新型低排废主机(英文)
2008.09.09
IMO II compliant engine - M43 Low Emission Engine (LEE)
One presentation that sure to get attention at this month’s SMM 2008 in Hamburg, Germany, will be on Caterpillar’s experience with the first practical trials of the MaK M43 Low emission engine on the chemical tanker “Fure West”.
The ship’s MaK 7 M43 C low emission engine already meets expected future IMO emission regulations. It is the first known vessel afloat with an IMO II-compliant engine running on heavy fuel oil (HFO), but also a technological milestone for any future cruise or cargo vessel.
The 16,000-dwt “Fure West” and its sister ship “Fure Nord” were delivered to Furetank Rederi AB of Donso, Sweden, by Edwards Shipbuilding,Shanghai, in 2006 and 2004 respectively. Both were delivered with MaK 7 43 C main engines rated at 6,180 kW at 500 rev/min. (图 1)
Back in 2000, Caterpillar Motoren identified three emission levels for the MaK marine product line. There were a base line IMO engine, which fulfils MARPOL 73/78, Annex VI, an IMO-compliant engine with invisible smoke emission and a Low Emission Engine which meets the expected NOx emission range of IMO II and is also invisible in smoke.
The key to low NOx emission is to increase the compression ratio of the base engine. Ten years ago, a compression ratio of 1-12 was standard, for IMO I the ratio was raised to 14-15 and for IMO II ratio of 17 will be needed. Another cornerstone of the MaK LEE concept is the Miller Cycle, i.e. modification of the engine’s valve timing to achieve cooler combustion. For IMO I only a small Miller effect of 5% was utilized. However, IMO II requires a Miller effect of 20%- a big challenge for the turbocharger, which has to provide boost ratios of 5 in order to maintain today’s Mean Effective Pressure (BMEP) values.
By combining increased compression ratio and the Miller effect, NOx emission can be reduced by around 30% without sacrificing engine efficiency. However, such a simple LEE engine would suffer from poor load pick-up at idle and visible soot emission at part load. Because of this, the MaK LEE concept uses a “flexible camshaft” to enable both low NOx emissions, excellent load pick up and invisible soot at all loads.
Flexible Camshaft Technology (FCT) enables variation of the fuel system and the air system at part load operation. By advancing the start of the fuel injection and increasing injection pressure, combustion id improved and soot emission are reduced by 509%. Shifted inlet valve timing switches off the Miller Cycle and contributes another 25% reduction in soot. Overall, MaK FCT reduces soot emission at part load by 75% while improving engine performance at transient operation.
The system essentially consists of a modified lower valve train, a pneumatic adjusting unit and a Programmable Logic Controller (PLC). It uses an eccentric lifter lever shaft that automatically influences both injection timing pressure and valve timing. The engine load required to activate the lever can be set according to the vessel operation’s needs. Either way, visible smoke is eliminated while IMO standards are complied with at all loads.
After comprehensive simulation and prototype of the MaK LEE technology along with some final adjustments Caterpillar Moteren together with Caterpillar Marine Power Systems, was ready to put its technology to the test. In cooperation with Furetank Rederi, a timetable was agreed to convert the existing MaK 7 M43 C on “Fure West” to LEE standard.
During a scheduled vessel stopover in Rostock, Germany, in October 2007, a service crew from Pon Power A/S, Caterpilar MaK dealer for Scandinavia, supported by engineers from Caterpillar Motoren facilities in Kiel and Rostock, completed retrofitting, including classification society approval, in just four days.
Inside this tight time-frame, the team reworked connecting rods, camshaft segments and lower valve trains to meet LEE requirements. First, a conrod spacer was mounted to lengthen the split-shaft connecting rod, reducing combustion volume and increasing compression ratio. As a result, the anti-wear ring needed replacing with a shorter version. (图 2)
In a second step, the camshaft segments were replaced with modified FCT versions, enabling load-dependent variation of the fuel and air system. Lower valve rains, injection pumps and injection nozzles were exchanged accordingly. In addition, specialists from ABB rebuilt the turbocharger for increased loading pressure replacing the diffuser and nozzle ring. Sea trials with “Fure West” confirmed the quality of this retrofit as did the final approval given by Germanischer Lloyd.
In fact, all existing MaK M20 C, M25 C, M32 C and M43 C series marine engines afloatd can be converted to MaK LEE standard – at about only 15-25% of the cost of a new IMO II-compliant engine. Building upon proven technology residing inside the engine, MaK LEE offers many advantages for vessel owners and operators.
The MaK 7 M43 C Low emission engine has been operating aboard “Fure West” since October 2007 and has exceeded both the expectations of owner Furetank and Team Caterpillar. The world’s first known IMO II- compliant medium-speed HFO-fueled marine engine afloat, it runs as quietly and reliably as its thousands of MaK predecessors. The bi differences, however, is that emissions have been significantly reduced compared with current standard IM0 I-compliant marine engines.
