Characteristics of unregulated emissions from biodiesel fuel with different mixing proportion

Abstract: As the alternative fuel of diesel, biodiesel has been applied widely. Apart from the regulated emissions like nitrogen oxides, hydrocarbon, carbon monoxide and particulate matter, the diesel engine produces unregulated emissions, such as carbonyl, mono-aromatic hydrocarbons, polycyclic aromatic hydrocarbons and metal particles in the process of burning biodiesel. These unregulated emissions can be further oxidized and polymerized into other substances. And the unregulated pollutants are important precursor of carbon smoke and nitrogen oxides. In order to realize the clean combustion of diesel engine, it's necessary to study the formation mechanism and emission characteristics of unregulated pollutants. According to the physical and chemical characteristics of the carbonyl and aromatic hydrocarbons, this paper chooses appropriate sampling method, sample pretreatment method and sample separation and determination method, adopts derivatization method and high performance liquid chromatography method to measure carbonyl, and uses activated carbon adsorption tube and gas chromatography/mass spectrometry to qualitatively and quantitatively analyze aromatic hydrocarbons. In a single-cylinder 186 diesel engine, this paper adopts biodiesel and blend fuel to carry out diesel engine bench test. The emission rule of carbonyl and aromatic hydrocarbons with different proportion under different condition is investigated. The ring number distribution characteristics of polycyclic aromatic hydrocarbon, and the gas phase and particle phase polycyclic aromatic hydrocarbons are emphatically analyzed in this paper. The results show that, the dinitrobenzene hydrazone sampling method combined with high-performance liquid phase chromatography technology can realize the rapid and accurate determination for 13 kinds of carbonyl compounds, and at the same time, the qualitative and quantitative analysis of aromatic hydrocarbon pollutants can be achieved by using activated carbon adsorption combined with gas chromatography-mass spectrometry. The carbonyl emissions of 3 fuels are not very different between the medium and low load condition; the total carbonyl emissions of BD0 and BD50 increase with the increase of load, yet the total carbonyl emission of BD100 decreases with the increase of load, and the total carbonyl emission of BD0 is higher than BD50 and BD100. In the whole load range, there is a big difference among the mono-aromatic hydrocarbon emissions for the 3 different fuels, and the mono-aromatic hydrocarbon emission of BD0 is the highest. Compared with diesel fuel, the polycyclic aromatic hydrocarbon emission can be reduced by 32% when the diesel engine is fueled with biodiesel fuel. There is a 'two-peak' characteristic under the low and high load operating conditions for gas phase polycyclic aromatic hydrocarbon, the hydrocarbon emissions are mainly derived from incomplete combustion when the diesel engine under the condition of low load, and the generation of aromatic hydrocarbon depends on the fuel cracking and subsequent oxidation rate under the high load condition. The distribution characteristics of polycyclic aromatic hydrocarbons for the 3 fuels are also different. Compared with BD0 fuel, the aromatic hydrocarbon concentration of BD100 decreases significantly, the emission concentration of naphthalene with 2 rings decreases by 37%, the emission of phenanthrene with 3 rings decreased by 27%, and the pyrene emission decreases by 33%. Obviously, biodiesel fuel is helpful to reduce the harm of polycyclic aromatic hydrocarbons to human body.