Butanol can be used as a blending agent in diesel to displace petroleum and reduce emissions of particulate matter without significantly increasing NOx or significantly lowering the cetane number, according to the results of a preliminary study by researchers at Argonne National Laboratory.
With properties superior to that of ethanol, butanol (C4H9OH) is generally being considered as a gasoline blend component. Test results presented by BP and DuPont at SAE World Congress 2007 showed that bio-derived 1-butanol (also called n-butanol) performs similarly to unleaded gasoline on key parameters, and that biobutanol formulations meet key characteristics of a “good” spark ignition fuel, including high energy density, controlled volatility, sufficient octane and low levels of impurities.
Click link to view graphical relationship of NOx versus filter smoke number at 35 mph forULSD and Bu40. http://bioage.typepad.com/.shared/image.html?/photos/uncategorized/2008/08/15/butanoldiesel.png
Butanol, however, can potentially also be blended with diesel for compression ignition engines without causing significant penalties. Blending butanol with diesel may also improve cold flow properties and extend oxidative stability. Although the potential exists to positively impact engine-out emissions through the use of butanol/diesel blends, limited research has been done to this point on the effect and operation of butanol in compression ignition (diesel) engines.
Butanol exists as different isomers based on the location of the OH group and carbon chain structure. Argonne used n-butanol, which has a straight-chain structure with the alcohol at the terminal carbon, in this project.
The butanol contains 21.5 mass-% oxygen, and its net heat of combustion on a mass basis is 23% lower than ULSD. On a volume basis, the net heat of combustion is 26.6% lower. The cetane number is 40% lower than ULSD: ~25, rather than 42. (The butanol cetane of 25 is significantly higher than that of ethanol, which is ~8.)
While 100% n-butanol would not operate properly in an engine designed and calibrated for diesel fuel, Argonne found that low to medium blends of 1-butanol and ULSD provide acceptable cetane along with the potential advantage of oxygen in the fuel.
| Butanol/Diesel Fuel Data | ||||
|---|---|---|---|---|
| Property | Neat fuels | Blends | ||
| ULSD | n-Butanol | Bu20 | Bu40 | |
| Composition (C, H, O) (mass-%) | 87, 13, 0 | 65, 13.5, 21.5 | 82.6, 13.1, 4.3 | 78.2, 13.2, 8.6 |
| Lower heating value (MJ/kg) | 43.04 | 33.1 | 41 | 39 |
| Density (kg/m3) | 850 | 810 | 842 | 834 |
| Energy density (MJ/L) | 36.6 | 26.8 | 34.5 | 32.5 |
| Cetane number | 42 | ~25 | 38.6 | 35.2 |
In a preliminary study, the Argonne team used Bu20 (20% butanol) and Bu40 (40% butanol) blends of ultra low sulfur diesel (ULSD) in a 1999 Mercedes Benz Euro-3 C220 turbodiesel. Cold- and hot-start urban (UDDS) and highway (HWFET) drive cycle tests were conducted with the two butanol blends and compared to the pure ULSD fuel. In addition, 35 and 55 mph steady-state tests were run under varying road loads for the blends.
Broadly, the study found that on the urban drive cycle, both total hydrocarbon (THC) and carbon monoxide (CO) emissions increased as larger quantities of butanol were added to the diesel fuel. THC increased significantly as the percentage of butanol increased for cold-start UDDS drive cycle and only modestly for the hot-start UDDS cycle. Oxides of nitrogen (NOx) were not significantly affected by the 20% butanol blend and decreased with the 40% butanol blend.
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