Study On The Gas Concentration Measurement Based On Laser Spontaneous Vibration Raman Scattering

With the development of the automotive industry, the total vehicle population isincreasing. It not only caused serious environmental pollution, but also triggered aseries of energy issues. Currently, the auto energy saving and emission reducing hasbecome a problem can not be ignored, got more and more attention. However, inorder to achieve this goal, simply rely on emissions regulations and policy constraintsis not enough, new breakthroughs must be achieved technically. This is thefundamental way to solve this problem. The new type of internal combustion enginecombustion mode has brought new hope for solving this problem in recent years, suchas the CAI combustion mode which has a very significant effect in two aspects ofenergy saving and emission reducing. However, the engine closed structure bringsgreat difficulties to the study of the cylinder combustion process of new combustionmode. So we need a new test technology to obtain the in-cylinder parametersaccurately. The laser testing technology is a very new testing method, currently, Theapplication is very extensive, it has important significance especially in the internalcombustion engine laser diagnostics and engine in-cylinder visualization, andprovided a powerful driving force for the research of the engine. This technology isthe hot research disciplines currently.The laser technology for laser testing method of spontaneous Raman scatteringtest technology has been researched in this paper, especially the laser spontaneousRaman measurement of gas concentrations. Raman scattering can not only analysisthe gas qualitatively, but also measure gas concentration quantitatively. In order tostudy the process of Raman measurement, we have finished a experiment, whichdivided into two parts, one is the sample pool Raman measurement experiment, theother part is the actual Raman measurements in the optical engine. First, weestablished a set of optical test systems, including the excitation light source, signalacquisition devices, pulse stretcher, and other auxiliary equipments, and the laserspontaneous Raman scattering measurement experiment was done in the sample pool.We measured and obtained the Raman spectroscopy of CO₂, N₂, O₂for differentconcentration ratio, analyzed its characteristics, found the Raman peak position ofeach gas, and then analyzed the law between the peak area, concentration andpressure changing. Calibrated the concentration and draw the calibration curve by analyzing the Raman spectroscopy of the gas in different pressure, and then verifiedthe calibration results by measuring another group of known concentration gas. Thepaper also build the optically accessible engine test platform and designed a set ofoptically accessible engine system, the system consists of two parts, Include theoptical engine and engine control systems, then do a laser Raman measurement on theoptical engine. The Raman spectra measured on the engine was not as good asmeasured in the sample pool, but the CO₂, O₂, N₂Raman peaks can be distinguished,too. After analyzing the Raman spectroscopy and calculating the gas Raman peak area,we can get the relative calibration factor according to the formula, calculate theconcentration ratio of CO₂and O₂, achieve the laser spontaneous Raman scatteringmeasurements in the optical engine.At the end of the paper, the data processing of spectrum was shown, includingsmoothing and baseline subtraction. Spontaneous Raman scattering signal is veryweak and can easily be disturbed by many factors, so the data processing is veryimportant. Besides, the paper also summarizes some errors, and explain someresponse measures. The errors are mainly caused by hardware, data processing, ICCDspectrometer grating and slit, CCD noise.