Designing a good rotary valve system is hard. Rotary valve engines fail because of friction, thermal problems or seal leaking. Lubrication failure is was a significant problem. Clearly hydrocarbon based lubrication should have been excluded as a viable option because the exhaust valve systems must operate at metal melting temperatures. When operating temperatures raise much above 300° f (150 C), oil/grease lubricants first lose their viscosity, they then volatilize and/or carbonize, finally at combustion temperatures the carbon burns off.
On the plus side of Coates’ technology is the use of Ceramic Carbon bearings and seals. There is some science behind this system. The history of carbon bearings go back some 5000 years to the Mesopotamian chariots. Red hot tapered axels were pressed into the hardwood hubs of the wheels to get a precise fit. This process boils the hydrogen out of the hardwood leaving hard carbon. Thousands of windmills still have wood based carbon bearings, they’ll last for decades with no care or lubrication.
When two metal parts are rubbed together without oil-grease lubrication between them, the oxide film on the metal parts will quickly wear off and the two metals will exhibit strong molecular attraction. This attraction results in high friction, high wear, and-at higher speeds or loads, you will get galling and seizing. You may have seen that in oil starved damaged engines.
On the other hand, when carbon materials are rubbed against metal, you don’t need any oil or grease lubricants because no strong molecular attraction exists between carbon and metals. A thin film of graphite is burnished onto the metal surface when the carbon materials is rubbed against metals. This thin layer of graphite produces a very low coefficient of friction and very little wear, even under rather high loads. These types of bearings and seals can also operate at very high temperatures, especially in low oxygen environments. You will find them in use on virtually all steam turbines.
My late friend Smokey Yunick gave points to the use of a spherical interface between the steel ball valve and the conforming carbon valve seat. This spherical interface seems like it should wear well and provide a good seal during both the cold starts and at operating temperatures. This is because the small change in the sphere’s size caused by thermal expansion will be more or less matched by the thermal expansion of the seal. However, the Coates patent clearly has an unresolved erosion problem on the exhaust valve seal design.
The reason for potential failure on the exhaust valve seal is simple. Carbon and graphite is flamable, it burns! (Ever hear of CO or CO2) With white hot exhaust gasses washing against both the inside and outside of the ball at temperatures a thousand degrees above graphite’s combustion temperatures, seal erosion becomes a very significant problem. A well designed poppet valve system does not have this problem. A poppet valve is seated against a water cooled valve seat 75% of the time, this is how it is kept below its melting point.
Smokey once told me that “an Indianapolis racing engine needs to hold together for only 501 miles, but so far no rotary valve engine has been able to do that”. I don’t think the Coates engine would pass that simple test either. In my opinion, it's a dead end technology.
I have no inside information save reading the patents and the website. Please keep in mind that my opinions are subjective as are all opinions. But I hope this puts into context some of the obvious problems Coates is trying to overcome before they ship product or sell the technology. It would be dishonest to sell the technology without resolving these problems. Their are ways to over come these problems, but they are proporitary and would require a redesign. I hope this helps.... James
AI
