Filters boost biodiesel applications

Adam Pearce, Racor Product Manager at Parker Hannifin's Filtration Division, explores the benefits of new biodiesel fuels to end users.

With crude oil prices now settling down (or should that be up?) at around US $60-70 a barrel, it's not surprising that the interest in biodiesel is increasing on both sides of the Atlantic.

Made from renewable indigenous crops, biodiesel raises the enticing prospect of self-sufficiency in fuel supply.

That day may be a long, long way off for most countries, but the first steps have been encouraging.

A 2003 EC Directive, for example, required member states to ensure that biofuels and other renewables would amount to 2% of transport fuels by the end of last year, a figure which rises to 5.72% by the end of 2010, with an EU Green Book target of 20% by 2020.

In the USA, meanwhile, production of biodiesel has grown exponentially from just half a million gallons in 1999 to last year's record of 75million gallons - itself three times greater than the 2004 output.

Even celebrities are lending their weight to the cause.

Country music legend Willie Nelson was honoured by the US Environmental Protection Agency in April this year for his support of the cleaner burning fuel through the promotion of his own biodiesel blend called, what else but "BioWillie".

Whatever the name, though, one thing that biodiesel is not is vegetable oil.

That is the raw material - commonly rape seed oil in Europe or soya bean oil in the USA - which is then converted by a chemical process known as transesterification into fatty acid methyl esters (FAME) that can be either be blended with conventional (petroleum) diesel to run in existing engines, or used neat as 100% biodiesel (known as B100) in specially adapted engines.

The most common blend is B20, a mixture of 20% biodiesel and 80% diesel.

But like other more "environmentally friendly" fuels, such as ultra low sulphur diesel (ULSD) for instance, biodiesel and biodiesel blends can present problems, particularly in cold weather conditions.

The more saturated the fatty acid in the FAME, the more impact there can be on the cold flow properties of the final fuel.

More specifically, both ULSDs and biodiesels can have a lowering effect on the cold filter plugging point (CFPP) - the standard bench test for treated fuels to determine the failure temperature below the fuel cloud point.

An added potential problem with biodiesels is that they can react chemically with rubber sealing components in the fuel system.

This is a slow process and one that can usually be avoided by normal maintenance schedules.

Another problem is not so straightforward, however.

Because of the inherent nature of the fuel and the refining process, biodiesels can contain a relatively high level of particulate matter especially in the 10-20um particle size range, which can be the most damaging to the fuel injectors and injection system.

Additionally the general chemical and thermal instability of the fuels can generate further particles, agglomerates, varnishes and oxides in the vehicle's fuel tank - all of which can contaminate the fuel flowing through the lines to the injectors.

The implications of these problems for engine manufacturers and end users are obvious, but the latest generation of fuel filters from the likes of Parker-Hannifin has gone some way to overcoming them.

The company's Racor division has a long record of designing and supplying diesel fuel filters, with a range that has filtration ratings down to as low as 2um.

Based on its widely used Spin-On filter series, the 400 Series HH filter assembly has been designed specifically for use with the more modern fuels like low sulphur and biodiesels.

This particular filter comes in three sises - based on maximum fuel flows of 250, 350 and 600 litre/h, respectively - but all are equipped with a 10um rated filter element, a high capacity see-through water collection bowl and a built in primer pump.

The filter thus copes with the typical levels of contamination that might be expected in a biodiesel, but it is also equipped to tackle the possible problems of operating in low ambient temperature conditions.

The actual filter head of the 400 HH now incorporates its own PTC (positive temperature coefficient) heater, which warms the fuel before the filter.

The whole assembly has an operating temperature range from -40 to +121C (or +80C on biodiesels).

Heaters similar to this are not unusual on diesel engines, of course, but a feature of the HH unit is that it self-regulates the power it draws depending on the temperature and flow rate of the fuel.

It runs off voltages from 12 to 42V DC.

The combination of being able to warm the fuel before the filter, and the fine levels of filtration achievable, can in some circumstances increase the cleanliness of the fuel flowing through to the injectors and engine by as much as tenfold.

Yes, there is a cost factor involved in fitting these finer filters, but this is easily outweighed by the combination of ensuring an engine's reliable running with the prospects of further tax breaks on the use of biodiesel and ultra-low-sulphur diesels.

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