Early Intake Valve Opening
Early intake valve opening is another variation that has significant potential to reduce emissions. In a traditional engine, a process called valve overlap is used to aid in controlling the cylinder temperature. By opening the intake valve early, some of the inert/combusted exhaust gas will back flow out of the cylinder, via the intake valve, where it cools momentarily in the intake manifold. This inert gas then fills the cylinder in the subsequent intake stroke, which aids in controlling the temperature of the cylinder and NO emissions. It also improves volumetric efficiency, because there is less exhaust gas to be expelled on the exhaust stroke.
Read more about this topic: Continuous Variable Valve Timing
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