Browse Publications Technical Papers 2015-24-2418

Comparison of the Lift-Off Lengths Obtained by Simultaneous OH-LIF and OH* Chemiluminescence Imaging in an Optical Heavy-Duty Diesel Engine 2015-24-2418

The presence of OH radicals as a marker of the high temperature reaction region usually has been used to determine the lift-off length (LOL) in diesel engines. Both OH Laser Induced Fluorescence (LIF) and OH* chemiluminescence diagnostics have been widely used in optical engines for measuring the LOL. OH* chemiluminescence is radiation from OH being formed in the exited states (OH*). As a consequence OH* chemiluminescence imaging provides line-of-sight information across the imaged volume. In contrast, OH-LIF provides information on the distribution of radicals present in the energy ground state. The OH-LIF images only show OH distribution in the thin cross-section illuminated by the laser. When both these techniques have been applied in earlier work, it has often been reported that the chemiluminescence measurements result in shorter lift-off lengths than the LIF approach. In order to investigate this discrepancy this work presents a dedicated comparison of the LOL obtained from these two diagnostic techniques. In diesel engines, the cycle-to-cycle variations in lift-off region are usually significant. To avoid misinterpretations caused by these variations simultaneous measurements are needed. The statistical analysis based on our simultaneous data can conclude that the OH-LIF method yields longer LOL than the OH* chemiluminescence method by a smaller sample size and more precisely than non-simultaneous data. This can be partially explained by the 3D geometry and flame axis asymmetry effects. A numerical simulation with OH and OH* distribution was performed for the comparison. It shows a great agreement with the experimental results in this study.


Subscribers can view annotate, and download all of SAE's content. Learn More »


Members save up to 18% off list price.
Login to see discount.
Special Offer: Download multiple Technical Papers each year? TechSelect is a cost-effective subscription option to select and download 12-100 full-text Technical Papers per year. Find more information here.
We also recommend:

Multi-Species Laser-Based Imaging Measurements in a Diesel Spray


View Details


Calibration of an RGB, CCD Camera and Interpretation of its Two-Color Images for KL and Temperature


View Details


Numerical Spray Modeling for Ultra Low Cost (ULC) Gasoline Engine


View Details