Influence of Bio-Hydraulic Oil on the Efficiency of a Mobile Machine

  Termperature-Viscosity Dependency of Various Oils with Experimental Excavator Copyright: © ifas

The efficiency of hydraulic systems can be influenced by selecting the oil viscosity or viscosity index. This shows that in particular a high viscosity index, i.e. a slight change in viscosity over temperature, is advantageous. By their very nature, bio-hydraulic oils have a much higher viscosity index than mineral oils. The aim of the project is therefore to quantify the influence of bio-hydraulic oil on the efficiency of an example mobile hydraulic system. Possible increases in efficiency and the associated savings potentials in fuel can contribute to increasing the market share of bio-lubricants.

Benefit Procedure
Measurement of the drive power when using mineral oil and bio-oil Equipping a test excavator with measuring electronics
Validation of the performance of biolubricants Acquisition of measured variables of the system
Determination of possible fuel savings Performance of a reference cycle with mineral oil



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Influence of Bio-Hydraulic Oil on the Efficiency of a Mobile Working Machine

Technical Requirements of Bio-Hydraulic Oils

At present, the market for bio-hydraulic fluids is stagnating. The significantly higher purchase price compared to mineral oil products is a market inhibitor. The proof and quantification of a possible fuel saving when using bio-hydraulic oil puts the higher purchase price into perspective and helps to further establish bio-hydraulic oils as high-performance oils.

In terms of technical properties, bio-hydraulic oils are nowadays largely on a par with mineral oil-based oils and meet the technical requirements of DIN ISO 15380. A disadvantage of ester-based fluids is their higher sensitivity to hydrolysis and oxidation processes. However, they are characterised in particular by more favourable rheological and tribological properties compared to mineral oils. The temperature-viscosity behaviour is decisive. This is described by the viscosity index (VI) of a fluid. A value is given which is reciprocal to the gradient of the viscosity curve over temperature. This means the higher the specified value, the lower the change in viscosity with temperature. A mineral oil based HLP hydraulic oil has a VI of about 100, whereas a native oil of class HETG has a value of more than 200.

Equipment of the test Excavator with Measurement Electronics

Important hydraulic consumers of the test excavator (e.g. cylinders, valves, pipes) are equipped with sensors for volume flow, pressure and oil temperature measurement. The converted hydraulic power results from the product of volume flow and pressure. With the temperature the local viscosity of the oil can be estimated. A fuel consumption measuring device records the fuel required for the cycles driven.

Reference Cycle and Oil Change

On the test site, the so-called "Dig and Dump" digging cycle is carried out by the test excavator. This cycle is common for performance measurements on excavators. The cycle is repeated until the measured data show sufficient statistical certainty. The environmental conditions (e.g. weather conditions, density of the bulk material) are also recorded. Accordingly, a test bio-hydraulic oil is produced, which has the required minimum viscosity at the maximum possible temperature, but the viscosity index is significantly higher than that of mineral oil. A fundamental reduction of the viscosity level compared to the mineral oil is not carried out, as the comparison with the mineral oil would otherwise be distorted. The test fluid produced consists of at least 25 % renewable raw materials. The test excavator is re-oiled on the bio-hydraulic oil produced. The maximum residual oil content is 2 %.

Comparison Cycle and Evaluation of the Measurement Results

According to the described procedure, the "Dig and Dump" cycle is repeated with the re-oiled test excavator. The measurement results are evaluated with regard to the energy consumption of the hydraulic system as well as the total energy consumption of the excavator. Subsequently, a possible energy saving is highlighted. The results are made available to the public, e.g. in technical journals or lectures.



The research project is funded by the Fachagentur Nachwachsender Rohstoffe e.V. (FNR). The project partners are Volvo Construction Equipment Germany GmbH and Panolin AG.