Three-Dimensional Computations of Combustion in Premixed-Charge and Direct-Injected Two-Stroke Engines

• Published in: SAE transactions 1992-01, Vol.101 (3), p.679-695
• Main Authors: Kuo, Tang-Wei, Reitz, R.D.
• Format: Article
• Language: English
• Subjects: Applied sciences; Boundary conditions; Combustion; Cylinders; Energy; Energy. Thermal use of fuels; Engines; Engines and turbines; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Flames; Fractions; Gas temperature; Induced substructures; Ratios; Residual gas
• ISSN: 0096-736X; 2577-1531

Combustion and flow were calculated in a spark-ignited two-stroke crankcase-scavenged engine using a laminar and turbulent characteristic-time combustion submodel in the three-dimensional KIVA code. Both premixed-charge and fuel-injected cases were examined. A multi-cylinder engine simulation program was used to specify initial and boundary conditions for the computation of the scavenging process. A sensitivity study was conducted using the premixed-charge engine data. The influence of different port boundary conditions on the scavenging process was examined. At high delivery ratios, the results were insensitive to variations in the scavenging flow or residual fraction details. In this case, good agreement was obtained with the experimental data using an existing combustion submodel, previously validated in a four-stroke engine study. However, at low delivery ratios, both flow-field and combustion-model details were important, and the agreement with experiment was poor using the existing combustion submodel, which does not account for the effect of residual gas concentration. To improve the agreement between modeling and experimental results, a modified combustion submodel was introduced that includes the effect of residual gas concentration on the laminar characteristic time. With the new submodel, agreement with the experiment has been improved considerably for all cases considered in this study. These levels of agreement between experiment and computations are similar to those found in previous applications of the laminar and turbulent characteristic-time combustion submodel to four-stroke engine combustion. Further improvement of the combustion submodel was made difficult by the observed coupling between the in-cylinder flow-field and the combustion-model details at low delivery ratios.