Ramachandra Diwakar

Effect of drop breakup on fuel sprays

Recently developed computer models are being applied to calculate complex interactions between sprays and gas motions. The three-dimensional KIVA code was modified to address drop breakup and was used to study fuel sprays. The results show that drop breakup influences spray penetration, vaporization and mixing in high pressure sprays. The spray drop size is the outcome of a competition between drop breakup and drop coalescence phenomena, and the atomization details at the injector are lost during these size rearrangements. Drop breakup dominates in hollow-cone sprays because coalescence is minimized by the expanding spray geometry. The results imply that it may be possible to use a simple injector and still control spray drop size and vaporization if the flow details are modified so as to enhance drop breakup and coalescence.

Analysis of Mixing and Thermal Effects on Low-Temperature Combustion in IC Engine Operation

The effects of thermal and mixing conditions of the in-cylinder charge in internal combustion (IC) engines on emissions in low-temperature combustion (LTC) regimes are analyzed numerically. In the analysis, concepts of an equilibrium temperature (Teq), peak temperature (Tpeak), and anticipated emissions (AE) are introduced. Also, mixture condition representations in temperature (T) vs. temperature (T) space (called T − T plot) and anticipated emissions (AE) vs. temperature (T) space (called AE − T plot) are proposed to represent the in-cylinder mixture quality and emission characteristics of the combustion. Five combustion pathways are identified using a Tpeak − Teq plot, and it is applied to describe both HCCI and DI engine combustion. An optimal temperature window and an optimal mixing window are defined and demonstrated in LTC engine operation. The results show that stratification of mixture temperature due to evaporation cooling and wall heat transfer significantly affects UHC/CO emissions of LTC engine operation. The T − T and AE − T plots reveal information about mixture inhomogeneity, completeness of burning of local mixtures, anticipated levels of emissions, and optimal timing of mixing that can maximize improvements in emissions. The new method of analysis is useful to identify and understand the evolution of in-cylinder mixture conditions in engine combustion.