The carbon-neutral feature of biodiesel

 

The carbon-neutral feature of biodiesel can be reduced to some extent because fossil fuels may be used in general transportation and in the manufacturing process. That is a variable depending on the detailed procedures but in any case should not be as much as a third.
Where specialized crops are grown on a vast commercial scale there is a distinct threat to diversity, natural forestation and the provision of foods.

Frequently biodiesel is combined with petro-diesel to ensure greater compatibility with unmodified engines. When used in standard compression-ignition engines biodiesel can increase nitrogen oxide emissions. This phenomenon is not due to nitrogen in the fuel but comes from the intake air as a result of the particular combustion process. This phenomenon is not replicated in some other applications such as oil fired boilers and the effect can be reduced in vehicle engines by refining the tuning. Now let's review some of the additional benefits of biodiesel.

Biodiesel produces less noxious emissions than petro-diesel.

Biodiesel reduces tailpipe particulate matter, hydrocarbon, and carbon monoxide emissions from most modern four-stroke compression ignition engines. The reason is mainly associated with the presence of oxygen in the fuel which allows more complete combustion. Particulates are mainly carbon dust, commonly described as soot, and contain very fine particles that can be dangerous since they can get into the lungs by bypassing the body's natural filter mechanisms. Together with the unburned hydrocarbons, particulates are suspected of being carcinogens and can cause other serious toxic effects. Carbon monoxide is well known for its lethal action in the bloodstream. Obviously, the higher the proportion of biodiesel in a mixture, the more these noxious exhausts are reduced. Biodiesel has a very low concentration of sulphur, which can lead to SO2 and acidic precipitation. The amount is very much less than traditional diesel oils.

And there are other fringe benefits of biodiesel.

The overarching benefit of biodiesel is that as a renewable fuel it is nominally carbon-neutral. An associated factor is that the global petroleum resources are being depleted rapidly and the term renewable is more significant than just reducing emissions. Biodiesel improves the lubricating power of the fuel and therefore ensures correct operation of key components in the engine system.

The fuel can be used in existing diesel engines especially at low proportions. Some modifications may be necessary, especially at higher concentrations of bio, and vehicle purchasers should be aware of engine specifications. The modifications are usually only minor and do not represent a basic change in the technology.

The fact that one possible raw material is used cooking oils etc gives a special advantage. Large caterers (think McDonald's) will have residues contaminated with meat. To be able to use this product for biodiesel is an opportunity to be welcomed, the only downside being that the contaminated materials would need to be filtered and 'washed' first.

But some disadvantages too.

Biodiesel has a lower energy density than petro-diesel and because it is a denser fuel, the statistics vary slightly depending on whether you want a figure of energy per gallon or per pound. Roughly speaking the reductions are in the vicinity of 10%. Viscosity at low temperatures is important with diesel, sometimes making cold-weather starting difficult; biodiesel can be at a disadvantage in this respect. We have read of occasional use of dual tank vehicles where petro-diesel is used to start and shut down but switched to biodiesel for main running. A more practical solution is to introduce some special additive or a proportion of petro-diesel.

The properties of biodiesel mean that rubber pipes may have to be replaced by plastic ones and it may remove engine deposits hence filters may need changing more frequently.

If biodiesel-from-crops was widely adopted as a motor fuel then there would be a knock-on effect with serious problems caused by reduced biodiversity, displaced forests and the disrupted supply of other vital agricultural products. There is no reasonable expectation that petro-diesel could be completely replaced by bio-diesel. There are already signs that over development of crops for bio fuels can be damaging to the environment.