High Resolution Scalar Dissipation Measurements in an IC Engine 2009-01-0662

The ability to make fully resolved turbulent scalar field measurements has been demonstrated in an internal combustion engine using one-dimensional fluorobenzene fluorescence measurements. Data were acquired during the intake stroke in a motored engine that had been modified such that each intake valve was fed independently, and one of the two intake streams was seeded with the fluorescent tracer. The scalar energy spectra displayed a significant inertial subrange that had a −5/3 wavenumber power dependence. The scalar dissipation spectra were found to extend in the high-wavenumber regime, to where the magnitude was more than two decades below the peak value, which indicates that for all practical purposes the measurements faithfully represent all of the scalar dissipation in the flow. The scalar energy and scalar dissipation spectra were found to agree quite well with Pope’s model spectrum at all but the highest wavenumbers where the effects of random noise (dominated by shot noise) overwhelms the measurement. The wavenumber where the dissipation reaches 2% of the peak value was used to estimate the Batchelor scale. The measured range of Batchelor scale, encompassing a range of engine speeds from 300–1800 rpm and intake pressures from 54–109 kPa, was 20–42μm. The measurements required high spatial resolution and high signal-to-noise ratios, and the experimental efforts required to achieve this are discussed in detail. A set of parametric investigations was performed by varying the intake flow conditions. The results follow an expected trend, but the quantitative scaling with Reynolds number was incorrect, suggesting that the definition of the characteristic Reynolds number has to be considered carefully.