Monday, October 29, 2012

Fuel Polishing


The good news about diesel engines is that with proper maintenance and clean fuel they will provide thousands of  hours of faithful service.  The bad news is that keeping diesel fuel clean is not that easy.  As soon as diesel leaves the refinery it starts degrading. 

Just for the record, we got clean fuel here.

Due to questionable storage facilities and delivery systems, the fuel you buy probably needs filtering by the time it gets to your tank.  But usually, most of the real trouble begins once it is in your tank.  


Dirty tanks and leaking deck fittings are usually the biggest contributors to bad fuel.  Bad fuel can clog your filters, damage your injector pump and/or foul your fuel injectors.  


There is a plethora of fuel additives on the market claiming to clean your fuel, dissolve water, kill bacteria (yes, bugs grow in diesel), give you better fuel economy, reduce exhaust smoke, and improve your love life.  Well, maybe not the last one, but all of the others.   Unfortunately, most of these products are “snake oil” and there are studies indicating that fuel additives may actually lead to early failure of injector pumps.  


To combat fuel problems, most boats are equipped with a primary and a secondary filtering system.  Motivator has dual Racors for the primary filter.  Only one of the Racors is use, the other is redundant in case the first is clogged.  The Racors are designed to separate any water that may be present from the fuel and filter it for impurities down to 10 microns. 


Then before the fuel reaches the injectors pump it filtered once again down to 2 microns through both of the secondary filters. 

250 Gallon Aft Tank under Bed

As previously stated, diesel does not like to be stored, and there is the rub.  Motivator has the fuel capacity that allows us to purchase fuel in locations with better prices.  The fuel we purchased in Puerto Rico was priced significantly less than any fuel we found down island. 


A system that allows us to store fuel then clean it on demand would be optimal.  Such a system is commonly referred to as a fuel polishing system.


DeFevers come with an impressive fuel manifold as standard equipment.  Motivator was also equipped with a fuel transfer pump allowing for the fuel to be transferred from one tank to another.  Commonly, the aft and lazerette tanks are used for storage while the two saddle tanks are used when motoring.

We decided that having the capability to pre-filter or polish the fuel during transfer or after it had been sitting in a tank would be useful, especially given our propensity for hedging on fuel.  


Basically, there are two ways to clean fuel.  It can be filtered or the impurities and water can be separated via a centrifuge.  A centrifuge works best and has the advantage of not requiring filter replacement, but most centrifuge systems are quite pricey.  There is one on the market, the RCI Fuel Purifier, that is reasonably priced, and claims to be effective. 


The system installed on Motivator included a RCI Fuel Purifier and a new fuel transfer pump.  


The original fuel transfer pump was only rated for a run time of 7.5 minutes.  This one is rated for 40 minutes. 

The jury is still out on the effectiveness of this system, but here are the lessons learned so far:
  •  Vane style fuel transfer pumps are rated for continuous run or less.  You will want a continuous run pump.
  •  Vane style pumps do not like to be over-sized.  The rating will say, “Use x inch minimum hose.”  The smallest tubing size in your system will determine the pump size.  A smaller, slower pump will probably be better.
  •  Work with RCI to determine the correct RCI Fuel Purifier.  Bigger is not necessarily better.
  •  Marine type fuel hoses (A1, A2, B1 and B2) meeting United States Coast Guard (USCG) regulations are only available in certain sizes.  Make sure hose is available in the size you intend to use.

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