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Generators are notoriously bad, when it comes to soot and oil slicks. MARPOL Annex VI, NOx & SOx, deals with engines above 130kW and so virtually excludes all generators onboard yachts below 50 meters & 650 GRT I’ve ran commercial vessels fitted with 100kW 3304 Caterpillar generators, with dry stack exhausts that had 25000 running hours between major rebuilds, put out less soot than the same generator package on a 1 year old motor yacht, because the commercial system was sized & installed correctly and run with consistent loads. Keeping emissions down and the soot associated with engine exhaust is achieved by proper management of the fundamentals and requires correct engine loading, correct exhaust back pressure, correct operation and maintenance procedures in conjunction with modern engine management systems. Whether we are talking about power generation or conventional prolusion systems soot reduction and fuel efficiency essentially become the same. As complete combustion ultimately means less un-burnt fuel gets passed out the exhaust pipe as pollutants. . The operation principal for 4 stroke diesel engines has existed since the early 1800’s. Stoichiometry is the science of determining the specific air fuel ratio’s for complete combustion. All 4 stroke diesels use the Otto cycle. Not getting the basics right Causes chocked air filters, chocked exhaust pipes, chocked turbo chargers, chocked charge air & intercoolers, and an ever increasingly sooty discharges and premature engine failure. Getting the basics right Achieves longer engine life, better fuel efficiencies and cleaner exhausts discharge. With hi-tech electronic engines you can expect even better results. Exhaust systems, catalytic converters & poorly installed or worn engines All the water drop mufflers, soot sinkers and catalytic converters in the world will not help a sick engine. Engine manufacturers spend hundreds of millions of research and development for getting it right. Improper installation, maintenance & operation are far more common than you would think. Installation A typical engine manufacture would not accept more than 76 mm of static water column at atmospheric pressure for an engine exhaust back pressure. I’ve often seen 300 mm readings and engines that last as little as 2000 hours on yachts. Check points & design features that help reduced engine exhaust emissions are; v Air, fuel and lubrication filter condition v Ambient and engine room temperature and barometric pressures v Common rail fuel injection systems with pre, main and post injection v Cylinder cut out at low speeds & supercharging v Cylinder scavenging performance and excess air v Engine control modules and monitoring systems that record historical data, which can be used for diagnostics in the field v Engine loads and RPM v Exhaust back pressure v Exhaust, cylinder, jacket water, fuel oil and lube oil temperatures v Fuel and lubrication oil consumption rates v Governor settings, acceleration and deceleration rates v Machinery condition monitoring & maintenance routines v Operator skill and correct techniques v Pressure and temperature differentials across all components v Sequential turbo charging Prolusion machinery is designed to operate at varied loads and speeds, where as generation plant is designed to operate at constant speed and with varied loads. Generator sets run in single & parallel modes Therefore power management systems and the governor controls automatically switch from speed droop to isochronous, which provides more stable control. v Speed droop = generator governor operates to decrease speed with increasing load. This is the mode that is commonly used to operate generators in parallel, as it allows them to share load in proportion to rated load. v Isochronous = constant speed operation. This mode is used when a generator is operating on its own and is used to maintain the frequency at rated 60 or 50 Hz. Electronically controlled engines Respond much faster than the older mechanical governors, but all governors use four (4) basic set points. v Droop – Governor Speed decreases as the load on machinery controlled by the governor increases. v Gain – The percentage change required before governor speeds increase or decreases. v Stability – The rate at which a governor speed changes. v Start fuel limit – Adjusts the amount of fuel required for staring & limits smoke. Correctly managing engines load and the rate at which acceleration and deceleration occurs ensures that governors, air induction, fuel injection and cooling systems have sufficient time to react to the changing loads. The time lag between the delivery of more fuel and sufficient air This is much less apparent with electronic engines. But jumping onto the throttle will always result in a period of incomplete combustion and excess smoke (black smoke = soot emissions). If you don’t believe me just get watch T.V. next time there is a diesel powered truck race. Generators present unique challenges as correctly sizing the generator to the ships load is not a truly perfect science A yacht with guests can require twice the electrical power, when compared to a yacht on standby. Electrical engineers tend to design systems around peak load applications and fail to recognize than many yachts spend the majority of time in low load conditions and require incremental power increase. I’d rather have four smaller generators to work with and have more system flexibility; two large machines simply double power output even if the load has not doubled. Automatic power management systems do not measure soot emissions Generators left to run at low loads are far less fuel efficient, than systems run @ 70% load capacity. A good chief engineer will monitor the power management system Either adjust the systems parameters according prevailing loads or manually operate the system. Shore power is often unreliable or insufficient to reliably power large yachts Generators often run even if there is not sufficient load to achieve full combustion, because this is the only option to power the vessel and it is up to the chief engineer to ensure generators are loaded correctly, or smaller generator sets are used. Load banks can artificially maintain optimum engine loads, but at what sacrifice to fuel economy? No single element or piece of regulation assures reduced exhaust emissions. Only through sound design, maintenance practice and skilled operation can it truly be achieved.
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