Measurement of Hydrogen Jet Equivalence Ratio using Laser Induced Breakdown Spectroscopy

Hydrogen exhibits the notable attribute of lacking carbon dioxide emissions when used in internal combustion engines. Nevertheless, hydrogen has a very low energy density per unit volume, along with large emissions of nitrogen oxides and the potential for backfire. Thus, stratified charge combustion (SCC) is used to reduce nitrogen oxides and increase engine efficiency. Although SCC has the capacity to expand the lean limit, the stability of combustion is influenced by the mixture formation time (MFT), which determines the equivalence ratio. Therefore, quantifying the equivalence ratio under different MFT is critical since it determines combustion characteristics. This study investigates the viability of using a Laser Induced Breakdown Spectroscopy (LIBS) for measuring the jet equivalence ratio. Furthermore, study was conducted to analyze the effect of MFT and the double injection parameter, namely the dwell time and split ratio, on the equivalence ratio. Simultaneously, the structural characteristics of the jet were examined within a constant volume chamber to assess the accuracy of the measurement results. The findings indicate that, as MFT lengthens, the width of the jet also increases. This leads to decrease in equivalence ratio in the center of the jet due to enhanced dispersion effects. A decrease in the proportion of first injection and an increase in dwell time lead to jet contraction, resulting in higher local equivalence ratio measured in the center of the jet. The measurement findings of equivalence ratio, integrated with the analysis of the jet, contribute to an increased reliability of LIBS results. Furthermore, these findings reveal the potential for achieving hydrogen lean stratification. This should make a significant contribution towards the advancement of hydrogen engines in the pursuit of achieving carbon neutrality.