4.1- bIOFUELS

4.1.1- PERFORMANCE ASPECTS

The great advantage of using biofuels is that they work in the ICV, the most mature propulsion technology currently available for transport. It offers a characteristic high autonomy (in the order of between 500 km and 1000 km), due to the great energy per volume ratio of the liquid fuels stored in the tank, even though that the heat content of biofuels is moderately lower than the one of the fossil counterpart. It also offers a fast combustible refilling time of less than ten minutes, unlike the electric car (which usually takes a few hours), a quality which makes the biofuel-powered ICV especially attractive for long road trips.

Typical ICVs fed by hydrocarbons have an average efficiency of about 15%. If biofuels were used instead of fossil fuels, this characteristic would improve slightly in the case of alcohols in the Otto engine due to the higher compression ratio allowable owing to their greater octane number. Besides, the idle stop consumption and its even lower in-city efficiency, makes of the internal combustion technology a bad choice as an urban vehicle.

4.1.2- ENVIRONMENTAL ASPECTS

The problem of using carbon-based fuels in ICVs is that their operation releases toxic compounds that have a negative effect on the human health. Accordingly, a massive switch to a traffic system fed with biofuel would not represent the eradication of the harmful in-city tailpipe gases.

Now, focusing the attention on the GHG (greenhouse gases) emission aspect, it is important to consider that the production of biofuels is, in the practise, an indirect system to store the sunlight energy in form of vegetal organic compounds in order to recollect, modify and commercialise them in form of alcohols or esters. Therefore, any energy spent in harvesting, transporting and treating the biomass and the resultant carbon emissions must be compared to the obtained energy in order to judge if there is a net thermodynamic gain and the CO2 emitted per heat unit produced.

In brief, as an energetic crop is produced to replace an oil-based fuel, this fact results in a theoretical reduction of the emitted CO2 per energy unit. Anyway, the massive production of energy crops would induce to a growing deforestation and use of phytosanitary chemicals, with the derived soil erosion and phreatic water contamination. Besides, if the prime vegetal matter is an alimentary product (i.e. corn or wheat) its use may cause severe food price raises.

4.1.3- ECONOMIC ASPECTS

In a technologic approach, the massive substitution of fossil fuels by biologically obtained alcohols and esters would not be an especially difficult task, since the existing global energetic infrastructure is designed to work in liquid fuels. Furthermore, their production is simple (if they are based on 1st generation methods, the easier and most common way), as well as their transport, handling and storage, given that they make use of established technologies.

Anyway, their production makes use of alcohol and ester plants in a similar way that oil-derivates are made in petroleum refineries. Consequently, a proper biofuel development would require great investments in production infrastructures.

Those fuels (except methanol) are currently sold as a vehicle fuel in most of industrialized countries with none or scarce price differences between them and their petroleum counterparts. However, their current production is low and they are still uncommon and unavailable in most of the gas stations, and habitually blended with fossil fuels (except in countries like Brazil). Because of that, their use often means to keep using established hydrocarbons.

Currently there is much controversy about the energy output/input ratio of the 1st generation biofuels, since proponents and critics offer very different statistics. Given that it is hard to check the objectivity of those sources, the author opted for not including that information in order to guarantee the veracity of the exposed data.