Denmark: MAN to Provide Engines for Chevron’s New Vessels

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 state that the engines for the first vessel have a delivery date in December 2012, with the second due in early 2014, with the vessels due for delivery in 2014. Chevron has also ordered 1 × MAN 8L27/38 + 2 × MAN 7L21/31 gensets for each vessel and Doosan Engine will construct these, along with the G-type engines, at its works in Korea.

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, Copenhagen have shown that EGR alone can achieve the IMO’s forthcoming Tier III NOx emission requirements.

Target group

The target group for MAN Diesel & Turbo’s EGR system is owners of ships of over 2,000 dwt, a segment that today comprises some 18,000-20,000 vessels operating globally. The EGR system offers great value and has a number of unique selling points, including its environmental performance, global seafaring flexibility, the added resale value it gives ships, and its disposal of the requirement for daily maintenance.

The G-type programme

MAN Diesel & Turbo’s G-type programme entered the market in October 2010 with the entry of the G80ME-C9 model. MAN Diesel & Turbo subsequently expanded the ultra-long-stroke programme in May 2011 with the addition of G70ME-C9, G60ME-C9 and G50ME-B9 models. The G-types have designs that follow the principles of the large-bore, Mark 9 engine series that MAN Diesel & Turbo introduced in 2006. Their longer stroke reduces engine speed, thereby paving the way for ship designs with unprecedented high-efficiency.

Rationale behind G-type introduction

Tankers and bulk carriers have traditionally used MAN B&W S-type engines with their long stroke and low engine speed as prime-movers, while larger container vessels have tended to use the shorter-stroke K-type with its higher engine speed.

Larger container vessels, in recent years, have also been specified with S80ME-C9 and S90ME-C8 engines because of the opportunity they offer to employ larger propeller diameters. Following efficiency optimisation trends in the market, MAN Diesel & Turbo has also thoroughly evaluated the possibility of using even larger propellers and thereby engines with even lower speeds for the propulsion of tankers and bulk carriers.

Such vessels may be more compatible with propellers with larger diameters than current designs, and facilitate higher efficiencies following adaptation of the aft-hull design to accommodate a larger propeller. It is estimated that such new designs offer potential fuel-consumption savings of some 4-7%, and a similar reduction in CO2 emissions. Simultaneously, the engine itself can achieve a high thermal efficiency using the latest engine process parameters and design features.

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. Again, 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.