The rotary engine, technically known as the Wankel engine, is a compact, light-weight engine that can pack a good amount of power inside. Internal workings of the rotary engine are less-known to the average car enthusiasts in comparison to the piston-style engine. Because of this, it may be a bit confusing as to why the rotary engine has been out of production since 2012.
There are several advantages to the rotary engine that have made it a popular choice among kit car builders and hot rod owners. The compact design allowed for a desirable power-to-weight ratio making it a stellar choice for smaller sport-type production vehicles. Internal workings of the engine are very simple with limited moving parts. In addition, all motion is rotational allowing high RPMs and smooth operation.
The question then arises, why did production of the rotary engine stop? The last known rotary was the Maxda RX-8, which sold less than 1,500 4-doors in 2010. The video from Engineering Explained provides an excellent answer. Ultimately the disadvantages of the rotary engine funnel down to emissions. With the ever-rising standards of emission control and fuel mileage requirements, the rotary engine in its current design just doesn’t make the cut.
Emissions and fuel economy are directly related to thermal efficiency. The elongated shape of the combustion chamber makes burning all of the intake charge difficult. Unused fuel and air make their way out the exhaust port resulting in low efficiency, unsatisfactory fuel mileage, and high emissions.
Efficiency is reduced further due to the difficulty in sealing off the intake, exhaust, and combustion chambers from each other. Three types of seals are used in conjunction with spring pressure to seal the chambers. However, due to the heat differential from the combustion side of the case to the intake side causing different expansion rates, the seal is difficult to maintain.
Oil is directly injected into the chambers to assist in sealing and for lubrication. Unlike cylinder walls in a piston-style engine, there isn’t a way to splash-lubricate the rotary engine. Therefore, oil is sprayed directly into the chamber causing oil consumption and an adverse effect on emissions. These emission related concerns ultimately resulted in the demise of the rotary’s 45-year run.
Interestingly, according to magazine Autocar – the rotary may be making a comeback. Writer Mark Tisshaw reported in October, “Mazda president and CEO Masamichi Kogai confirmed: “One day rotary will make a comeback. This gives form to our brand’s vision of the future. It expresses our intention to make rotary. There are many issues to overcome but we will continue our efforts. We’re working steadily. Keep your eyes on Mazda.”
Should be interesting.