MAN BOOSTS MID-RANGE ENGINE FUNCTIONALITY
MAN Energy Solutions has sought to give extra competitive edge to its 460mm-bore two-stroke offering by introducing a development based on the S46ME-B engine, writes David Tinsley.
The new S46ME-C version has more advanced engine control and achieves lower specific fuel oil consumption (SFOC) than its immediate forebear, and also provides scope for a dual-fuel variant.
The lineage began with the S46MC-C in 1996, followed by the S46ME-B four years later, and which became increasingly favoured for its electronically-controlled fuel injection. More than 900 engines of the series have been ordered to date. The S46ME-B has wide application appeal, and is a popular choice for bulk carriers in the 25,000-50,000dwt segment, tankers in the smaller sizes, and feeder and intra-regional containerships.
The S46ME-C development project has been motivated by the growing weight of legislation to curb NOx and CO2 emissions. Meanwhile, emission abatement equipment is becoming more efficient and less costly to produce, but also requires more sophisticated engine control.
As a consequence, it has been decided that the S46ME-B8.5 diesel will be superseded by the S46ME-C8.6, giving full flexibility of the opening and closing time of the exhaust valve.
The S46ME-C8.6 also yields a slightly higher, maximum continuous output of 1,390kW per cylinder, at a marginally higher running speed of 130rpm, relative to the 1,380kW/cyl at 129rpm of the S46ME-B8.5.
To achieve the requisite functionality, some ME-B parts have been removed and new ME-C parts have been added. Various modifications to the engine structure, the introduction of the flexrod-type conrod, and component upgrades around the combustion chamber have allowed for an increase in combustion pressures, leading to improved SFOC. This is stated to be 167g/kWh at the L1 maximum continuous rating compared to the 170g/kWh of the S46ME-B8.5.
Part-load and low-load optimisation is available through the exhaust gas bypass (EGB) tuning method and also, on request, with high pressure tuning (HPT). SFOC is reduced by between 3-4g/kWh for both options.
The combustion pressure increase necessitated an upgrade of certain flange thicknesses in the bedplate and frame box. The removal of camshaft housings, given the dispensation with the chain-driven camshaft of the S46ME-B type called for a re-design of the cylinder frame.
The operating flexibility conferred by the exhaust valve timing arrangements enhances the Dynamic Limiter Function (DLF, to improve engine and ship acceleration) and facilitates possible subsequent creation of a gas-injected, ME-GI/ME-GIE version for the S46 engine family.
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