Diesel Fuel Analysis

Terra Analytical can test diesel fuel and similar fuels such as Jet A1 or boiler fuels.  Due to dangerous goods legislation these sample must be sent to the lab via a dangerous goods approved handler.  The diesel test kits contain the appropriate containers, labeling, documentation and courier pack. 

Dangerous goods such as fuel must not be sent via NZ Post in the standard oil test kit mailing containers - please order a Diesel test kit for fuels.   

Terra Analytical cannot test petrol.  There is very strict legislation surrounding the transportation of dangerous goods with a low flash point such as petrol.  We recommend that you contact your petrol supplier/oil company if you have concerns about petrol quality as they have access to test certificates and, if necessary, the appropriate test facilities. 

Water Contamination

 The most common source of diesel fuel contamination is water.  Typically this is condensation from the air volume in the tank.  For every litre of fuel used a litre of air must enter the tank to replace this.  Air contains water - as much as 17 mL in 1000L.  Water can condense on cool surfaces such as the walls of tanks and over time a layer of water will accumulate.  The best way to reduce water accumulation is to keep the tank as full as possible by filling up each night.  This applies to all tanks in the chain, including the running tanks of vehicles.  A routine maintenance plan to remove water should be put in place.  Unfortunately many fuel tanks don't have a drain point at the lowest point so this not be so easy.

Most large commercial fuel tanks will have a water layer that is routinely pumped out by fuel contractors.  The pumps can't reach to the very bottom so this water layer is maintained within controlled limits.  We advise that you should not purchase fuel from a commercial site if you can see a fuel tanker on the site as there is a high chance you might get a little more water than expected.  The NZ Government Fuel Specifications allow 200 mg/kg of water maximum for retail sale.  

Oil and water naturally separate and water has a higher density than oil, so water tends to gravitate to the bottom of any system.  It can be possible to operate for years with a tank that contains a lot of water at the bottom, and problems may only be found when the tank is run abnormally low.  At that point, the source of the water is highly debatable.  It could be from condensation, or there could be holes in the tank, or rainwater might be getting in via a fill point or breather.    

We strongly recommend that any tank in your care be monitored with water finding paste on the dipstick.  This will tell you how high the water layer is in the tank.  For example - it is possible to have a tank with 50% water content - but this would be sitting on the bottom.  It would be possible to take a sample of fuel from the top of that tank and it could be tested and the water content could be found to be below 100 mg/kg.   

Water can be very damaging to engines - water can pass through most fuel filters and cause severe damage to  injectors.  Some fuel filters may eventually block up with water, but possibly not soon enough to prevent damage.  Some filters are better than others, but water is a serious hazard in a fuel system.

 Biological Contamination

Along with air entering a tank through the breather, there are millions of airborne contaminants including many microbiological lifeforms.  Algae, Bacteria, Fungi, Mold, Yeast etc.  Given a water layer, a food source (the fuel or material in the fuel such as sulfur) and the right temperature conditions, these organisms can start to multiply.  This may become visible as organic looking material, from black slime to white fuzz and many other forms. 

This is a common occurrence - especially in marine environments or warm humid areas.  The problem tends to be called 'diesel bug' and there are many additives and treatments on the market for this.  There are some myths and misunderstandings about this.  The high temperatures used to distill and crack fuel mean that there is no significant water or bug in the diesel fuel produced at the refineries.  But all tanks in the shipping and distribution chain could possibly be contaminated with water and bugs of all types. 

Some literature focuses on Cladosporium Resinae as being a common diesel bug that tends to block filters.  Our postion is that any form of biological growth is a problem - but that water itself is a bigger problem.  Bug it often the result of a water layer, and bug can block filters.  But the best course of action is to prevent or remove the water layer first.  

Identification of the specific bugs is not so important, as the recommended course of action is the same regardless.  Terra Analytical uses a 7 day incubation program using agar strips.  One side of the agar strip is dosed with a bacteriocide which reduces bacteria growth and allows the slower growing lifeforms to be visible.  This method allows us to give a positive Yes/No recommendation for treating the fuel with microbiocide or not.  

Although there are many 'diesel bug' additives on the market, we do not recommend dosing a fuel tank before removing the water layer.  If a water layer is made toxic, it becomes an environmental hazard when it eventually needs to be removed.  It also becomes a health hazard to the fuel contractor.  We recommend removing water will it is still just stagnant water.  For this reason (and because we take 7 days in a temperature controlled incubator to check for any growth) we release our fuel reports in two stages.  If we find water you will know in the first report - which gives you time to remove the water from the tank.  If growth is found after 7 days we recommend treating with microbiocide (aka 'diesel bug additive') but only if there is something there to kill.

Water is the main problem.  But we also check a range of tests - elemental analysis can identify the sulfur content and possible contamination.  Viscosity and flashpoint can alert to contamination with other fuels such as petrol or oil.