Re-design for this Atkinson 4-stroke engine; January 2010
I made a re-design for this engine inclusive a complete new CAD drawing plan for two reasons:
1. I had implemented a lot of changes compared to the original drawing plan (which wasn't mine), mainly to improve the original very violent behavior of this engine. I described that as good as possible on this page below but I got questions about that all the time. Another thing was that the drawing plan had no English texts so my English speaking friends have much problems to understand the odd Dutch language. I made the new plan with CAD this time and added (my school) English to it. The readability of this plan also is much better a.o. because of the three dimensional views of the parts.
2. This Atkinson is running well and reliable, but its behavior is still rather violent. The reasons are the abrupt and reverse movements in the typical driving rods but probably also the valve tumbler system with the very long pushers. Now I made a very compact overhead cam shaft without tumblers as I did successfully with my Otto 4-stroke engine. This cam shaft is driven by a flexible tooth belt around a cog wheel on the fly wheel axis and the same wheel on the cam shaft (1 to 1 distribution).
3. In stead of the classic carburetor I implemented the Petrol Vapor Carburetor as I do successfully for all my IC engines.
There are some other small (cosmetic) changes such as a smaller exhaust muffler mounted directly on the cylinder head and the wooden base.
Below sheet 1 of the drawing plan and the YouTube video.
I have not yet rebuild my own old engine according to this new design. That's why I can't show a live video right now but only the video of the old version and animations on the video of the re-design; see right on the top of this page.
But Petr did; see:
http://s191.photobucket.com/albums/z173/RaceSoft/Atkinson%20engine/And look at this very beautiful replica made by Lorenzo Porro:
Description of the old design
The idea
After building a lot of small hot-air engines I found that I was ready for building my first internal combustion engine. Since my persuit always is to make engines as simple as possible it was not easy to find suitable designs, f.i. on Internet. Finally I found what I was looking for on the web site of Kees Goverde : the Atkinson engine with a very special traction system for the piston. Typical for this design is that the piston makes all four strokes with only one revolution of the crankshaft on the flywheel, which is exciting to see! Look at www.keveney.com/Engines.html for a very nice animations.
The first results
Building this engine was relatively simple because there are no difficult parts and one can make it by only lathing and milling standard materials; it took me about 80 net manhours.
After a lot of attempts and experiments I succeed in to let running the engine. But it ran only with very high speed (2000 to 3000 rpm) with the result that the machine-behaviour was very turbulent due to the abrubt and multiple reverse movements of this special traction system. I had to fix the engine on my working table to get him on place. A more serieus problem was that the enormus forces damaged several parts of the whole driving system.
Changes I made to improve the engine behaviour
At first I have to state that the original drawing plan is not on my web site since it not my property. But Kees Goverde allowed me to provide for it if one put a special request to me, without any commercial intentions. Unfortunately I didn't make drawings of my changes as desribed below, but I count on it that my explanations below and the illustrating photographs on this web site will be enough for everyone who want to take the challenge building this unique engine.
First change: Ignition with a piezo cristal.
With the original design the ignition of the spark on the spark plug is made with a high tension coil as used in (classic) autocars. The switch with capacitor for interrupting the primair current was mounted against the upright headstock (original drawing sheet 1) and was driven with a cam on the flywheel axis (original drawing sheet 5).
I got the idea to make this ignition spark with a piezo element out of a lighter for gas cooking stoves. A pushing rod, driven by a cam on the flywheel axix takes over the role of the human hand operating the gaslighter. A very compact and simple system without the need of a rather big high tension coil and external electrical feed! The piezo delivers a short row of sparks which is even better to ignite the gas mix.
I used this system for my Otto engine later too. You can find the principal construction for this piezo ignition on drawing sheet 7 and 7a of this Otto four stroke engine.
You well may have to adapt this construction a little bit for your available lighter. Choose the biggest one you can get and it will work perfectly.
Second change: Strengthening the driving system.
To avoid the mentioned damaging I first introduced some strengthenings in the mechanical system, a.o. hardsoldering the crank on the (thicker) 12mm flywheel axis and making the main part of the traction system out of one piece of 6mm thick aluminium. Finally everything stays alive, but the very wild behaviour remains of course.Third change: "taming" the engine
I was convinced that I only could "tame" this wild guy by reducing the revolution speed significantly. It turned out that this was not only possible through any adjustment of the classic carburettor, because the engine always stopped running at speeds below 2000 rpm. There were no other adjustments possible such as changing the timing for the intake valve versus the exhaust valve, because the original design is based on a self-sucking system. That means that the intake-valve is not driven by a pushrod against a camshaft but that it has only a spring that closes this intake valve as long as the overpressure in the cilinder is higher than the springforce. The determination of the correct spring strength is therefore rather critical as well: too low means leakage, too high means no intake of the fuel mix.
So I decided to add a second pushing system for the intake valve, similar to that of the pushing system for the exhaust valve. There was just enough space for adding a second cam on the camshaft. Except for the possibilty to adjust any different timing, the spring on the intake valve can be choosen now a lot stronger to be sure of a 100% closing. The camshaft can easily perform the needed force to open this valve.
Experiments provides me the best cycle timing at which the engine runs at much lower speed of about 500 rpm. I did this measurements with a protractor on the fly wheel:
0º Upper position of the piston;
10º Inlet valve starts to open, also 10º after the upper position of the piston;
75º Inlet valve is completely closed. The gas mix in the cylinder is compressed after 90º;
185º Piezo spark, also 5º after the upper position of the piston. An earlier spark can cause backstroke with the relative low speed of this engine;
260º Exhaust valve starts opening; also about 10º before the lowest position of the piston;
370º(10º) Exhaust valve completely closed, also at the same moment at which the inlet valve opens.
With this change the engine behaviour is well acceptable. It stays on place on the table with revolution speeds between 300 and 800 rpm. But it stays more or less tempestuous, but it is exiting to see this guy running!
Fourth change: The carburettor
The carburator is one of the most important parts of a combustion engine. It determines the performance and the behaviour of an engine to a high extent. For sure however, it is not easy to make a carburator for a modelengine. Problems such as unreliable start-up, "flooding" the engine, and carbonsoot on the sparkplug are almost classic.
So, although the engine did run with the classic carburettor (see original drawing sheet 6) I wasn't very happy with it. For me it was reason to developed a new and unique carburettor system that didnot have this disadvantages: see page Petrol foam carburettor for the description, the multiple avantages and the drawing plan. The engine starts without the need for choking, flooding never occurs and the same counts for carbonsoot or wetted sparkplug.General remarks
1. For the cylinder as well as for the piston I used cast iron. In this case this material is at least highly preferable, may be even conditional. The expansion of cast iron is very low and in any case equal for cylinder and piston. Together with the fact that it is more or less self-greasing due to the relative high carbon grade, it prevents jamming of the piston, even whithout oil greasing!
Furthermore cast iron is highly temperature resistant and working up is rather easy. I use only one piston ring, but the engine will run even without a ring if the surfaces of the piston and the drilling in the cylinder are made accurate and smooth.
2. The cylindertemperature don't exceed 110ºC after 15 minutes runtime and at speed below 800 rpm. Since I never be in the need for longer runtimes and higher speed there is no reason to add a complex watercooling system under this conditions. Generally 10 minutes runtime is more than enough for a succesful demontration.
3. At some 10mm from the bottom of the cylinder I made a small and transverse bore-hole of about 2mm. From time to time I put one drop of oil in it, not necessary to avoid jamming but for my feeling that it will keep the piston and cylinder surfaces in a good condition.
Some technical specifications
Global dimensions: lxbxh= 350x200x250mm;
Cylinder: bore 24mm, length 61mm, perlytisch cast iron;
Zuiger: diameter 24mm, length 28mm, perlytisch cast iron;
Piston strokes: intake ca 26mm, compression ca 21mm, power ca 29mm, exhaust ca 34mm.
The different piston stroke-length are typical for the Atkinson engine!
Flywheel: diameter 155m, width 20mm, aluminium or (preferably) steel;
Revolution speed: adjustable between ca 300 and 800 rpm;
Fuel: normal petrol for autocars without oil addition.
Piezo element: a big as available piezo out of a handlighter for gas cooking stoves.
Video with beautiful replica made by
Lorenzo Porro
Nice replica made by TJ Willis
Replica made by Anton Grieder:
