Rotary Fuel
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Rotary Fuel
Having just read articles on carbon in rotaries and then fuel octane I thought that I should share some history.
Charles F Kettering the inventor of the self starter for the automobile credited his assistant Thomas Midgley Jr. with developing anti knock gasoline.
The following are the words of Kettering. "Ever since we had put the self starter on the automobile, engineers were inclined to blame the engine knock on the battery ignition which was part of the starter. About 1913 we had done some work on the cause of this difficulty but for lack of time it was laid aside. Thomas Midgley and a group of us talked this over one Saturday at lunch and I said ""Why don't you get the old apparatus out of my closet and see what you can find out?"" Engine knock in those days was supposed to be caused by either ignition or carbon. Our preliminary studies had showed that there was more to it, so the first job that Midgley did was to devise a means of determining just what it was.
On the afternoon of February 2, 1923 a car drove into a filling station in Dayton Ohio and the driver said, "Give me five gallons of that new Ethyl Gas advertised on the sign." That simple event is important because it was the first sale of this anti knock gasoline to the public."
PRIOR TO THIS TIME
All engines were slow speed and had explosion chambers built into the head. I read a few years ago that the model T Ford had a four to one compression ratio.
A piston engine has slow piston movement for a long duration while close to top dead center. The old fuel would ignite and hammer on the piston but the piston had not yet turned to the crankshaft two o'clock position so lots of knock and little torque was derived from the fuel.
The new Ethyl fuel had additives in it and the ignition of it was slower so it was a more elastic combustion and this would press against the piston creating more torque.
Now we have the rotary engine that has an explosion chamber that increases in size immediately upon ignition and we should want to use the faster burning fuel.
Another problem with the higher octane fuels is the additional additives that could increase carbon problems.
Just my thoughts and a little bit of history on the matter.
Cheers
Ken McKenzie
www.starapex.com
Charles F Kettering the inventor of the self starter for the automobile credited his assistant Thomas Midgley Jr. with developing anti knock gasoline.
The following are the words of Kettering. "Ever since we had put the self starter on the automobile, engineers were inclined to blame the engine knock on the battery ignition which was part of the starter. About 1913 we had done some work on the cause of this difficulty but for lack of time it was laid aside. Thomas Midgley and a group of us talked this over one Saturday at lunch and I said ""Why don't you get the old apparatus out of my closet and see what you can find out?"" Engine knock in those days was supposed to be caused by either ignition or carbon. Our preliminary studies had showed that there was more to it, so the first job that Midgley did was to devise a means of determining just what it was.
On the afternoon of February 2, 1923 a car drove into a filling station in Dayton Ohio and the driver said, "Give me five gallons of that new Ethyl Gas advertised on the sign." That simple event is important because it was the first sale of this anti knock gasoline to the public."
PRIOR TO THIS TIME
All engines were slow speed and had explosion chambers built into the head. I read a few years ago that the model T Ford had a four to one compression ratio.
A piston engine has slow piston movement for a long duration while close to top dead center. The old fuel would ignite and hammer on the piston but the piston had not yet turned to the crankshaft two o'clock position so lots of knock and little torque was derived from the fuel.
The new Ethyl fuel had additives in it and the ignition of it was slower so it was a more elastic combustion and this would press against the piston creating more torque.
Now we have the rotary engine that has an explosion chamber that increases in size immediately upon ignition and we should want to use the faster burning fuel.
Another problem with the higher octane fuels is the additional additives that could increase carbon problems.
Just my thoughts and a little bit of history on the matter.
Cheers
Ken McKenzie
www.starapex.com
84SE-EGI helpy-helperton
Joined: Oct 2002
Posts: 3,584
Likes: 542
From: Phoenix, AZ
Rotary engines can 'detonate', which is a term used to describe the condition when the fuel doesn't burn, but explodes. Knock on piston engines can be caused by detonation, which results in extreme forces being applied to the connecting rods and crankshaft, which are felt as 'knock' - this is the sound of the piston wrist pin and crankshaft journal bearings being pounded together as the piston is exploded against their mounts. For this reason, knock is damaging to a piston engine. A fuel which retards explosive forces has a better resistance to knock, which can increase performance and decrease internal engine stresses.
Enter the rotary; with rotary combustion, pre-ignition or detonation can cause the same explosive forces in the combustion chamber and damage apex and side seals when these forces are brought to bear against the sealing surfaces. Due to the large friction surface of the rotors bearing journal to the E-shaft, knock cannot usually be 'felt', but damage is occuring, nonetheless. Detonation in a rotary engine is more a function of timing than anything, since the expansion chamber during ignition expands rapidly to allow the burning fuel to create torque and power. In this case, having a high octane (low knock) fuel doesn't net the same results as you'd see in a piston engine, so the money spent on octane boosters (pre-ignition retarding chemicals) is lost, and efficiency is reduced.
The very design of the rotary engine lends itself to using volatile fuels or involatile fuels equally well with minor modifications to fuel delivery systems. In other words, you could build a rotary to run on propane or kerosene about the same, given some engineering to get the correct air/fuel mixture and tuning.
The risks of detonation in a rotary can be easily ruled out by sticking to manufacturer timing recommendations. I run 87 octane or the lowest available in my area to both save costs, increase fuel mileage and decrease wear. HTH,
Enter the rotary; with rotary combustion, pre-ignition or detonation can cause the same explosive forces in the combustion chamber and damage apex and side seals when these forces are brought to bear against the sealing surfaces. Due to the large friction surface of the rotors bearing journal to the E-shaft, knock cannot usually be 'felt', but damage is occuring, nonetheless. Detonation in a rotary engine is more a function of timing than anything, since the expansion chamber during ignition expands rapidly to allow the burning fuel to create torque and power. In this case, having a high octane (low knock) fuel doesn't net the same results as you'd see in a piston engine, so the money spent on octane boosters (pre-ignition retarding chemicals) is lost, and efficiency is reduced.
The very design of the rotary engine lends itself to using volatile fuels or involatile fuels equally well with minor modifications to fuel delivery systems. In other words, you could build a rotary to run on propane or kerosene about the same, given some engineering to get the correct air/fuel mixture and tuning.
The risks of detonation in a rotary can be easily ruled out by sticking to manufacturer timing recommendations. I run 87 octane or the lowest available in my area to both save costs, increase fuel mileage and decrease wear. HTH,
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