Crank-angle-resolved laser-induced fluorescence imaging of NO in a spark-ignition engine at 248 nm and correlations to flame front propagation and pressure release

Abstract

Inside the combustion chamber of a spark-ignition engine, NO fluorescence is excited with a narrow-band tunable KrF excimer laser. The fluorescence light is detected by an intensified CCD camera that yields images of the NO distributions. Rotational-vibrational transitions of NO are excited by the A(2)Σ+ ? X(2)Π (0, 2) band system around 248 nm. Single laser shot planar NO distributions are obtained with good signal-to-noise ratio at all crank angles and allow us to locate areas of NO formation during combustion. The pressure within the combustion chamber is measured simultaneously with the NO distributions, which allows the evaluation of correlations between indicated work and NO formation. The crank-angle-resolved sequences of two-dimensional NO distributions and averaged pressure traces are presented for different engine-operating conditions. In addition, laser-induced predissociation fluorescence of OH excited by the same laser source is measured in order to visualize the corresponding flame front propagation and to compare the time of formation of NO relative to that of OH.

Attenuation effects on imaging diagnostics of hollow-cone sprays

“…However, in addition to distortion of measured spray images by attenuation of the exciting laser light, the images can suffer further from nonuniform attenuation of the signal. As reported by Hildenbrand et al 4 and Knapp et al, 3 the attenuation can be wavelength dependent. Investigations of the effect of signal loss that is due to scattering or absorption therefore need to be carried out with a suitable wavelength resolution.…”

“…1 Optical measurements in engines require a careful examination of the optical properties of all processes and equipment involved, in particular when the measurement of absolute quantities is required. It has been shown in engine experiments that laser beam 2 and signal 3,4 attenuations have a significant influence, eventually perturbing or preventing investigations of extended areas within the cylinder or leading to significant misinterpretation of signal intensities. Many of the frequently used laser techniques rely on excitation and detection in the UV spectral region where absorption by transient combustion products such as polycyclic hydrocarbons is strong even at small concentrations.…”

Nitric-oxide planar laser-induced fluorescence at 10 kHz in a seeded flow, a plasma discharge, and a flame

“…Over the years, PLIF imaging of NO has been extensively carried out for many laboratory flames and practical combustion systems [31][32][33]. The results discussed here provide the demonstration of high-frequency NO-PLIF imaging as a diagnostic tool for optimization of both current and future propulsion and chemical-energy conversion systems.…”

Development of a Raman spectroscopy technique to detect alternate transportation fuel hydrocarbon intermediates in complex combustion environments.

“…For sooty flames, some researchers have taken advantage of the fact that unlike incandescence and fluorescence interference sources, Raman scattered light has very little depolarization from the incident light source. Separation techniques have been developed whereby both the parallel (p) and perpendicular (s) polarization components are simultaneously recorded, with the unfiltered incandescence/fluorescence removed using detailed information about the Raman emission spectrum depolarization ratio [42,43].…”