Pregunta 16 The size of the engine intake valve is A Smaller than that of exhaust valve B Does not depend upon the size of exhaust valve Larger than that of exhaust valve D Larger than engine E Same as that of exhaust valve
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This article contains the following:
Why is the intake valve larger than the exhaust valve
Influence of airflow resistance
Influence of engine speed
1.Why is the intake valve larger than the exhaust valve
The valve is opened by the cam and the valve spring is closed. When the mixture needs to be sucked into the cylinder, theintake valve will open; when the exhaust gas after combustion needs to be discharged, the exhaust valve will open.
Since the intake air is "sucked in" and the exhaust gas is "pushed" out, the intake air is more difficult than the exhaust gas, and the more intake air, the better the combustion and the better the engine performance. The intake air is sucked by vacuum, and the exhaust gas is pushed out to push the exhaust gas. Therefore, exhaust is easier than intake. In order to get more fresh air to participate in the combustion, therefore, more intake air is needed. For this reason, the intake valve needs to be larger, and the overall size has not changed, and the exhaust valve can only be made smaller. Therefore, the intake valve is generally designed to be larger than the exhaust valve to reduce the difficulty of intake and increase the amount of intake air. Some simply design an additional intake valve, which only has 3 valves (2 into 1 row) and 5 valves (3 into 2 rows) design.
2.Influence of airflow resistance
In theory, the amount of inflation and the amount of exhaust are equal, and the opening and closing time of the exhaust valve and the opening and closing time of the intake valve are also equal.
But this is not the case, because the throttle valve controls the rotation speed, the valve opening and closing are large and small, and the cylinder should be filled with a mixture of air equal to atmospheric pressure (about 1 kg / cm2) when the suction is completed. But when the gas flows through the intake pipe and the intake valve, it is subject to resistance. In order to overcome these resistances and allow the mixture to flow at a certain speed, part of the pressure must be consumed by the wave, so the air pressure in the cylinder is always lower than atmospheric pressure. The gas density changes with the pressure, and the low pressure density is reduced, and the actual weight of the mixed gas is reduced. To solve and reduce the influence of air flow resistance, the cross-sectional area of the air flow path at the intake valve must be increased, that is, the area of the air valve should be increased. In the case of thin air in the plateau area, the area of the air intake passage should be increased, otherwise the engine will not reach its rated power in these areas.
Respuesta:
Larger than that of exhaust valve
Explicación:
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