Tractors suitable for vegetable oil (exhaust gas stages I to IV) in long-term test

Since the beginning of 2002, the Technology and Research Center (TFZ) in Straubing has been working on questions such as what alternative solutions to finite fossil raw materials would exist and to what extent they can be used, for example, in transport (on- and off-road).

Given that a general improvement considering the environmental impact is demanded from agriculture, the Expert Group on Bioenergy Resource Management (ExpRessBio) is ever since researching the use of plant oil fuel in agricultural and forestry vehicle fleets. In doing so, not only climate protection and other ecological factors are taken into account, but also the social acceptance as well as economic opportunities and risks.


Currently, the research focus lies mainly on rapeseed oil is the main research and has arose as the standard test fuel alternative, even though there are actually thousands of other oil plants worldwide. However, it is largely unknown how sustainable these other plants can be used without special modification. Even sunflower, palm or soybean oil are feared to cause long-term damage to engines. In the past, it was as lamp oil, lubricant or as a raw material in soap production, but after various breeding processes the harmful erucic acid and bitter substances could be removed. Thus, rapeseed became the most popular oil plant in Germany and is used in the kitchen, as animal feed, as technical multiplayer but also as fuel.

Unfortunately, the use of this natural, liquid gold instead of diesel has become economically unattractive for the average petrol consumer since the tax concession was abolished in 2013. In addition, the still ongoing, impartial discussion about the use of an alimentary as gasoline puts this solution in a negative light. As a result, the manufacturers lack a reason for a corresponding series production of engines, and the infrastructure (fueling stations) that had been established in the meantime has also collapsed. However, there is still cause for use in agriculture and forestry until the end of 2020: here, a full energy tax refund of 45 cents per liter (from 2013) will be granted upon application in accordance with § 57 of the Energy Tax Act (EnergieStG).

Test project with 20 vegetable oil tractors in field use

In order to prove the suitability of rapeseed oil as a fuel in agriculture, Dr. Edgar Remmele (TFZ) and his colleagues have carried out various studies in recent years. The aim was and is to further reduce the limited pollutant emissions as well as the greenhouse gas emissions. According to the research team itself, rapeseed oil fuel has a greenhouse gas reduction potential of up to 91%. In addition, sustainable production must be certified in accordance with the Renewable Energy Directive (RED) and fuel quality must be standardized according to DIN 51605. Added to this, of course, is the considerably lower impact on the vegetation and eventually the groundwater when using the vehicles on the sensitive areas such as farmland and forests.

In a separate test series, 20 vegetable oil tractors from Fendt, Deutz-Fahr and John Deere were tested over more than 60,000 operating hours (OH) in the field and in the laboratory. All models are equipped with specially developed common rail engines, which compensate the differences in viscosity and compressibility of the vegetable oils compared to conventional diesel due to their electronically controlled injection or engine control software, thus avoiding the previously problematic reduced performance. Up to that point, there had hardly been any experience, especially with modern tractors, i.e. models with a complex exhaust after-treatment (stages IV and V), to evaluate especially the operating and emission behavior when using rapeseed oil fuel.

In this project, the tractors were used both on state experimental farms as well as on the cultivation areas of the TFZ and always carried a "Portable Emission Measurement System" (PEMS) with them during normal activities. Depending on the model and bodywork, the measuring device was installed in a protective box and with appropriate fixings at the front or rear. The tractors were operated almost exclusively with rapeseed oil fuel according to the valid standard (DIN 51605:2016). The few, minor surpasses of the emission limit values were mostly in the range of the measuring accuracy of the test procedures and could therefore be evaluated as uncritical.

So at the beginning, the emission behavior was observed in the laboratory, but what does it look like in real operation? Over the course of the 60,000 hours of operation, the vegetable oil tractors proved to be almost consistently reliable, the few malfunctions were mostly limited to the low-pressure fuel system or the sensor technology. Thanks to the injection software, the common rail injectors were still fully functional in operation with rapeseed oil even after more than 6,000 operating hours and hardly suffered any loss of performance. In addition, regular engine oil analyses showed that thanks to the common rail injection technology, wear and tear as well as maintenance costs were comparatively low.

The review is therefore quite positive: the operation of the tractors was reliable both on the test bench and in the field, and the vegetable oil tractors were in no way inferior to the diesel models in terms of exhaust after-treatment systems. On the contrary, the test bench even fell below the limits of exhaust gas stage IV, and emissions of carbon monoxide (CO), hydrocarbon (HC) and particulate matter can be kept within the detection limit by means of particulate filters and oxidation catalysts. Best of all, however: both on the test bench and in the field, the measured emission values were below the possible limits, i.e. those being discussed for the coming legislation

Good is never good enough

It would not be Dr. Remmele and his colleagues though if there were not already further investigations underway: on the one hand, the long-term operating behavior of the exhaust gas after treatment of the rapeseed oil tractors is to be tested. In addition, it is still to be determined whether the next generation of tractors (exhaust gas stage V) with rapeseed oil fuel will meet the new limit value for the number of particles on the test bench. Last but not least, the emission behavior in actual driving operation with regard to particle number and particle size distribution will be tested in order to enable a potential market launch of rapeseed oil fuel-compatible tractors by the industry.

Up to that point, the conclusion can be articulated as such: Modern vegetable oil tractors of exhaust gas stages I to IV can be operated reliably and with low emissions. Within the scope of the test project, 584,000 liters of diesel fuel could be replaced, thus avoiding greenhouse gas emissions of approx. 1,389,000 kg CO2 equivalents. And also the by-product press cake, in total approx. 1,100,000 kg, contributes to climate protection as a domestic protein animal feed.

Now all that is missing are the legal incentives to grant this diesel alternative a long-term market entry.

Detailed information can be found on the TFZ website (publications)

Technologie- und Förderzentrum im Kompetenzzentrum für Nachwachsende Rohstoffe (TFZ)
Schulgasse 18
D-94315 Straubing

Copyright Bilder: TFZ Straubing