Biodiesel is a clean-burning alternative fuel that is derived from renewable sources. Its rise in interest as an engine fuel matches the increasing global concern about human-caused climate change.
The diesel engine was invented in the 1890s by the German engineer Rudolf Diesel. From the outset the diesel engine had one advantage over its petrol counterpart in that it had the capacity to run on fuels derived from a variety of sources, including vegetable oil. Indeed, at the Paris Exposition of 1900 a diesel engine running on peanut oil was exhibited.
However, petrochemical diesel soon became the ubiquitous source of diesel fuel, and remained so until the end of the twentieth century. The ready availability of petrochemical fuel meant that there was no commercial interest in alternatives. Scientists still continued to experiment, however. In the nineteen-thirties a number of researchers were working on trying to create viable diesel fuel by splitting the fatty acids in vegetable oils from the glycerine it also contained.
In Belgium this research produced some limited success: a gentleman by the name of G. Chavanne was granted a Belgian patent in 1937 for a process he devised to extract ethyl ester from palm oil. His process created a product that was closely akin to modern biodiesel. Chavanne’s biofuel was used in a number of successful practical trials: during 1938 a bus service from Brussels to Louvain was powered by ethyl ester fuel extracted from palm oil.
During the Second World War, from 1939 to 1945, a number of countries which struggled to access petrochemicals resorted to extracting diesel fuel from vegetable oils. Biodiesel industries were operated in Argentina and Brazil in South America and in Japan, China and India in the Far East. However, once the war was over and the global petrochemical trade was restored these biofuel initiatives were ended.
Biodiesel is a fuel produced by a process known as transesterification. By stimulating a chemical reaction in a vegetable oil, be it from a specially-grown crop or from commercial waste, the raw material is converted into a fuel that can power diesel engines. Animal fats can also be used in this process.
Palm oil, sunflower, canola, soya and jatropha are among the commonest raw materials for biodiesel. However, due to production costs, most biodiesel is currently produced from waste vegetable oil gathered from restaurants, fast-food outlets and food manufacturers. Growing crops for biofuel is an industry with huge potential, but current transesterification costs are a limiting factor on its expansion: waste vegetable oil is free and requires far less processing to be converted into biodiesel.
Biofuels are by definition a renewable source of energy in that they are derived from crops which can be grown again year after year. Some advocates will go so far as to argue that biofuels are also carbon-neutral by suggesting that the carbon produced when they are burned is offset by the carbon absorbed by the crops grown to create them. Many of biofuel’s supporters in the United States argue in favour of its strategic importance as a source of power which is not reliant on foreign imports and global markets.
Biodiesel has the additional advantage of being able to power current diesel engines without any significant mechanical modifications. It is also a cleaner-burning and more efficient fuel with less hazardous waste produced in its manufacture than is the case with fossil fuels.
One of the chief debating points about biofuels concerns whether or not they are in fact carbon-neutral. Sceptics will argue that the machinery used to raise crops for biofuel uses a large amount of energy and that the fuel used is rarely from biofuel sources. Despite these doubts, however, the fact remains that biofuels can reduce carbon emissions by some fifty to sixty per cent when compared with fossil fuels.
Critics will point out that the land used for biofuel crops will reduce the amount of agricultural land available for growing food crops. This is a particular concern for developing countries were food production is under constant pressure to feed these nation’s growing populations. Biofuel crops also swallow up large amounts of water and fertilizer that could otherwise be diverted to food production.
While welcoming some aspects of the movement towards biofuel, environmentalists have voiced concerns about the effect of monoculture on delicately-balanced rural eco-systems. Vast swathes of a single crop, such as soya or jatropha for biofuel, can have a detrimental effect on local flora and fauna.
Some experts in the field of diesel engineering have questioned the overall efficiency of machinery run on biofuel. In particular they have voiced concerns over its efficiency at low temperatures, variations in the fuel’s quality when sourced from different raw materials, frequent clogging of the engine and a slight increase in nitrogen dioxide emissions. Furthermore, conventional diesel may also be used in the manufacture and distribution of biodiesel.
The primary benefit of biodiesel when compared with petrochemical diesel is that it is effectively carbon-neutral. In other words biodiesel produces no net output of carbon in the form of carbon dioxide (CO2) emissions. This occurs because the crop grown for biofuel absorbs as much carbon as the CO2 emissions given off by the fuel when it is combusted. However, this does not reflect the entire carbon-balance equation. For instance, the fertilizer used to promote the growth of the vegetable oil crop is derived from petrochemical sources and that process produces additional greenhouse gases.
Besides the fertilizers used there are other potential sources of pollution in the production of biodiesel, in particular the manufacturing and distribution processes. Electricity and other sources of fuel which consume energy and produce greenhouse gases are widely used in the esterification, solvent extraction, drying and distribution of biofuels.
A comprehensive assessment of the carbon footprint of biofuel production requires the application of a detailed process known as Life-cycle Analysis (LCA). LCA involves an assessment of the total environmental impact of a product, taking it from raw material production through to manufacturing, distribution, consumer use, disposal and recycling.
On a further positive note, one of the key benefits of biofuel is that it is biodegradable and relatively non-toxic, so spillages present far less risk than those of conventional diesel fuels. Biodiesel also has a much higher flash point than petrochemical diesel, which is significant in the event of a crash or an incident in storage and distribution.
In Europe oil seed rape is the main provider of vegetable oil for the production of biodiesel with some seventy per cent of fuel production coming from this source. Other sources include sunflower oil and the recycling of waste animal and vegetable oils from the food and catering industries. European Union (EU) biofuel production in 2005 was in excess of 3,180 tonnes, representing an increase of sixty-five per cent on the previous year. Within the EU there are some forty biofuel manufacturing facilities located for the greater part in Italy, Germany, France, Sweden and Austria.
Making use of waste oils significantly reduces the environmental impact of biofuel production. Growing crops for fuel production may well be effectively carbon-neutral, but is controversial if done on a large-scale because it uses up land that would otherwise be given over to food production.
The amount of biodiesel produced from oil-seed crops varies with the species of plant, but the EU calculates that on average 1,230 litres of fuel are currently derived from each hectare. This calculation is based on some 2.9 tonnes of crop per hectare and around 427 litres of fuel extracted from each tonne of raw material.
Europe is already very intensively and efficiently farmed so only very modest improvements in yields can be expected in the coming years. For biodiesel to replace just five per cent of the Europe’s current petrochemical diesel usage some fifteen per cent of the EU’s agricultural land would have to be given over to oil-seed production.
In terms of greenhouse gas emissions vehicles powered by biodiesel offer a considerable improvement on vehicles which use fuel derived from mineral oil. This is because of the offset resulting from the CO2 the oil-seed plant absorbs when it is grown.
However, in the United States all vehicles built since 2010, whether fuelled by biodiesel or conventional fuels, are already required to adhere to the same stringent emission standards. This is achieved by sophisticated fuel, engine and exhaust control systems.
Carbon dioxide (CO2) is one of the key greenhouse gases that scientists believe is responsible for global climate change. Engines powered by biodiesel give off CO2 emissions in exactly the same way as engines fuelled by diesel derived from fossil fuel. The difference is, however, that the oil-seed plants raised to produce biodiesel absorb CO2 from the atmosphere as they grow.
The process by which plants take in CO2 is known as photosynthesis. This complex chemical reaction allows the plant to store and use energy from the sun by converting it into starches and sugars. This sun-derived energy is released once again after the plant is converted into biofuel: some is used to power biodiesel engines and the remainder is released into the atmosphere as CO2.
The extent to which a biofuel can be said to be carbon-neutral is dependent upon a complicated calculation of the whole process of producing and using the fuel. This involves the kind of Life-cycle Analysis (LCA) we referred to earlier.
Companies in the United States are required to operate within the strict guidelines of the Clean Air Act of 1990. Biodiesel is, in fact, the only non-conventional fuel that has been found to satisfy the requirements of the Act’s Health Effects Testing framework (Tier I and Tier II).
Particulate emissions from the vehicle’s exhaust are a particular concern with diesel fuels. These fine particles are a significant health concern. The emission of particles can be reduced by the addition of sulphur to the fuel and by introducing a catalytic converter into the vehicle’s exhaust system. Further recent developments include selective non-catalytic reduction (SNCR) systems and exhaust gas recirculation (EGR) initiatives.
With such measures in place biodiesel can reduce particulate emissions by up to fifty per cent when compared with petrochemical-derived diesel. Furthermore, biodiesel has a higher cetane rating than conventional diesel. A diesel fuel’s cetane number (CN) indicates the compression and combustion speed needed for ignition. A high CN, as with biodiesel, means that the fuel will ignite more quickly and that the engine will run more smoothly and produce less particulate emissions.
An aromatic hydrocarbon is an unsaturated cyclic, stable compound formed from hydrogen and carbon. Biodiesel contains fewer aromatic hydrocarbons than petro-diesel and is, therefore, less polluting. With biodiesel benzopyrenes are reduced by up to seventy-one per cent and benzofluoranthene by fifty-six per cent.
Researchers in the United States made a close examination of the economics of biodiesel, particularly when compared with another biofuel, ethanol.
The researchers’ key conclusion was that the economics of biodiesel production were not as efficient as those of ethanol production. Using soybeans, the most common source of biodiesel in the US, one bushel of beans produced 1.49 gallons of biodiesel, whereas by using corn to produce ethanol one bushel of corn would produce 2.7 gallons of ethanol.
The same American research suggests that ethanol is more cost-efficient than biodiesel. Biodiesel from raw feedstock soybeans is typically $1.50 to $2.10 per gallon. Ethanol from raw feedstock corn, on the other hand, comes in at £0.74 to $1.11 for a gallon. Obviously agricultural commodity prices will vary from season to season, so these costs are purely indicative. To compare these costs with petrochemical-derived fuel it is worth noting that crude oil ranges from $1.19 to $1.67 per gallon, based on $50 to $70 per barrel.
Biofuel is a relatively new industry and does not currently enjoy the economies of scale enjoyed by the petrochemical industry, so unit production costs for biofuels are inevitably higher. Exact costs are difficult to calculate, however, as biofuel production is subject to a number of frequently-changing variables. These include agricultural commodity prices, production and distribution fuel costs and fuel taxation which varies from territory to territory.
However, in an era of increasing global action against the factors causing climate change, national governments often offset the higher production costs of biofuel by reducing fuel excise duties in an attempt to encourage production.
In a number of European Union states excise duty is zero-rated for biofuels provided they meet a regulated standard. The idea is to make the biodiesel pump price comparable with that of conventional fuels. In practice, the rise in crude oil prices in recent years has made biodiesel a much more attractive option in countries, such as Germany, which give biofuels a very favourable excise duty status. This is not the case in territories where an across-the-board level of purchase tax is applied to all fuels.
The most powerful and efficient diesel engine in production today is the Wärtsilä -Sulzer RTA96-C turbocharged two-stroke diesel engine. The engine was designed by Finnish engineers and constructed at Diesel United Limited’s Aioi Works in Japan.
These inline diesel engines are available from a six-cylinder version right up to a fourteen-cylinder model. They are designed primarily to power large container shipping vessels and are particularly suited to today’s new generation of larger ships. Shipping companies like the fact that the RTA-96C suits the single engine/single propeller design they prefer and that it offers enough power for the larger vessels now coming into service.
The engine’s cylinder bore is just a touch under thirty-eight inches and the stroke is slightly in excess of ninety-eight inches. Each of these cylinders exerts a force of 7,780 horsepower and displaces 111,143 cubic inches, or 1,820 litres. For the fourteen-cylinder engine the total displacement volume is 1,556,002 cubic inches, or 25,480 litres.
The fourteen-cylinder is the largest of the RTA-96C diesel engines and boasts some staggering specifications. It weighs in at 2,300 tonnes, with the crankshaft alone totalling an incredible three-hundred tonnes. Its length is eighty-nine feet, while in terms of height it measures some forty-four feet. The engine’s maximum torque is 5,608,312 lb/feet at 102rpm, while its maximum power is 108,920 horsepower at 102 rpm.
The fourteen-cylinder version’s fuel consumption at maximum power measures 0.278 lbs per horsepower per hour. This measurement is known as its Brake Specific Fuel Consumption (BSFC). Fuel consumption at maximum economy is 0.260 lbs/horsepower/hour, while at maximum economy the engine exceeds fifty per cent thermal efficiency. In other words, more than half of the energy in the fuel in converted into motion. By way of a comparison, most automotive and small aircraft engines have BSFC figures in the 0.40-0.60 lbs/horsepower/hour range and twenty-five to thirty per cent thermal efficiency range. Even at its most efficient power setting, the fourteen-cylinder engine consumes 1,660 gallons of diesel per hour.
The most recent version of the Wärtsilä RTA-96C is the Wärtsilä RT-flex96C. The first vessel in which this fourteen-cylinder version was installed was the giant Emma Maersk container ship in 2006. This latest version features a new common rail technology which has replaced the traditional chain gear, camshaft, hydraulic actuators and fuel pumps. This change has produced better performance at low revolutions per minute (rpm), reduced fuel consumption, and reduced harmful emissions.
This summary of the RT-flex96C’s statistics serves to emphasise its nature as a veritable giant of the diesel world: