Laser-induced breakdown spectroscopy for on-line engine equivalence ratio measurements

Area of Science:

• Spectroscopy
• Combustion Analysis
• Optical Diagnostics

Background:

• Accurate measurement of engine equivalence ratio is crucial for performance and emissions control.
• Laser-induced breakdown spectroscopy (LIBS) offers a non-intrusive method for elemental and molecular analysis.

Purpose of the Study:

• To investigate the feasibility of using LIBS for quantifying the equivalence ratio in a spark-ignited engine.
• To evaluate spectral features for accurate measurements and assess the impact of engine operating conditions.

Main Methods:

• Utilized LIBS to analyze spectral emissions from C, O, N, and CN species in engine exhaust.
• Correlated spectral peak ratios (C/N, C/O, CN/air) with equivalence ratio (φ = 0.8–1.2).
• Compared LIBS measurements with a standard exhaust gas oxygen analyzer.

Main Results:

• C/N and C/O peak ratios demonstrated success in averaged measurements, correlating well with the exhaust gas oxygen analyzer.
• Single-shot CN/air ratio measurements agreed well with averaged data, despite higher scatter at lower equivalence ratios.
• Measurements showed slight sensitivity to engine load, potentially due to pressure or particle size variations.

Conclusions:

• LIBS is a viable technique for measuring engine equivalence ratio in laboratory settings.
• Spectral ratios of C, O, N, and CN provide effective metrics for equivalence ratio quantification.
• Further investigation is needed to mitigate load-dependent variations for robust real-time engine monitoring.