Predicting NOX Emissions from HCCI Engines Using LIF Imaging 2006-01-0025
Our previous work applied LIF measurements of in-cylinder fuel distribution to predict CO2, CO, and HC emissions from an HCCI engine under low-load stratified-charge conditions. The prediction method is based on the premise that local fuel-air packets at a given equivalence ratio (characterized using LIF imaging) burn as if in a homogeneous charge at the same equivalence ratio. Thus, emissions measured during homogeneous operation provide an emission-versus- equivalence-ratio look-up table for predicting stratified-charge emissions.
The present paper extends the technique to predict engine-out NOX emissions. Because of operating-range limitations, NOX look-up data for homogeneous operation cannot adequately be determined by experiment. Instead, a CHEMKIN-based model provides this look-up table data instead. The model is validated against pressure traces measured at low equivalence ratios where experiments are possible, and then extended to higher equivalence ratios, to determine NOX emissions at these conditions. The NOX look-up table is then combined with LIF fuel-distribution measurements to predict NOX emissions during stratified-charge operation. The predicted NOX trends compare well with corresponding measurements. This paper goes on to postulate in-cylinder fuel distributions that can provide both high efficiency and low NOX emissions.