Stability of Biodiesel Used as a Fuel for Diesel Engines and Heating Systems Summary Report August 2003

Transcription

1 Stability of Biodiesel Used as a Fuel for Diesel Engines and Heating Systems Summary Report August 2003

2 Stability of Biodiesel Used as a fuel for diesel engines and heating systems. Summary Report. Wieselburg, August Published by BLT Wieselburg, Austria (2003). Supported by the European Commission Copyright 2003, BLT Bundesanstalt für Landtechnik, A 3250 Wieselburg, Austria Legal Notice: The responsibility for the content and the Copyright for further use of the entries lies with the authors. Compensation for faulty, incomplete or omitted entries is excluded. All rights reserved. Published by: BLT Bundesanstalt für Landtechnik (Hrsg.) Federal Institute of Agricultural Engineering Rottenhauser Strasse 1, A 3250 Wieselburg, Austria

3 BIOSTAB Summary report Page 1 Project identification Title of the project: Acronym of the project: Contract number: Framework programme Stability of Biodiesel BIOSTAB QLK5-CT th Framework programme Quality of Life and Management of Living Resources Key action Sustainable Agriculture, Fisheries and Forestry Project costs: 1.4 mill. Duration: 1 March August 2003 Co-ordinator: BLT Bundesanstalt für Landtechnik (Austria) (Federal Institute of Agricultural Engineering) Heinrich PRANKL A 3250 Wieselburg, AUSTRIA Tel.: Fax: heinrich.prankl@blt.bmlfuw.gv.at Website: Partners: ITERG (France) Dr. Florence LACOSTE SSOG (Italy) Dr. Paolo BONDIOLI Institute of Chemistry University Graz (Austria) Univ.-Prof. Dr. Martin MITTELBACH TUG University of Technology Graz (Austria) Jürgen BLASSNEGGER OMV AG (Austria) Dr. Thomas BREHMER TEAGASC (Ireland) Dr. Andreas FRÖHLICH NOVAOL (France) Bertrand DUFRENOY OLC Ölmühle Leer Connemann (Germany) Dr. Jürgen FISCHER

4 BIOSTAB Summary report Page 2 Content 1 Objectives Project Workplan Determination methods Storage tests Antioxidants Utilisation of biodiesel Biodiesel as automotive diesel fuel Biodiesel as heating fuel Results Determination methods Storage tests Antioxidants Work package 4: Utilisation of biodiesel Biodiesel as automotive diesel fuel Biodiesel as heating fuel Summary and Conclusions...10

5 BIOSTAB Summary report Page 3 1 OBJECTIVES In order to ensure customers' acceptance, standardisation and quality assurance are key factors in the market introduction of biodiesel as a transport and heating fuel. In 1997 the European Commission gave a mandate to CEN to develop standards concerning minimum requirements and test methods of biodiesel. It was turned out, however, that in one complex key parameter, fuel stability, detailed research is absolutely needed. The objective of the project was to establish criteria and the corresponding analytical methods to determine the stability of biodiesel. The detailed aims are: 1. appropriate methods for the determination of stability under realistic conditions 2. understanding of the influence of storage conditions on the quality of biodiesel 3. definition of a minimum level of natural and/or synthetic antioxidants 4. determination of the effects of the fuel stability during utilisation of biodiesel as automotive diesel fuel and as heating fuel. 2 PROJECT WORKPLAN Nine experienced partners from industry, science and research representing biodiesel research in Europe were involved in the project. The project was divided into 4 thematic work packages. For each work package (WP) a leader is responsible to co-ordinate the tasks between the several partners. The project started in March 2001 and could be finished in August Determination methods (Dr. Florence Lacoste, ITERG, France) The objectives of the work package were to evaluate and/or develop accurate methods for determination of oxidation, storage and thermal stability. Three items referring to behaviour of biodiesel submitted to oxidative conditions have been defined by the CEN working group in charge of specifications in the execution of Mandate M/245, depending on the uses of biodiesel : Oxidation stability (presence of oxygen): although EN (Rancimat test) has been chosen as the test method for thermal oxidation stability in the biodiesel standards, it has to be to clarified the relationship between the induction period provided by this test and other quality parameters. Indeed, this test is unfavourable to distilled biodiesels compared to undistilled products without correlation of experience on the field. Thermal stability (absence of oxygen) and storage stability: Due to a lack of knowledge no test method could be fixed for these two items in the standards for biodiesel. One of the main goals were to select a method for each item considering criterions such as reflection of real conditions, correlation with quality parameters of biodiesel, precision, cost. 2.2 Storage tests (Dr. Paolo Bondioli, SSOG, Italy) In this work package different storage environments were simulated. Previous research demonstrated that storage conditions (i.e. temperature, light, atmosphere, presence of pro-

6 BIOSTAB Summary report Page 4 oxidant metals, etc.) have a strong impact on storage behaviour. Also the nature of feedstock may dramatically influence the final results. The main objective of this work package was to carry out a systematic study of the changes occurring in biodiesel samples, prepared using different feedstock and different production technologies, during a long term storage experiment in real conditions. For each sample 15 parameters were monitored periodically. After the results became available of a questionnaire issued by WP1 regarding the common storage conditions of biodiesel in practice, storage tests in presence of direct light and at temperatures higher than ambient temperature were discarded. Major emphasis was devoted to the study of storage behaviour of additivated samples. 2.3 Antioxidants (Univ.-Prof. Dr. Martin Mittelbach, University Graz, Austria) Within the European specifications the value for the oxidative stability, expressed as the induction period using a Rancimat instrument, has to be higher than 6 h and should be guaranteed during the whole supply chain of the fuel. However, the stability of biodiesel varies significantly depending on the feedstock as well as the process technology. Biodiesel produced from rapeseed oil showed higher induction periods, whereas biodiesel produced from used frying oil, sunflower oil, soybean oil or animal fat had similar or significantly lower values for the induction period. In the future, biodiesel of lower than specified stability will need to be stabilised with antioxidants. Different commercially available natural and synthetic antioxidants were evaluated and the optimum cocentrations of the most suitable antioxidants were determined. In addition the effects of selected antioxidants on parameters specified in the EU biodiesel standard EN were also determined. 2.4 Utilisation of biodiesel Biodiesel is used both as automotive diesel fuel and as heating fuel. Bench tests and field tests were carried out on vehicles and injection systems, as well as on heating systems. The results will help to find a relationship between laboratory test methods and effects during the utilisation. Due to the variety of applications the test program is very comprehensive Biodiesel as automotive diesel fuel (Jürgen Blassnegger, University of Technology, Graz, Austria) The test programme comprised: bench tests with 3 different injection systems and test fuels with a low, a standard and a high stability long term tests with two diesel engines a fleet test using biodiesel with a low stability a fleet test with blends of fossil diesel and biodiesel with a low stability Biodiesel as heating fuel (Dr. Thomas Brehmer, OMV, Austria) The objective of the work package was to investigate the effects of the fuel stability while being used in heating systems. The effects of the fuel stability during the application and the operation parameters of the residential heating systems using blended fuels were studied. Therefore bench and field tests were carried out on different heating systems. The test programme comprised: bench tests with heating systems (emission, operation, long term test) field tests with 8 heating systems.

7 BIOSTAB Summary report Page 5 3 RESULTS 3.1 Determination methods Oxidation stability: The Rancimat test (pr EN 14112) was evaluated for seven biodiesel samples (Methyl ester from rape seed oil, sunflower oil, used frying oil and tallow). Determination of quality parameters was carried out on aliquot samples along every each ½ hour. All parameters present a visible variation along the Rancimat test except UV 270 nm. At the end of the Rancimat induction period (RIP), the samples do not meet FAME or Oils and Fats specifications such as viscosity, acid value, ester content or peroxide value. The main conclusion is that induction period determined by conductivity is well correlated to degradation of quality parameters along Rancimat test. Storage stability: At the beginning of the project it was decided to evaluate two test methods. The first one is the petroleum field reference method (ASTM D4625 : storage at 43 C during 24 weeks), the second one corresponds to an accelerated IP48/IP306-like method at 90 C with an airflow above the surface of the sample. For each test method, a list of seven quality parameters was defined. Critical review of evaluation storage stability with ASTM D4625 was carried out. Because it was difficult to make a correlation between ASTM D 4625 and results of accelerated method initially proposed (accelerated IP48/IP306-like method at 90 C), it was decided to use Rancimat apparatus, specially modified for storage stability evaluation. A stream of purified air (10l/h) is passed above the surface of 3 grams of sample heated at 80 C during 24 hours. Then peroxide value, ester content and polymer content are measured. The modified Rancimat test is suitable for use in terms of repeatability, significance and it is easy to handle. Peroxide value determination shows the best correlation with ASTM D 4625 (storage at 43 C during 24 weeks). Using this method bad stability and good stability samples can be separated. Thermal stability: At the beginning of the project it was decided to keep the ageing conditions of ASTM D 6468 (150 C, 180 or 90 minutes) as they were considered not too far from the real conditions. A list of seven quality parameters to be looked at before and after the ageing test, was defined. But the variation of quality parameters (acid value, Rancimat, ester content) after the ageing test was too low to be measured correctly. Thermal stability tests at 200 C (oil bath) during 5 hours applied to all samples collected for WP1 demonstrate that samples coming from European productions are really stable when heated at high temperature in absence of air flow. Viscosity and acid value were chosen to evaluate the ageing effect. But repeatability results were not acceptable. So, it was decided to use Rancimat apparatus with a procedure specially modified for thermal stability evaluation. Eight grams of sample are aged for 6 hours at 200 C in open tubes with air exposure. After ageing and cooling, polymer content is determined by HPLC. The modified Rancimat test is suitable for use in terms of repeatability and it is easy to handle. 3.2 Storage tests A systematic study on the chemical and physical changes of eleven different samples of biodiesel has been carried out during July 2001 and October The results obtained so far allow to evaluate the impact of the different feedstock, of the different technology and of the use of selected antioxidant on the chemical properties of aged biodiesel samples. The scenario of different real possibilities in terms of feedstock and production technology can be regarded as more as complete, because also samples from beef tallow and from used frying oils, actually representing a niche market with a wide future potential have been included in these storage tests.

8 BIOSTAB Summary report Page 6 After the discussion on all experimental data we can come to some conclusions: After a one year storage study carried out on eleven different biodiesel samples, we can say that it was not possible to observe strong changes in 15 monitored characteristics. All samples met the specification limits even at the end of storage period, with the exception of RIP (Rancimat induction period); PV (peroxide value) changes are different depending on samples. For samples initially not too oxidised, PV increase is slow. For samples initially oxidised, PV first increases and then decreases due to the formation of secondary oxidation products. We must remember that PV is not included in the biodiesel specification table; the most important changes were recorded in oxidation stability, evaluated according to Rancimat test: this fact means that ageing takes place in biodiesel, independently from the monitored parameters and makes biodiesel less stable during time. This phenomenon can be monitored by means of Rancimat test EN The Rancimat takes a picture of the actual situation, but it is impossible with this test to predict the RIP value after a long term storage. There are ageing processes that can t be observed by analysing the parameters reported in pren and pren and a method for storage stability prediction is hence necessary; RIP decreases with time: the rate of this decrease depends on the quality of the sample and on storage conditions as well; a proper additivation allows RIP to increase even greatly: studies could be carried out to identify quality and minimum quantity of antioxidant. The results of work package 3 (Antioxidants) provides several answers to this question. the right additivation must, in our opinion, allow the sample to fulfil specification for oxidation stability for at least six months; super-additivation procedures leading to a RIP higher than 20 hours have no meaning and might have a negative impact on other parameters (e.g. Conradson Carbon Residue); once again the necessity of correct storage and logistic solutions, to avoid the contact of biodiesel with air during its complete life cycle has been pointed out. The impact that a simple and occasional shaking of product in presence of air is really impressive and biodiesel actors must take account of it. 3.3 Antioxidants Based on the findings of an extensive literature survey, twenty natural and synthetic antioxidants were selected, all of which are commercially available at an affordable price. The stabilising effect of the selected antioxidants was evaluated with biodiesel prepared from four different raw materials: RME (rapeseed oil methyl ester), SME (sunflower oil methyl ester), UFOME (used frying oil methyl ester) and TME (tallow methyl ester). Both distilled and undistilled biodiesel samples were evaluated and Rancimat induction times were used to indicate oxidation stabilities. Antioxidants with good stabilising effect were tested at different concentrations in order to determine the optimum antioxidant levels. The effect of natural antioxidants on the oxidation stability of biodiesel was also evaluated. The relatively high stability of RME which cannot be attributed to the detected natural antioxidants is being investigated. The results can be interpreted as follows: Generally, the limit for the proposed oxidative stability could be reached by addition of antioxidants with all different types of biodiesel.

9 BIOSTAB Summary report Page 7 Within the variety of antioxidants, synthetic antioxidants were more effective than natural. The stabilising effect of the different antioxidants is strongly dependent on the composition of biodiesel and the production process. Under the given conditions, no significant negative influence of antioxidants on fuel behaviour could be observed. Influences of additives on engine performance have not been investigated within the project. However, to minimize possible negative effects it is recommended to use antioxidants at very low concentrations. Tocopherols, α-, δ-, and γ- delay the oxidation of SME (sunflower oil methyl ester), RME (rapeseed oil methyl ester), WCOME (waste cooking oil methyl ester) and TME (tallow methyl ester), in some cases by more than a factor of 10 compared to methyl esters without tocopherols. γ-tocopherol was found to be the most effective of the three, α-tocopherol the least, and their antioxidant effect increased with concentration up to an optimum level. Above the optimum level the increase in antioxidant effect with concentration is relatively small. The stabilising effect of tocopherols was also found to depend on the composition of the methyl ester, the order of effectiveness was found to be: TME>WCOME>RME>SME. Oxidation of methyl esters begins with the build-up of peroxides. Irreversible oxidation, indicated by viscosity increase, starts only after peroxides reach a certain level. Tocopherols stabilise the methyl esters by reducing the rate of peroxide formation, thereby extending the time needed to reach the peroxide level where viscosity starts to increase. The carotenoids astaxanthin and retinoic acid had no detectable effect on the stability of SME. Similarly β-carotene added to CME along with some α-tocopherol, to give the same tocopherol composition and maximum absorbance as RME, had no stabilising effect on the methyl ester. However a carotenoid, at much higher level than β-carotene, was detected in RME, but it was not present in less stable methyl esters such as CME and SME. The effect of the detected carotenoid on the stability of RME is being investigated. 3.4 Work package 4: Utilisation of biodiesel Biodiesel as automotive diesel fuel Bench tests: Long term tests were carried out with 3 different modern injection systems on the test bench. 3 fuel qualities, rape seed oil methyl ester with a low (induction period hours according pren 14112), a standard (induction period 6 hours) and a high stability (induction period hours) were used. The fuels were tested in long term tests in 3 different modern injection systems (heavy duty common rail, passenger car distribution pump, passenger car common rail). Wear and sedimentation were analysed after the tests. Chemical analysis of the fuels accompanied the tests. Wear and sedimentation were found to be normal for the runtime at each injection system. All enumerated effects were more salient at those parts which were operated in test runs with fuels with the lower oxidative stability. Fat similar deposits could only be detected at system parts which were operated under very strong conditions (RME low oxidation stability, no change of the fuel during the complete test run at the injection system test bed). At all other systems no critical sedimentations could be detected. After the test runs, the functionality was given in each tested system.

10 BIOSTAB Summary report Page 8 Two long term real world engine tests were carried out on the test bench fuelled by biodiesel with a low (induction period 3.5 hours according pren 14112) and a high stability (induction period 20 hours). The direct injection diesel engine were equipped with a modern common rail injection system. The test duration at each test was 500 hours. The measured differences in emissions and power between diesel- and RME-operation at the begin of each test were normally for biodiesel use. The power loss and the different in the injection amount after a 250-hour runtime were higher than expected. The analyses of the test run engines show that the abrasion was normal for a 500-hour runtime and no significant difference to diesel operation was notified. Fleet test with pure biodiesel: Four passenger cars were operated in a fleet test with a low stable biodiesel from July 2001 to November The test fuel was pre-aged by a special treatment with temperature and air. The oxidation stability determined by the induction period (Rancimat, 110 C) could be reduced from 7 hours to lower than 2 hours. Two cars were equipped with a fuel distribution pump, the other cars with a pump injector system. The passenger cars were used in typical operation, mainly on the motorway. Distance and fuel consumption were recorded in a log book. Some temperatures (engine oil, fuel filter, fuel tank, ambient) were recorded automatically during the whole test period. The total driving distance ranged from to km per car. Initial and final tests were carried out at the roller test bed at TUG - University of Technology in Graz. The tests comprised performance and exhaust emission analyses (CO, HC+NOx, particles). The differences in emissions and performance could not be assigned to the biodiesel operation (in combination with the results of the injection system check after the test run). The diesel measurement at the end of the biodiesel field test can only be assessed to a certain extent (short conditioning time). Before and after the field test all limited emissions were below the EURO 3 level (EURO 3 limit vehicle group 2, 1305 kg<rw<1760 kg). After the tests the injection systems were inspected by the manufacturer. The functions of all systems were found to be okay. Swelling of elastomers was found in a distributor pump which can lead to leakage particularly when using diesel fuel. RME deposits could be found on several parts of a distributor pump. Traces of oxidation and notable corrosion were found on some parts of the pump injectors. The continued use of the UI-pumps could lead to fault. One fuel filter blocked and some fuel filters had to be changed in winter. The results of the field test are obtained from four individual cars. A general conclusion about the performance with low stability biodiesel cannot be drawn. This would require an extensive car fleet and a total coverage of all field influences. It would have to include the employment of critical car applications as well as boundary operation conditions like full load and idle periods extending over several weeks. Vehicle fleet test with a diesel fuel/fame blend In a 19 months fleet test run with 4 diesel vehicles (light duty LD; heavy duty HD, passenger car) the performance of a diesel fuel (EN 590) blended with 5% UFOME (used frying oil methyl ester) was evaluated. Parameters controlled regularly during the test were fuel quality, cleanness of the fuel storage and supply system and its operability, vehicle exhaust emissions, engine lubricant performance, driveability of the vehicles in warm and cold conditions, cleanness and wear of the vehicles` fuel systems and fuel injection equipment.

11 BIOSTAB Summary report Page 9 Having successfully ended the test at a total distance of approximately 66,000 km driven in daily traffic no significant complaints about the operability of the vehicles were registered. No excessive wear or deposit build up occurred during this period compared to previous results gained in fleet tests with diesel fuel. The engine lubricant showed a similar performance to the experience with pure diesel fuel and there was no need for a premature change of the lubricant. A moderate increase in exhaust emissions was measured during the test interval. The fuel storage and delivery system did not suffer from deterioration. The quality of the fuel remained constant in terms of most specification parameters. Microbial contamination was not recorded, probably due to proper cleaning of the logistic system at the start of the test. The oxidation stability in the bottom layers of the storage vessels increased dramatically and exceeded the limit of EN 590 (25 g/m³; EN ISO 12205) by far Biodiesel as heating fuel In general the bench tests with 5 different heating units showed different results depending on the operation mode of the heating system: stationary or non stationary conditions. Under stationary conditions the emissions are as low as expected. All 5 tested units show emission parameters within the limits for small scale heating systems given by the authorities. However during the starting procedure of the heating units (medium warm start non stationary condition) the concentration of unburned hydrocarbons and carbonmonoxid in the flue gas were some what higher than under stationary conditions. These irregularities depend very much on the technology of the heating units. Additionally, these heating systems having high emissions during the starting process, show worse CO and CxHy emissions with increased FAME percentage in the blend. In the long term test of three different heating units with different fuels there occur minor irregularities. Unit 1 and 2 operate under the following test circumstances: 1.) new heating system installations, 2.) clean filter, 3.) good maintenance of the heating units 4.) proved good quality of the LHO (light heating oil) and FAME (5% and 20% blends), 5.) 2500 hours test duration and 6.) 5000 litre total fuel consumption. LHO with 5% FAME+Antioxidants (fuel of Unit 2) was additionally treated with water (about 2300 ppm). The water caused the expected microbiological (bacterial, mouldy) growth in the storage tank. After two weeks the test resulted in a total blockage of the filters and lead to a break down of the unit. The tank was cleaned and filters were changed and the long term test could be started again with new, dry fuel without further problems. Unit 3 had 3 times a blockage of the oil feed rate counter. This took place by using a 5% blending component FAME with low stability. Following blending components were used: 1: UFOME artificial aged (simulation of storage) 2. UFOME fuel stored for 1 year 3. RME distilled and stored for 1.5 year. Up to now in the field test no significant problems can be reported (no break downs, no significant changes of the investigated fuel parameters, no significant changes of the emission values and the combustion behaviour). Emission values were checked only in the stationary combustion conditions. But it has to be taken into account that the conditions for the field test were as perfect as possible. - proved good quality of the blending components LHO and FAME (RME, UFOME) - only 5% blends with UFOME or RME - 4 of 8 units run with a fuel where an antioxidant was added - consumption of fuel blend differ in the test households from litre

12 BIOSTAB Summary report Page 10 - test duration: 18 months - new installations, burner, boiler, tanks, oil pipes - one pipe fueling system, - new oil filters, - good maintenance of the heating units Open Questions which remains to be answered Microbiological attack of the blends by bacteria or germ - because of the fast biological decomposition of FAME Storage stability of the blends - influenced by the materials of the tank, plastics, softening agents Reason for higher foaming behaviour during filling - problems with tank run-over - problems with a correct volume measurement at the filling procedure Decomposition of the EUROMARKER - or other additives - EUROMARKER (European tax marker) Effects of the used plastic material - Sealing, Pipes, parts in flow counter, pumps, nozzles. 4 SUMMARY AND CONCLUSIONS Stability determination methods: The method for determination of oxidation stability (EN Rancimat test) is well correlated to the development of quality parameters. Biodiesel shows a high resistance against temperature. A method for detecting the thermal stability can be proposed using the Rancimat equipment: The difference of polymer content is evaluated by HPLC. A method for determination of the storage stability can be proposed also by using the Rancimat equipment. Samples with a bad and a good stability can be separated clearly. Biodiesel storage: Biodiesel can be stored under normal storage conditions without a dramatic change of quality parameters during a period of one year. The most changes can be observed on oxidation stability and on peroxide value, depending on the quality and on the storage conditions. The right additivation ensures that the samples fulfil the specification also after a storage period of one year. Nevertheless correct storage and fuel logistic is absolutely necessary. Contact of air, water and sunlight has to be avoided properly. Antioxidants: The limit for oxidation stability can be reached by appropriate addition of antioxidants with all different types of biodiesel. Within the variety of antioxidants, synthetic antioxidants are more effective than natural. The efficiency and the necessary amount of the different antioxidants are strongly dependent on the feedstock and biodiesel production technology. No significant negative influence of antioxidants on fuel behaviour could be observed so far. Influences of additives on engine performance have not been investigated within the project. However, to minimize possible negative effects it is recommended to use antioxidants at very low concentrations. α-, δ- and γ-tocopherols delay the oxidation of methyl esters significantly. γ-tocopherol was found to be the most effective of the three.

13 BIOSTAB Summary report Page 11 Bench and field tests with biodiesel as automotive fuel: Functionality was given with all injection systems after long term tests with different fuel stabilities. Wear and sedimentation were found to be normal for the runtime. Fat similar deposits could only be found at parts being operated at very strong conditions Long term engine tests didn t lead to effects related to the fuel stability. The injection systems of 4 vehicles from a field test fuelled by a low stability biodiesel were found to be ok after the test. But traces of oxidation could be found on some parts of the pump injector. Fuel deposits could be found on several parts of a pump injector. Although no problems in relation with the low stability of the fuel occurred it is recommended to ensure the minimum stability required by the standards in order to avoid problems during application under very sharp conditions. The field test using a low stability biodiesel as 5% blending component to fossil diesel did not lead to negative effects in terms of wear, deposits, engine lubricant, fuel storage and delivery, microbiological contamination, fuel quality. As critical points remain oxidation stability (EN ISO as requested by EN 590) and the absolute need to clean and keep clean the storage infrastructure (vessels, pipes) of biodiesel. Bench and field tests with biodiesel as heating fuel: In the 5 tested heating units no differences were found in short term bench tests with heating units under stationary conditions. In contrast the HC- and CO-emissions during the starting procedure were higher than with pure fossil heating fuel. The results depend very much on the technology of the heating units. In long term tests of three units with different fuels problems occurred in the oil feed rate counter at fuels with a very low stability. Up to now no significant problems can be reported from a field test with 8 heating units during two heating seasons. Fossil heating fuel containing 5% FAME (RME and UFOME and Antioxidants) was used. Open questions concentrate on microbiological attack of blends, storage stability of blends, foaming and material compatibility of blends.