Publications

The high-level objective of this project is to solve national-s ecurity problems associated with petroleum use, cost, and environmental impacts by enabling more efficient use of natural-gas-fueled internal co mbustion engines. An improved sci ence-base on end-gas autoignition, or "knock," is re quired to support engineering of more efficient engine designs through predictive modeling. An existing optical diesel engine facility is retrofitted for natural gas fueling with laser-spark-ignition c ombustion to provide in- cylinder imaging and pressure data under knocking combustion. Z ero-dimensional chemical-kinetic modeling of aut oignition, adiabatically constr ained by the measured cylinder pressure, isolates the role of autoignition chemistry. OH* chemiluminescence imaging reveals six different c ategories of knock onset that de pend on proximity to engine surfaces and the in-cylinder deflagration. Modeling resu lts show excellent prediction regardless of the knoc k category, thereby validating state-of-the-art kinetic mechanisms. The results also provide guidance for future work t o build a science base on the factors that affect the deflagration rate.

In this LDRD project, we developed a capability for quantitative high - speed imaging measurements of high - pressure fuel injection dynamics to advance understanding of turbulent mixing in transcritical flows, ignition, and flame stabilization mechanisms, and to provide e ssential validation data for developing predictive tools for engine combustion simulations. Advanced, fuel - efficient engine technologies rely on fuel injection into a high - pressure, high - temperature environment for mixture preparation and com bustion. Howe ver, the dynamics of fuel injection are not well understood and pose significant experimental and modeling challenges. To address the need for quantitative high - speed measurements, we developed a Nd:YAG laser that provides a 5ms burst of pulses at 100 kHz o n a robust mobile platform . Using this laser, we demonstrated s patially and temporally resolved Rayleigh scattering imaging and particle image velocimetry measurements of turbulent mixing in high - pressure gas - phase flows and vaporizing sprays . Quantitativ e interpretation of high - pressure measurements was advanced by reducing and correcting interferences and imaging artifacts.