Rotary Valves Make Normal Valves Look Silly - Why Aren't We Using Them?
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Published 2024-03-24
And this is exactly what poppet valves do. They are great at sealing the chamber because the conical shape of the valve face fits into the conical shape of the valve seat creating a positive seal. Both the face and seat are made of hardened metals which offer impressive resistance to wear and increased temperature. As compression or combustion pressure acts on the valve head it actually pushes it harder against the countersunk seat. The greater the pressure the better the seal.
Unfortunately other than being great at sealing the chamber poppet valves realistically don’t have any other inherent advantages. From an engineering perspective we could even say they are a necessary evil that we managed to make reliable only with a lot of technological advancements. Did you know that back in the 50s and 60s one of the reasons why fuel was leaded is to protect the valve seats. The intense hammering of the valve against the seat under high temperature would cause microwelds between the two and as the valve opened again these welds would tear eventually leading to valve seat recession or failure. It is only when we started to phase out leaded fuel that valve seats began to become more reliable and longer lasting.
Valve springs are also a problem. At very high rpm the camshaft is trying to open and close the valve so fast that the spring simply can’t keep up. So instead of fully closing and opening the valve tends to float around the seat leading to a loss of power or even to contact between the valve and the piston in an interference engine. Valve float used to be such a limiting factor on engines that Ducati came up with the complex and maintenance-heavy desmodromic valve system just to get rid of the valve spring. Koengseeg came up with the extremely complex freevalve system to get rid of the camshafts.
But engineers persisted, they improved valve spring designs and materials and we got engines with valve springs that can rev to the moon. They pushed even further and invented variable valve timing and lift systems that can do almost anything that Freevalve can. And so the poppet valve stayed with us.
But the big problem that no amount of technology can ever eliminate is that poppet valves are an impediment to airflow. But we got around this too. We created clever intake manifolds with variable lengths and clever resonances to ram the air past the valve. We created forced induction in the form of super and turbochargers to stuff more air into the chamber. We created long and complicated exhaust manifolds to help suck the exhaust gas out of the chamber.
When you think about it a lot of the development of the internal combustion engine is actually an effort to work around the valve. To overcome its limiting factors. If you observe an engine you will see that the cylinder head and the intake and exhaust manifolds actually take up more space than the heart of the engine which is the engine block, where the crankshaft, pistons, and rods are. We need more space for the breathing equipment of the engine and we need it because the poppet valve makes breathing hard.
But what if there was a better way? What if we simply got rid of the valve instead of trying to constantly work around it.
Of course many engineers asked this question throughout they yerars and they did indeed come up with many alternatives. One of the more elegant and promising alternatrives is called a rotary valve
Instead of a poppet valve, valve seat, spring, retainer, rocker arm, lifter and camshaft all we have is a rotating barrel with cavities. As the barrel rotates the cavities in the barrel line up with cavities in the head to let air in and out of the engine.
There is no valve spring we need to overcome so this system does not drain the energy of the engine to operate which means more power and more efficiency. And because there is no valve spring there can never be any valve float at any rpm, achieving ridiculous rpm is much easier now.
This system is also very simple and it has much less moving parts which means a very low chance of failure and reduced engine size and weight.
So it’s better in every way than the poppet valve….ok…..where is it then? If it’s better in every way then why have we been using the poppet valve for the past 100 years and not this?
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All Comments (21)
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This man just makes me want weird engines in my cars.
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I designed a rotary valve system once for a project, and the sealing was always a headache. I could never get it to last more than a few hours. Bravo to these engineers for solving these issues.
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I don't really speak engine mechanics, but your explanation was so clear that I was usually a half step ahead of what you were going to say next! A really good presentation.
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I designed a dual overhead rotary valve system in 1963 using single long shafts. In 1966 I was living in France and met a guy who had designed a similar system and manufactured a custon head for a Renault Alpine engine, He raced the car that year at Le Mans. Unfortunately I was unable to accept his invitation to accompany him and his team to the 24 Hour race that year and due to returning to the states I never found out how it performed, although I believe their car finished the race. Very interesting video, thank you.
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You can have 20 advantages for a thing, but one disadvantage can be too harsh and kills it. Thanks for the video
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As a young man, many years ago, I remember ruminating over the limitations of conventional poppet valve designs. The idea of interrupted cylindrical rotary valves exactly like this occurred to me. I remember showing my sketches to an engineer friend of mine. He got very excited and enthusiastic about my idea. This was years before a quick Google search was even a thing. When we began to search patents and technical designs, I realized that my "brilliant ideas" was decades old, and literally thousands of people had come up with variations on this idea, and the issues with sealing, expansion under heat and pressure, and all the technical problems you list in this video were well understood and my idea wasn't unique or novel at all. For about three days I thought I might have stumbled upon that million dollar idea all tinkerers and want to be engineers dream of, only to realize I was at least fifty years late to the party.😂. This was an excellent video, and watching the excellent animations of the rotary valve idea was like seeing my rough sketches come to life. I hope someone is able to truly make such a drivetrain into a reliable real-world design. Seeing that BSA V-twin engine actually running and racing is delightful.
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I did my Masters degree in university on Rotary Valves engines . Not only do they breath better, but their volumetric efficiency bandwidth is wider, meaning there is no need for variable valve timing for normal road going cars or even high rpm race cars. They work best with any forced induction. A small 1.5l engine could easily achieve 500kw (670 hp) assuming the engine can handle it. Also since there is no piston/valve collision risk, the valve timing could be much more aggressive.
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I just discovered this channel today. I'm a mechanical engineer with a licensed automotive technician background. Yes , I'd like to strangle myself some days. Moving on. Very impressed with your presentation of the rotary valve. It was explained in such a manner that the average person interested in such a topic would understand. I don't think my 31 year old daughter with 4 little kids would be even slightly interested. She hates when I talk technical about anything. Very well done sir. I will definitely look into some of your other videos. Thank you.
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As an automotive engineer for 37 years, I love the way you deliver your knowledge on an easy to understand level for all.
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Back before the last ice age when I was an apprentice mechanic, at Fords training center there was a 6 cylinder engine with twin rotary valves. This was a live and working motor that was in the dyno room. The normal pop valve 6 would rev to max 6500 RPM, the same engine with the rotary valves would rev to 11000 RPM, the weakness was the bottom end. The pop valve 6 would make 147KW power and 287NM torque at 6000RPM and 3000RPM respectively. The rotatory valve engine 235 KW and 315NM at 8000RPM and 3400RPM respectively. Great video on this topic.
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I brainstormed this idea in the early 00's. I couldn't find any info on this being done and I thought I had a unique idea, until now, thanks for shattering my dreams.
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Your way of explaining things is pure perfection. I don't even care about cars that much, but I'm subscribed now. Thank you!
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This channel is great weapon against cynicism and lethargy. I don't want to wax poetic but your videos really lift my spirits up and give me food for thought! Cheers mate, great video as always!
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It never ceases to amaze me how not only is a valve train capable of doing that so fast, but with proper maintenance it can do it for such a long time... My 2000 AU Ford Falcon ute (Australian pick-up basically) for example has done 510,000km and she still functions like the day it left the factory, never uses a drop of oil and gets the same fuel economy as it did new. It's never, ever let me down, not even hinted at it. And I use it tow and all sorts, so it doesn't live the easiest life. That intech in-line six is the definition of a workhorse, a truly great example of engineering the right tool for the job. Sure she's well looked after, but it amazes me every time I turn the key and it works perfectly. It's one of those cars I bought as a cheap work car stop gap and now I never plan on letting her go, BEST car I've ever owned. Even more reliable than my 70 series TDV8 LandCruiser, which has let me down twice and cost ten times the money I have into old Ford. Now that's reliability.
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Very good description and demo of engine valves and their problems. Yes, the rotary valves always leak because of the necessary clearance to permit rotation but also allow for expansion. A solution is four longitudinal seals on the barrel, as used on Wankel engine lobes, but that introduced a lot of friction and heat.
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Best articulated explanation of valve operation i have seen.
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I worked at a company where one of the owners was involved in the prototyping of a rotary valve head. Along with the sealing difficulties, he explained to me that one of the big drawbacks was poor airflow when the opening was misaligned. They were able to improve it by adjusting the shape of the porting, but it was not as good as a poppet valve when it is partially opened. Additionally, when the port and spool was half opened, for example, the fuel and air flow would separate in an unpredictable way. Ultimately, they abandoned it because it was not better than poppet valves and WAY more expensive.
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Not sure where you went to engneering school, brother, but if you ever get tired of content creation, you really should teach at a major university. Your enthusiasm and ability to explain things clearly and make challenging topics easy to understand is just fantastic! Definitely the best automotive engineeing channel on the interwebs.
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I'm a chef by trade, I don't even have a drivers license... yet I love videos like this. It's super interesting listening to someone talk about something that I lack any real knowledge about and doing it in a efficient and entertaining manner!
