Study On Combustion And Particulate Matter Components For A Diesel Engine Fueled With Blending Biodiesel

With the gradually prominent energy crisis and air pollution problems, more and more researchers in internal combustion engine field are engaged in the finding of clean alternative fuels and the improvement of engine efficiency and emissions. Among the alternative fuels, biodiesel is very promising for the reason that it can be mixed with diesel easily and the blending can be used directly without changing the main parameters of the engine. The intention of this paper is to explore the changes of combustion and exhaust particle composition when the engine is fueled with diesel and blending biodiesel and offer a theoretical guidance to the spread and application of biodiesel in the engine. An experimental study was carried out on a single cylinder four stroke air-cooled diesel engine and the effects of biodiesel on combustion characteristics of the engine and particle properties, including particle composition, gravimetric characteristics and elements distribution,were explored by using combustion analyzer, Gas Chromatography-Mass Spectrometer(GC-MS), Thermal Gravimetric Analyzer(TGA) and Energy Dispersive Spectrometer(EDS) respectively.Firstly, the fuel properties including fuel composition, density and viscosity were measured by GC-MS, densitometer and viscometer respectively. The cetane number and calorific value of biodiesel were estimated by analyzing the composition of biodiesel.Results showed that, the main components of biodiesel including methyl oleate, methyl hexadecanoate, methyl stearate and the mass fraction were 62.78%, 28.15% and 6.48%respectively. Moreover, the viscosity and cetane number of biodiesel are slightly higher than diesel while the calorific value of biodiesel is slightly lower than diesel.Secondly, the indicator diagrams of engine fueled with different blending biodiesel were measured and analyzed by using cylinder pressure sensor and combustion analyzer.Results showed that, with the increase of biodiesel blending percentage, the maximum value of explosive pressure, peak pressure rise rate and heat release rate increased, thepressure curve moved forward. Moreover, the peak heat release rate of diffusion combustion increased while the peak heat release rate of premixed combustion decreased.The ignition delay decreased, and the combustion duration increased along with the biodiesel blending increased.Thirdly, the particle matter emitted from diesel engine were collected by using Micro-Orifice Uniform Deposition Impactor(MOUDI). The Soxhlet extraction was used to extract the Soluble Organic Fractions(SOF) from particle matter into the solution. Then,the GC-MS was used to study the components of the SOF. Results showed that, the mass fractions of SOF in the particle matter were 29.32%, 32.08%, 34.26% and 35.67%respectively when the engine was fueled with B0, B5, B10, B20. The main components of SOF were alkanes, acids, esters, phenols and PAHs. With biodiesel percentage increasing,the alkanes, phenols and PAHs decreased, acids and esters increased and the carbon atoms of SOF decreased.Finally, the thermogravimetric characteristics and elements distribution were explored. The thermogravimetric characteristics curve under nitrogen atmosphere exhibited three status, namely first smooth, then stiff and finally smooth with the temperature range of 50℃ to 500℃. Most of the Volatile Organic Compounds(VOCs) in the particle matter volatilized under the temperature rage of 150℃ to 350℃ and the mass of particle get stable when the temperature reached 500℃. When the atmosphere changed to oxygen, the gravimetric characteristics curve exhibited with steps and the corresponding two peak mass loss rate of differential derivative thermogravimetric curve appeared at the temperature range of 180℃ to 200℃ and 500℃ to 600℃.With biodiesel percentage increasing, the mass loss rate of particle matter increased and the start point of mass loss moved forward.The ignition temperature of the particle matter decreased when fueled with blending biodiesel. The main elements in the particle matter are C, O, Fe, Al, Si, S, and a little K, Ca, Ba, Au.