Article by Capt. Steve Katz
Diesel Fuel Filtration
This is not another story about changing your fuel filters; you already know you need to do that. This is about best practices for where, what, and how to supply the proper diesel fuel and filters for the main engines and generators. While the principles of fuel filtration have not changed, many engines have changed, fuel composition has changed and some older habits may need to be updated for today’s newer engines and fuel types.
Before we talk about filters, let us talk about newer High Pressure Common Rail (HPCR) marine engines. Some of these engines have final fuel pressures as high as 30,000 psi. "The higher pressure of the common rail fuel injection allows the engine to atomize the fuel and air mixture better so more of the fuel burns in the cylinder, reducing particulate emissions", said Jeff Sherman, marine sales manager for MTU. The critical maximum particle sizes for modern injection systems are between 4-6 microns. These particles are smaller than what we can detect by eye.
As many of you know, the low emission and high power of today’s engines have drastically increased the reliance on technology and electronics to operate today’s high-performance diesels. The requirements for extra clean fuel are part of this equation, along with clean electrical power and precise maintenance requirements for components such as oil and coolants. The cleanliness of fuel is not just for keeping the system from clogging, that is a given these days, but clean fuel can prevent abrasive damage and subsequent accelerated wear. Damage and wear from dirty fuel can quickly occur, affecting the injectors and other system components, resulting in degraded performance, increased emissions, or component failures.
Additionally ultra-low-sulfur diesel (ULSD) is lacking the sulfur that helps kill microbiological “bugs” (bacteria and fungi) that can live in diesel fuel. Microbiological “bugs” can grow in a diesel fuel tank when there is a presence of water. Microbial colonies proliferate at the interface between fuel and water in the tank. This growth is often mistaken as algae which needs light to live and grow; there is no sunlight in a closed fuel tank so algae cannot survive.
On-Board Filtration
Once the boat’s fuel tanks are filled, the best way to assure you have clean fuel going to the engines is through multistage filtration. This is a system where the fuel from the boat’s storage tanks flow through progressively finer filters before it gets to the finest (smallest micron) engine mounted filter.
There are some folks who do not like changing the engine mounted fuel filters (secondary filters), understandably so, they are expensive, time consuming and can easily induce air into the fuel system during a change. This causes some operators to think they found a better way by installing a finer (smaller micron) filter in the primary filter location in the hopes they can prolong the life of the secondary filter. This is not acceptable in today’s engines and not recommended by engine manufacturers. The popular Racor Turbine Series primary fuel filter is designed to remove water and particulates of larger size and the engine mounted filter is designed to remove smaller particulate down to about 10 microns or smaller, depending on the manufacturer. These multiple filters work in unison sharing the filtering task, resulting in the cleanest fuel for the engine.
On the topic of secondary filters, when changing these filters, they should be installed dry, NOT filled with fuel before installation. Once installed on the engine, the fuel priming system should be used to fill the new secondary filter and purge air out of the fuel filter and system components. If you were to fill the secondary filter by pouring fuel from a jug or container directly into the filter you bypass the primary filter and at the same time allowing unfiltered fuel to go directly into the fuel injection pump and injectors.
Changing the primary and secondary fuel filters at regular intervals is important and monitoring engine performance is an effective way to know when a fuel filter has become restricted or clogged. Modern engines can begin to have accelerated fuel system wear before there is a noticeable performance decrease. Changing fuel filters at regular intervals or even more often is good practice, there is no such thing as "too clean" when it comes to your fuel. §
