Two-strokes gear up for latest emission regulations

EGR unit (shown in orange) on MAN low-speed engine EGR unit (shown in orange) on MAN low-speed engine

The two main low-speed engine designers continue to bring upgraded versions of their range to the marketplace.

The low-emission versions of the engines will allow the more progressive owners and operators to stay one step of the upcoming emission limits – including IMO Tier III which is still not due in force for some time. The latest generation of engines offer much-reduced fuel consumption, with a view to the new energy efficiency design index (EEDI) rules, and meeting demands for ‘greener’ engines which will allows shippers and charterers to gain an advantage by demonstrating their environmental credentials to customers with ‘green’ policies.

MAN Diesel & Turbo recently picked up the first order for a low-speed engine fitted with its second- generation exhaust gas recirculation (EGR) system, which enables compliance with Tier III NOx limits due to enter into force in 2016. The system will be integrated wit hthe 6S80ME-C9 main engine onboard a 4,500TEU newbuild Maersk Line container vessel. The engine is being built by Hyundai Heavy Industries’ engine & machinery division.

Søren H. Jensen, vice president and head of R&D at MAN Diesel & Turbo said: “We have taken an important step forward in the development of exhaust gas recirculation with the release of this second-generation system. This configuration will mirror the final design for our Tier-III NOx EGR engine programme. The main focus has been on integration of the entire EGR system into one unit which is a part of the engine as a charge-air cooler. The EGR unit comprises a cooler, a scrubber, a water mist catcher and a blower unit, and is designed to be fitted on the engine in the same way as a charge-air cooler. Since the first-generation EGR was tested in service, we have achieved significant technical advances as well as improvement in performance. We have optimised the performance of the EGR so that the system recirculates 40% of the exhaust gas so as to meet the Tier-III reduction criterion.”

In order to fit the EGR system, only minor changes to the engine outline are required, so it can be incorporated into existing designs with negligible changes by shipyards. The ship involved is one of a series of 22 ‘C’ class container vessels ordered by Maersk, and which will be delivered in early 2013. Upon delivery, the vessel will operate between East Africa and the Far East. For a test period of three years, the engine will be operated partly with IMO Tier III NOx emission levels.

MAN Diesel & Turbo says that its EGR system allows full fuel flexibility, permitting operation on HFO, distillates and natural gas. It directs part of the exhaust gas back into the engine’s scavenge air, reducing the oxygen content of the air in the combustion chamber, thereby reducing the combustion temperature and, as a result, reduces the NOx formation. Tests at MAN Diesel & Turbo’s Diesel Research Centre in Copenhagen have indicated that it should be possible to achieve IMO Tier III NOx limits using EGR without other after-treatment measures.

The company says that itsEGR system is best suited to ships of over 2,000dwt, a segment that currently numbers 18,000-20,000 vessels operating globally, and for which it provides a means of meeting Tier III at economical cost, in both capital and operational terms.

At the lower end of the low-speed engine size range, Wartila has recently introduced smaller- bore electronically-controlled engines targeted specifically at the Chinese market. The first example of this engine, one of the 35cm-bore  X35 series, has recently been started for the first time at the Yuchai Marine Power (YCMP) plant in China.

The X35 series employs Wärtsilä's common-rail RT-flex technology, and incorporates features designed to meet the needs of the fast-changing Chinese shipping sector. An extra long stroke enables good fuel economy, and the common-rail technology achieves a high degree of operational flexibility.

The X35, and the slightly larger X40 series, are both completely new designs, intended to cover a market segment where Wärtsilä has not been present for some time. They were introduced in May2011 as the RT-flex35 and RT-flex40 respectively, and the designations were subsequently changed to be consistent with the rest of the latest Wärtsilä portfolio. At the start-up ceremony for the first X35, YCMP signed the first supply contracts for X40 engines.

Another first-time start-up for Wärtsilä occurred in November 2011 when the new six-cylinder RT-flex48T engine was inaugurated at Chinese licensee QMD (Qingdao Qiyao Wärtsilä MHI Linshan Marine Diesel). This is the latest development of the RTA48T engine, and marks completion of Wärtsilä’s programme of adding electronic versions of all bore sizes in its low-speed engine range

The RT-flex48T is targeted at bulk and tanker vessels in the Handysize and Handymax ranges. The RT-flex common-rail technology provides electronically controlled fuel injection and exhaust valve activation for reduced emissions and fuel consumption, and claimed smokeless operation at all load levels. The fuel injection can be precisely controlled in terms of timing, quantity and pressure, for steady running throughout the speed range, while the electronically-actuated exhaust valve opening/closing allows optimum engine tuning for each individual engine rating. 

"We are extremely pleased to add the Wärtsilä RT-flex48T engine to our portfolio of common-rail low-speed engines. We now have this industry-leading technology available for all bore sizes in our current low-speed engine portfolio," said Martin Wernli, president, Wärtsilä Switzerland and vice president, product centre two-stroke.

The RTA48T shares the rail unit and supply unit with the established RT-flex50 type engine. It consists of one common rail pipe for fuel injection and another common rail pipe for the system oil driving the exhaust valves. Both are integrated within the rail unit where all pipe works and components are accessible from above. The rail unit is located just below the cylinder covers along the complete engine length.

Wärtsilä RT-flex48T marine diesel engine

Cylinder bore: 480mm

Piston stroke: 2,000mm

Stroke/bore ratio: 4.16

Power, R1 MCR: 1,455 kW/cylinder

Speed range, R1-R3: 102-127rev/min

Mean effective pressure at R1: 19.0bar

Mean piston speed at R1: 8.5m/s

Maximum cylinder pressure: 160bar

Number of cylinders: 5 - 8

Power range: 5,100-11,640kW

BSFC at full-load, R1-R2: 164-170g/kWh


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