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The intake valve is opened before the exhaust gases have completely left the cylinder, and their considerable velocity assists in drawing in the fresh charge. Engine designers aim to close the exhaust valve just as the fresh charge from the intake valve reaches it, to prevent either loss of fresh charge or unscavenged exhaust gas. In the ...
The goal of tuning is to arrange the runners and valve timing so that there is a high-pressure wave in the port during the opening of the intake valve to get flow going quickly and then to have a second high pressure wave arrive just before valve closing so the cylinder fills as much as possible.
A mass of air (working fluid) is drawn into the cylinder, from 0 to 1, at atmospheric pressure (constant pressure) through the open intake valve, while the exhaust valve is closed during this process. The intake valve closes at point 1.
A possible downside to early intake valve closing is that it significantly lowers the temperature of the combustion chamber, which can increase hydrocarbon emissions. [3] 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 ...
In most automotive engines, the intake valve closure (which seals the cylinder) takes place during the compression phase (i.e. after bottom dead centre, BDC), which can cause some of the gases to be pushed back out through the intake valve. On the other hand, intake port tuning and scavenging can cause a greater amount of gas to be trapped in ...
These Crossley Otto Scavenging Engines were made possible by the recent change from slide valves to poppet valves, which allowed more flexible control over valve timing events. [1] The closing of the exhaust valve occurred more than 30 degrees later than on earlier engines, giving a long 'overlap' period (when both the intake and exhaust valves ...
So using delayed intake valve closing on the compression stroke means also delaying the valve opening on the induction stroke, reducing the fresh air charge volume in the first place, acting as an ersatz PWM-type throttle (gating by duration of opening instead of merely inducing drag or vacuum), and minimising the back-and-forth motion of air ...
Under low-speed, high load, MIVEC ensures optimal torque delivery with the intake valve closing timing advanced to ensure sufficient air volume. At the same time, the exhaust valve opening timing is retarded to provide a higher expansion ratio and improved efficiency. At idle, valve overlap is eliminated to stabilize combustion.