14basic_diesel - Basic Practical diesel cycle The textbook...

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Basic Practical diesel cycle define some units 3 3 kN := 10 N kPa := 10 Pa The textbook Diesel cycle is represented by all heat addition at constant pressure. The Otto cycle which is implemented by the spark ignition internal MPa := 10 6 Pa kJ := 10 3 J combustion engine adds all heat at constant volume. We will model a combined or dual (Seiliger) cycle with a portion of the heat added at constant volume, the kmol := 10 3 remainder at constant pressure. Setting some parameters to be defined = 1 will reduce to either the Otto or Diesel cycle. This model will use an ideal air standard cycle with air as an ideal gas with constant specific heats and reversible processes to represent the behavior. The gas relationships are useful. air-standard cycles . .. 1. air as ideal gas is working fluid throughout cycle - no inlet or exhaust process 2. combustion process replaced by heat transfer process 3. cycle is completed by heat transfer to surroundings 4. all processes internally reversible 5. usually constant specific heat (page 311) basic practical diesel cycle Assumptions for analysis . .. 1. reversible cycle with all reversible processes 2. working fluid is air assumed to be a perfect gas with constant specific heats, γ = c p /c v = 1.4 3. mass of air in cylinder remains constant 4. combustion processes are represented by heat transfer from an external source. Constant volume or constant pressure pocesses are done. 5. cycle is completed by cooling heat transfer to the surroundings until the air temperature and pressure return to the initial conditions of the cycle (constant volume process). 1-2 isentropic compression 2-3 constant volume heat addition 3-4 constant pressure heat addition 4-5 isentropic expansion 5-1 constant volume cooling data for plot this is the shape . .. p-v Dual Cycle volume (m^3/kg) pressure (bar) T-s Dual Cycle entropy (relative to s1) Temperature (K) next we will put numbers on the plots => themodynamic analysis of dual (Seiliger) cycle 10/24/2006 1
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The original notes are sourced from VanWylen and Sonntag. They could be revised to use the form of some of the relationships from Woud, but at considerable effort. Rather what follows is the application of the equations developed in the gas relationships lecture applied to the combined air-standard cycle deriving the relationships summarized in Table 7.3 Analytical prediction of the Selinger process on page 245 of the text. v 1 p 3 v 4 r c , a , b r c = a = b = v 2 p 2 v 3 stage 1-2 isentropic adiabatic compression (expansion) _______________________________ volume ratio known γ γ γ− 1 1 v initial v initial v 1 v 1 v 2 γ v initial v final = v 1 v 2 1 r c = = p final = p initial p final = = r c T final T initial T final = = r c v final v final v 2 v 1 1 γ γ = r c = = r c r c v 2 T initial p initial stage 2-3 heat transfer at constant volume . ... ________________________________________ RT initial final = a p initial = p final = = T final p 3 p final p 3 = = a v constant 100 v constant 100 T initial p 2 p initial p 2 v 1 p 3 T final = 1 = a = a v 2 p 2 T initial stage 3-4 heat transfer at constant pressure .
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This note was uploaded on 02/24/2012 for the course MECHANICAL 2.611 taught by Professor Davidburke during the Fall '06 term at MIT.

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14basic_diesel - Basic Practical diesel cycle The textbook...

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