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Soot reduction & diesel engine tech
Dean
Posted: Tuesday, August 19, 2008 11:39 PM
Joined: 17/06/2008
Posts: 71


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.

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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.


Robertmech
Posted: Sunday, November 11, 2012 12:57 PM
Joined: 15/02/2011
Posts: 15


I have seen one yacht with an extra smaller airconditioning plant to aircondition the engine room, a unit
with a no. of smaller commpressors could effectively be used as a load bank to maintain optimal load on
a generator with commpressors cutting in and out as necessary, this would also add to the compfort of the engine
room when the generator is not fully loaded,  I looked at a Westport during a boat show last year and was told
that they aircondition the engine room on boats for the Arab market where the ambient temperature during the
summer can be 50deg. celcius.

junior
Posted: Wednesday, November 14, 2012 4:14 PM
Joined: 14/01/2009
Posts: 1026


No need for a dirty diesel. When I see black topsides, I think poor maintenance schedule. Follow the guidelines for injectors ,injector pumps, air cleaners.... One service that is always overlooked is the exhaust. On a water cooled system, the water injection jacket builds up carbon deposits fast as the gas is cooled. After 1500 or so hours water jacket ID can be reduced 50 percent .
Chief
Posted: Friday, November 30, 2012 2:50 PM
Joined: 02/06/2008
Posts: 341


Have any readers been told by engine manufacturers, shops, or dealerships that using a fuel additive to reduce soot will impact the engine warranty?

 

 


junior
Posted: Friday, November 30, 2012 4:49 PM
Joined: 14/01/2009
Posts: 1026


Sorry for the crappy Dockwalk format. Ive been told to avoid useing metalic smoke suppresssants and fuel additives. . A note from Chevron. "Smoke Suppressants " Some organometallic compounds act as combustion catalysts. Adding these compounds to fuel can reduce the black smoke emissions that result from incomplete combustion. Such benefits are most significant when used with older technology engines which are significant smoke producers. There is significant concern regarding potential toxicological effects and engine component compatibility with metallic additives in general. During the 1960s, before the Clean Air Act and the formation of the U.S. EPA, certain barium organometallics were occasionally used in the U.S. as smoke suppressants. The EPA subsequently banned them because of the potential health hazard of barium in the exhaust. Smoke suppressants based on other metals, e.g., iron, cerium, or platinum, continue to see limited use in some parts of the world where the emissions reduction benefits may outweigh the potential health hazards of exposure to these materials. Use of metallic fuel additives is not currently allowed in the U.S., Japan, and certain other countries. " A note from Detroit Diesel....." Additives containing calcium, barium, zinc, phosphorous, sodium, magnesium, iron, copper, and manganese are known to cause combustion ash deposits that can foul fuel injectors and create deposits which may adversely affect cylinder life."
Chief
Posted: Friday, November 30, 2012 9:40 PM
Joined: 02/06/2008
Posts: 341


Thank you, Junior, I appreciate the labor that went into typing that reply but that is the standard manufacturer disclaimer and warning language.

 

I am looking for comments from engineers who have been told by dealers or techs that use of additives generally or specifically will void their warranty or words to that effect.

 

I am interested in what they said and what the context was. Bottom line, what are engineers being told?


junior
Posted: Saturday, December 1, 2012 8:19 AM
Joined: 14/01/2009
Posts: 1026


In my MTU operators manual is a section .......approved liquids and lubricants. It states................ ............Attention is drawn to the fact that the use of diesel fuels or additives other than those stipulated in the MTU Fluids and Lubricants Specification is always the responsibility of the operator............ This implies that warranty is void if the additive used is not on the approved list.
ESSOBEA12
Posted: Wednesday, December 26, 2012 9:03 PM
Joined: 25/01/2011
Posts: 6


Any one use g2 for an additive?
Chief
Posted: Thursday, December 27, 2012 12:41 PM
Joined: 02/06/2008
Posts: 341


Only on boats that keep chickens and and pigs.


http://www.efsa.europa.eu/en/efsajournal/pub/2930.htm

 
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