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Evaluation of Fuel Properties of Butanol-Biodiesel-Diesel Blends and Their Impact on Engine Performance and Emissions Rakhi N. Mehta,†,‡ Mousumi Chakraborty,‡ Pinakeswar Mahanta,*,§ and Parimal A. Parikh*,‡ Chemical Engineering Department, SarVajanik College of Engineering and Technology, Surat 395 009, India, Chemical Engineering Department, S.V. National Institute of Technology, Surat 395 007, India, and Centre for Energy, Indian Institute of Technology, Guwahati 781039, India
Present work deals with the development of butanol-diesel-biodiesel blends to substitute for petrodiesel. These blends were tested for physical stability and various fuel properties conforming to ASTM standards. Subsequently engine performance and emission tests were conducted with each blend. Observations revealed the blends to be thermally and physically stable, and they showed good resemblance to the properties of diesel, with the exception of flash point only. Brake power showed marginal decrease and fuel consumption an increase in the range of 4.9%-10.7% as compared to diesel for identical performance. Exhaust gas temperature showed a drop in the range of 3.3%-9.4% due to quenching effect of butanol, whereas brake thermal efficiency showed a reduction of 6.3%-10% to that over petrodiesel. Exhaust gas emissions showed a significant decrease in CO (42%) at medium and higher loads, whereas NO showed an average increase of 2.4%-11% as compared to diesel. 1. Introduction The importance of the search for environment-friendly fuels needs to be emphasized in the current scenario. One of the recent trends of fuel research is the search for blends of petro- and biofuels, e.g., alcohols from biomass and biodiesel. Biodiesel has been reported to reduce the emissions of various regulated pollutants such as particulate matters (PM), hydrocarbons (HC), and carbon monoxide (CO) from the compression ignition (CI) engines.1 Here the biodiesel (ethyl ester of jatropha oil) acts as an amphiphile (surface active agent) forming micelles that have their nonpolar tails oriented toward diesel and the polar heads toward ethanol.2 Of late, butanol, which can be easily blended with both gasoline and diesel, has been drawing attention of researchers.3 Use of butanol has been attempted to keep an option ready for ethanol substitution should such a need arises. Further, advantages of butanol over ethanol such as lower vapor pressure, higher miscibility with gasoline and diesel (lower affinity for water), and higher stoichiometric air/fuel ratio, thereby improving combustion and reducing the CO emissions, are the driving forces for replacing ethanol with butanol.4 Also fuel testing conducted over the last 12 months by DuPont and BP demonstrates that high octane biobutanol can deliver the exceptional performance characteristics as compared to 10% ethanol blend, which has further resulted in improved energy density/fuel economy as compared to current biofuel blends for use in the existing fuels infrastructure.5 An additional advantage with butanol is its being manufactured from biomass or its CO2 neutrality. Butanol can be blended at the refinery, relieving pressure on the logistics. Existing ethanol manufacturing raw materials such as starch, sugar, or cellulose can be adapted to produce biobutanol.5 Engine performance and emissions for butanol-gasoline and butanol-diesel blends have been reported.6,7 However, hardly any work has been carried out on diesel-biodiesel-butanol blends. The motivation of blending * Corresponding authors. P.A.P.: phone, 0091 261 220 16 42; fax, 0091 261 222 73 34, 222 83 94; e-mail,
[email protected]. P.M.: phone, 0091 361 258 31 26; fax, 0091 361 269 07 62; e-mail,
[email protected]. † Sarvajanik College of Engineering and Technology. ‡ S.V. National Institute of Technology. § Indian Institute of Technology.
bioderived butanol to the mixture of diesel and biodiesel could be justified by the fact that its addition improves the values of kinematic viscosity, reduces environmental pollution, strengthens an agricultural economy, creates job opportunities, reduces diesel requirements, and thus contributes to conserving a major commercial energy source. Thus, in the light of the above discussion, to increase the substitution of bioderived fuels, namely, biodiesel and butanol in petrodiesel, the stability, fuel properties, engine performance, and emission characteristics of various blends have been studied and discussed here. 2. Materials and Methods 2.1. Physical Properties of Blends. Certified diesel, nbutanol (99.9% pure, Merck India), and the ethyl ester of Jatropha Curcas oil based biodiesel (locally make) have been used in the present study. Different blends of petrodiesel, biodiesel, and butanol were prepared with a check for phase separation at 15, 28, and 45 °C for 24 h. Four blends were identified based on their stability (Table 1). Blend stability was analyzed using transmission and backscattering profiles, on scanning the sample for 20 min by light rays of 880 nm wavelength using Turbiscan classic MA 2000 (Formulaction). Density, kinematic viscosity, and flash- and firepoints of the blends were determined using an Anton Parr densitometer model DMA 4500, a Herzog kinematic viscosity meter model HCP 852, and a Herzog closed-cup Pensky Martens apparatus, respectively. Cold filter plugging point and surface tensions of different blends were determined using a Scavini CFPP apparatus and a Kluss T9 tensiometer, respectively. These tests were performed in accordance with ASTM standards. 2.2. Engine Test Setup. Engine performance was studied on a four-cylinder, four-stroke, direct injection diesel engine schematically shown in Figure 1, and its specifications are given in Table 2. In order to determine the engine torque, the shaft of the test engine was coupled to eddy current type dynamometer. Table 1. Selected Blends blend B1 B2 B3 B4 butanol/diesel/biodiesel (vol %) 5/85/10 10/75/15 20/55/25 25/50/25
10.1021/ie1006257 2010 American Chemical Society Published on Web 07/15/2010
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Figure 1. Engine setup.
3. Results and Discussions
Table 2. Specifications of Test Engine test engine engine make engine model/type cylinder bore, piston stroke compression ratio (cm3) combustion chamber rated power output injection nozzle
specifications Bajaj Tempo, model-D301-E2 four cylinder, four stroke, water cooled, Diesel bore -78 mm, stroke -94 mm 19.8:1 direct injection (DI) 34 kW at 3800 rpm needle valve and five hole nozzles
dynamometer
specification
type make model rating air box fuel tank temperature indicator
eddy current Saj Pune AG80 75 V dc, 5 A max with orifice and manometer 20 L capacity with metering column digital, PT-100 type temperature sensors (three locations) pipe in pipe with rotameter
calorimeter
The engine speed was measured by an electromagnetic speed sensor installed on the dynamometer and was equipped with an orifice meter connected to an inclined manometer to measure mass flow rate of the intake air. Exhaust temperature was measured with the help of a RTD sensor. Engine tests were conducted with full throttle condition and the speed variations were obtained by increasing the load in the dynamometer. Initially, engine tests were performed with pure petrodiesel at fully throttled and no-load conditions. A separate fuel feed line was used to feed the various blends to the engine in subsequent tests. Then the prepared blends were fed one by one in the engine fuel cylinder and the tests were conducted to evaluate the performance characteristics such as specific fuel consumption, brake power, exhaust gas temperature, A/F ratios, and brake thermal efficiency. Before running the engine to a new fuel blend, it was allowed to run for sufficient time to consume the remaining fuel from the previous experiment. Emissions of CO, NO, and HC were measured using a Quintox KM9106 exhaust gas analyzer (Kane International Ltd.). Soot particles in exhaust gas were collected on wet Whatman paper and analyzed for the amount and size of soot emitted with the help of Zeiss optical microscope. Each experiment was repeated three times, and the average values of the readings were considered to ensure the reproducibility of the results.
3.1. Blend Stability. The blends were scanned from bottom (0 mm) to top of the cuvette (60 mm) for a period of 20 min. The backscattering (BS) profile of one of the blends (B2) is elucidated in Figure 2, where the left-hand ordinate shows the percentage of backscattering, the right-hand ordinate shows time in minutes, and the abscissa shows the length along the test cuvette (mm). Figure 2 shows that the BS profiles at different time intervals are superimposing, indicating that the phases have not separated and the mixture remains stable over a period of 20 min, although a little variation is seen at the top (60 mm) due to the release of bubbles. 3.2. Blends’ Fuel Properties. The applicability of the blends selected was further justified by determining different properties and are depicted in Table 3. All the tests were performed according to the ASTM standards, which are also listed in the Table 3. The flash points of blends showed reduction due to the presence of butanol. However, it is worth noting that there is a considerable improvement in the flash point values as compared to those reported for ethanol.8 The net heating values of blends were less by 2%-8% with increment of butanol percentage in the blends. Cetane indices of the blends were found to reduce with simultaneous addition of butanol (lower cetane index) into the blends. Blend B1 showed a reduction of 3.1% and B4 15.5% as compared to diesel. 3.3. Engine Performance. 3.3.1. Brake Power (BP). Figure 3 presents the variation of brake power (BP) with engine speed for biodiesel and various blends. Results were compared with petrodiesel as fuel. An increase in BP was observed with an increase in torque and speed and it is obvious, as BP is a product of torque and angular speed.9 When the engine was fueled with oxygenated blends, a marginal reduction in BP was observed as compared to diesel, which may be attributed to the lower heating value and cetane index of butanol (Table 3). Blends B1, B2, B3, and B4 showed a reduction of 1.7%, 2%, 3.4%, and 4.38%, respectively; as for low cetane fuels with long delay, ignition may occur sufficiently late during the expansion process and due to this the burning process is quenched, resulting in incomplete combustion, resulting in reduced power and poor fuel conversion efficiency.9 3.3.2. Brake Specific Fuel Consumption (BSFC). Values of specific fuel consumption of engine when fueled with different blends and pure diesel at different speeds are shown
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Figure 2. Turbiscan backscattering profile of blend B2. Table 3. Observed Fuel Properties of Prepared and Selected Butanol-Diesel-Biodiesel Blends properties
diesel
butanol
biodiesel
B1
B2
B3
B4
ASTM standards
density at 15 °C, g/mL kinematic viscosity at 40 °C, cSt flash point, °C pour point, °C net heat of combustion (MJ/kg) cetane index copper strip corrosion oxidation stability mg/10 mL
0.835 2.12 69 13 43.5 46 not worse than 1(a) 2.5
0.810 3.64 29 -45 33
