| Resource & environmental sciences |
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| Measurement and analysis of diesel exhaust particulates based on light scattering |
| LU Yeqiang, SHI Yunbin, SUN Zai, SONG Yijin, LOU Xiaochun |
| 1. College of Youth Automotive, Hangzhou Vocational & Technical College, Hangzhou 310018, China; 2. College of Mechanical and Electrical Engineering, China Jiliang University, Hangzhou 310018, China |
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Abstract Due to the characteristics of mixture formation and combustion of diesel engine, it has far higher tail gas particulate matter (PM) emissions than those of gasoline engine. It has been proved that soluble organic fractions (SOF) adsorbed on the PM surface of diesel engine are mutagenic. More than 90% of the components are carcinogens. Therefore, PM emissions have become an important factor restricting the popularization and application of diesel engine vehicles. To analyze and test PMs in diesel engine tail gas (DETG) also becomes a hot spot in current research. PMs in DETG mainly include carbon smoke (C), SOF, sulfate (SO4) and ash, which account for 40%—50%, 35%—45%, 5%—10% and 3%—6% in PMs respectively. According to a physicochemical analysis of PMs in DETG, PMs are very tiny and complicated, containing volatile components and heavy metals. This raises higher requirements for the reliability, self-purification and anti-interference of PM testers. To measure PMs using light scattering method (LSM) is a non-contact modern photoelectric measurement technique and has the advantages of real-time, online and harmless to sample, etc. It is superior in the diameter spectrum analysis and concentration measurement of PMs in DETG. The diameter ranges from 1 to 10 000 No./cm3. PM concentration, though very low in emissions, can be measured. The counting efficiency of (41±1) nm PM was 90% or more and the counting precision was ±10%. Based on this, this article proposes to measure diameter spectrum and concentration of PMs in DETG, using LSM. By calculating the numerical relationship between parameters like dimensionless parameter x, acceptance angle of scattered light θ, diameter D and intensity of scattered light Is, as well as the numerical relationship between acceptance solid angle of scattered light β and flux F, this article obtained a theoretical basis for measuring diameter and concentration of PMs in DETG using LSM. 1) With the increase of D, Is increased significantly and the distribution fluctuated more drastically with θ. In a certain scattering angle, Is and D were no longer proportional and corresponding to each other. It was required to measure Is in multiple angles and calculate the diameter spectrum; 2) F near the acceptance range of 90° scattered light and relative volume D3 of particles had a good linear relationship. By measuring F, the volume concentration of particles can be obtained. Meanwhile, by selecting acceptance solid angle of scattered light β=30°, a good measurement effect can be achieved. According to the above conclusion, a diameter spectrum and concentration tester for PMs in DETG based on LSM was developed. This tester was composed of sampling probe, flow meter, water filter, PM filter, pump, dilute air duct, heating device, photoelectric detector, IPC and on-off valve, etc. The working process was to pump air into a dilute channel and heating device, through flow meter, water and PM filter, dilute and heat the tail gas to be tested, analyze and test the diameter distribution of PMs in DETG in ideal state. This tester conducted an experiment by measuring the diameter distribution of DETG. By comparing with precision testing instrument, from the measured data, this tester had better consistency than precision testing instrument. It was more advanced and practical. By analyzing the physicochemical characteristics of PMs in DETG and the numerical relationship between all parameters, intensity of scattered light Isand flux F, the following conclusions are drawn: 1) The correctness and feasibility to measure diameter spectrum and concentration of PMs in DETG using LSM are analyzed theoretically; 2) According to the above principle, a diameter spectrum and concentration tester for PMs in DETG is designed; 3) By comparing the experimental results, this tester has the advantages of real-time, online and harmless to sample, etc.
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Published: 20 May 2016
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基于光散射法柴油发动机尾气颗粒测试分析
通过计算无因次参量(x)、散射光接收角(θ)、粒径(D)等参量和散射光强(Is)之间的数值关系,以及散射光接收立体角β和散射光通量(F)之间的数值关系,得到光散射法测量柴油发动机尾气颗粒粒径谱和单位体积中颗粒含量的理论依据。1) 随着D的增大,Is显著增加并且分布随θ波动越大,某一散射角内Is与D之间不再具有成正比的一一对应关系,需测量多角度内Is而计算得到颗粒粒径谱;2)90°散射光接受范围附近光通量F与颗粒的相对体积D3参数具有很好的线性关系,通过测量F可得到颗粒单位体积的含量,并且选取散射光接收立体角β =30°,能够取得很好的测量效果。依据上述结论设计的测量装置用于柴油发动机台架的尾气粒径分布测量实验，并将该测量装置用于柴油发动机的尾气粒径分布的实际对比测试实验,结果表明该测量装置稳定性、实用性好，测量精度高,并具有实时、在线、不损坏样品等优点。
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