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The road to pure plant oil in diesel engines?


The most important results are listed below.


Using PPO from rapeseed as a transport fuel is only possible if the vehicle’s engine is modified to run only on PPO. Driving unmodified vehicles, or using mixtures of diesel and PPO will damage the engine.
There is currently no industrial standard for PPO fuel quality. The production method (warm/cold pressing, purifying, refining) varies per manufacturer. Regional differences in crops also result in oil quality differences that cannot be equalled out by mixing various batches. This means that fuel quality fluctuates all the time, so that modern engines will not
operate at maximum performance.
Opportunities for using PPO are currently limited to a section of the vehicle market – i.e. to vehicles with indirect-injected (IDI) engines, and vehicles with central injection pumps.
Conversion packs are still being developed for other direct injection (DI) systems and for the most modern vehicles.
Greenhouse gas balance Greenhouse gas emissions are reduced by an average of 30% when replacing diesel with PPO. The reduction can vary depending on the rapeseed yield and production technique used, from –15% (i.e. an increase in greenhouse gas emissions) to 65% reduction. This is in line with the information concerning biodiesel found on the UBA (German federal environment office) website.
The greenhouse gas emissions from the PPO chain – expressed with respect to the greenhouse gas emissions in the diesel chain 1 - are as follows:


a) The average CO2 emissions from transport, agricultural activities, use of natural gas and electricity for industrial processes during PPO production, result in a contribution of 20- 35%.

b) N2O emissions during fertiliser production for rapeseed cultivation result in a contribution of 15-30%. The use of a calcium ammonium nitrate fertiliser (KAS) is assumed. The N2O emission depends on the nitric acid processed when producing the KAS.

c) The average N2O emissions at the field (from using fertiliser) provide a contribution of anywhere between 5% and 60%. This huge variation is partially due to the range of rapeseed yield per hectare, but particularly depends on the huge uncertainties concerning the extent to which nitrogen from fertiliser is converted into N2O. This uncertainty in the emissions factor, according to the IPCC methodology, amounts to 80%.

Figure S.1: Relative breakdown of the contribution to climate change(total diesel-chain

As this figure clearly shows, the feasible reduction in greenhouse gas emissions from using PPO is extremely uncertain. In particular, the yield per hectare and the N2O emissions at the field are very uncertain factors.
The specific greenhouse gas emissions per unit of PPO are relatively low (best case) when there is a high yield per hectare. The year 2004 was therefore a very good year for rapeseed, with a high yield of almost 5 ton/ha, but a warm and dry year (such as 2003) results in a low yield of only 3-4 ton/ha.
N2O emissions at the field depend on this type of climatological and soil-related aspects. The N2O emissions are generally low when, for example, there is a low groundwater table, it does not rain during fertiliser distribution (whereby the fertiliser does not reach the crops) and when rapeseed is cultivated in clay soil.
Options for improving the greenhouse gas balance The research team found little opportunity for improving the greenhouse gas balance from PPO production alone.

  • Using PPO for PPO-related agricultural activities and transport leads to little reduction of average greenhouse gas emissions because the reduction achieved is cancelled out by the lower net PPO yield. This falls within the uncertainty margins of the results;
  • Replacing the fertiliser with animal manures probably results in higher greenhouse gas emissions for winter rapeseed, because animal manure is less efficient than fertiliser and results in N2O emissions that are twice those for fertiliser. Ammonia and nitrate emissions will also increase considerably;
  • It is possible that another type of N-fertiliser (containing no nitric acid) could be used instead of the standard calcium ammonium nitrate (KAS). The fact that KAS is used is purely due to its characteristics, e.g. crops use the nitrogen in this fertiliser immediately.
    The question is whether other types of fertiliser might contain similar characteristics to those in KAS.

In the long term, N2O emissions from nitric acid production will probably be reduced by 80- 90% through additional gas cleaning. There is considerable pressure on the fertiliser industry to develop and apply such techniques. Replacing diesel with PPO would increase the feasible reduction in the contribution to climate change to around 50%.

Other emissions

Production and use of PPO from rapeseed very probably leads to higher emissions of acidic and fertiliser substances (NOx, NH3, NO3) in comparison to that of low-sulphur diesel.
Expressed in acidic equivalents, these emissions will increase by around 100%. Emissions of these air-polluting substances primarily depend on rapeseed cultivation.
Production and use of PPO results in lower emissions of VOS, CH4 and fine substances than when using low-sulphur diesel. Reduction percentages over the entire chain are somewhere between 10-20%. Possible reductions of VOS and PM10 depend on the reduced emissions from running on PPO compared to diesel. Possible CH4 reductions depend on the fact that such emissions occur in the natural oil chain through venting and leakage of the associated gas.
Emissions from vehicles running on PPO are not easy to estimate, as there are still too few emission measurements to allow specific evaluations. The aforementioned conclusions are therefore given for indicative purposes only.


The costs of using PPO are significantly higher than for diesel. The production costs for PPO amount to € 0.50-0.90 per litre PPO, including regional distribution, but excluding vehicle conversion costs. The production costs for diesel amount to € 0.30 per litre. The fuel-related kilometre price is € 0.08 - € 0.15 when conversion and distribution of PPO are factored in. In comparison, the fuel-related kilometre price for conventional diesel (in 2003) averaged € 0.02 (both excluding duty and VAT). The details of the PPO kilometre price are shown in the following figure.

Cost-effectiveness of using PPO as a climate measure

The costs of using PPO as a way of reducing greenhouse gas emissions are very high. Based on the aforementioned costs and an average reduction in the contribution to climate change, the specific reduction costs for greenhouse gases amount to an average of € 950/ton CO2 equivalent, taking into account the saved costs for purchasing diesel (just the production costs).
In comparison: energy saving policies allow maximum reduction costs of € 50/ton CO2 equivalent and the expected trade price for CO2 (up to 2010) is estimated at € 10/ton CO2.

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