Two-stroke companies prepare for IMO Tier III

MAN Diesel & Turbo offers both selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) methods to enable its two-stroke engines to meet IMO Tier III NOx limits, which are due to take effect from 1 January 2016.

The choice of which technology to adopt will depend mainly on the time spent within the ECA, in which Tier III limits will apply. Ships spending more time in controlled areas will probably find it more economical to adopt the EGR solution, which involves higher capital cost but lower operation expenditure.

The SCR system has already been taken up by several operators of ships with four-stroke engines which operate primarily in ECAs, and ships with two-stroke engines have successfully trialled the SCR system at sea. In 2012 MAN Diesel & Turbo, together with HHI-EMD, the engine and machinery division of Hyundai Heavy Industries, launched what it says was the first IMO Tier III-compliant diesel engine utilising EGR.

The integrated EGR system on the MAN B&W 6S80ME-C9 engine can, says the company, meet Tier III limits without significantly compromising engine performance. Søren H. Jensen, MAN head of marine low speed R&D said: “Testing achieved a low penalty, equivalent to 1-3 g/kWh, which was even better than our most optimistic expectations.”

A promising spin-off benefit of the EGR is that the engine can be run in a fuel-optimised Tier II mode that represents a fuel oil consumption reduction of around 4 g/kWh at part load. This is accomplished through a combination of sequential turbocharging, turbocharger cut-out and low EGR rates.

The first EGR engine has been in service with Maersk Line in a C class container ship with encouraging results.

“We are ready for IMO Tier III”, says executive board member Dr Stephan Timmermann. “We have the technologies in place to support our customers for this new era of environmentally efficient shipping.”

“While fuel prices remain high and emissions become ever more stringent, ship owners look for the most efficient solutions for newbuildings and existing ships”, said Ole Grøne, senior vice president for MAN’s low speed business unit. “Any percentage point of fuel saving means lower operational costs and lower emissions – it’s a win-win situation”, Grøne concluded.

High pressure SCR

The first Wärtsilä two-stroke engine fitted with a high pressure SCR system manufactured in China, a 5-cylinder Wärtsilä RT-flex58T-D 2-stroke, low speed engine produced at Hudong Heavy Machinery, is to be installed in a new 22,000 dwt multi-purpose vessel currently under construction at the Ouhua shipyard for China Navigation Co. The SCR reactor was also manufactured by HHM. Wartsila says that this is the first SCR system that complies with IMO Tier III regulations for engine emissions of NOx.

The SCR system has been jointly developed by HHM and Winterthur Gas & Diesel (WinGD), the joint venture company of Wärtsilä and China State Shipbuilding Company (CSSC). The basic design concept from Wärtsilä has been adapted to suit the particular requirements of the engine and ship. Wärtsilä says it has produced high pressure NOx-reducing SCR systems since the late 1990s. The system injects a solution of urea into the exhaust gas flow to react with and eliminate the NOx emissions. The ‘high pressure’ designation comes from the location of the SCR unit, between the engine exhaust valves and the turbocharger turbine inlet. The company claims that this provides the most compact and efficient system without compromising engine performance or impacting fuel consumption.

“HHM is very happy to deliver the first 2-stroke high pressure SCR produced in China. We have been working on development of the SCR with major designers during the past three years and now the cooperation with WinGD shows what is possible. We look forward to continued growth in this market,” says Zhou Weizhong, HHM executive director of R&D.

Test bed trials of the SCR-equipped engine were observed and approved by Lloyds Register. “These trials show that the technology to produce IMO Tier III compliant engines is actually available and hence give confidence that IMO Tier III certified engines will be ready for January 1, 2016,” said John Bradshaw, principal technical specialist, Lloyds Register.

Low pressure EGR

Mitsubishi Heavy Industries Marine Machinery & Engine Company (MHI MME) says it has developed a low pressure EGR system which offers several advantages over the established high pressure EGR technology.

Because the system is fitted at the low pressure side of the turbocharger system, where the air is cooler, recirculating gas from the turbocharger outlet, the blower unit and the ancillary systems, including the scrubber, can be of light and simple construction, with reduced maintenance requirement. Because the blower uses turbocharger suction pressure, power requirement is lower than for a high pressure system. MHI MME believes that a high pressure EGR may result in smaller amounts of steam for the economiser unit, so additional boilers may be needed for EGR operation. This does not apply to the low pressure unit, says the company – in fact slightly more steam may be produced. Like the high pressure system, the low pressure EGR will be able to achieve 80% NOx reduction, with less effect on specific fuel oil consumption, and no risk of harmful acid deposits in the economiser. The low pressure system needs just a simple valve to switch the EGR in and out, where the high pressure system needs a complex control unit.

MHI MME says that the system has been tested on its 4UE-X3 research engine, with sea trials anticipated during 2015 with a view to entering the commercial market place in 2016.