Application and assessment of background oriented Schlieren for laminar burning velocity measurements

Schlieren imaging has been established as a reliable optical measurement technique for flame visualizations and retrieval of laminar burning velocity information. However, it is off limited capability and adaptability due to the optical configuration of a conventional Schlieren setup. In this regard, background oriented Schlieren (BOS) provides a unique opportunity to quantitatively characterize density varying flows by means of an inexpensive and uncomplicated setup. BOS is here demonstrated as an alternative approach for flame visualization in a Bunsen burner and to perform laminar burning velocity measurements of methane (CH4)/air mixtures. The results obtained with a variety of flame front reconstruction approaches are compared with direct chemiluminescence imaging, 1D numerical simulations using the GRI3.0 combustion mechanism and experimental data from literature for which significant agreements are documented. The BOS technique extends the capabilities of Schlieren imaging and its ability to visualize flame structures of low luminescence, e.g. burning hydrogen or diluted mixtures under flameless conditions, makes it applicable for studies of combustion concepts aimed at reducing CO2 emissions. •Optical techniques for Laminar burning velocity (LBV) measurements are valuable.•Background oriented Schlieren (BOS) can provide high-fidelity data with low complexity.•The application of BOS for LBV measurements of CH4/air is assessed.•BOS provided a good match with reference results and available data in the literature.•BOS enables visualization of reactive flows of low luminescence or with high dilution.