Particulate emissions, diesel

The first case covers for example flue-gas treatment, which requires the filtration of fly-ash and the reduction of NOx, or gasification processes, where particulates and high-boiling tars have to be removed. An example of the second case is that of combustion processes, where incomplete combustion leads to the emission of carbonaceous particulates. The most relevant topic in this category is the reduction of diesel particulate emissions ( diesel soot ) by catalytic filtration. A more exotic example is the reaction cyclone for the thermal conversion of biomass, which also combines chemical reactions and separation in one apparatus, though its separation mechanism is not filtration. 

For other physical properties, the specification differences between diesel fuel and home-heating oil are minimal. Note only that there is no minimum distillation end point for heating oil, undoubtedly because tbe problem of particulate emissions is much less critical in domestic burners than in an engine. 

The main justification for diesel fuel desulfurization is related to particulate emissions which are subject to very strict rules. Part of the sulfur is transformed first into SO3, then into hydrated sulfuric acid on the filter designed to collect the particulates. Figure 5.21 gives an estimate of the variation of the particulate weights as a function of sulfur content of diesel fuel for heavy vehicles. The effect is greater when the test cycle contains more high temperature operating phases which favor the transformation of SO2 to SO3. This is particularly noticeable in the standard cycle used in Europe (ECE R49). 

Desulfurization will become mandatory when oxidizing catalysts are installed on the exhaust systems of diesel engines. At high temperatures this catalyst accelerates the oxidation of SO2 to SO3 and causes an increase in the weight of particulate emissions if the diesel fuel has not been desulfurized. As an illustrative example, Figure 5.22 shows that starting from a catalyst temperature of 400°C, the quantity of particulates increases very rapidly with the sulfur content. 

Influence of the sulfur content in diesel fuel on particulate emissions as a, function of the catalytic converter inlet temperature. 

Influence of hydrotreating a diesel fuel on particulate emissions. 

Diesel fuels, like gasoline, are formulated with additives that affect the process of combustion, in this case to improve the cetane number. Diesel fuels also contain detergents for irijection systems as well as compounds for improving the fuel s low tempierature rheology. Finally, decreasing particulate emissions is a problem of increasing concern, but the mechanism of action to promote this effect is not clearly understood. 

Additional research for both ethanol and methanol showed that the amount of ignition improver could be reduced by systems increa sing engine compression (63). Going from 17 1 to 21 1 reduced the amount of TEGDN requited for methanol from 5% by volume to 3%. Ignition-improved methanol exhibited very low exhaust emissions compared to diesels particulate emissions were eliminated except for small amounts associated with engine oil, NO was even lower with increased compression, and CO and hydrocarbons were also below diesel levels. 

These catalysts contained promoters to minimise SO2 oxidation. Second-generation systems are based on a combined oxidation catalyst and particulate trap to remove HC and CO, and to alleviate particulate emissions on a continuous basis. The next phase will be the development of advanced catalysts for NO removal under oxidising conditions. Low or 2ero sulfur diesel fuel will be an advantage in overall system development. 

Most urban rail service is electric-powered and most urban bus service is diesel-powered, although diesel rail and electric bus operations do exist, as noted above. The efficiency and environmental impacts of electricity depend gi eatly on the source of electric power. Although electric vehicles produce no tailpipe emissions, generation of electricity can produce significant emissions that can travel long distances, Eor example, coal-powered electricity plants produce particulate emissions that travel halfway across North America, Urban buses also can be powered by a variety of alternative fuels. 

Understanding particulate emissions, their formation and control, is another key issue in meeting the new particulate emission Hmits set by the new EURO emission standards. The particulate emissions formed in diesel engines have a mass median diameter of 0.05-1.0 gm. Particle consists of carbon with various HCs adsorbed on it including polyaromatic hydrocarbon (PAH) as well as nitro-PAH compounds. 

The small particles are reported to be very harmful for human health [98]. To remove particulate emissions from diesel engines, diesel particulate filters (DPF) are used. Filter systems can be metallic and ceramic with a large number of parallel channels. In applications to passenger cars, only ceramic filters are used. The channels in the filter are alternatively open and closed. Consequently, the exhaust gas is forced to flow through the porous walls of the honeycomb structure. The solid particles are deposited in the pores. Depending on the porosity of the filter material, these filters can attain filtration efficiencies up to 97%. The soot deposits in the particulate filter induce a steady rise in flow resistance. For this reason, the particulate filter must be regenerated at certain intervals, which can be achieved in the passive or active process [46]. 

Although various restrictions have been placed on carbon particulate emissions from different types of power plants, these particles can play a beneficial, as well as a detrimental, role in the overall plant process. The detrimental effects are well known. The presence of particulates in gas turbines can severely affect the lifetime of the blades soot particulates in diesel engines absorb carcinogenic materials, thereby posing a health hazard. It... 

Sidhu S, Gullet B, Striebich R, Klosterman JR, Contreras J, DeVito M (2005) Endocrine disrupting chemical emissions from combustion sources diesel particulate emissions and domestic waste open bum emissions. Atmos Environ 39 801-811... 

Faxvog, F. R., and D. M. Roessler, 1979. Optoacoustic measurements of diesel particulate emission, J. Appl. Phys., 50, 7880-7882. 

N., D Anna, A., D Alessio, A., Zahoransky, R., Laile, E., Schmidt, S., and Ranalli, M. The diesel exhaust aftertreatment (DEXA) cluster A systematic approach to diesel particulate emission control in Europe. SAE Technical Paper No. 2004-01-0694 (SP-1861) (2004). 

When biodiesel is blended with diesel fuel, the emissions results change somewhat. A significant decrease in hydrocarbon and carbon monoxide emissions is typical, no change or a small increase in oxides of nitrogen emissions, and significant reduction in particulate emissions. Emissions of toxins would also decrease according to the percentage substitution of diesel fuel. 

Cooper BJ, Thoss JE (1989) Role of NO in diesel particulate emission control, SAE Technical Paper 890404, doi 10.4271/890404... 

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