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One political and economic aim in Europe is to increase the use of renewable energy resources. In the transport sector, up to 10 % of fossil diesel fuel should be replaced by biogenic fuels by 2020. This also means a reduction in crude oil dependency. In the area of diesel fuel, fatty acid methyl esters are introduced since over 20 years as biodiesel. However, biodiesel can lead to an increase of engine oil dilution in passenger cars with diesel particulate filters. During the regeneration of the particulate filters, there is an entry of fuel components in the engine oil. While most of the diesel fuel (DF) evaporates from the engine oil, biodiesel remains in the oil and can cause sludge formation in the engine. A promising approach to reduce this problem is the use of a new type of biogenic fuel, called hydrotreated vegetable oil (HVO). This is also produced from vegetable oil or animal fat. Like biodiesel, HVO is free of sulfur and any aromatics.

The European diesel fuel specification limits the biodiesel content to 7 %. It is, however, desirable to increase the amount of renewables in the transport sector; therefore blending with a higher biogenic fuel content is of interest. Blending of fuels can lead to chemical reactions between fuel components and may result in undesired products. In detail, aged biodiesel from unsaturated FAME and fossil diesel fuels can form oligomers and precipitations with a maximum in the range of B10 to B20. Precursors are oligomers that can be separated from the biodiesel or the blends in an amount of up to 20 %. These oligomers are soluble in the fuel, but they seem to have potency for chemical reactions with fuel components or the engine oil. To prevent tentative problems in the fuel filter, the injecting system and the combustion process itself, the formation of oligomers should be disabled in blends. Alcohols have been proven and tested to dissolve precipitations in the fuel.

A 500 hours endurance test was performed with a heavy-duty engine (Euro IV); MAN type D 0836 LFL 51 equipped with a PM-Kat®. As fuel 100% biodiesel was used that met the European specification EN 14214. The 500 hours endurance test included both the European stationary and transient cycle (ESC and ETC) as well as longer stationary phases. During the test, regulated emissions (carbon monoxide, nitrogen oxides, hydrocarbons and particulate matter), the particle number distribution and the aldehydes emission were continuously measured. For comparison, tests with fossil diesel fuel were performed before and after the endurance test. During the endurance test, the engine was failure-free for 500 hours with the biogenic fuel. There were almost no differences in specific fuel consumption during the test, but the average exhaust gas temperature increased by about 15°C over the time. Emissions changed only slightly during the test.

Rapeseed oil methyl ester, two common fuels and one artificial blend were investigated their effects on particulate emissions. A heavy-duty diesel engine equipped with a diesel oxidation catalyst (DOC) was used for this test. Properties such as composition of particulate matter, as well as particle size and number distributions were measured using an electronic low pressure impactor (ELPI) and a scanning mobility particle sizer (SMPS) besides the regulated emissions: carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM). Furthermore investigations were carried out regarding the influence of dilution temperature on particle number distribution measured via SMPS. Studies were carried out with and without a DOC. Additionally the mutagenic potency of the particulate and gaseous emissions was determined using the Ames test. RME led to lower regulated emissions than common diesel fuel with exception of NOx.

The replacement of petrol derived fuels by biogenic fuels from renewable resources has become of worldwide interest and is scientifically investigated for its environmental costs and benefits. Biodiesel has been proven as a suitable alternative to fossil diesel fuel and blends up to 20% biodiesel with common diesel fuel are a strongly pushed policy in the U.S.A. and the EU. To investigate the influence of blends on the emissions and possible health effects, we performed a series of studies with several engines (Euro 0, III and IV) measuring regulated and non-regulated exhaust compounds and determining their mutagenic effects using the Bacterial Reverse Mutation Assay (Ames-Test) according to OECD Guideline 471. Emissions of blends showed an approximate linear dependence on the blend composition, in particular when regulated emissions are considered. However, a negative effect of blends was observed with respect to mutagenicity of the exhaust gas emissions.

Diesel engine emissions (DEE) are classified as probably carcinogenic to humans. Since 1995 we observed an appreciable reduction of mutagenicity of DEE driven by reformulated or newly designed fuels in several studies. We compared the mutagenic effects of DEE from two different batches of rapeseed oil (RSO) with rapeseed methyl ester (RME, biodiesel), natural gas derived synthetic fuel (gas-to-liquid, GTL), and a reference diesel fuel (DF). Additionally, we determined the regulated emissions of total hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOX), and particulate matter (PM). Compared with the reference DF the two RSO qualities significantly increased the mutagenic effects of the particle extracts by factors of 9.7 up to 59. RME extracts had a moderate but significant higher mutagenic response. GTL samples did not differ significantly from DF.

Two batches of rapeseed oil methyl esters containing approximately 10 ppm phosphorus (RME10), one rapeseed oil methyl ester with a content of less than 1 ppm phosphorus (RME) and common diesel fuel (DF) were investigated regarding their effects on regulated and non-regulated emissions of a modern diesel engine (Euro IV) equipped with an SCR system (selective catalytical reduction of nitrogen oxides). The regulated emissions of carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) and particulate matter (PM) were determined for RME10 and DF. Non-regulated emissions alkenes, alkynes, aromatics, aldehydes, ketones and the particle size distribution were measured for all fuels. Additionally the mutagenic potency of the PM emissions was determined using the Ames test. RME10 led to lower regulated emissions than conventional diesel fuel. Regarding the non-regulated emissions RME showed the lowest values compared with RME10 and DF.

The more stringent regulations for diesel engine emissions lead to the requirement that both fuels and engines must be developed jointly. In the future, so-called designer fuels will help to achieve the stringent limits. In our research, conventional diesel fuel, biodiesel, Swedish low sulfur diesel fuel MK1 and a specially designed diesel fuel were compared using a DaimlerChrysler diesel engine, running the modes of the ECE 49 test cycle. The results for regulated and non-regulated gaseous emissions, particulate matter size distributions as well as mutagenic effects of particle extracts are reported.

In Germany 100.000 tons of biodiesel (rape seed oil methylester, RME) were produced in 1998. 200.000 tons are expected in 2000. Therefore, it is necessary to judge the environmental and health effects deriving from the use of RME in combustion engines. The analysis of particle size and particle number distributions of diesel soot and the determination of its mutagenic effect were investigated. Additionally, emissions of ozone precursors were analyzed for both fuels. Finally, regulated and some important non-regulated emissions from different blends of RME and fossil diesel fuel were determined.

Ecological aspects, the finiteness of fossil resources and the effort to maintain the agricultural structures motivate the use of renewable materials. Since the seventies, the German Federal Agricultural Research Centre (FAL) has been dealing with the technical use of rape seed oil as alternative fuel. It was easy to demonstrate that pure rape seed oil is not suitable for long-term use in conventional diesel engines, because of the severe engine troubles that occurred. Nevertheless, the use of rape seed oil is possible if either the engine concept or the fuel is changed. Via a different combustion concept or the transesterification of the rape seed oil - mostly to rape seed oil methylester (RME) - rape seed oil can successfully be used as fuel. RME resembles diesel fuel (DF) in its physical properties. Since 1982, an agricultural tractor with unmodified engine has been running in a long term experiment at the FAL. No problems caused by this fuel have occurred.