Exhaust Emissions and Physicochemical Properties of Hydrotreated Used Cooking Oils in Blends with Diesel Fuel

Abstract

Hydroprocessing of liquid biomass is a promising technology for the production of “second generation” renewable fuels to be used in transportation. Its products, normal paraffins, can be further hydrotreated for isomerization in order to improve their cold flow properties. The final product, usually referred to as “paraffinic diesel,” is a high cetane number, clean burning biofuel which is rapidly gaining popularity among researchers and the industry. Nevertheless, the costly isomerization step can be omitted if normal paraffins are to be directly mixed with conventional diesel in low concentrations. In this work, nonisomerized paraffinic diesel produced through hydrotreating of used cooking oil (hydrotreated used cooking oil (HUCO)) has been used in 4 blends (up to 40% v/v) with conventional diesel fuel. The blends’ properties have been assessed comparatively to European EN 590 and EN 15940 standards (concerning conventional automotive diesel fuels and paraffinic diesel fuels from synthesis or hydrotreatment, resp.). Furthermore, the HUCO blends have been used in a standard stationary diesel engine-generator set. The blends have been considered as “drop-in replacements” for standard diesel fuel. As such, no engine modifications took place whatsoever. The engine performance and exhaust emissions of steady-state operation have been examined in comparison with engine operation with the baseline conventional diesel fuel.

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

“…Furthermore, at full load, the HUCO increase in the blend seemed to cause a slight increase of CO emissions. This behavior was reported on a larger scale in a previous work, where HUCO samples did not contain any oxygenate to compensate for the CO increase [39].…”

“…The products of catalytic hydroprocessing of liquid biomass (normal paraffins) can be further hydrotreated for isomerization in order to improve their cold flow properties [36]. Nevertheless, the extra cost of the isomerization step can be avoided if normal paraffins are directly mixed with conventional diesel in low-to-moderate concentrations [39].…”

“…Fuel consumption was measured by mass using a digital scale. The experimental set-up (shown in Figure 1) was located in the Laboratory of Fuels Technology and Lubricants of the National Technical University of Athens, Greece, and was also employed in previous work [24,39]. Particulate matter was measured with units of mass per exhaust gas volume.…”

“…The engine loads used for the measurement of exhaust emissions and fuel consumption were 1.5 kW (low), 3.5 kW (medium), 4.5 kW (medium-high), and 5.5 kW (full), as presented in Table 5. The experimental procedure was developed and optimized for the specific apparatus in hand over the last few years and, as a result, the basic aspects of the methodology are the same as those described in previous work [24,39]. However, some parameters (such as the duration of sampling for the PM measurement, or the imposed loads on the engine) were carefully chosen after trial and error runs with each sample set, according to the scope and the particularities of each separate work.…”

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

“…Specifications can be further enhanced when biodiesel is blended with diesel. Blends studied in the literature [37][38][39] can offer optimized properties.…”