rotor housing, evident on higher mileage engines. The problem was exacerbated when the engine was stressed before reaching operating temperature. However, Mazda Wankel engines solved these initial problems. Current engines have nearly 100 seal-related parts. The problem of clearance for hot rotor apexes passing between the axially closer side housings in the cooler intake lobe areas was dealt with by using an axial rotor pilot radially inboard of the oils seals, plus improved inertia oil cooling of the rotor interior (C-W , C. Jones, 5/8/63, , M. Bentele, C. Jones. A.H. Raye. 7/2/62), and slightly "crowned" apex seals (different height in the center and in the extremes of seal). Fuel economy and emissions As is described in the thermodynamic disadvantages section, the Wankel engine is a very inefficient engine with a poor fuel economy. This is caused by the Wankel engine's design with its bad combustion chamber shape and huge surface area. The Wankel engine's design is, on the other hand, much less prone to engine knocking, which allows using low-octane fuels without reducing compression. As a result of the poor efficiency, the Wankel engine with peripheral exhaust port has a larger amount of unburnt hydrocarbons (HC) released into the exhaust. The exhaust is, however, relatively low in nitrogen oxide (NOx) emissions, because the combustion is slow, and temperatures are lower than in other engines, and also because of the Wankel engine's good exhaust gas recirculation (EGR) behavior. Carbon monoxide (CO) emissions of Wankel and Otto engines are about the same. The Wankel engine has a significantly higher (ΔtK>100 K) exhaust gas temperature than an Otto engine, especially under low and medium load conditions. This is because of the higher combustion frequency and slower combustion. Exhaust gas temperatures can exceed 1300 K under high load at engine speeds of 6000 min−1. To improve the exhaust gas behavior of the Wankel engine, a thermal reactor or catalyst converter may be used to reduce hydrocarbon and carbon monoxide from the exhaust. According to Curtiss-Wright research, the factor that controls the amount of unburnt hydrocarbons in the exhaust is the rotor surface temperature, with higher temperatures resulting in fewer hydrocarbons in the exhaust. Curtiss-Wright widened the rotor, keeping the rest of engine's architecture unchanged, thus reducing friction losses and increasing displacement and power output. The limiting factor for this widening was mechanical, especially shaft deflection at high rotative speeds. Quenching is the dominant