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Unformatted text preview: 9-1Chapter 9 GAS POWER CYCLES Actual and Ideal Cycles, Carnot cycle, Air-Standard Assumptions 9-1CThe Carnot cycle is not suitable as an ideal cycle for all power producing devices because it cannot be approximated using the hardware of actual power producing devices.9-2CIt is less than the thermal efficiency of a Carnot cycle. 9-3CIt represents the net work on both diagrams.9-4CThe cold air standard assumptions involves the additional assumption that air can be treated as an ideal gas with constant specific heats at room temperature.9-5CUnder the air standard assumptions, the combustion process is modeled as a heat addition process, and the exhaust process as a heat rejection process. 9-6CThe air standard assumptions are: (1) the working fluid is air which behaves as an ideal gas, (2) allthe processes are internally reversible, (3) the combustion process is replaced by the heat addition process, and (4) the exhaust process is replaced by the heat rejection process which returns the working fluid to its original state. 9-7CThe clearance volume is the minimum volume formed in the cylinder whereas the displacementvolume is the volume displaced by the piston as the piston moves between the top dead center and the bottom dead center. 9-8CIt is the ratio of the maximum to minimum volumes in the cylinder.9-9CThe MEP is the fictitious pressure which, if acted on the piston during the entire power stroke,would produce the same amount of net work as that produced during the actual cycle.9-10CYes. 9-11CAssuming no accumulation of carbon deposits on the piston face, the compression ratio will remainthe same (otherwise it will increase). The mean effective pressure, on the other hand, will decrease as a cargets older as a result of wear and tear.9-12CThe SI and CI engines differ from each other in the way combustion is initiated; by a spark in SI engines, and by compressing the air above the self-ignition temperature of the fuel in CI engines. 9-13CStroke is the distance between the TDC and the BDC, bore is the diameter of the cylinder, TDC is the position of the piston when it forms the smallest volume in the cylinder, and clearance volume is the minimum volume formed in the cylinder.9-29-14The four processes of an air-standard cycle are described. The cycle is to be shown on P-vand T-sdiagrams, and the net work output and the thermal efficiency are to be determined.Assumptions1The air-standard assumptions are applicable. 2Kinetic and potential energy changes are negligible.3Air is an ideal gas with variable specific heats. PropertiesThe properties of air are given in Table A-17. Analysis(b) The properties of air at various states are Pqoutqin3421qoutqin3421+ ,+ ,+ ,kJ/kg828.149.101310kPa2668kPa100kPa2668kPa800K539.8K18001310kJ/kg1487.2K1800K539.8kJ/kg389.22088.111.386kPa100kPa800386.1kJ/kg300.19K300434223322233333221211343121ooooohPPPPPTTPTPTPPuTuPPPPPhTrrrrrrvvTvTFrom energy balances,kJ/kg570.19.527.1098kJ/kg527.919.3001.828kJ/kg1098.01098....
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This note was uploaded on 09/21/2009 for the course ME 311 taught by Professor Ferrenberg during the Fall '09 term at Nevada.
- Fall '09