice is correct, you should find it here. Thanks Terry, it worked.

 

So I am not sure where to look now. The problem is not friction (because it is misfiring when cranked) and not the ball valve (because it is still there when the poppet valve is substituted for the ball valve).

 

I am wondering if, when it fires, it blows the next incoming charge back or contaminates it in some way. The only way I can think of to test this is to put another non-return valve right at the transfer port on the cylinder where the mixture in injected.

 

Any advice anyone? I am running out of ideas.

 

Jim

 

Hello Jim,

I am beginning to think your engine is "poisening" itself (too much burned gases left in the cylinder). The flushing process can be influenced by the adjustment of the cylinder relative to the exhaust opening. You can vary that by srewing the piston rod more or less in its fork. I found out that at the best adjustment the piston in its lowest position (BDC) is equal or somewhat below the bottom edge of the exhaust hole (so completely open). But you I already know that I suppose.But maybe you can do some experiments anyway.
Once I perceived somebody mounted the cylinder upside down (which is easily possible) and then the exhaust opening is on the wrong place of course. But I can't imagine that you did something like that.
Friendly greetings,

Jan

 

Hi Jan,

Yes, I think something like that is happening. I have the piston just a bit lower - about 1.5mm below the exhaust port. That is where the transfer port is completely uncovered on my engine.

 

But just in case the exhaust gases are not being completely expelled, I put a vacuum cleaner on the exhaust port to extract them. It made no difference.

 

I also reduced the volume of the expansion chamber (just put tube in its place) to increase the pressure and velocity of the mixture as it is injected into the cylinder to assist scavenging. That made difference either (except that the extra pressure blew the tube off after a while).

 

My cylinder would look upside down to you because I am in the southern hemisphere where everything is upside down (as John Somers keeps reminding me) but it is the right way up for me.

 

I have now designed another poppet valve to go on the transfer port to stop any gases being drawn back into the expansion chamber. The next job is to build it and see what happens.

 

This is a very interesting problem.

 

Jim

I have now tried the engine with a poppet valve at the transfer port to prevent cylinder gases getting into the transfer passage and contaminating (poisoning) the incoming mixture.

 

Video of the test is here.

 

It made no difference. The engine still misfires.

 

When looking at the captured video, I noticed what appears to be condensation in the transfer tube. Further testing indicates that it appears to be oil from the bottom of the cylinder, picked up by the mixture and then deposited on the walls of the tube.

 

I don't think this is fuel condensing out of the mixture and thus changing the ratio because heating everything with a hot air gun made no difference, and it was 30 degrees in my workshop anyway so additional heat was hardly needed.

 

That, plus the fact that the mixture remained rich as shown on the Colortune test part.

 

Jim

 

So that's it. I am now giving up on this engine. I have tried everything I can think of and it still misfires and won't run.

 

The problem is not friction because it misfires when driven by the drill.

It is not being driven too fast because it misfires at all speeds.

It is not the ball valve because it misfires with Jan's original arrangement (on John Somers' engine) and with Jan's arrangement on mine and with a poppet valve instead of the ball valve.

It is not the fuel because it misfires on petrol and on Coleman fuel,

It is not the exhaust because putting a vacuum cleaner on the port to extract the burnt gases made no difference.

It is not gas contaminating the incoming mixture because the non-return valve made no difference.

It is not spark quality because it uses an RCEXL CDI system and we can see the spark in the Colortune video.

It is not mixture because we can see it firing on rich, correct and lean mixtures.

It is not compression ratio because I have tried different piston locations.

 

So I now join the others in this Forum who have given up without getting Debbie (or Sabrina which is similar) going.

 

But I will put it in a box, at least until I need to rat it for bits, in the hope that someone will solve the problem and put it on this Forum.

 

Jim

A safety note about applying vacuum cleaners to the exhaust ports of IC engines:

 

if ANY fuel/air mixture is present in the cylinder or ports and gets carried into the vacuum cleaner, there is a real chance of generating a big flame as the fuel/air mix travels over the motor brushes. In most vacuum cleaners the cleaned air passes over the motor to cool it, and often there is electrical arcing at the brushes. You might get a flamethrower out ot the deal with potentially disastrous consequences.

 

Please be very careful with all fuels and especially fuel/air mixtures around any electrical applicances.

JD

I guess this little story might add some emphasis to Jeff's post... A school friend of mine had a habit of trying interesting and sometime hazardous experiments. So one time he built a petrol burner, which used a surface carburettor with the air being forced through it by a vacuum cleaner on blow. I never saw it going but other friends who did said it went very well. Until the day when he was showing one of my mates and forgot to put it on blow. The vacuum cleaner went up quite spectacularly, just as Jeff describes.The insurance company was very mystified, but paid up. I think one reason that I never saw it was that I was not all that keen to go near the thing at the best of times.

 

regards

John

 

 

John you'll know the situation, back in the 60s, on the west coast of the South Island, before the days of Deer farming, deer were shot and flowen out in Cessna 185s, one of these crashed, and arrived at our hanger in Dunedin. One of the engineers(not me) found that under the floor was full of maggots, so he started to clean it out with a vaccuum cleaner, after he had been working for 10 miniuts or so, there was a "boom", then woosh, a fuel line was broken, and he sucked up 100/120 octane av fuel. The insurance co bought us a new vaccuum cleaner--- the old one was 1940 vintage. Fortunately no other damage was done, and a month or so later the aircraft was back in the air. Ian S C

John Somers re your video:

 

I think after seeing and hearing John's starting video this engine has a spark timing issue. The timing does not sound right to my ear. I don't remember what the timing arrangements for Mr.Ridder's engines are, but if they have points and coil ignition I would offer the following troubleshooting tips. As a starting point set the points to open between .060 and .080" before top dead centre. Use a known good coil, ie one from a small engine, or motorcycle or car that is known to run. If the timing plate is made adjustable for spark at say 0 to .120" BTDC the "sweet spot" can be adjusted for conditions that day. Also it is important to use proper high tension/high voltage spark plug wire, not ordinary electric hookup wire, for spark plugs. If ordinary wire and alligator clips are used, spark can leak away and not reach the plug. An ex small engine plug lead is a cheap way to get such a wire. If a small engine coil is used, many of them have the lead attached to the coil. Last, make sure the plug gap is open and dry, I would try .015" to .020" gap to start with.

 

Don't put your engine away in a box just yet. It sounds very close to being able to run. Good luck with spark tests.

JD

Hi Jeff

 

Many thanks for your observations which are much appreciated and very welcome Jeff !

 

Initially I tried a coil and contact breaker set up which did produce a good healthy spark but for the contact breaker I used a micro switch but this didn't have the stamina for this kind of use. After destroying six of them I replaced the setup with an RCEXL CDI ignition system but became confused between static and dynamic timing. I have now had the difference explained to me by Jim (see his earlier posts on this thread) and am hoping to reset my ignition in the next day or so.

 

If this doesn't produce the desired result I shall go for plan B which is to try a modified version of Jan Ridder's carburetor which adds throttle control http://www.homemodelenginemachinist.com/index.php?topic=9587.0

I have a gut feeling that my engine would pick up and run unaided if I was able to increase the volume of fuel mixture.

 

I must add that Jim has carried out exhaustive tests to get to the cause of the problem which he, I and others on this forum have encountered - unfortunately with no success.

Jan has been extremely helpful in his efforts to resolve this issue and I am sure he is as frustrated as we all are by our failure to get this engine running.

 

Like most of us I hate being beat and will persevere a little longer before throwing in the towel.

John

 

 

 

 

 

Hi John,

 

I don't know anything about your specific RCEXL CDI ignition system but I have been stung before with CDI units. The ones that caused problems for me were eventually found to have internal electrickery which was changing voltages and capacitor charging values as speed changed. They were designed for engines with no manual timing adjustments and had "smarts" which were interfering with adjustment attempts. The more I messed with them the worse things got!

 

I'm suggesting going back to basics with a cam and wiper or simplified points system. I am not surprised that commercial microswitches did not stand up to the engine timing job. They are not made for that high speed service and usually have soft silver contacts.

 

If you take the hard tungsten contacts from a $5 set of car or small engine points and braze one to a cam on your engine (or press it into the flywheel) and put the other on a steel spring on a timing bracket, so the other one wipes it as it goes by, you will find this will last a very long time. If the timing bracket is made so it can pivot around the same centre as the crank, and be set at a given angle BTDC, it will give a simple timing adjustment. You could also make the cam operate a pushrod to open and close the points as intended for small engines and cars, the points being mounted remotely and used as supplied as a set. You will probably need to use a lever bewteen cam and op rod to multply the operating force in this case without slowing the engine down too much, as commercial points have a fairly heavy spring.

 

JD

Special message for Jim.

Reaction on the contribution of Jeff Daymann about spark ignition:

First of all I have no experience with any CDI ignition systems except that they also are not always without any problems as I hear from time to time.
I always use the classic system with a high tension coil with points (switch) and a capacitor over the switch. For the high tension coil I use the ones for classic motor bikes (diameter 40mm, length 130mm). With the smaller coils as used for i.e. moppets I only have bad experiences; they apparently are not suitable for a direct 6 or 12 volt DC supply: poor spark or not at all and growing very very hot untill they die!
For the switch I use the well known small micro switches. They are easy to mount, they need very few force and you can buy them everywhere for almost nothing. You are right that they are not made for this task (switching about 3 amps DC inductive with frequencies of 1000 to 2000 rpm). So they are not "heavy duty" , but nevertheless I seldom need to replace them by a new one because of burned contacts, but it happens sometimes indeed. I never let my engines run with more than 2000 rpm and with that I never had any (frequency) problem with these switches.
I always make my own spark plugs: a mild steel housing with a Teflon isolator screwed in that housing. Through the centre of the Teflon a spring steel wire with 0.8mm as the high tension electrode, soldered on top on a 3mm brass threaded end in the Teflon. Never never any problem; even better than an industrial spark plug as far as I tried. Luck of the stupid I suppose. I have a drawing plan for this own made spark plug.

Thanks for your reaction and friendly greetings,

Jan Ridders