The Advantages of Pure Vegetable Oil Compared to other Biofuels
Pure vegetable oil use as engine fuel has potential for the most comprehensive ecologic, economic and social benefits of all biofuels. The production involves few process steps and can be done economically with small production units. The production process leads only to small energy losses, because no thermal or chemical process steps are involved. It can be implemented in decentralised small units, without loosing cost-effectiveness and provides potential for additional income generation on farms, thereby strengthening rural economic structures and social coherence in the EU as well as in hot arid and tropical countries. The non-toxicity and the low flammability are further advantages from a logistics point of view.
All other biofuels have a longer production chain and higher associated energy losses. E.g. ethanol production shows high energy losses because of the required distillation step and synthetic biofuels produced by the thermo-chemical pathway can hardly be produced with efficiency higher than 50% due to high thermal losses of the gasification stage and the fuel synthesis (Fischer-Tropsch or similar).
All biofuels except pure vegetable oil also present a more or less pronounced risk for the environment or for safety due to some degree of toxicity and the generally high flammability.
The low flammability of pure vegetable oil makes it unsuitable for use in conventional diesel engines first of all. Different engine adaptation concepts exist which help to overcome this principle difficulty, including bivalent operation, preheating of vegetable oil and a number of mechanical modifications, notably of the injection system.
Apart from trans-esterification to biodiesel and cracking/ hydrogenation of pure vegetable oil to BtL, both considered as different biofuels, no attempts have been made so far to modify pure plant oil, in order to better match with engine requirements. The reason for that is that the majority of the advocates of pure plant oil use as engine fuel consider any modification of the oil as manipulation of its “natural” character. This unpronounced dogma is questioned in this project.
Pure vegetable oil chemical and physical properties which are relevant for engine combustion are little influenced by growing conditions of the seeds, but depend strongly on the oil press parameters. This leads to very different oil qualities on the market. Engine operation problems in previous fleet demonstration projects were almost exclusively due to vegetable oil not fitting to the only presently existing norm, the German pre-norm DIN V 51605. Hence, fuel quality definition and control are paramount if vegetable oil should play a larger role in the biofuels market.
When used in non-modified engines, pure vegetable oil not only leads to engine damages, in particular in advanced engines, but also to unacceptably high emissions. Especially, particulate emissions at cold starting are tremendously high, while at most other operating ranges pure vegetable oil shows advantages compared to conventional diesel.