rotary valves
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Rotary Valves for ICE Engines?

by Larry Carley copyright 2023-02-10

I recently read a very interesting article on about a company that says it has figured out how to make rotary valves work in internal combustion engines (ICE). The rotary valve concept is nothing new and has been considered as a possible alternative to poppet valves. Rotary valves have the potential for better airflow, which in turn allows an engine to make more power. But the main challenge with rotary valve has been sealing the rotary shaft so it does not bind up when it gets hot or leak air or exhaust. Seal design and durability have been a problem.

A company called Vaztec claims they have developed a solution for the sealing problem with rotary valve cylinder heads. They call their technology ECOREV� and say that it can be applied to a wide variety of ICE engine applications,everything from motorsports to motorcycles.

Why are Rotary Valves Better Than Poppet Valves?

Virtually all four-stroke gasoline and diesel engines use poppet valves to control airflow into and out of the engine’s cylinders. Poppet valves are held shut by stiff valve springs, and are pushed open by a camshaft in overhead cam (OHC) engines, or by a camshaft, lifters, pushrods and rockers in a pushrod engine. Poppet valves have been used in overhead valveproduction engines since the 1950s, but they have their limitations.

The main limitation with poppet valves is that they don’t allow as much airflow as an open port would. The presence of a valve stem in the middle of the intake and exhaust ports in the cylinder head obstructs airflow in and out of the head.

Air and exhaust must also flow around the circular head of the valve. This creates turbulence that further hinders efficient airflow.

The curvature of the valve head, how the head blends with the stem, and the angles machined on the valve seats also affect airflow. Multi anagle valve seats flow better than seats with a single 45 degree seat. But no matter how much care is given to optimizing the valves and seats for maximum airflow and velocity, poppet valves still can’t flow as well as a totally open port with nothing that hinders airflow.

The idea behind the rotary valve is to replace the poppet valves, lifters, pushrods, rockers and camshaft with a pair of tubular shafts, one for the intake ports and the other for the exhaust ports. Openings are then machined through each shaft that align with the ports in the head. The position, size and shape of these openings then determine when each port opens and closes as the shafts rotate. This corresponds to the valve timing and valve lift that would otherwise be controlled by a camshaft and poppet valves.

rotary valve engine by Vaztec
Experimental rotary valve engine developed by Vaztec.

In theory, rotary valves open and close much faster than poppet valves, and they have no RPM limitations because there are no valve springs or up and down motion of valves that can result in valve float, misfires and loss of power if the engine is revved too high.

Most stock pushrod engines have a redline of about 5500 to 6500 rpm, while OHC engines can typically rev somewhat higher to about 7000 RPM. Racing engines can rev much higher (9,000 RPM for NASCAR engines, and over 10,000 RPM for Pro Stock drag racing engines), but this requires much stiffer double or triple valve springs, lightweight titanium valve spring retainers, lightweight forged aluminum or billet steel rockers, stiffer pushrods and special cam profiles.

Besides having a much higher rev limit, rotary valves also eliminate the flow restrictions created by poppet valves. More air can flow through the ports with a rotary valve. More airflow means more peak horsepower.

rotary valve diagram by Vaztec

So what’s not to like about rotary valves?

The Drawbacks of Rotary Valves

Assuming the latest design improvements by Vaztec have overcome the sealing and durability issues of previous rotary valve designs, there are other hurdles that remain in the way of widespread acceptance and use. For one, each application would require an entirely new cylinder head design to accommodate the rotary valve shafts. It’s not a simple swap, and a lot of development work would be required to optimize valve timing, port configuration and airflow requirements for a particular engine.

Most auto makers today would be very hesitant to invest money to develop, test and produce new cylinder heads for current production engines. Most of the development money these days is being spent on developing new electric powertrains, not soon-to-be-obsolete ICE engines.

For motorsports applications, there might be some niche markets for certain racing engines if a rotary valve cylinder head can deliver a significant performance increase. But many types of racing are heavily regulaated as to what is legal and what is not. And if new head suddenly showed a significant advantage over existing cylinder heads, chances are the rotary valve heads would be outlawed to equalize competition.

I agree that rotary valves are potentially more efficient than poppet valves. But it's a development that has come too late in the evolution of the internal combustion engine. Times have changed and ICE engines will eventually fade into history as they are gradually replaced by electric motors. The only exception I see to this future would be big over-the-road heavy trucks which will likely remain diesel-powered.

The basic problem with all ICE engines is poor thermal efficiency

The main problem with all ICE engines, regardless of what type of valves they use, is their terrible thermal efficiency. They waste up to 2/3 of the heat energy in the fuel they burn. Diesels are up to 20 percent more efficient than gasoline engines because of their higher compression ratios, but they still waste about 60 percent of the fuel they burn.

Attempts have been made to develop ceramic engines that can run at very high temperatures without melting but so far they have not panned out.

Turbocharging reuses some of the waste heat in the exhaust to spin a turbine that boosts airflow coming into the engine for more power. But turbocharging does not reduce heat loss out the tailpipe.

ICE engines are doomed because ICE engines are too complex, costly and bulky compared to electric motors.

Another disadvantage of ICE engines (even with a rotary valve setup) is that they have a LOT of moving parts. ICE engines are expensive to build and assemble. They require ongoing maintenance such as regular oil changes plus air filters, and eventually they need new spark plugs at 100k miles.

ICE engines also require large bulky cooling systems, and they need a large, heavy and expensive transmission to multiply torque to the drive wheels.

By comparison, electric motors are 94 or better efficient, they have ONE moving part (the rotor), and most require ZERO maintenance (no oil changes, no filter replacements, no sensor replacements, no hoses or belts, no spark plugs, ignition coils, fuel injectors or fuel pumps, no starters and no water pumps. Most electric motors are air cooled although some higher output motors do benefit from oil cooling.

Electric motors are far cheaper to build than ICE engines, and they are much smaller and lighter for the amount of horsepower and torque they produce. Electric motors deliver high torque right from zero RPM, and can rev like crazy (10,000 up to 16,000 RPM) eliminating the need for a multi-speed transmission.

The biggest advantage of electric motors over ICED engines is that electric motors produce ZERO emissions. No carbon dioxide (CO2), no carbon monoxide (CO), no oxides of nitrogen (NOx), no sulfur dioxide, no soot, no carbon nanoparticles (HC), no exhaust smell, not even a drop of water vapor. Thus, there is no need for an expensive catalytic converter to clean up tailpipe emissions. Nor is there a need for annual emissions testing. The Check Engine light is gone and there are no complicated emission control systems or sensors to worry about. And finally, electric motors make almost no noise! Electric vehicles are exceptionally quiet.

The battery is still the weak link with today's EVs

The weak link in today's EV powertrains is the battery. Although most of today’s EV batteries have proven to be fairly reliable and safe, there have been some instances of batteries shorting out and starting fires either during or after charging, or after an accident And once an EV battery starts to burn, there’s no putting it out. It’s almost like a magnesium flare that continues to burn until it eventually burns itself out.

Today’s EV batteries are expensive, bulky, heavy (up to 1000 lbs. or more for larger 100 kilowatt battery packs), and lack the range for long distance driving without long charging stops.

But battery breakthroughs are happening almost every day. A tremendous amount of R&D is going into EV battery technology, and within 3 to 5 years we should have much better next generation EV batteries that are cheaper to produce, that use few if any rare earth minerals or exotic metals, that are smaller, lighter, more energy dense and capable of faster charging. Changes in battery technology will also greatly reduce or eliminate any fire hazards associated with EV batteries.

So will rotary valves revolutionize ICE engines? I don't think they will have any impact on production engines because they do not overcome the basic disadvantages of all ICE engines (poor thermal efficiency, exhaust emissions and dependence on fossil fuels). Rotary valves might find some acceptance for certain small engines or very specialized racing, but I don't see the technology as having a major impact on the way things are headed today.

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