Reformulated Diesel Means Cleaner Ship Emissions


A new fuel mixture has been developed to cut air pollution from cruise ships, oil tankers, and container ships burning traditional bunker oil, the cheapest and most highly polluting form of diesel fuel.

Thick and viscous, bunker fuel is called the dregs of oil refining because after small molecules like propane, naptha, gasoline and jet fuel - all with relatively low boiling points - are removed at the start of the distillation process, and after heavier diesel and lubricating oil precipitate out, you're left with bunker oil's long hydrocarbon chains that resemble a runny tar, which just happens to burn efficiently in huge, slow-speed diesel engines.

Global shipping has become increasingly important

The world's 90,000 ships consume 7.29 million barrels of the sticky stuff each day, making the commercial shipping industry the biggest transport polluter in the world. A stark example: while the world's 760 million cars release 78,599 tons of sulphur oxides (SOx) annually, the 90,000 vessels emit 20 million tons - more than 260 times the entire car fleet. Even more mind-boggling, just 15 of the newest and largest ships release as much SOx as the world's 760 million cars.

In the past 15 years, as China has emerged as the world's manufacturing capital, the title of world's largest container ship is now held by eight identical ships owned by Danish shipping line Maersk. The eight 1,300-foot-long ships can carry 15,200 shipping containers around the globe at a steady 25.5 knots. Watch a short demo video:

These huge ships also use the world's largest reciprocating engine, the W?rtsil? RT-flex96C. Five stories tall and weighing 2300 tons, this 14 cylinder turbocharged two-stroke behemoth can consume 16 tons of fuel per hour or 380 tons per day while at sea (

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Air pollution has been of particular concern when such ships steam close to shore and enter urban harbors and in recent years, and a lot of pressure has come to bear on passing laws to reduce emissions.

The glycerol solution

Harakas and colleagues from the Maine Maritime Academy and SeaChange Group LLC added two ingredients to low-sulfur diesel to produce Bunker Green fuel. One ingredient was glycerol, a thick, colorless liquid widely used in foods, medicines and other products. Glycerol is also a byproduct of biodiesel production, making it a cost-effective, carbon-neutral and domestically sustainable fuel. Since blending glycerol and diesel fuel is literally like trying to mix oil and water, they then added a surfactant to solve that problem.

This simple addition had impressive results. According to the team's report, the additive helps remove the sulfur and reduces soot emissions by 15 percent and nitrogen oxide by 26 percent.

Is shipping ripe for biofuel or nuclear innovation?

Images: Emma Maersk, Maersk Group; Wartsila engine, Wartsila