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Effect of Piston Dwell on Engine Performance P M V Subbarao Professor Mechanical Engineering Department Sufficiency of time to Execute a Process…..

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Dwell Piston Mechanism The design geometry creates a pause or dwell in the piston’s movement at the TDC and the BDC., while the output shaft continues to rotate for up to 20 degrees.

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Instantaneous Displacement & Velocity of Dwell Piston

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Piston path for Dwell four stroke cycle

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Comparison of standard and Dwell four stroke Cycles

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PV diagram due piston dwell in TDC and BDC

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Comparison of standard and Dwell four stroke cycles in PV diagram

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Comparison of volumetric efficiency

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Comparison of power

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Comparison of temperature during working process

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Comparison Of Efficiency Curves

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Closing Remarks The automobile industry is under large pressure to keep developing automobiles with IC engines, to reduce fuel consumption and exhaust gas emissions, as well as to seek better alternatives for vehicle drive. A thorough understanding of engine geometry will create new avenues. A global optimization of eccentricity and rod ratio will create a best kinematics for a given fuel. A thorough thermodynamic design and analysis is first step to generate optimal design parameters.

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Thermodynamic Design : A tradition of Post Carnot Research Major portion of motive power generation occurs in any Reciprocating IC engine during closed cycle (control mass/closed system). The thermal operation of any IC engine is a transient cyclic process. Even at constant load and speed, the value of thermodynamic parameters at any location vary with time. Each event may get repeated again and again. So, an IC engine operation is a transient process which gets completed in a known or required Cycle time. Higher the speed of the engine, lower will be the Cycle time. Needs many models for each process/events.

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Thermodynamic Modeling Modeling of IC engine process can be carried out in many ways. Multidimensional, Transient Flow and heat transfer Model. Thermodynamic Transient Model USUF. Fuel-air Thermodynamic Model. Air standard Thermodynamic Model

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Irreversible I.C. Engine Cycle

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Actual Engines Process : Control mass : Variable Property gas mixture, heat transfer, frictional losses

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First Law Analysis: Transient Compression of gaseous Control Mass Compression Process Fuel/Air Mixture Air SI EngineCI Engine

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Compression process of Gaseous Control Mass For a infinitesimal crank rotation of an engine: a known dV For an ideal gas the equation of state is expressed as: By differentiating above equation, the following equation is obtained:

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Also, for an ideal gas the change in internal energy is expressed as:

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Dividing by dθ Infinitesimal Ideal gas compression Process

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