Vegetable oils as Diesel Fuels for Rebuilt Vehicles
44th International Petroleum Conference, Bratislava, Slovak Republic, September 21-22, 2009 1 Vegetable oils as diesel fuels for rebuilt vehicles 1 Kleinová A., 2Vailing I., 3Franta R., 3Mikulec J., 1Cvengroš J.1 Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, 812 37 Bratislava, Slovak Republic, e-mail: firstname.lastname@example.org; email@example.com 2 RASOL, Nitra, Slovak Republic, e-mail: firstname.lastname@example.org 3 Slovnaft VÚRUP, Bratislava, Slovak Republic, e-mail: email@example.com; firstname.lastname@example.orgAbstract Vegetable oils and animal fats are applicable as fuels in standard diesel engines afterhaving adapted the fuel system for electronically controlled dual fuel (oil/fat – fossil diesel)regime. In this study, performance and emission characteristics of the engine running onrapeseed oil or chicken fat are given and compared to those of fossil diesel. The results ofengine tests of these fuels show a decrease in maximum power and maximum torque incomparison with fossil diesel. When compared to fossil diesel, the opacity of vegetable oil oranimal fat based fuels is lower for an engine with higher injection pressures. The level of bothcontrolled and uncontrolled emissions is low for all tested biofuels and it is low also for thereference fossil diesel. The results of performance and emission tests for rapeseed oilcontaining 3 and 6 vol. % of anhydrous ethanol are comparable to those obtained for pure oil.Key words: Vegetable oils, animal fats, bioethanol, alternative fuels, diesel engine, dual fuel operation1 Introduction Pure plant oils and also animal fats (PPO) represent promising alternative in the field ofbiofuels , they are renewable and environmentally friendly. Utilization of this group ofnatural products leads to further diversification of liquid fuel resources for transport, ina simple and easily accessible form [1–4]. PPO are non-toxic incombustible liquids with the flash point above 170 °C, i.e. withminimum risk for storage, handling or transport. Their cetane number is relatively low,ranging from 39 to 44. When PPO are used as fuels for diesel engines, some qualitativeparameters must be fulfilled and also the vehicle fuel systems must be appropriately adapted
44th International Petroleum Conference, Bratislava, Slovak Republic, September 21-22, 2009 2for this kind of fuel. The qualitative requirements for PPO are defined in the DIN V 51605standard . The content of free fatty acids, phosphorus, calcium and magnesium need to bemonitored. For trouble-free engine run, these parameters should reach the lowest possiblelevels. Their increased values indicate the necessity of appropriate PPO treatment beforeusing as fuel . The main drawback of PPO for direct utilization as fuel in conventional diesel engines isrelated to their high viscosity [7, 8] which causes incomplete fuel atomization, formation ofcarbon deposits on injectors, piston ring sticking, engine oil deterioration, etc. [9, 10]. Despitethese problems, literature data [11–18] show that PPO are applicable for conventional dieselengines without their adaptation. Moreover, some benefits appear: reduced PAH emissions,reduced opacity  and lower NOx values [20–22]. There are several approaches to solve the viscosity problem in an effective and simpleway, such as blending, microemulsions, transesterification, and cracking [10, 22–26]. Variousmixtures of PPO and conventional diesel fuel (DF) with a low (5–30 %) [16, 18, 19] and highshare (up to 75 %) of PPO [17, 22] are discussed. Heating of PPO before its input into fuelinjection system [27–31] also leads to viscosity decrease. Temperatures about 70 °C , 100°C , but even 150 °C  are mentioned. These approaches cause low emission, reducedopacity and positive performance. Alcohols-PPO blend represents other way of fuel viscositydecrease [20, 33, 34]. A low-viscosity solvent decreases significantly the mixture viscosityand opacity when compared to run on pure oil. Dual fuel operation of engines represents a new approach in the use of PPO [35–37]. Here,electronically controlled dual fuel (DF-PPO) system is built and PPO is pre-heated to reduceits viscosity. Without any engine adjustments, the vehicle fuel system contains a fuel pre-heater and the dual fuel tank. System allows switching over between DF and PPO, bothcontrolled by a microcomputer. The engine is started and runs on DF for the first few minuteswhile the PPO is heated. The engine is then switched over to the second tank and runs onPPO. At the end of operation, the engine runs again on DF. The optimal operation onindividual fuel is ensured by an automatic control system . Literature related to testsperformed using animal fats as fuel in diesel engines with modified fuel system is scarce. Nowadays, there is an extensive know-how for optimized adjustment of standard vehicleswith the diesel engine running on PPO. It is estimated that in Germany, there is about 60 000vehicles adjusted in such way (situation in 2006). The fuel consumption of these vehiclesapproaches 300 000–400 000 t/y rapeseed oil, i.e. about 0.5 % of the liquid fuel consumption
44th International Petroleum Conference, Bratislava, Slovak Republic, September 21-22, 2009 3in Germany. Demand for this fuel is considerable , in the next years a yearly increase by10 % is anticipated. Although ethanol (EtOH) does not belong to typical and optimal components of dieselengine fuel, there are tendencies to exploit it as a component of diesel fuels [40, 41], in spiteof its negative properties, such as low cetane number, decreased flash point, worsenedlubricity, low energy content. However, addition of EtOH to PPO can improve its low-temperature flow properties. The results in [40, 41] show that addition of EtOH to DF up to 5vol. % does not lead to substantial worsening of the fuel performance properties, withexception of flash point. Therefore, we decided to pay attention to test EtOH as a part ofblended fuel. In this work, we studied the performance and emission characteristics of standard engineswith unit injection system in vehicle with adapted fuel system running on PPO as main fuel.Obtained results were compared with those of the same engine running on DF. Tests wereperformed also using animal fat. A further objective lies in analogous investigation using thementioned engine running on the blended fuel consisting of PPO and anhydrous EtOH.2 Experimental part2.1 Testing vehicle To provide all performance and emission tests, a passenger car VW Touareg R5 2.5 UI(Unit Injection System), year of production 2007, was chosen. Basic characteristics of theused all-wheel drive car are given in Tab. 1. Testing vehicle was equipped with a RASOL system for dual fuel regime and all the necessities, too. Tab. 1 Characteristics of testing engine Type of engine 2.5 UI Cylinder number 5 Bore (mm)×Stroke (mm) 81×95.5 Volume (L) 2.5 Compression ratio 19.5:1 Maximal power output (kW/rev) 128/3500 Maximal torque (N m/rev) 400/2000 Injection pressure (bar) 2050 Vehicle weight (t) 2.42.2 Tested fuels – characteristics and preparation The reference fuel, DF, was provided by Slovnaft Bratislava. Parameters of DF are givenin Tab. 2. Low-temperature properties of the used diesel fuels were modified by commercialadditives, detergent (200 ppm) and depressant (300 ppm).
44th International Petroleum Conference, Bratislava, Slovak Republic, September 21-22, 2009 4 The properties of the used alternative fuels are summarized in Tab. 3. Rapeseed oil (RO)was cold pressed, subsequently adsorbed by clay, filtered through a filter press and re-filteredthrough a 1 μm filter. Its acid value (AV) was 1.7 mg KOH/g. To prepare blends of PPO withEtOH, anhydrous denaturated EtOH (Slovnaft VÚRUP Bratislava) containing less than 1000ppm water was used. Chicken fat (CF) with AV = 4.0 mg KOH/g was supplied by JAV-AKCVlčany. Viscosity/temperature plots for tested fuels are shown in Fig. 1. Tab. 2 Characteristics of used diesel fuel Characteristic Unit Value Method Density at 15 °C kg m-3 832.6 EN 12185 Viscosity at 40 °C mm2 s-1 2.376 EN 3104 Cetane index 50.7 EN 4264 Cetane number 50.6 EN 5165 Water content mg kg-1 26.2 EN 12937 Flash point °C 70 EN 2719 Cloud point °C - EN 23015 Filterability (CFPP) °C -30 EN 116 Lubricity μm 605 EN 12156-12.2 Performance and emission tests, fuel consumption measurements All measurements of performance characteristics were carried out using the chassisdynamometer MAHA LPS 2000 (MBH Haldenwang/Allgäu, Germany). Emissionmeasurements were performed with an exhaust gases analyzer MAHA MGT 5 by means ofthe emission determination at steady-state regime during idle running and the constant speedsof 60, 90 or 120 km/h. Diesel engine opacity determination was performed by the method offree acceleration with a dynamometer AVL DiSmoke 435. Aldehydes and ketones weredetermined as described in [42, 43]. Fuel consumption measurements were done by weightingof tested fuel samples in the regime of engine run in-town and non-city cycles following theECE 83 method. The results of individual tests are compiled in the corresponding tables. Thevalues in the tables represent an average of five measured values.3 Results and discussion3.1 Viscosity of tested fuels Objections to the direct use of PPO as fuels for unmodified diesel engines relate mainly totheir higher viscosity in comparison with that of DF. In Fig. 1 temperature dependences of theused PPO (rapeseed oil and chicken fat) viscosities are shown together with the dependencefor DF. It is obvious that in spite of increased temperature, a substantial decrease in theviscosities was not achieved and they are still higher than that of DF. According the literature
44th International Petroleum Conference, Bratislava, Slovak Republic, September 21-22, 2009 5data, the temperature of PPO about 70 °C is already sufficient for the study of performanceand emission characteristics. Addition of 3 and 6 vol. % of EtOH does not decrease viscosityof RO significantly when compared to DF. Further increase in temperature induces viscositydecrease . However, the presence of a volatile component with the boiling point of 78 °Cis limiting factor. Viscosity decrease may be reached also by increasing the EtOH content inthe blend. In general, it is not expected to add more than 7 % of EtOH permitted bythe standard. In separate study of the low-temperature behavior of blended fuel RO–EtOHcontaining 3 and 6 % EtOH at –10 °C, a high phase stability was manifested at long-term testlasting several tens of hours. The system was permanently homogeneous without anyindication of the phase separation. 45 DF 40 RO RO+3% EtOH 35 RO+6% EtOH CF viscosity [mm s ] -1 30 2 25 20 15 10 5 0 35 40 45 50 55 60 65 70 75 temperature [°C] Fig. 1 Viscosity/temperature dependence of tested fuels3.2 Engine performance tests The results of performance tests of the investigated fuels using unmodified diesel engine2.5 UI indicate lower obtained values of peak performance and torque when compared to DF(Tab. 3), which proved their potential to act as alternative diesel fuel. At the performancecharacteristics in the Tab. 4, the different fuel densities are respected. The highest values ofperformance and torque were obtained for DF. For the other fuels, the obtained values of thepeak performance are lower by 12–13 %. The decrease in the peak performance is associatedwith a decrease in maximum torque. The obtained values of maximum torque are decreased
44th International Petroleum Conference, Bratislava, Slovak Republic, September 21-22, 2009 6by 12–14 %. In general, a decrease in the engine performance characteristics is related toa lower energy content of such fuels due to a higher share of oxygen in TAG molecule (cca 10%). The presence of a small share, 3 and 6 vol. %, of EtOH leads to a negligible increase ofoxygen content (by 1–2 %). Based on the measured data (Tab. 3), EtOH has no effect on theperformance characteristics when compared with RO. Lower performance characteristics ofthe engine fueled with tested biofuels relate to their lower energy content. At the performancecharacteristics in the Tab. 3 the different fuel densities are respected. Tab. 3 Performance characteristics of tested fuels RO RO Fuel DF RO CF + 3 % EtOH + 6 % EtOH Max. output 127 112 110 114 113 (kW) Max. torque 476 418 410 416 412 (N m) Reached accelerations were similar for TAG based fuels and DF. Within acceleration testsin the given speed ranges (Tab. 4), shorter time intervals were measured for the fuels with asmall content of EtOH in spite of unchanged performance characteristics of the engine. Thespeed ranges in the Tab. 4 are as follows: 40→80 km/h, 60→100 km/h and 80→120 km/h. Tab. 4 Accelerations in seconds for tested fuels RO RO Fuel DF RO CF + 3 % EtOH + 6 % EtOH 40→80 (2nd gear) 5.28 5.48 5.44 5.32 5.12 60→100 (3rd gear) 10.2 10.5 10.4 10.14 9.52 80→120 (4th gear) 21.7 22.5 22.4 20.32 19.523.3 Emission tests Based on the previous study , opacities of tested alternative fuels exceed 3.5–4 timesthose measured for DF. Higher opacity values are probably related to the presence of aglycerol moiety in the TAG molecule. Obtained opacity values (Tab. 5) are lower in the caseof engine with higher injection pressures. This is achieved in engines with modern injectionconception, equipped with a common rail (CR) injection or unit injection system UI (pump-nozzle). Here, the injection pressures reach 2050 bar while in TDI engines  thesepressures reach 850 bar only. Such an engine fueled by DF does not need so higher pressuressince low opacity is obtained even at lowered injection pressures. The engines manufacturedafter 2000 use almost exclusively these types of injection, where in one cycle several fuel
44th International Petroleum Conference, Bratislava, Slovak Republic, September 21-22, 2009 7injections are realized. Higher opacity values can be reduced using in-series produced andcommercially available filters of solid particles. Applying this approach, the opacity reachesvalues lower than those permitted by a standard. Measured opacity values (Tab. 5) are thelowest for CF. The filters for solid particles were not used during the mentioned tests. Opacities of the engine fueled with the RO containing EtOH are lower than those usingreference DF, however, the differences in the values for pure RO and RO–EtOH blends arenot relevant (Tab. 5). Tab. 5 Opacities of tested fuels at free acceleration Opacity Fuel (%) DF 17.0 RO 13.9 CF 11.7 RO + 3 % EtOH 13.8 RO + 6 % EtOH 13.4 The contents of CO, CHx and NOx in exhaust gases are given in the Tab. 6. The content ofCO was very low, practically at determination limit. There are no substantial differences inCHx content for all tested fuels. Generally, the level of unburned hydrocarbons in exhaustgases is low. The content of NOx is the lowest in conditions of idling and increases with theincreased speed. Higher content of NOx is usually connected with higher operationaltemperatures in the cylinder. In cases of all tested PPO, the content of NOx is lower incomparison with DF, the differences are decreasing with the speed increase. Tab. 6 CO, CHx and NOx emissions of tested fuels DF2 RO CF RO RO + 3 % EtOH + 6 % EtOH Idling 0 0.052 0 0 0 60 km/h 0 0 0 0 0 CO 90 km/h 0 0 0 0 0 120 km/h 0 0 0 0 0 Idling 0 4.8 1.6 11.6 3.6 60 km/h 19.6 15 17.2 22 16.8 CHx 90 km/h 31 25.4 23.8 25.4 26.2 120 km/h 20 20 17.2 20.6 22.6 Idling 44 30.2 27.4 29 9.2 60 km/h 87.6 76.8 116.2 124.6 94 NOx 90 km/h 294.6 302.8 337.2 340.2 285 120 km/h 476.2 472.8 491 475.8 426
44th International Petroleum Conference, Bratislava, Slovak Republic, September 21-22, 2009 8 In Tab. 6, the values of CO, CHx and NOx emissions of the tested fuels with the smallshare of EtOH are also given. The CO content in the exhaust gases was very low. Contents ofCHx and NOx are almost identical for RO containing EtOH as those for DF, the emissionprofile is not influenced by EtOH content. The concentrations of uncontrolled emissions (aldehydes and ketones) are at level ofdetermination by all tests and the results are not presented in the table form.3.4 Fuel consumption measurements Fuel consumption determined within the test cycle ECE 83 was most favorable for DF(Tab. 7). Consumption of PPO based fuel was higher by 12–16 % than that of DF. Theconsumption of fuels containing small amount of EtOH are higher by 14–20 % comparing toDF and by 2–7 % comparing to pure RO. Tab. 7 Consumptions of tested fuels according to ECE 83 Fuel consumption Fuel (g/cycle ECE 83) DF 780.5 RO 873 CF 904 RO + 3 % EtOH 889.5 RO + 6 % EtOH 937.04 Conclusions Performance and emission tests of investigated fuels based on natural triacyglycerols ofvegetable and animal origin documented that the parameters of these fuels are comparable tothose of fossil diesel. The presence of ethanol in PPO has no negative impact to theperformance and emission characteristics, with exception of flash point. Operation of avehicle fueled with chicken fat was, from technical viewpoint, trouble-free. In this case,noteworthy results of performance and emission tests, fuel consumption including, wereachieved. A remarkable potential is anticipated in the case of animal fats use for stationaryengines in cogeneration units operation.AcknowledgementThis work was supported by the Slovak Research and Development Agency under the contractNo.APVV-20-037105.
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