Single-laser-shot temperature measurements at a data rate of 1 kHz employing femtosecond coherent anti-Stokes Raman scattering (fs-CARS) spectroscopy of N(2) are demonstrated. The measurements are performed using a chirped-probe pulse to map the time-dependent frequency-spread dephasing of the Raman coherence, which is created by approximately 80-fs pump and Stokes beams, into the spectrum of the coherent anti-Stokes Raman scattering signal pulse. Temperature is determined from the spectral shape of the fs-CARS signal for probe delays of approximately 2 ps with respect to the pump-Stokes excitation. The accuracy and precision of the measurements for the 300-2400 K range are found to be approximately 1%-6% and approximately 1.5%-3%, respectively.

Femtosecond, two-photon-absorption laser-induced fluorescence (fs-TALIF) is employed to measure space-and time-resolved distributions of atomic hydrogen and oxygen in moderatepressure, non-equilibrium, nanosecond-duration pulsed-discharge plasmas. Temporally and spatially resolved hydrogen and oxygen TALIF images are obtained over a range of low-temperature plasmas in mixtures of helium and argon at 100 Torr total pressure. The high-peak-intensity, low-average-energy fs pulses combined with the increased spectral bandwidth compared to traditional ns-duration laser pulses provide a large number of photon pairs that are responsible for the two-photon excitation, which results in an enhanced TALIF signal. Krypton and xenon TALIF are used for quantitative calibration of the hydrogen and oxygen concentrations, respectively, with similar excitation schemes being employed. This enables 2D collection of atomic-hydrogen and -oxygen TALIF signals with absolute number densities ranging from 2 × 10 12 cm −3 to 6 × 10 15 cm −3 and 1 × 10 13 cm −3 to 3 × 10 16 cm −3 , respectively. These 2D images are the first application of TALIF imaging in moderatepressure plasma discharges. 1D self-consistent modeling predictions show agreement with experimental results within the estimated experimental error of 25%. The present results can be used to further the development of higher fidelity kinetic models while quantifying plasmasource characteristics.

No abstract

We discuss photolytic-interference-free, high-repetition-rate imaging of reaction intermediates in flames and plasmas using femtosecond (fs) multiphoton excitation. The high peak power of fs pulses enables efficient nonlinear excitation, while the low energy nearly eliminates interfering single-photon photodissociation processes. We demonstrate proof-of-principle, interference-free, two-photon laser-induced fluorescence line imaging of atomic hydrogen in hydrocarbon flames and discuss the method's implications for certain other atomic and molecular species.

Increasingly stringent US fuel economy regulation has emphasized the need for automotive engines to achieve greater levels of efficiency. Lean operation in spark ignition engines has demonstrated the ability to increase thermal efficiency, but this is typically accompanied by increased nitrogen oxides (NO x) emissions. Ultra-lean operation (λ > 2), however, has demonstrated increased thermal efficiency and the potential for significant reductions in NO x. Turbulent Jet Ignition (TJI) enables ultralean operation by utilizing radical turbulent jets emerging from a pre-chamber combustor as the ignition source for main chamber combustion in a spark ignition engine. This study seeks to better understand the interaction between the pre-chamber and main chamber combustion events, specifically the effect that particular TJI design parameters have on this interaction.