Engines piston-ported

Note in Figure 5 that with the piston near BDC, both intake and exhaust ports are open concurrently. This provides a pathway whereby some of the incoming charge can short-circuit the cycle and exit with the exhaust gas. If the engine uses an upstream carburetor to mix fuel into the air before the charge enters the crankcase, then a fraction of the fuel leaves with the exhaust gas. That penalizes fuel economy and iticreases exliaust emissions. This escape path for unburned fuel can be eliminated by injecting fuel directly into the cylinder after both ports are closed, hut at the cost of increased complexity. 

The four-cycle engine takes two complete piston strokes for exhaust, scavenging, and charging. The two-cycle engine exhausts, scavenges, and charges for about 25% of its piston travel before bottom center, and until about 25% after bottom center. The two-cycle machine does not have intake and exhaust valves but uses ports. 

Design for turbulent combustion is another critical way that the design engineer can affect or improve the stoichiometry of a system. Turbulence helps the mixing process between the fuel and oxidizer. Injection ports, piston design, and cylinder design all contribute to good combustive characteristics. Further improvements in combustion are achieved by catalytic converters and exhaust gas recirculation. 

The second area of application is as a potential material for inclusion in reciprocating internal combustion engines, principally diesel engines. The goals here are to insulate components such as pistons, valves, intake manifolds and exhaust ports, and to protect the moving parts from wear and corrosion. 

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