Concentration measurement of injected gaseous fuel using quantitative schlieren and optical tomographyEmishaw D. Iffa, A. Rashid A. Aziz and Aamir S. MalikJ. Eur. Opt. Soc.-Rapid Publ., 5 (2010) 10029DOI: https://doi.org/10.2971/jeos.2010.10029