Imaging gas in a combustion engine with high-energy X-ray Compton scattering

We have developed a time-resolved Compton-scattering imaging technique for visualizing gas behaviours in operating internal combustion engines. This technique employs a digital processing system to record both the pulse height and the timing of detected X-rays, enabling the derivation of Compton-scattered X-ray spectra for each crank angle, which corresponds to the piston position. The observed crank-angle dependency of Compton-scattered X-ray intensity allowed us to successfully capture the density changes of the gas in the combustion chamber associated with piston motion and combustion. In addition, the capability of temperature estimation is discussed with a combination of X-ray Compton-scattering experiments and pressure measurements. This study demonstrates that time-resolved Compton-scattering imaging is a powerful and unique technique for characterizing gas behaviours in an operating internal combustion engine.