Effects of partial hydrogenation, epoxidation, and hydroxylation on the fuel properties of fatty acid methyl esters

The properties of biodiesel depend on the chemical structure of individual fatty acid methyl esters (FAME). In this work the chemical structure of fatty acid chains was modified by catalytic hydrogenation, epoxidation and hydroxylation under controlled conditions. Hydrolysis of ester functionality or oxidation of fatty acid chain was not observed during these reactions. The properties of hydrogenated FAME strongly depend on the hydrogenation time. The total saturated fatty acid (SFA) percentage increased from 29.3% to 76.2% after 2 h of hydrogenation. This hydrogenated FAME showed higher oxidation stability and higher cetane number but poor cold flow properties. Formation of trans FAME was observed during hydrogenation. Both hydroxylation and epoxidation resulted in a decrease of unsaturated fatty acid methyl ester (UFA) fraction. The percentages of total unsaturated FAME decreased 39% in the epoxidation reaction and 44% in the hydroxylation reaction. The addition of hydroxyl groups to the unsaturated regions of the fatty acid chain yields biodiesel with better cold flow properties, increased lubricity and slightly increased oxidative stability. However, epoxy FAME shows some interesting properties such as higher oxidation stability, higher cetane number and acceptable cold flow properties, which met the limits of ASTM D6751 biodiesel specifications.     

Performance and durability of a generator set CI engine using synthetic and petroleum based fuels for military applications

The long term performance and durability evaluation of a compression ignition (CI) engine of a diesel power generator using ultra-low sulfur diesel (ULSD) and Synthetic Paraffinic Kerosene, (S-8) fuels have been investigated under military specifications. The brake specific fuel consumptions (BSFC) were 0.308 ± 0.013 and 0.267 ± 0.019 kg/kW-h for ULSD and S-8, respectively. The corresponding brake thermal efficiencies (BTE) were 0.287 ± 0.002 and 0.309 ± 0.005. Degradation of engine performance or engine part wear was not observed during these test periods. Analysis of lubricating oil suggests negligible engine part wear. The frequency and power output of the generator, however, were not as stable with S-8 as those with ULSD. These power and frequency instabilities can be attributed to higher volatility and lower density and viscosity of S-8, all of which affect the fuel injection characteristics.     

Quality survey of biodiesel blends sold at retail stations

A quality survey of the biodiesel blends sold in 24 retail stations in March and April 2007 was performed. The main feedstock for the biodiesel blends sold was determined to be soybean oil based. The total acid numbers (TAN) for all of the samples were below 0.3 mg/g, and the derived cetane numbers (DCN) were above 40 for all but one of the samples. The viscosity of all the samples was within the proposed ASTM range for B20. The cold-flow properties were adequate, with the pour point (PP) being below ?36 °C for most samples, suggesting the presence of a pour point depressant. However, the oxidative stability for the samples is of concern, with over 45% having an induction period (IP) of less than 6 h. Moreover, the actual blending level of the biodiesel blends generally differed from the blending level on the pump label, and fuel properties varied over a wide range even for the same blend composition.     

Investigation of the Parameters Affecting the Cetane Number of Biodiesel

The cetane number is the most significant property for measuring the ignition quality of fuels for compression ignition diesel engines. In this study, the derived cetane number (DCN) of several types of biodiesel, biodiesel components and ultra-low sulfur diesel (ULSD) was determined using an Ignition Quality Tester (IQT™). The chemical structure of FAME leads to a higher cetane number of biodiesel compared to ULSD. The contribution to DCN from minor components present in biodiesel is not significant. Oxidation of biodiesel samples results in higher DCN values while depending on the conditions of oxidation. A greater than 25% increase was observed when oxidation was carried out in a way to retain volatile oxidative products such as carboxylic acids and aldehydes. Accelerated oxidation of cotton seed oil (CSO) biodiesel at 110 °C and 10 L/min air flow rate after 210 min resulted in a loss of 14% of the FAME content, of which 10% can be attributed to the oxidation of methyl linoleate (C18:2), whereas oxidation of soy bean oil (SBO) biodiesel resulted in a loss of 21% total FAME after 210 min. A significant amount of methyl linolenate (C18:3) remained un-reacted after 210 min of oxidation. Ambient oxidation of distilled biodiesel samples resulted in a very high cetane number. Oxidative products such as aldehydes, hydroperoxides and oligomers of FAME are probably responsible for this higher DCN. This study enhances the understanding of the effect of composition on the cetane number of biodiesel as well as the effect of oxidative aging on both biodiesel composition and the resultant DCN.     

Limitations of the use of cetane index for alternative compression ignition engine fuels

The cetane number of a fuel is an important factor in determining the quality of ignition in compression ignition (CI) engines. The significance of accurate measurement of cetane number has become even greater since the use of alternative fuels and modern CI engines. In this work, the comparison of different methods of cetane value measurement for fuels with different chemical composition such as ultra low sulfur diesel (ULSD), synthetic jet fuel (S-8) and military grade jet fuel (JP-8), trace amounts of additives and biodiesel blends under different conditions is reported. The cetane index was calculated by ASTM D4737 and ASTM D976 and the derived cetane number (DCN) was measured using an Ignition Quality Tester (IQT) as a basis of comparison with the cetane index. The best agreement among three methods was observed for ULSD, while S-8 showed the largest discrepancy. The cetane indices for S-8 were 70.2 and 67.3 calculated using D4737 and D976 respectively, while the DCN was 52.8. The addition of biodiesel to ultra low sulfur diesel (ULSD) fuel alters the chemical properties of the fuel. The derived cetane number reflected the increase in ignition quality with the addition of biodiesel while calculations for cetane index did not. The cetane indices for a commercial B20 were 45.30 and 46.70 while the DCN showed a significantly higher value of 48.50. Blending 5% oxidized biodiesel with ULSD caused an 8% increase in the derived cetane number of the blend. The cetane index of the 5% biodiesel was not significantly affected by oxidation. The effects of fuel additives on cetane measurements were reflected in the DCN measurements, but not with cetane indices.     

2009 Quality survey of retail biodiesel blends in Michigan

A fuel quality survey of biodiesel blends collected in June 2009 from 26 Michigan retail stations was performed, 8 months after the publication of ASTM D7467. Measured blend levels were not consistent in stations where pump labels indicate specific biodiesel blend levels. Fatty acid methyl ester (FAME) analyses revealed that majority of the samples are soybean oil-based (SBO) biodiesel. Full compliance with the ASTM D7467 requirements for kinematic viscosity and flash point (FP) were observed with the biodiesel blends; all but one for cetane number (CN). Barely half of the samples were able satisfy the total acid number (TAN) specification with select samples reflecting as high as 1.6 mg KOH/g. The most pressing is that only 45% were able to meet the 6 h induction period (IP) requirement; out of those that did not qualify 42% are even low blends hinting the degraded quality of the biodiesel component. Inconsistencies on the expected correlations of the tested properties were evident, suggesting that additives may be present in many samples. When compared with results from a similar survey in 2007, the properties of the 2009 samples are even poorer, indicating poor observance of fuel standards by the producers.