The Triton

Engine Room

Tier 4 diesel engines require cleaner fuel


If you have been to any major boat shows in the past few years, and lurked around the tents and booths of companies that make the engines for yachts, you know that change is in the air. It is a change for cleaner air.

MARPOL  Annex VI addresses air pollution from marine engines on ocean-going vessels. This international convention on pollution from ships limits the amount of emissions from nitrogen oxides (NOx), sulfur oxides (SOx), particulate matter (PM) and requires the use of low sulfur diesel fuel.

These combined pollutants significantly contribute to smog, acid rain, ozone damage to the ecosystem and respiratory problems.

In the United States, the MARPOL Annex VI guidelines are written into the Code of Federal Regulations (CFR), which are enforced by the Environmental Protection Agency (EPA) and the U.S. Coast Guard. Worldwide, marine diesel engine manufacturers have been developing new technologies for propulsion and power generation aboard yachts that meet these stringent requirements.

Since 1997, stricter pollutant limits for marine engines have been phased in through a series of four steps called tiers. The higher the tier number, the greater the pollution reduction requirements. Tier 4 Final emission standards are being implemented, based on engine size, now through 2017.

To yacht engineers and captains, a Tier 3 diesel engine doesn’t look much different from other marine engines. It uses high pressure common rail fuel injection, advanced turbocharging, microprocessor and electronic controlled engine management along with ultra low sulfur diesel fuel (ULSD) to achieve the mandated emissions levels with “in-engine” technology.

Fuel sampling can be done with a portable particle counter. PHOTO FROM AXI INTERNATIONAL

Fuel sampling can be done with a portable particle counter. PHOTO FROM AXI INTERNATIONAL

Tier 4 engines, however, will achieve the necessary pollution reduction through Tier 3 in-engine techniques plus new “after-engine” treatments. These after-engine technologies include scrubbing exhaust gases using Selective Catalytic Reduction (SCR), Diesel Particulate Filters (DPF) and Exhaust Gas Recirculation (EGR).

Ford, GM and Chrysler have been using SCR in their new diesel pickup trucks since 2010. In order to reduce NOx, Diesel Exhaust Fluid (DEF) is injected into the hot exhaust gases, then the catalyst turns the noxious exhaust into nitrogen, carbon dioxide and water vapor. DEF is made up of one-third urea (an agricultural fertilizer) and two-thirds water.

Whether yacht engines are Tier 3 or Tier 4, at the heart of addressing MARPOL Annex VI is fuel quality. As manufacturers increase the pressure of the fuel injected through the common rail system, fuel cleanliness becomes paramount. These newer engines have particulate filters to catch contaminants as small as two or three microns, since larger particles can clog the injection system. Remembering that the average diameter of a human hair is 80 microns, it doesn’t take a large-size particle to create an expensive injector failure. And injector failure due to poor quality fuel is not covered under warranty repair.

Therefore, the quality of fuel should be sampled for the quantity and size of contaminants before it is bunkered on board and regularly while it is in storage in your yacht’s fuel tanks, before it is burned. This sampling can be done with a portable particle counter. Using the International Organization for Standardization’s cleanliness code (ISO 4406), the particle counter samples fuel to determine the number of particles of different sizes present per milliliter of fluid. ISO 4406 is a shorthand method of defining cleanliness in fluids using a three-number system.

The particle counter expresses levels of contaminants using these same three numbers that correspond to the amount of particles present that are greater than four, six and 14 microns in diameter, in that order. There are handy charts available to understand what these three numbers mean. For example, a typical batch of diesel fuel delivered to your yacht has a cleanliness level of 22/21/18. Deciphered with the key, that means every milliliter of that fuel contains about 30,000 particles greater than four microns in size, about 15,000 particles greater than six microns wide and about 1,900 particles greater than 14 microns in diameter.

That delivery of diesel fuel is considered fairly contaminated, and should immediately be polished upon bunkering. The new fuel should be polished until it reaches the target cleanliness level of 14/13/11 needed for pumping diesel fuel from your yacht’s tank to its Tier 4 engines. Those numbers translate into about 120 particles greater than four microns, about 60 particles greater than six microns and 15 particles greater than 14 microns.

It is imperative that every yacht has a multi-stage fuel cleaning system on board to polish the fuel when needed per the analysis of the particle counter. And using this fuel polishing system as part of the diesel preventive maintenance program will also keep water, mold and bacteria out of the fuel. Diesel fuel is the lifeblood of your engine, and with the lower tolerances of Tier 4 engines to contaminants, a rigorous fuel sampling, testing and polishing regimen is must.

Capt. Jeff Werner has been in yachting for more than 20 years on private and charter yachts, both sail and power. He is an instructor for RYA, MCA, USCG and US Sailing courses and owns Diesel Doctor ( Comments on this column are welcome at

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