Biodiesel puts less of a burden on systems for the after-treatment of exhaust gases than previously thought
Brief study by the UFOP considers more than 7900 items of market-relevant analysis data extending over the previous ten years
When it comes to approving exhaust aftertreatment systems, the content of trace elements in fuels plays an important role. All metals that are emitted during engine combustion can increase the exhaust gas backpressure in the aftertreatment system to impermissible values due to the formation of ash. In addition, metal coatings on exhaust aftertreatment systems and catalytic converters are contaminated or deactivated by phosphorous and alkali elements.
Taking these facts as a basis, the Union zur Förderung von Oel- und Proteinpflanzen e.V. (UFOP) commissioned Analytik-Service GmbH (ASG) with the evaluation of market-relevant Biodiesel analysis results for the years 2000 to 2010.
More than 7900 individual items of data regarding element contents (Na, K, Ca, Mg, P, S) in Biodiesel samples are evaluated in the brief study now available. The databases of the Arbeitsgemeinschaft Qualitätsmanagement Biodiesel e.V. (AGQM) and ASG served as a data basis.
To be able to provide developers of engines and exhaust aftertreatment systems with realistic data for estimating the potential loads of ash forming agents and catalytic converter toxins, three different calculation methods were selected and their results compared with data from field and test bench inspections by Deutz AG. Worst case scenarios based on the limit values indicated in the Biodiesel standard DIN EN 14214 have proven to be unsuitable here. Model calculations based on these values are sometimes ten times over the actual results. Significantly better results are provided by mean values, based on measured values of real samples, and which also integrate results below the relevant limit of determination into the statistical evaluation. The mean value calculations were specified more precisely using the re-evaluation of measured results below the limit of determination, as well as the introduction of weighting factors, in order to allow for the influence of individual measured results, taking into account the market significance of the company examined.
Comparison of the mean values from the simulation calculation for the alkaline earth, alkali and phosphorus contents with data from the field tests, in respect to the loading of SCR catalytic converters and tractor or bus engines made by Deutz AG, revealed very good correspondences. The evaluation also confirmed the benefit of quality assurance measures introduced by the AGQM for Biodiesel producers over the past 10 years. Taking the relevant measuring conditions into account, the data reveals a development towards lower element contents in the Biodiesel.
In summary, it can be established that the role played by Biodiesel in the loading and deactivation of exhaust gas aftertreatment systems is significantly less than previously assumed. Instead, the majority of harmful elements result from the engine lubricating oil.
The UFOP assesses the results of this evaluation, unique in the present form, as evidence that reservations in respect to the contamination of exhaust gas aftertreatment systems for the elements examined are unjustified. These elements do not pose a risk of a functional impairment or reduced service life, if the Biodiesel is produced at the highest level with corresponding quality assurance. DEUTZ AG therefore refers to Biodiesel in AGQM quality with good reason in its approvals.
In the opinion of the UFOP, the elements examined in this study should not therefore be used as an argument countering an approval of Biodiesel as a blend component or as a pure fuel. The Biodiesel quality is clearly much better with these parameters than specified in the standard for Biodiesel. The UFOP therefore regards further development as necessary to improve the quality analysis for these elements.
The detailed study is available as a download.