We present a novel method for low noise, high-speed, real-time spectroscopy to monitor molecular absorption spectra. The system is based on a rapidly swept, narrowband CW Fourier-domain mode-locked (FDML) laser source for spectral encoding in time and an optically time-multiplexed split-pulse data acquisition system for improved noise performance and sensitivity. An acquisition speed of ~100 kHz, a spectral resolution better than 0.1 nm over a wavelength range of ~1335-1373 nm and a relative noise level of ~5 mOD (~1% minimum detectable base-e absorbance) are achieved. The system is applied for crank-angle-resolved gas thermometry by H(2)O absorption spectroscopy in an engine motoring at 600 and 900 rpm with a precision of ~1%. Influences of various noise sources such as laser phase and intensity noise, trigger and synchronization jitter in the electronic detection system, and the accuracy of available H(2)O absorption databases are discussed.

A combined velocity and temperature measurement method using a high-speed camera, a pulsed UV laser, and temperature-sensitive phosphor particles is proposed. The temperature was calculated from the phosphorescence lifetime, while the velocity was obtained from images of the phosphor particles during a single decay. This method was applied to in-cylinder measurements of gas flow at high temperatures under motoring conditions. Tumble flow was observed at the top dead center. The temperature-change dependence on the crank angle agrees qualitatively with the gas temperature and the pressure.

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This paper details a new design for fiber-optic access to harsh environments, with a particular focus on absorption spectroscopy in high-temperature, high-pressure combustion systems.A key component is a fiber-fused rod lens assembly which tolerates temperatures above 1100 C and enables simple optical access without interferences from etalons or ambient absorbers. The fibers, rod lenses, and supporting ports are designed to provide line-of-sight optical access without the need for adjustable optomechanics. Fiber modal noise was minimized by actively aligning a photodiode to the multimode fiber's output facet, resulting in a shot-noise-limited SNR of 53 000 for the system.Index Terms-Absorption spectroscopy, modal noise analysis, optical fiber sensors.

In this study, in-cylinder flow has been measured using high speed PIV to investigate turbulent characteristics of in-cylinder flow and to give a guiding principle for optimization of intake port and combustion chamber for down sized boosted engine. To clarify turbulence characteristics which will affect combustion process in engines, decomposition method of turbulence component from instantaneous velocity are investigated. Since velocity spectrum in 1 cycle from intake to compression stroke has a specific frequency where slope of the spectrum changes, a time filtering method for turbulence decomposition is proposed using this specific frequency as a cutoff. A characteristic of turbulent kinetic energy extracted by the proposed method well represents the expected flow characteristics at each test condition and shows good correlation with combustion characteristics such as burning speed and geometry of flame front. The obtain results show that turbulent intensity is high at a vortex center of tumble flow, which suggests that a control of tumble flow was very important in design of a boosted engine.