Researches On The Measurement Of Equivalence Ratios Of Mixed Combustion Gases Based On Laser-induced Breakdown Spectroscopy

Equivalence ratio is a very important parameter of mixed combustion gasessystem.The raal-time and accurate measurement of equivalence ratio is very important.Laser induced breakdown spectroscopy（LIBS）is a method that can require theelemental information of the material by analysis of the emission speetroseopy of theplasma. It has manyadvantages, such as simple experiment system and fast operation,and it has been applied in laser ignition, measurement of equivalence ratio in engine. Inthis subject, the experimental research and theory analysis on the measurement ofequivalence ratio of the mixed combustion gases was presented.In this thsis, the research progress of LIBS and LIBS on measurement ofequivalence ratio was introduced firstly. Based on the two hypothesis:that plasma isoptical thin and Local thermodynamic equilibrium, the calculation model of electrontemperature was established. And then based on the theory of atomic spectrum, therelationship of line intensity ratio and equivalenceratio of mixed gas was calculated. thecalculation model of the measurement of equivalence ratio based on LIBS wasestablishedOn experiment, the LIBS experiment platform was build sing this experimentequipment, we acquired the plasma speetroseopy of nitrogen, oxygen and methane,under the pressure is2×104Pa and the laser energy is40mJ. Using the calculation model,we acquired the electron temperature of the three gases:33100K,13600K,20700K.Then the electron temperature of nitrogen with different pressure（2×104Pa-1×105Pa）and different laser energy（20mJ-100mJ）was analysised. The phenomenon thatpressure and laser energy have no impact on electron temperature. The electrontemperature of nitrogen keeps33000K or so.In the premixed flame of nitrogen, oxygen, methane, the plasma spectrum of theflame with different equivalence ratio（0.5-1.5）at different laser pulse energy（3-7mJ）was measured, with the concentration of oxygen is constant（50%）. Also, the plasmaspectrum of the flame with different equivalence（0.5-1.5） at different concentration ofoxygen （21%-50%）was measured,, with the laser pulse energy is constan（t5mJ）.ThenThe relationship between the intensity ratio of H, O and equivalence ratio wereobtained. The effect of laser pulse energy and concentration of oxygen on the relationshipbetween the intensity ratio and equivalence ratio were analysisied. It reveals that therelationship between the intensity ratio and equivalence ratio is linear, and the laserpulse energy and concentration of oxygen have no effect on the relationship.