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01.05.2007 » Pressrelease » Bio Energy
MAN Diesel group’s advances in the field of renewable energy
Worldwide commitment to the continuous growth of renewable energy production is giving increasing room for the
use of liquid biofuels in internal combustion engines.
Larger bore medium-speed Diesel engines are best suited to burn low cost liquid biofuels such as some crude vegetable oils, waste oils and recycled fat.
MAN Diesel carried out initial workshop tests to determine biofuel compatibility with Diesel engines and to compare respective performance and emission data with the results of most commonly used mineral fuels (MGO, HFO).
Biofuels have been found to match the minimum quality requirements for operation in medium-speed Diesel engines
although some aggressive waste and residual oils/fats have acidity above the accepted operating limits for conventional injection systems.
The tests showed no major deviations in Diesel engine’s combustion and injection patterns as well as no significant changes on the engine performance and reduction of main noxious emissions with the exception of NOX.
Commercial operation topping 15,000 hours revealed good long term operational reliability for biofuels. The possibility of combining sound economics and superior eco-friendliness is driving the development and optimisation of Diesel engine’s biofuel combustion to affirm this prime mover as one of the best available technologies for renewable power generation applications.
In the next five years liquid biofuels are set to play a major role in the carrying out of the European Union’s policies and strategies on the promotion of the use of renewable fuels for its internal electricity and transport markets.
The use of liquid biofuels to replace diesel or Heavy Fuel Oil in internal combustion engines, such as the ones used to power vehicles and electricity generation plants, carries clear global environmental benefits. Combustion of biofuels in replacement of mineral fuels actually promotes a net reduction of greenhouse gas emissions (see the case of rapeseed oil illustrated at figure A1) and other combustion related pollutants, while allowing simultaneously for appropriate disposal of waste biological oils of residential, commercial and/or industrial origin. Other consensus arguments in favour of biofuels is its potential for local and regional development, promotion of social and economic cohesion, local job creation and improvement of regional fuel supply security by reducing the need for fuel imports.
A number of small bore high-speed engine manufacturers reported potential problems when using biodiesel2 in concentrations above 5%, some related to deficiencies in handling and storage of these fuels, causing severe problems on the engine level including power loss and deterioration of performance, fuel leakage, corrosion, coking, blocking,lacquering and seizure of fuel injection equipment, filter plugging,
formation of sludge and sediments, reduced service life, etc. Lower quality fuels such as raw vegetable oils
have been reported as simply not acceptable for use in any concentration: in some high-speed engines these oils do not burn completely and finally cause engine failure by leaving deposits on the injectors and in the combustion chamber.
Due to its design and construction characteristics larger bore medium-speed Diesel engines are best suited to burn low quality liquid fuels such as crude vegetable oils and some waste and recycled biofuels, which are also the cheapest available biofuels in the world. The possibility of combining sound economics and superior eco friendliness in the operation of its prime movers led MAN Diesel to enter the development and optimisation of liquid biofuel combustion in its medium speed family of Diesel engines.
The paper hereinafter introduces innovative applications of raw biological oils and recycled fat in medium speed Diesel engines for power generation purposes, from early research and development work at MAN Diesel in Holeby, Denmark to field tests. It also presents the most recent results of the biofuel combustion development in larger bore Diesel Engines at MAN Diesel’s Augsburg centre of competence. Finally the paper also presents green-power generation applications by commercial operation of Diesel engines with
biofuels including vegetable oils (e.g. rape seed oil and palm oil) and recycled biofuel (e.g. waste cooking oil, frying fat).
Discussion / Analysis
>> Physical and chemical properties for the majority of the biofuels tested were within the minimum quality requirements for operation in medium speed Diesel engines. Higher viscosity biofuels need to be heated up sufficiently to reduce viscosity to injection levels between 12 to 15 cSt (this corresponds to heating these biofuels up to a level of 60-80ºC).
>> Biofuel has the following identifying features when compared to Marine Gas Oil: lower net calorific value, higher viscosity and density, lower stoichiometric airto- fuel ratio because of higher oxygen content.
>> Some waste and residual oils/fats have acidity (measured by the TAN - Total Acid Number) above the accepted operating limits for conventional injection systems.
>> There is no major deviation in the combustion process when running Diesel engines with biofuels. The tests showed similar patterns in the rate of heat release during the combustion as well as measured maximum cylinder pressure rise with increased loads on engines running both with biofuels and Diesel oil.
>> There is no substantial change on the engine efficiency and measured specific exhaust gas flows. Carbon
dioxide specific emissions of biofuel combustion in Diesel engines are therefore very similar to the ones when using mineral fuels since the lower calorific value of biofuels is compensated by the lower carbon content of these fuels. In the case of vegetable oils one should account for the positive contribution to the carbon dioxide cycle since this greenhouse gas is captured back when growing the crop.
>> While sulphur oxides are negligible and smoke emissions are significantly lower, nitrogen oxides emissions could experience however an increase by operation with biofuels. Installation of catalytic ‘DeNOx’ systems allow the abatement of these emissions down to the level of the strictest environment regulations (e.g. German Clean Air Act - TA-Luft).
>> Reliable commercial operation of medium-speed engines with biofuels is proven by over 15,000 operating hours burning biofuels with FFA content of 2% (TAN 4).
MAN Diesel medium-speed Diesel engines are biofuel compatible. Its fuel quality capabilities are far beyond the restrictions found in automotive applications.
Several commercial green-power plants have now been realised in Europe and good long-term operational reliability has been confirmed. Availability of large quantities of biofuels is however necessary to ensure reliable and continuous power. The capacity of medium-speed Diesel engines to burn a wide variety of these fuels is therefore vital to secure continuous operation of the engines.
The possibility of combining sound economics and superior eco-friendliness is leading to the optimisation of Diesel engine’s biofuel combustion to affirm this prime mover as one of the best available technologies for renewable power generation applications.
Dipl.-Ing.José N. Carranca, MAN Diesel do Brasil
Praia de Botafogo, 440-9° andar
22250-908 Rio de Janeiro - RJ, Brasil
MAN Diesel SE Germany
Phone Fax +49 821 322-3382
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