US Oil Major Places Order for Ultra-Efficient Tier III-Compliant Engines

By Peter Pospiech at February 28, 2013 04:56
Filed Under: Company News, drive systems, Fuels & Lubes, MAN Diesel&Turbo

Chevron Corporation orders G-type units with integrated exhaust gas recirculation

G-type engines with integrated EGR system offer both high efficiency and low NOX emissions. MAN Diesel & Turbo has received an order from Chevron Corporation, the American multinational energy company, for two lightering newbuildings with each vessel to be powered by an MAN B&W 6G70ME-C9.2 prime mover. The newbuildings will each use an MAN Diesel & Turbo EGR (Exhaust Gas Recirculation) system to help their ME-C prime movers meet Tier III emission standards well in advance of requirements coming into effect. The engines will also retain the ability to switch to Tier II operation when outside the ECA (Environmental Control Area). MAN Diesel & Turbo states that the engine for the first vessel has a delivery date in December 2012, with the second due in early 2014 and the vessels due for delivery in 2014. Chevron has also ordered 1 × MAN 8L27/38 + 2 × MAN 7L21/31 gensets for each vessel. Doosan Engine will construct both gensets and G-type engines at its works in Korea.

Graphical rendering of the G-type engine. The adaptation of aft-hull designs to accommodate larger propellers offers potential fuel savings of some 4-7%

Exhaust gas reduction

Generally, ships use HFO as fuel, which contains sulphur and forms NOx and SOX during combustion. MAN Diesel & Turbo’s EGR system ensures full fuel flexibility, ranging from HFO to distillates and natural gas, and reduces NOx by directing part of the exhaust gas back into the engine’s scavenge air. This reduces the oxygen content of the air in the combustion chamber, thereby lowering the combustion temperature and, as a result, reduces NOx formation. Tests at MAN Diesel & Turbo’s Diesel Research Centre in Copenhagen have shown that EGR alone can achieve the IMO’s forthcoming Tier III NOx emission requirements.

G-type efficiency

MAN Diesel & Turbo has previously compared its 7S80ME-C9.2 engine with a G80 engine installed aboard a 319,000-dwt VLCC, where the G80 engine had a greater efficiency of 1%. Assuming optimum running conditions, including an optimum propeller set-up, the company found that propeller efficiency could be improved by about 3.6%. Under the same ship-speed conditions, overall running costs could accordingly be reduced by 4.6%, a significant saving that the company’s own figures suggest can even be bettered, depending on individual circumstances. Under the same ship-speed conditions, the EEDI would be reduced by some 8.2% when using the G80 as opposed to an S80 engine. The G80’s longer stroke results in a lower rpm for the engine driving the propeller: a reduction from 78 rpm for the S80 engine to 68 rpm for the G80. This lower optimum engine speed allows the use of a larger propeller and is, ultimately, significantly more efficient in terms of engine propulsion. Together with an optimised engine design, this reduces fuel consumption and reduces CO2 emissions.

MAN Diesel & Turbo believes that, just as MAN B&W S-engines became first choice for container ships, G-engines will become first choice for bulkers, tankers and some box ships.


Image: Courtesy of MAN

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