Pure plant oil for vehicle propulsion

Basic Information

Mobility solution ID



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Ljubljana is exploring the use of pure plant oil as fuel to reduce the damaging effects of greenhouse gas and pollutant emissions.

Implementing sustainable mobility

The innovative aspect at the local and national level is the use of pure plant oil (100 %) for the vehicle propulsion. This can help reducing dependence on diesel fuels and negative impact of greenhouse gas and pollutant emissions on the environment. Plant oil is a real alternative to fossil fuels and can now be used as fuel on modified diesel engines and other vehicles. Ljubljana tested the use of pure plant oil for vehicle propulsion in laboratory settings and in practice.

The main objectives of the measure were to:

  • Promote the use of environmental friendly biofuels at the local and national level;
  • Reduce the dependency on fossil fuels by increasing use of bio fuels;
  • Reduce CO2, CO, HC and PM emissions from vehicles;
  • Promote fuel diversification in Slovenia;
  • Promote domestic bio fuels;
  • Test in laboratory and practical conditions the use of pure plant oil for vehicle propulsion;
  • Increase best-practice exchange.
  • Engine modifications will be made with domestic producers. Converted engines initially used mineral diesel fuel and then switched to pure plant oil.


The pilot project of testing pure plant oil was implemented in laboratory – stationary engine and real conditions – in three vehicles: a car and two tractors. The latter have been chosen as technically and costly more favourable solution for pilot testing than bus engines.

Data collection has been conducted since 2010 for four diesel engines modified to use pure plant oil: one car engine with 51 kW power, two tractor engines (one is 26 kW power and other 100 kW power) and stationary laboratory engine with 26 kW power. Environmental, energetic and economic indicators are controlled on mentioned vehicles and laboratory engine in laboratory and real conditions of use.

The pilot use of pure plant oil contributes to further diversify the renewable fuels choice. Through strengthened cooperation of bio-fuel producers, research institutions, students and other involved stakeholders, a network was created around the applicative research and implementation of measures.


Ljubljana expects from the measure:

  • Diversification and increase of possible alternative fuels for the vehicle propulsion;
  • Reduction of CO2, CO, HC and PM emissions;
  • Zero sulphur emissions;
  • Complete combustion due to higher quantity of O2 in fuel;
  • Production of fuel in decentralised producing units;
  • Local transportation of fuel, which will contribute to decrease pollution due to shorter transport distances of fuel;
  • Increase of general public information on bio-fuels;
  • Opening of new jobs in the field crop production and in the processing industry.

As AIS is determined to continue to test and promote pure plant oil, measure results can be regarded as a basis for the expansion/ up-scaling of pure plant oil use. Farmers may start producing pure plant oil by themselves, thereby reducing the dependence on (imported) fossil fuel.

Key result 1 – Economic viable
The heat of combustion for PPO is about 1% lower in comparison to D2 fuel on per volume basis (about 7.6% lower in comparison on per weight basis). The PPO fuel consumption is about 4 to 10% higher (in comparison to D2, considering the per volume basis) as measured at the laboratory engine (at controlled conditions). Considering the prices of the fuels, this supports the assessment that the PPO is an economic alternative to the D2 or B100 fuels.

Key result 2 – No expected problems in maintenance
For all engines, scales formation due to fuel burning, as well as engine oil quality during use is comparable or even better while using PPO of both high and low quality in comparison to D2 fuel. However, this is also due to the fact that engine oil was preventively replaced at double frequency in comparison to D2 fuel use conditions. In overall, the uncertainty and additional preventive maintenance costs due to PPO use were proved to be low.

Key result 3 – Lower emissions
The pollutant emissions are for all engines at the comparable or even lower concentrations when using PPO fuel in comparison to D2 or B100 fuels. Results are dependent also on the engine's speed and here a further refinement of the engine's ignition system is possible in the future – system shall consider both speed and type of the fuel. That should further improve the combustion of the fuels.

Lessons learned
The use of the pure plant oil is a viable alternative to the use of the conventional diesel or pure biodiesel fuels in the diesel engines of the agricultural engines (e.g. tractors) or vehicles. The recognition and use of the PPO as alternative fuel for agricultural engines by the farmers (especially through their own rape seed production) was gaining importance during the measure duration. However, to use pure plant oil for practical applications, social/political/perception issues need to be solved, as well as the uncertainty from the impact of future oil, biofuels, food prices and CO2 emissions prices. This means that political issues (duty tax policy in Slovenia) and dialog/persuasion with authorities is at present more important than technical issues within the measure for wider acceptance of the PPO use as fuel for vehicles.



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