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EVIC Update #9 July 15, 2001
A second EVIC Engine
Congratulations to Bob Heide on getting the world's second EVIC engine running. Bob took my book and my spare set of electronics home with him from NAMES and had his engine running in June. Bob made some changes and improvements to the mechanical design. He used aluminum bronze valve cages similar to those Ron uses on the Offy 270 and put 2 compression and an oil ring on his piston. He ran into some EMI problems with the electronics that led me to improve the EMI filtering on the sensor inputs. After making the changes on his control board Bob reports that his engine is running much better. Bob's next step will be to try the "Electronic Throttle" on his engine. I have attached a picture of Bob's engine to this update.
Help Received as a result of Update #8
In update #8 I mentioned that Bob had made mea set of 3 rings for my engine. I made a new piston and installed the 2 0.032" wide compression rings and the 0.050" wide oil ring. I am now a firm believer in "Trimble rings". The oil stays in the crankcase. My EVIC has quit smoking and no longer spits out oil. If you are building any small engine and you haven't read the articles in Volume 2 Numbers 7, 8 & 9 of strictly I.C. I suggest you order the back copies and study them.
In update #8 I also told you that the intake valve on my engine was leaking when the engine heated up. Ron Colonna and Joe Ruitenbeek both provided information on valve seat distortion caused by a lack of symmetry in the head around the valve seats and/or too little material between the intake and exhaust valve seats. Thanks for the help guys! As a result I cleaned up the area around the valve seats and reground the valves/seats to ensure a good seal. I haven't detected any valve leaking since making these modifications.
But the engine still wouldn't idle when hot. An "air" bubble always appeared in the fuel line right at the carburetor and the engine stalled. While demonstrating the engine at a Toronto Society of Model Engineers picnic, one of the fellows asked me if I had considered vapor lock. While I had heard the term before I had to admit I didn't know anything about it. To make a long story short a few days later I read up on it a couple of engine design books. I learned that gasoline can vaporize in the fuel line at temperatures well below the operating temperatures of our air cooled model engines. One book suggested that gasoline blended for winter use is more volatile than that blended for summer use and that vapor lock could occur with a carburetor temperature as low as 160 degrees F, 71 degrees C. I made a 3/32" plastic spacer and put it between my carburetor and the engine. Problem solved! Now it doesn't matter how hot the engine gets it idles fine with no sign of that "air" (fuel vapor) bubble.
The "Electronic Throttle"
With the improved EMI filtering and the vapor lock problem solved the "Electronic Throttle" operation became much more consistent. If I set the high speed needle valve so that I get a top speed of about 6000 RPM I can "throttle" the engine to less than 1700 RPM by changing only the valve timing. To achieve this speed control I am closing the exhaust valve later, opening the intake valve later and closing the intake valve earlier. The change in each of these events between top speed and idle is nearly 50 degrees. As a result the intake valve is open for nearly 100 fewer degrees of crankshaft rotation at idle than it is at top speed.
Because nothing moves in the carburetor with the "Electronic Throttle" the idle needle valve no longer gives the desirable richer mixture at idle. I am considering using a radio control servo, controlled by the micro computer, to adjust the needle valve. The needle valve would be opened 1/8 to 1/4 turn as the engine is slowed down. It could also be momentarily opened a bit more to improve acceleration and then returned to the high speed position as the speed builds up. By setting the high speed needle valve a bit leaner the engine will consistently reach 7500 RPM but with this setting I have been unable to achieve a slow idle with the "Electronic Throttle". With the normal carburetor throttle the less than 1700 RPM minimum can still be achieved. This leads me to believe that I can achieve this same speed range with the "Electronic Throttle" coupled with the proposed needle valve adjustment. Perhaps fuel injection would be an even better solution but I am reluctant to start experimenting with a pressurized fuel system in my workshop. Please give me your comments and suggestions on these ideas.
Recently I have tried to run some load tests to see how much power the engine is generating. Using a DC motor as a generator I was able to generate 50 watts of power. I had expected much more. However I am using a small V belt to couple the engine to the motor/generator. I tried to measure the efficiency of the belt drive and the generator and find it to be very low, 20 to 30%. Assuming 30% is a reasonable number the engine is generating over 150 watts (1/5 hp). I am now looking for an easy way to make a more efficient and easily calibrated electrical dynamometer. An alternator from a car may be the answer. Anyone tried this? Anyone have any other suggestions?
Appearing in Strictly I.C.
The EVIC engine will be on the front cover of the August September issue of Strictly I.C. and part 1 of a series on it's construction will appear in this issue.
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