BIODIESEL – A COMPLEX MINEFIELD

The subject of biofuel is vast and often controversial, and very topical right now as the world seeks more sustainable fuel sources.

Biofuels are energy sources made from recently-grown biomass (plant/animal matter), are continually replenished and have been around a long time. Biofuels are making a resurgence due to increasing oil prices, dwindling fossil fuel reserves, the desire to have a renewable, reliable source of energy and to mitigate the effects of climate change.

Till now, fossil fuels (petroleum, coal etc.) have been popular energy sources due to their high abundance, high energy value, and cheap prices. Although fossil fuels also come from biomass, they are not renewable since they require millions of years to form.

In many countries, successful biofuel projects are propped up by government subsidies. This is not the case in SA, resulting in many back-yard stills producing uncertified ‘biofuels’ that can cause havoc in an internal combustion engine.

During the development of SANS 1935:2004, it became apparent that SA does not have the technical and analytical capability to test biofuels. To counter this, the SABS invested over R2,9 million in test equipment some years ago.

The authoritative SAPIA book, Petrol & Diesel in South Africa states: Care needs to be taken to regulate acceptable quality of the manufactured biodiesel (SANS 1935), so that when blended with conventional diesel at up to 5% by volume, the resultant product complies with the national automotive diesel specification (SANS 342) and is therefore fit for use as an on-road transport fuel.’

SA Government Gazette No. 44363 of 30 March 2021 indicates a forced pace of change – a ‘mandatory blending of biofuels with petrol and diesel’. Sulphur in diesel fuel is forecast at 10ppm in five years.

Biofuel combustion chemistry is more complex than petroleum-based fuels. Generally, biofuel is associated with only a few select chemical compounds, especially ethanol (used exclusively as a gasoline replacement in spark-ignition engines) and very large methyl esters in biodiesel (used as a diesel fuel replacement in diesel engines). Biofuels are oxygenated fuels, which distinguishes them from hydrocarbons in conventional petroleum-based fuels.

Three Biofuel Generations

Biofuels are classified into first, second and third generations. Each generation aims to meet the global energy demand while minimising environmental impacts, and each generation has different benefits and drawbacks.

The main drawback of 1st generation biofuels is that they come from biomass that is also a food source – this presents a problem when there is not enough food to feed everyone. 2nd generation biofuels come from non-food biomass, but still compete with food production for land use.  

Variations in feedstock material can have a significant effect on the processing chemistry – one can’t simply pour any vegetable oil into a tube with a standard outcome while it is only viable to test and certify large batches. The problem for biodiesel is adherence to standards and the consequences for modern diesel engines.

Biodiesel interacts with engine oil, but to what extent does this impact lubricant performance level and service intervals? Biodiesel can affect the engine oil durability in several ways, specifically:

Fuel dilution: Differences in volatility can cause the biodiesel to accumulate in the sump, diluting the engine oil.

Viscosity decrease: Engine oil viscosity is reduced with high levels of unburnt fuel, shortening the lubricant’s useful service life.

Increased piston deposits: Biodiesel causes increased piston deposits. However, it is very dependent on the engine oil formulation. Testing should be conducted to ensure that the formulation is robust with biodiesel and biodiesel blends.

Increased lubricant oxidation: Biodiesel in engine oil increases the lubricant oxidation rate, which increases the engine oil viscosity. This could lead to sludging of the engine oil.

Vehicles should only ever use the correct OEM-approved engine oil to avoid problems.

Engine oil formulating is complex, with biodiesel introducing additional challenges. Engine oils can be formulated to reduce the impact of biodiesel; however, high levels of fuel dilution may need to be addressed via reductions in oil drain intervals. This could have a significant impact on service maintenance plans and customer operation, and hence should be avoided, if possible, through engine design and lubricant.

Petrol & Diesel in SA points out – In certain quarters, there is a growing resistance to the use of biodiesel because it tends to have blending and performance characteristics that are inconsistent, especially with new ultra-high pressure common rail injection systems and associated emission control devices.’

So, if you are operating a modern, common-rail diesel-powered truck, you dare not tank up with diesel of unknown quality. The tendency to offer power-train warranties that include unlimited distances over two years and more does not extend to diesel fuel that cannot match consistent laid-down standards. Insist on a batch certificate or fill up at reputable sites. And even then, audit your suppliers on a regular basis.

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