We report the first application of a vertical-cavity surfaceemitting laser (VCSEL) for calibration- and sampling-free, high-speed, in situ H2O concentration measurements in IC engines using direct TDLAS (tunable diode laser absorption spectroscopy). Measurements were performed in a single-cylinder research engine operated under motored conditions with a time resolution down to 100 μs (i.e., 1.2 crank angle degrees at 2000 rpm). Signal-to-noise ratios (1σ) up to 29 were achieved, corresponding to a H2O precision of 0.046 vol.% H2O or 39 ppm · m. The modulation frequency dependence of the performance was investigated at different engine operating points in order to quantify the advantages of VCSEL against DFB lasers.

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Instantaneous two-dimensional measurements of reaction rate, mixture fraction, and temperature are demonstrated in turbulent partially premixed methane/air jet flames. The forward reaction rate of the reaction CO ‫ם‬ OH ⇒ CO 2 ‫ם‬ H is measured by simultaneous OH laser-induced fluorescence (LIF) and two-photon CO LIF. The product of the two LIF signals is shown to be proportional to the reaction rate. Temperature and fuel concentration are measured using polarized and depolarized Rayleigh scattering. A three-scalar technique for determining mixture fraction is investigated using a combination of polarized Rayleigh scattering, fuel concentration, and CO LIF. Measurements of these three quantities are coupled with previous detailed multiscalar point measurements to obtain the most probable value of the mixture fraction at each point in the imaged plane. This technique offers improvements over two-scalar methods, which suffer from decreased sensitivity around the stoichiometric contour and biases in fuel-rich regions due to parent fuel loss. Simultaneous reaction-rate, mixture-fraction, and temperature imaging is demonstrated in laminar (Re ‫ס‬ 1100) and turbulent (Re ‫ס‬ 22,400) CH 4 /air (1/3 by volume) jet flames. The turbulent jet flame is the subject of multiple numerical modeling efforts. A primary objective for developing these imaging diagnostics is to provide measurements of fundamental quantities that are needed to accurately model interactions between turbulent flows and flames.

An investigation of the interaction between the in-cylinder flow and the spray topology in two spray-guided direct injection optical engines is reported. The bulk flow field in the combustion chamber is characterized using particle image velocimetry. Geometrical parameters such as the axial penetration and the spray angle of the liquid spray are measured using Mie scatter imaging and/or diffuse back-illumination. The measured parameters are compared with data from a constant volume chamber available in the literature. For a late injection strategy, the so-called ECN Spray G standard condition, the mean values of the spray penetration do not seem to be significantly perturbed by the in-cylinder flow motion until the plumes approach the piston surface. However, spray probability maps reveal that cycle-to-cycle fluctuations of the spatial distribution of the liquid spray are affected by the magnitude of the in-cylinder flow. Particle image velocimetry during injection shows that the flow field in the vicinity of the spray plumes is heavily influenced by air entrainment, and that an upward flow in-between spray plumes develops. Consistent with previous research that demonstrated the importance of the latter flow structure for the prevention of spray collapse, it is found that increased in-cylinder flow magnitudes due to increased intake valve lifts or engine speeds enhance the spray-shape stability. Compared with cases without injection, the influence of the spray on the in-cylinder flow field is still noticeable approximately 2.5 ms after the start of injection.

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