Characterization of renewable diesel particulate matter gathered from non-premixed and partially premixed flame burners and from a diesel engine

Particulate matter coming from the combustion of renewable diesel (RD), ultra-low sulfur diesel (ULSD) and a volumetric blend of 30% of RD with ULSD (RD30) were collected and physico-chemically characterized. Soot samples were generated in two flame burner types (non-premixed flame, NPF, and partially premixed flame, PPF) trying to simulate the diffusion and premix regimes found in diesel engines. The impact of both fuel nature and burner type was assessed on soot mass, particle size and morphology, particle nanostructure and surface functional groups. In general, although the results of HRTEM and SMPS suggested that the addition of RD reduced the average particle size and increased the concentration of ultra-fine particles, the mass emission of soot was drastically mitigated regardless of the burner used. The results also suggest that the changes in the chemical characteristics of the soot were slightly more sensitive than the changes in the internal nanostructure of the particles, since the graphitic character (as showed by Raman and infrared analysis) increased as the RD content increased, being stronger for the PPF system. Comparisons between engine soot and flame soot confirmed that the addition of RD into ULSD produced smaller and more carbonized particles. In fact, some engine results were located in between those obtained in PPF and NPF burners, suggesting that both combustion regimes are contributing to soot characteristics in engines. This consistency suggests that a first assessment of the impact of alternative fuels on the characteristics of particulate matter can be conducted through the basic approach offered by laboratory flames, thereby avoiding the costs associated with generating large quantities of fuel and the complexities of in-cylinder physical interactions and engine parameters.

Quality Characteristics of Biodiesel Produced from Used Cooking Oil in Southern Europe

The potential of households’ used cooking oil (UCO) recycling for biodiesel production is massive. This study aims to promote the shift from UCO inappropriate disposal to sustainable recycling. UCO is classified as municipal waste under the code 20 01 25 (edible oils and fats), according to the European Waste Catalogue. Inappropriate UCO disposal increases the operating cost of wastewater treatment, the risk of groundwater contamination, as well as the greenhouse gas emissions that are associated with its biodegradation. Recycling UCO-to-biodiesel offers a sustainable solution in the exploitation of a problematic waste and its transformation into an energy resource, thus contributing to the reduction of environmental pollution and fossil fuel dependence. This paper includes critical recommendations in order to overcome bottlenecks to successfully promote the UCO-to-biodiesel chain. Quality control of the biodiesel—produced exclusively from UCO—was performed according to the European Standard EN 14214 and the results are presented in the paper. The analysis studies the outcomes from four Southern European countries (Spain, Portugal, Italy, and Greece), which hold the top four places in annual per capita olive oil consumption in the European Union (EU).

Exhaust Emissions and Physicochemical Properties of n-Butanol/Diesel Blends with 2-Ethylhexyl Nitrate (EHN) or Hydrotreated Used Cooking Oil (HUCO) as Cetane Improvers

Currently, n-butanol is a promising oxygenate (potentially of renewable origin) to be used in blends with conventional diesel fuel in compression ignition engines. However, its poor ignition quality can drastically deteriorate the cetane number (CN) of the blend. In the present work, the effects of adding n-butanol to ultra-low-sulfur diesel (ULSD) were assessed, aiming at simultaneously eliminating its negative effect on the blend’s ignition quality. Concentrations of 10% and 20% (v/v) n-butanol in ULSD fuel were studied. As cetane-improving agents, a widely used cetane improver (2-ethylhexyl nitrate—EHN) and a high-CN, bio-derived paraffinic diesel (hydrotreated used cooking oil—HUCO) were used. The initial investigation of ignition quality improvement with the addition of either EHN or HUCO produced four “ignition quality response curves” that served as mixing guides in order to create four blends of identical ignition quality as the baseline ULSD fuel. These four blends (10% and 20% v/v n-butanol in ULSD fuel, with the addition of either EHN or HUCO, at the cost of ULSD volume share only) were evaluated comparatively to the baseline ULSD fuel and a 10% (v/v) n-butanol/90% ULSD blend with regards to their physicochemical properties and the effect on the operation and exhaust emissions of a stationary diesel engine.