Quantitative measurements of fuel concentrations in direct-injection methanol-n-hexane sprays by laser induced breakdown spectroscopy

Abstract

Methanol is considered to be one of promising alternative fuels, and direct-injection (DI) of methanol-gasoline blends is attracting more and more interest due to the thermal efficiency advantages. However, quantitative measurements of component concentrations in DI methanol-gasoline blend sprays are still difficult. In this study, a novel approach based on the laser induced breakdown spectroscopy (LIBS) is developed to quantitatively and simultaneously measure the gas concentrations of n-hexane and methanol in methanolgasoline blend sprays in a constant volume vessel. Firstly, the calibrations between peak intensity ratios (PIR) of H656/N745 and atomic number ratios (ANR) of H/N, and PIR of O777/N746 and ANR of O/N are established respectively for three kinds of fuels (M0, M50, M100). The results show a good consistency of calibration curves for different fuels and different ambient pressures, suggesting the potentials of LIBS to measure multi-component fuels even at varied-pressure conditions. Then, the high-speed shadowgraph and diffused back-illumination method are employed to simultaneously image the entire spray and the liquid phase, and therefore determine the LIBS measuring positions. Finally, the fuel concentration measurements in M0 and M15 sprays are conducted and the radial distribution and the effects of ambient pressure are investigated. It is found that the blending fraction in M15 spray is increased with the radial distance increasing due to the lower boiling temperature and higher vapor diffusivity of methanol. The equivalence ratios in both M0 and M15 sprays are reduced with the increased ambient pressure, which can be attributed to the larger air density while nearly constant entrainment speed at higher ambient pressure. These results are believed to be valuable for development of numerical models and design of DI combustion systems.

Machine Learning-Assisted Determination of C6H14 Mole Fraction From Molecular Emissions of Laser-Induced Hexane–Air Plasmas

“…6,33 Hexane is commonly used in these types of applications in the literature to generate relevant species of interest produced from the combustion of hydrocarbons. [34][35][36] For each data collection point, a different partial pressure of air was introduced into the chamber to mix with hexane. These quantities were monitored by a manometer gauge.…”