Utilizing a cycle simulation to examine the use of exhaust gas recirculation (EGR) for a spark-ignition engine: including the second law of thermodynamics

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Title: Utilizing a cycle simulation to examine the use of exhaust gas recirculation (EGR) for a spark-ignition engine: including the second law of thermodynamics
Author: Shyani, Rajeshkumar Ghanshyambhai
Abstract: The exhaust gas recirculation (EGR ) system has been widely used to reduce nitrogen oxide (NOx ) emission , improve fuel economy and suppress knock by using the characteristics of charge dilution . However , previous studies have shown that as the EGR rate at a given engine operating condition increases , the combustion instability increases . The combustion instability increases cyclic variations resulting in the deterioration of engine performance and increasing hydrocarbon emissions . Therefore , the optimum EGR rate should be carefully determined in order to obtain the better engine performance and emissions . A thermodynamic cycle simulation of the four -stroke spark -ignition engine was used to determine the effects of EGR on engine performance , emission characteristics and second law parameters , considering combustion instability issues as EGR level increases . A parameter , called 'Fuel Fraction Burned ,' was introduced as a function of the EGR percentage and used in the simulation to incorporate the combustion instability effects . A comprehensive parametric investigation was conducted to examine the effects of variations in EGR , load and speed for a 5 .7 liter spark -ignition automotive engine . Variations in the thermal efficiencies , brake specific NOx emissions , average combustion temperature , mean exhaust temperature , maximum temperature and relative heat transfer as functions of exhaust gas recycle were determined for both cooled and adiabatic EGR configurations . Also effects of variations in the load and speed on thermal efficiencies , relative heat transfers and destruction of availability due to combustion were determined for 0 % EGR and 20 % EGR cases with both cooled and adiabatic configurations . For both EGR configurations , thermal efficiencies first increase , reach a maximum at about 16 % EGR and then decrease as the EGR level increases . Thermal efficiencies are slightly higher for cooled EGR configuration than that for adiabatic configuration . Concentration of nitric oxide emissions decreases from about 2950 ppm to 200 ppm as EGR level increases from 0 % to 20 % for cooled EGR configuration . The cooled EGR configuration results in lower nitric oxide emissions relative to the adiabatic EGR configuration . Also second law parameters show the expected trends as functions of EGR . Brake thermal efficiency is higher for the 20 % EGR case than that for the no EGR case over the range of load (0 to WOT ) and speed (600 rpm to 6000 rpm ) . Predictions made from the simulation were compared with some of the available experimental results . Predicted thermal efficiencies showed a similar trend when compared to the available experimental data . Also , percentage of unused fuel availability increases as the EGR level increases , and it can be seen as one of the effects of deteriorating combustion quality as the EGR level increases .
URI: http : / /hdl .handle .net /1969 .1 /86044
Date: 2008-10-10

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Utilizing a cycle simulation to examine the use of exhaust gas recirculation (EGR) for a spark-ignition engine: including the second law of thermodynamics. Available electronically from http : / /hdl .handle .net /1969 .1 /86044 .

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