Lloyd’s Register’s CEO Richard Sadler examines the potential of biodiesel as a fuel for
marine engines
Lloyd’s Register’s CEO Richard Sadler examines the potential of biodiesel as a fuel for
marine engines
The use of vegetable oils for engine fuels may seem insignificant today but such oils may become in the course of time as important as petroleum and the coal tar products of the present time.” - Rudolf Diesel, 1911
Biofuels are evidently not a new concept: the first diesel engines designed by Rudolf Diesel ran successfully on peanut oil and the Ford Model T engine ran on hemp-derived biofuel.
First generation biofuels refer to those made from sugar or starch, (producing bioethanol) and vegetable oil or animal fats (producing biodiesel). Such biofuels provoke criticism because of their dependence on food crops and issues of biodiversity, land use and human rights.
Technical challenges exist in blending them effectively with conventional petrol or diesel, most biofuel blends today being no higher than 5-20 per cent. They can, however, be burned in 100 per cent blends if required.
Second generation biofuels can be the solution to some of the problems associated with first generation products. They do not compete directly with food crops since they are made from waste biomass from agriculture and forestry, fast-growing grasses and trees specially grown as ‘energy crops’.
With technology, sustainability and cost issues to overcome, second generation biofuels remain several years away from commercial viability, and many such mass-produced biofuels are still under development (including the biomass-to-liquid Fischer-Tropsch production technique). Technology may promote greater use of biomass or second generation fuels in power generation.
Finally, third generation biofuels are green fuels and products made from energy and biomass crops that have been designed in such a way that their structure or properties conform to the requirements of a particular bioconversion process. Another example is algae fuel, which is formed solely from waste material, such as sewage, and grown on ponds.The production and use of biofuels has grown significantly in recent years, the focus mainly on bioethanol blended into fossil motor gasoline (petrol) or used directly, and biodiesel or Fatty Acid Methyl Ester diesel blended into fossil diesel or also used directly.
The Fischer-Tropsch process is a catalysed chemical reaction to produce a synthetic petroleum substitute, typically from coal, natural gas or biomass, for use as synthetic lubrication oil or synthetic fuel. Synthetic fuel runs (so far) only in diesel engines and some aircraft engines as typical gasoline-burning engines ignite the vapours at much higher temperatures, rendering the synthetic fuel unusable.
While the use of biofuels in land-based transport is becoming commonplace, usage at sea is still under investigation but promises some technical merits. Marine engines are generally of lower speed and more tolerant to burning alternative fuels than smaller, high speed automotive designs.
Royal Caribbean Cruise Lines has trialled a palm oil-based biodiesel since 2005. Reportedly optimistic results encouraged the operator to contract last August for the delivery of a minimum 15 million gallons and, for the four years after, a minimum of 18 million gallons of biodiesel for its fleet. The contract represented the single largest long-term biodiesel sales deal in the USA.
Greener fuels are also targeted by the US Coast Guard, whose chief of staff, Vice Admiral T W Allen, reported in early 2007 that his fleet would increase its use of biofuels by 15 per cent over the next four years.
Biomass in the Fischer Tropsch process can also be used to produce bio lubricants, hydraulic oils and grease, whose main advantages are biodegradability and non-toxicity.
Bio lubricants are particularly valuable in the marine industry from an environmental perspective. Higher viscosity, flash point and better technical properties (such as increased sealing and lower machine operating temperatures) are appearing as additional merits.
The properties of biofuels and the way they behave in the engine vary significantly, depending on the source of the fuel, which makes any standardisation in the industry today very difficult. Shipowners must be sure of the quality of biodiesel burnt in their engines.
Currently, the fuel standard for marine applications – ISO 8217 – relates solely to fossil fuels and has no provision for biofuels. There are, however, a number of available national standards for biodiesel in the automotive sector, such as the European EN 14214. The marine bunker supply market would need to work closely with regulators to develop appropriate international marine standards.
‘Fuel oil’ in the IMO’s latest Annex VI regulations, proposed for adoption in October, covers any fuel delivered to and intended for combustion on a ship. This leaves the door open to biofuels. Worldwide availability of biodiesel supply is limited, however, and such fuels are expected initially to benefit smaller craft operating in areas particularly sensitive to air and water pollution.
For merchant shipping, the way in which biodiesels are supplied to the vessel must also be considered. There are two options: either the biodiesel is delivered premixed to the required blend, or the biofuel and diesel are supplied separately and then mixed onboard.
Biodiesel blended prior to delivery to the ship is affected by shelf life. Fuel ageing and oxidation can lead to high acid number, high viscosity and the formation of gums and sediments. Fuel management will therefore become ever more complex.
Separate supplies of biofuel and diesel for onboard mixing enable the operator to dictate the exact blend of biofuel depending on the conditions, but that would require new technology installed onboard and extra complexity for the crew to handle.
Some operational problems can occur from using biodiesel, related to the Cold Filter Plugging Point (CFPP) at which the fuel starts to turn to gel. Considered to be the indication of low temperature operability, the CFPP is in a range between 0oC and 15oC for different types of biodiesels and can cause problems with filter clogging, which can only be overcome by carefully monitoring the fuel tank temperature.
Such a problem could well affect ships operating in cold climates, where additional tank heating coils might be required to prevent it happening. Careful choice of the biodiesel type can ensure the problem is avoided.
Another challenge in using biofuels is corrosion caused in the fuel injection and fuel treatment systems as biodiesels are hygroscopic and maintain 1,200-1,500 ppm water. It is essential therefore that the fuel is conditioned thoroughly prior to injection, and also important that the fuel acid number is monitored to ensure no rancid, acidic fuel is introduced to the injection system.
A typical fuel treatment system should incorporate separators to ensure water is removed, as well as heaters at various stages to ensure the fuel is at the correct temperature for introducing in the engine.
How are engine lubricants likely to be affected by the increased use of biodiesel?
The primary concerns for the crankcase lubricant are the impact of biodiesel on engine cleanliness and the potential consequences of fuel dilution. Furthermore, the droplet characteristics and lower volatility of biodiesel compared with conventional diesel fuel, together with spray pattern and wall impingement in modern engines, may assist non-combusted biodiesel to get past the piston rings, make contact with the cylinder liner and be scraped down into the oil sump.
Any unburnt biodiesel tends to remain in the sump and the level of contamination may progressively build up over time, resulting in reduced lubricant viscosity and higher risk of component wear. A serious concern is the possibility that the unburnt biodiesel entering the oil sump may be oxidised, thus promoting oil thickening and dictating more frequent oil changes.
Another issue to be considered is fuel injector fouling. Given the increased likelihood for biodiesel to produce deposits, the quality of the biodiesel is critical. The presence of fatty acid and water in the fuel can foster increased corrosion of the injector system; and the presence of glycerol and viscous glycerides can contribute to further injector coking.
It should also be remembered that, due to its chemical properties, biodiesel degrades, softens or seeps through some gaskets and seals following prolonged exposure. Such effects clearly become more significant when using higher percentage biofuel blends. MP
Source: Biofuels and their effect on the shipping industry, Richard Sadler, CEO, Lloyd’s Register (IMarEST Stanley Gray lecture)
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