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  • effect of valve diameter

    mechky

    Member

    Updated: Oct 21, 2024
    Views: 887
    Does anyone know the effect of inlet & exhaust valve diameter on the engine performance?
    What will happen if both the inlet & exhaust valve diameter is decreased maintaining the same initial ratio? What parameters of engine will change?
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  • CE Designer

    Member • Jan 3, 2012

    Diesel or petrol engine?
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  • mechky

    Member • Jan 3, 2012

    CE Designer
    Diesel or petrol engine?
    petrol engine
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  • Siddhant Mukherjee

    Member • Jan 3, 2012

    Decreasing valve dia upto a certain limit will increase engine performance of petrol engine . This is so because as valve dia dec. , the pressure of charge at inlet manifold will decrease due to increase in flow velocity. This will result in decrease in temperature of charge, reducing chances of preignition and knocking. So you can easily increase the compression ratio resulting in more power output in same fuel consumption... Thus bsfc increases. The efficiency also increases as a result .

    Decreasing the dia too much will result in problems bcoz the charge temp will dec. too much making it difficult for fuel to reach its self ignition temperature.
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  • mechky

    Member • Jan 3, 2012

    S.mukherjee
    Decreasing valve dia upto a certain limit will increase engine performance of petrol engine . This is so because as valve dia dec. , the pressure of charge at inlet manifold will decrease due to increase in flow velocity. This will result in decrease in temperature of charge, reducing chances of preignition and knocking. So you can easily increase the compression ratio resulting in more power output in same fuel consumption... Thus bsfc increases. The efficiency also increases as a result .

    Decreasing the dia too much will result in problems bcoz the charge temp will dec. too much making it difficult for fuel to reach its self ignition temperature.
    So, it probably means that whatever engines are manufactured their valve dia is already upto that 'certain limit' of getting maximum engine performance.
    Correct me if I am wrong.
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  • CE Designer

    Member • Jan 3, 2012

    Less fuel = Less compression = less power
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  • mechky

    Member • Jan 3, 2012

    CE Designer
    Less fuel = Less compression = less power
    I seriously doubt that. Its because with decreasing valve dia the flow velocity will increase, provided the inlet passage dia remains constant. So amount of fuel shall remain the same.
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  • CE Designer

    Member • Jan 3, 2012

    I misinterpretted. I thought valve and passage were one and the same.
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  • zaki_whiz03

    Member • Jan 8, 2012

    mechky
    I seriously doubt that. Its because with decreasing valve dia the flow velocity will increase, provided the inlet passage dia remains constant. So amount of fuel shall remain the same.
    If there is to be a change in the valve dia then the passage dia should be changed accordingly in order that the valve has a leak proof seat on it.
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  • zaki_whiz03

    Member • Jan 8, 2012

    By reducing the inlet valve dia there should be a subsequent reduction in the passage dia. The flow velocity is increased during the suction stroke and turbulence is created in the combustion chamber which is essential for proper and complete combustion of the fuel-air mixture. If the exhaust valve dia is decreased then the resistance of the combustion products to flow out is increased as a result the stresses within the cylinder and especially on the piston is increased.
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