Rotary engines are not a common option that you will find in the modern automobile. Their design offers a drastically different choice when compared to the conventional piston-based combustion engines. This early technology did help to fuel the car revolution as vehicles began to replace horses, but the inherent limitations of the approach made this engine almost entirely obsolete by the 1920s.
It is essential to remember that a rotary engine is not the same as a radial one. Cylinders are arranged radially around a central crankshaft in with the rotary option, with the entire block rotating around it. The radial engine would use a fixed cylinder block with a rotating crankshaft instead.
Most rotaries were built with an odd number of cylinders. That design made it possible for every other piston to fire in order, creating a smooth operation.
There are still several pros and cons of rotary engines to look at today even though this technology is rarely used. The Mazda RX series is the only major vehicle lineup today that still focuses on this technology.
List of the Pros of Rotary Engines
1. It features a smooth operation.
The rotary engine delivers power smoothly because there are no reciprocating parts relative to the engine mounting point. That means the large, rotating mass of the cylinders and crankcase as a unit acts more like a flywheel. You couldn’t eliminate all of the vibration or stuttering since it is still an internal combustion engine, but the results are undeniable. That’s one of the primary reasons why people enjoy driving the Mazda RX series today. The ride is remarkably better, and the only way to realize that fact is to experience the technology personally.
2. Rotary engines provide an enhanced cooling experience.
When a rotary engine is running, then the rotating assembly with the cylinder and crankcase creates a cooler airflow by itself. The rotation acts like a self-cooling fan that pulls colder air from the outside into the compartment. Even if the vehicle is at rest, this advantage still applies. Since the internal combustion engine isn’t operating in high-temperature conditions, then there is less of a risk of overheating or damage. You can see this advantage working with aircraft today with their propeller technologies.
3. It offers a weight advantage that’s still worth considering.
Conventional engines have heavy flywheels added to them because it is the best way to smooth out the power impulses that occur during operations. That option can also reduce the levels of vibration experienced in the vehicle. Rotary engines get an incredible power-to-weight ratio with the design since there is no need to add the flywheel with the way that it operates. It shares the advantage of having a flatter, smaller crankcase with other radial configurations at the same time.
The air-cooling system efficiencies also make the cylinders capable of being made with thinner walls and shallower cooling fins. That fact reduces the weight of the rotary engine even more.
4. Rotary engines offer more mechanical simplicity than other designs.
A rotary engine contains fewer parts than an equivalent piston engine. This design may decrease the cost of design and manufacture. It is an advantage that also leads to reduced weight. Compared to conventional reciprocating piston engines, rotary engines contain no camshaft, valves, rocker arms, flywheel, or timing belts.
This design element means decreased weight levels and fewer opportunities for malfunction. That makes the rotary engine easier repair. During the first development of rotary engines, they were used to drive aircraft. It was possible to do so because the early planes were taking advantage of the rotary engine’s high power-to-weight ratio.
5. Rotary engines are less likely to experience a seizing event.
Rotary engines are much less likely to seize during operational failure. That means aircraft still employ this technology because it gives a pilot the opportunity to land safely even if the engine fails. Sports and racing cars use this tech for the same reason since it operates at a high RPM and produces more power of a shorter duration compared to the modern internal combustion engines of today.
You’ll also see rotary engines in personal watercraft, motorcycles, or tools like chainsaws because of the high degree of smoothness and certainty that are possible with this engine design.
6. You can receive a lot more power from a rotary engine.
Despite the size of a standard rotary engine in an automobile like the Mazda RX-8, this technology offers the highest horsepower per displacement of any naturally aspirated motor produced in the United States. It packs a real punch that deserves consideration. The 13B-MSP Renesis is a 1.3L engine producing 232 horsepower. That equates to 178 HP per liter. That’s the equivalent to a Corvette’s LS2 6L engine producing 1,068 horsepower directly from the factory.
7. Rotary engines are almost immune to catastrophic failure.
When you have a piston motor powering an automobile, then it can seize and cause all sorts of damage under the hood. If you experience a failure with a rotary engine, then the worst-case scenario is that you will see a sharp decline in power output until it eventually dies. The engines like to stay at their peak RPM range, which is at 9,000 RPM when looking at the 13B-MSP Renesis that’s found in the Mazda RX-8.
List of the Cons of Rotary Engines
1. The rotary engine has an inefficient total-loss oiling system.
The primary issue with the rotary engine design is that it is fundamentally inefficient with its total-loss oiling system. The lubrication must enter the crankcase through a hollow crankshaft before it can reach the entire engine. This disadvantage in the design means that the centrifugal forces of each revolution would be directly opposed to any re-circulation of the oil. The only practical solution to solve this problem was to put the lubricant into the fuel and air mixture in the same way that a two-stroke engine operates.
2. Power increases must come from size and mass increases.
When you step outside of the Mazda RX series, the vehicles that use rotary engines could only increase their power if they were also improving their size and mass. That would allow for a multiplication effect to occur with the gyroscopic precession as the entire engine mass rotates. The outcome of this increase resulted in control problems for aircraft that included stability issues. If an inexperienced pilot was at the helm of the craft, then there was a greater risk that the vehicle would be unable to maintain is flight trajectory.
3. You will go through more fuel with a rotary engine.
Rotary engines produce a low compression ratio, even though you can rev it like crazy to get some tremendous power for it. There is a significant amount of fuel that remains unburned at the end of a combustion cycle with this technology. That means you’ll experience a poor fuel economy when driving a car equipped with this technology. There are also more emissions that come from this design, which can make it difficult to have a vehicle make it through carbon testing in areas where it is necessary.
4. It goes through an incredible amount of oil to function correctly.
The design of the rotary engine, especially the ones invented by Wankel, is to burn oil during operation. This consumption feature helps to lubricate the engine, ensuring that it isn’t damaged in the process. It is a disadvantage that enhances the issues with fuel consumption and carbon emission problems that exist with this engine.
Using the Mazda RX-7 as a real-world example of what to expect with a rotary engine, owners average about 18 miles per gallon with its fuel. Some were only receiving eight MPG with their vehicle. Fuelly took the information from 135 RX-7 owners over 642,000 miles driven to measure the fuel economy. The highest number recorded in their information collection was only 24 mpg.
5. Rotary engines require more maintenance than their counterparts.
You’ll be managing more maintenance issues with a rotary engine instead of the conventional internal combustion engines used in most vehicles today. The amount of oil they leak can be enormous, and that’s an immediate fix you must manage since the technology requires you to burn the oil for it to be useful. You’re going to be popping the hood frequently to check your fluid levels to ensure the smooth operation can continue. Because it is such a rare option in today’s automotive market, you might find it tricky to locate a mechanic who knows how to repair the issues that can creep up on a Wankel engine.
6. It can be expensive to fix a rotary engine.
The simplicity of a Wankel engine often makes people think that they are relatively cheap to fix. The problem is that most individuals familiar with automotive engines don’t know how to work on them. You are forced to go to a specialist in almost every community around the world if something breaks down on your vehicle if you don’t know how to fix that problem. That means your repair or regularly scheduled maintenance is likely to be a lot more expensive than what your mechanic would charge normally.
7. Seals can be a significant problem for rotary engines in cold climates.
A rotary engine tends to produce about the same amount of torque as you will find in a screwdriver. That means the seals don’t receive the same levels of lubrication with this option as they would if it were a conventional engine. That doesn’t matter much if you live in a warmer climate, but cold weather can create significant issues for owners with this disadvantage. This problem can lead to flooding when trying to make a cold start.
The older 13B engines have more issues with this disadvantage than the modern ones, but it is still a good idea to let your motor warm to operating temperature before you decide to start driving.
The automotive industry wouldn’t be where it is today without the influences of the rotary engine. We are not using this technology as often as we once did, but there are still specific applications where having it equipped to a vehicle makes sense.
If you are thinking about the purchase of a Mazda or another make and model equipped with this technology, managing the disadvantages must be your top priority. You’re going to burn through oil and fuel quickly, so you’ll want to budget for those expenses.
The pros and cons of rotary engines can also point you in the opposite direction by showing you that alternative products are better for your needs. At the end of the day, the decision is yours as to whether or not you are going to take advantage of what this technology provides.
Brandon Miller has a B.A. from the University of Texas at Austin. He is a seasoned writer who has written over one hundred articles, which have been read by over 500,000 people. If you have any comments or concerns about this blog post, then please contact the Green Garage team here.