Temperature measurements under diesel engine conditions using laser induced grating spectroscopy

Crank angle-resolved temperatures have been measured using laser induced grating spectroscopy (LIGS) in a motored reciprocating compression machine to simulate diesel engine operating conditions. A portable LIGS system based on a pulsed Nd:YAG laser, fundamental emission at 1064nm and the fourth harmonic at 266 nm, was used with a c.w. diode-pumped solid state laser as probe at 660 nm. Laser induced thermal grating scattering (LITGS) using resonant absorption by 1-methylnaphthalene, as a substitute fuel, of the 266 nm pump-radiation was used for temperature measurements during non-combusting cycles. Laser induced electrostrictive grating scattering (LIEGS) using 1064nm pump-radiation was used to measure temperatures in both combusting and non-combusting cycles with good agreement with the results of LITGS measurements which had a single-shot precision off 15K and standard error of +/- 1.5 K. The accuracy was estimated to be 3 K based on the uncertainty involved in the modified equation of state used in the derivation from the LIGS measurements of sound speed in the gas. Differences in the in-cylinder bulk gas temperature between combusting and non-combusting cycles were unambiguously resolved and temperatures of 2300 +/- 100K, typical of flames, were recorded in individual cycles. The results confirm the potential for LIGS-based thermometry for high-precision thermometry of combustion under compression-ignition conditions. (C) 2018 The Authors. Published by Elsevier Inc. on behalf of The Combustion Institute. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/)