1Internal Combustion Engines – ME422Ideal Standard CyclesProf.Dr. Cem SoruşbayInternal Combustion Engines – ME422Ideal Air Standard Cycles¾Introduction¾Comparison between thermodynamic and mechanical cycles¾Performance parametersimep, bmep, mechanical efficiency, indicated eff., volumetric eff.¾Ideal cycles and thermal efficienciesOtto cycle, Diesel cycle, Dual cycle¾Comparison of cycles¾Deviations from actual engine cycles
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2AssumptionsAir standard cycles,serve as introduction to the more detailed and accurate models of IC enginesprovide insight into some of the important parameters that effect engine performanceAssumptions;•Neglect heat transfer to and from cylinder walls,•Replace combustion process by a heat addition process that occurs at constant volume (in Otto cycle) or at constant pressure (in Diesel cycle),•Do not consider gas exchange process,•Assume cylinder charge as a perfect gas (cpand cvare assumed constant) which is pure air.Otto CycleThe Otto cycle is used as a basis of comparison for SI enginesThe cycle consists of four processes,1 – 2isentropic compression from V1to V22 – 3addition of heat Q23at constant volume3 – 4isentropic expansion to the original volume4 – 1rejection of heat Q41at constant volume