In-cylinder temperature measurements are vital for the validation of gasoline engine modelling and useful in their own right for explaining differences in engine performance. The underlying chemical reactions in combustion are highly sensitive to temperature and affect emissions of both NO_x and particulate matter. The two techniques described here are complementary, and can be used for insights into the quality of mixture preparation by measurement of the in-cylinder temperature distribution during the compression stroke. The influence of fuel composition on in-cylinder mixture temperatures can also be resolved. Laser Induced Grating Spectroscopy (LIGS) provides point temperature measurements with a pressure dependent precision in the range 0.1 to 1.0% when the gas composition is well characterized and homogeneous; as the pressure increases the precision improves. The well-established method of Two-Colour Planar Laser-Induced Fluorescence, TC-PLIF allows 2-D temperature distributions to be determined from measurement of fluorescence signals at two different wavelengths. However, the challenge with PLIF is making the qualitative temperature measurements quantitative, so simultaneous LIGS measurements have been used for in situ calibration.
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