EFFECTS OF BIODIESEL CHEMICAL COMPOSITION ON THE CHEMICAL AND PHYSICAL PROPERTIES OF THE PRIMARY AND SECONDARY DIESEL PARTICULATE MATTER Ali Mohammad Pourkhesalian Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy School of Chemistry, Physics and Engineering Science and Engineering Faculty Queensland University of Technology 2015 To “Sahar” whose unconditional love opened my eyes to an entirely new world… Keywords Atmospheric Aging, Diesel Particulate Matter (DPM), Particle Number Concentration (PNC), Particle Size Distribution (PSD), Biodiesel, Fatty Acid Methyl Ester (FAME), Biodiesel Feedstocks, Fuel Chemical Composition, Fuel Physical Properties, Oxygen Content, Viscosity, Surface Tension, Carbon Chain Length, Unsaturation, Scanning Mobility Particle Sizer (SMPS), Differential Mobility Spectrometer (DMS), Volatilization Tandem Differential Mobility Analyzer (V-TDMA), Volatility, Count Median Diameter (CMD), DustTrak, , Reactive Oxygen Species (ROS), Volatility, Ultra Violet Light (UV), Ozone, Semi- volatile, Partitioning, Atmospheric Simulation. Effects of Biodiesel Chemical Composition on the Chemical and Physical Properties of the Primary and Secondary Diesel Particulate Matter i Abstract In recent years, there has been an increasing movement from conventional fossil diesel fuels to non-petroleum based fuels. Biodiesel is gradually finding its place as a reliable alternative to petrodiesel. However, a number questions remain unanswered in terms of the suitability of such fuels. This thesis investigated fresh and aged particulate matter emissions due to the combustion of biodiesel. Moreover, this study investigated the influence of the above mentioned parameters on the potential toxicity of diesel particulate matter, by measuring its reactive oxygenated species content. In order to achieve the above aim, a number of biodiesel fuels with controlled chemical composition were tested in a modern diesel engine. The biodiesels tested in this manuscript were chosen in such a way so that it was possible to assign a change in the physio-chemical properties of the emitted diesel particulate matter to a specific chemical characteristic of the biodiesel used. The engine ran on neat biodiesel, as well as blends of biodiesel and petrodiesel, and the diesel exhaust was sampled and diluted using a multi-stage diluter system. Then, the diluted and cooled diesel exhaust was guided to a flow-through reactor, where the diesel exhaust was mixed with high concentrations of ozone and irradiated with ultra-violet light for a short time. A variety of physical and chemical properties of the particles inside the chamber were continuously monitored using different instruments and techniques. Experimental measurements showed that the diesel particulate matter emitted by different biodiesels was different in terms of both its physical properties and chemical composition, depending upon its fatty acid methyl ester composition. For example, particle matter mass concentration increased with an increase in the carbon chain length and degree of unsaturation of the fuel. Short-chain saturated biodiesels caused the lowest particulate matter emissions; as well particles due to such fuels smaller in terms of median diameter. It was shown that NOx emissions due to biodiesel could be reduced by controlling the composition of the fatty acid methyl esters in biodiesel. Particle emissions decreased linearly with the oxygen content of the blends regardless of the type and percentage of biodiesel in the blends. However, iiEffects of Biodiesel Chemical Composition on the Chemical and Physical Properties of the Primary and Secondary Diesel Particulate Matter since the fuel oxygen content weight ratio increased with decreasing carbon chain length, it was not clear which of these factors was responsible for the reduction in PM emissions. Further, particle emissions decreased linearly with reductions in the viscosity and surface tension of the fuel, but only for specific blends; nevertheless significantly different particulate matter emissions were observed for various blends with the same viscosity and surface tension. It was found that the volatility and oxidative potential of particles depended upon the fatty acid methyl ester carbon chain length of the biodiesel fuel. Particles emitted from the combustion of short-chain-saturated biodiesel were found to have a higher fraction of volatile organic substances adsorbed onto them, leading to higher reactive oxygen species emissions. The particles overall volatility and reactive oxygenated species correlated exponentially with the oxygen content of the blend, which could either be due to a reduction in soot onto which the volatiles condense, or an actual increase in the amount of volatile materials. However, the exponential relationship observed between overall volatility and reactive oxygen species indicated a combination of both effects. These results further highlighted the importance of fatty acid methyl ester composition on the toxicity of particles emitted from biodiesel combustion. In addition, they also challenge the effectiveness of current mass and number based emission standards in addressing the health effects of diesel particulate matter, while reinforcing the importance of more inclusive emission standards. Analyzing the results from the experimental campaigns showed that the chemical composition of the fuel not only affected primary emissions, but it also had an effect on secondary emissions. Saturated fuels, which emitted less particulate matter, also emitted more volatile particulate matter and significantly more semi- volatiles in the gas phase. The volatile and semi-volatile fractions had the potential to partition between the gas phase and particle phase upon aging. Aged particles from more saturated fuels with higher oxygen content had a higher oxidative potential as expressed through the increase of reactive oxygenated species concentration. It is apparent from the findings of this study that the chemical characteristics of different biodiesel fuels may be more important than its physical properties, in terms of particulate matter emissions and particulate toxicity. They also suggest the introduction of new standards, and alteration of existing regulations to categorize Effects of Biodiesel Chemical Composition on the Chemical and Physical Properties of the Primary and Secondary Diesel Particulate Matter iii biodiesel fuels based on their fatty acid methyl ester profile. To be able to exploit the benefit of biodiesel and avoiding potential harms, it is also recommended to take into account the excessive amount of volatiles and semi-volatiles released by the combustion of biodiesels, both in the gas and particulate phases. ivEffects of Biodiesel Chemical Composition on the Chemical and Physical Properties of the Primary and Secondary Diesel Particulate Matter Table of Contents Keywords .......................................................................................................................................... i Abstract ............................................................................................................................................ ii Table of Contents.............................................................................................................................. v List of Figures ............................................................................................................................... viii List of Tables ................................................................................................................................... xi List of Abbreviations ...................................................................................................................... xii Acknowledgements......................................................................................................................... xv CHAPTER 1: INTRODUCTION .................................................................................................. 1 1.1 The investigated research problem .......................................................................................... 1 1.2 Study aim .............................................................................................................................. 4 1.3 Specific objectives of the study .............................................................................................. 5 1.4 Evidence of research progress linking the research papers ....................................................... 6 1.5 References ........................................................................................................................... 10 CHAPTER 2: LITERATURE REVIEW ..................................................................................... 15 2.1 IntroducTion ........................................................................................................................ 15 2.2 Background and definitions .................................................................................................. 15 2.2.1 Aerosol and particulate matter ................................................................................... 15 2.2.2 Nucleation mode ....................................................................................................... 16 2.2.3 Accumulation mode .................................................................................................. 16 2.2.4 Aitken mode.............................................................................................................