A two-dimensional numerical simulation of diesel autoignition using a quasi-global multi-step kinetic mechanism

A "quasi-global," 26-step chemical kinetic reaction mechanism proposed by R. B. Edelman and P. T. Harsha (14) was implemented into a transient, two-dimensional, finite-difference numerical simulation to model diesel engine autoignition and combustion. Information provided by Detroit Diesel for the Series 60 11.1 Liter engine was used to set the model engine geometry and operating conditions of the simulation. A modified form of the k-{dollar}varepsilon{dollar} equations was used to account for the effects of turbulence on the flowfield. Fuel spray injection and evaporation were modeled using a discrete-particle method. For comparison purposes, a single global chemical kinetic reaction was also used to model diesel autoignition and combustion. The use of the Edelman-Harsha mechanism predicted an ignition delay time of 2.1ms and a maximum average cylinder pressure of 3.33 MPa (32.9 atm), occurring at 8.0{dollar}spcirc{dollar} ATDC. The use of the single global kinetic reaction predicted an ignition delay time of 2.8ms and a maximum average cylinder pressure of 4.09 MPa (40.3 atm), occurring at 12.5{dollar}spcirc{dollar} ATDC. As expected, the model predicting the shorter ignition delay also predicted the smaller pressure rise. Fuel mass burning rate plots indicate that the Edelman-Harsha kinetic mechanism provides a better qualitative model than does the single global kinetic reaction of the three phases of diesel combustion: ignition delay, rapid combustion, and mixing controlled combustion. Predicted results were observed to be highly sensitive to Arrhenius reaction rate coefficient constant values and to computational mesh spacing.