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Oxygenates present in partially hydroprocessed lignocellulosic-biomass pyrolysis oils were examined for their impact on the performance properties of gasoline and diesel. These included: methyltetrahydrofuran, 2,5-dimethylfuran (DMF), 2-hexanone, 4-methylanisole, phenol, p-cresol, 2,4-xylenol, guaiacol, 4-methylguaiacol, 4-methylacetophenone, 4-propylphenol, and 4-propylguaiacol. Literature values indicate that acute toxicity for these compounds falls within the range of the components in petroleum-derived fuels. On the basis of the available data, 4-methylanisole and by extension other methyl aryl ethers appear to be the best drop-in fuel components for gasoline because they significantly increase research octane number and slightly reduce vapor pressure without significant negative fuel property effects. A significant finding is that DMF can produce high levels of gum under oxidizing conditions. If the poor stability results observed for DMF could be addressed with a stabilizer additive or removal of impurities, it could also be considered a strong drop-in fuel candidate. The low solubility of phenol and p-cresol (and by extension, the two other cresol isomers) in hydrocarbons and the observation that phenol is also highly extractable into water suggest that these molecules cannot likely be present above trace levels in drop-in fuels. The diesel boiling range oxygenates all have low cetane numbers, which presents challenges for blending into diesel fuel. There were some beneficial properties observed for the phenolic oxygenates in diesel, including increasing conductivity, lubricity, and oxidation stability of the diesel fuel. Oxygenates other than phenol and cresol, including other phenolic compounds, showed no negative impacts at the low blend levels examined here and could likely be present in an upgraded bio-oil gasoline or diesel blendstock at low levels to make a dropin fuel. On the basis of solubility parameter theory, 4-methylanisole and DMF showed less interaction with elastomers than ethanol, while phenolic compounds showed somewhat greater interaction. This effect is not large, especially at low blend levels, and is also less significant as the size and number of alkyl substituents on the phenol ring increase.

The introduction of more stringent standards for fuel economy as well as greenhouse gas emissions [1] is driving research to increase the efficiency of spark ignition (SI) engines. Approaches for increasing SI engine efficiency include increased compression ratio, direct injection (DI), turbocharging, downsizing, and down-speeding. Higher octane number (more highly knock resistant) fuels allow improved combustion phasing and operation at higher loads at the same engine speed, while also allowing the higher in-cylinder temperature and pressure generated by increased compression ratio and turbocharging which are critical for downsizing and down-speeding [2,3,4]. At the same time, renewable fuel usage is mandated to increase in the United States under the Renewable Fuel Standard [5], and globally under laws enacted in other countries. Ethanol, the most commonly used renewable fuel, has a research octane number (RON) of approximately 110 [6] compared to typical U.S. regular gasoline at 91-93 [2]. Accordingly, high octane number ethanol blends containing from 20 volume percent (vol%) to 40 vol% ethanol are being extensively studied [3,7,8,9,10]. A unique property of ethanol is its high heat of vaporization (HOV), which significantly increases charge cooling for DI engines, providing additional knock resistance.The tendency of a spark-ignited engine fuel to autoignite and cause knock is measured as the octane number, a critical performance parameter for SI engines. In the United States, octane number at the retail pump is given as the anti-knock index, the average of two octane number measurements: research octane number (RON) (ASTM D2699-13b) and motor octane number (MON) (ASTM D2700-13b). The primary differences between the RON and MON measurements are fuel-air charge temperature and engine speed, with the RON test using a comparatively low fuel-air charge temperature (that is dependent on the fuel's latent heat of evaporation) and slower engine speed while the MON test is conducted at a significantly higher fuel-air charge temperature (149°C) and faster engine speed. Recent studies have demonstrated that MON is correlated with different effects in modern engines than was the case when these tests were introduced in 1932, and in fact increasing MON at constant RON may actually lower the fuel knock resistance [11]. The ABSTRACTThe objective of this work was to measure knock resistance metrics for ethanol-hydrocarbon blends with a primary focus on development of methods to measure the heat of vaporization (HOV). Blends of ethanol at 10 to 50 volume percent were prepared with three gasoline blendstocks and a natural gasoline. Performance properties and composition of the blendstocks and blends were measured, including research octane number (RON), motor octane number (MON), net heating value, density, distillation curve, and vapor pressure. RON increases upon blending ethanol but with diminishing returns above about 30 vol%. Above 30% to 40% ethanol the curves flatten and converge at a RON of about 103 to 105, even for...

<div class="section abstract"><div class="htmlview paragraph">Mixing controlled compression ignition, i.e., diesel engines are efficient and are likely to continue to be the primary means for movement of goods for many years. Low-net-carbon biofuels have the potential to significantly reduce the carbon footprint of diesel combustion and could have advantageous properties for combustion, such as high cetane number and reduced engine-out particle and NO_x emissions. We developed a list of over 400 potential biomass-derived diesel blendstocks and populated a database with the properties and characteristics of these materials. Fuel properties were determined by measurement, model prediction, or literature review. Screening criteria were developed to determine if a blendstock met the basic requirements for handling in the diesel distribution system and use as a blend with conventional diesel. Criteria included cetane number ≥40, flashpoint ≥52°C, and boiling point or T90 ≤338°C. Blendstocks needed to be soluble in diesel fuel, have a toxicity no worse than conventional diesel, not be corrosive, and be compatible with fuel system elastomers. Additionally, cloud point or freezing point below 0°C was required. Screening based on blendstock properties produced a list of 12 that were available as fuels or reagent chemicals or could be synthesized by biofuels production researchers. This group included alkanes, alcohols, esters, and ethers. These candidates were further examined for their impact fuel properties upon blending with a conventional diesel fuel. Blend properties included cetane number, lubricity, conductivity, oxidation stability, and viscosity. Results indicate that all 12 candidates can meet the basic requirements for diesel fuel blending, although in some cases would require additive treatment to meet requirements for lubricity, conductivity, and oxidation stability.</div></div>

Several high octane number oxygenates that could be derived from biomass were blended with gasoline and examined for performance properties and their impact on knock resistance and fine particle emissions in a single cylinder direct-injection spark-ignition engine. The oxygenates included ethanol, isobutanol, anisole, 4-methylanisole, 2-phenylethanol, 2,5-dimethyl furan, and 2,4-xylenol. These were blended into a summertime blendstock for oxygenate blending at levels ranging from 10 to 50 percent by volume. The base gasoline, its blends with p-xylene and p-cymene, and high-octane racing gasoline were tested as controls. Relevant gasoline properties including research octane number (RON), motor octane number, distillation curve, and vapor pressure were measured. Detailed hydrocarbon analysis was used to estimate heat of vaporization and particulate matter index (PMI). Experiments were conducted to measure knock-limited spark advance and particulate matter (PM) emissions. The results show a range of knock resistances that correlate well with RON. Molecules with relatively low boiling point and high vapor pressure had little effect on PM emissions. In contrast, the aromatic oxygenates caused significant increases in PM emissions (factors of 2 to 5) relative to the base gasoline. Thus, any effect of their oxygen atom on increasing local air-fuel ratio was outweighed by their low vapor pressure and high double-bond equivalent values. For most fuels and oxygenate blend components, PMI was a good predictor of PM emissions. However, the high boiling point, low vapor pressure oxygenates 2-phenylethanol and 2,4-xylenol produced lower PM emissions than predicted by PMI. This was likely because they did not fully evaporate and combust, and instead were swept into the lube oil.