Sandy Nelson is a qualified Chartered Accountant and director at Walker Wayland Auckland. Sandy has broad experience in advising a wide variety of businesses and their differing needs from over 25 years in public practice. Walker Wayland Auckland Limited is a member of the Walker Wayland Australasia network and BKR International. wwauckland.co.nz
When your generators foul the air and water around the boat with diesel fumes, oil slicks, and floating islands of soot in addition to staining the paintwork, it’s time to take a closer look at the generator and exhaust systems.
A perfectly operating diesel would exhaust nothing other than a little bit of oxygen, the same amount of nitrogen that passes through the air filter, some water vapor, and carbon dioxide. Unfortunately, there is no such thing as a perfectly operating engine of any sort, and the conditions under which diesel generators function on yachts make them particularly imperfect.
Careful attention to generator loading, fuel and oil consumption, air filter condition, crankcase blowby, and turbocharger condition is a critical first line of defense against exhaust pollution. Some engines are inherently “dirty” and even under the strictest maintenance regime will produce unacceptable exhaust emissions. The only solution other than replacing those generators is fitting a diesel particulate filter (DPF).
Careful attention to generator loading, fuel and oil consumption, air filter condition, crankcase blowby, and turbocharger condition is a critical first line of defense against exhaust pollution.
The simplest and least expensive version is called a “flow through” filter, which is made with a catalyst coated metallic element that’s open from one end to the other and creates low exhaust backpressure compared to other types. This type will remove about 50 percent of soot and other particulates.
The most effective type of DPF is the “wall flow” filter made of a catalyst coated porous ceramic substrate with thousands of channels open at the inlet end and closed at the outlet. The exhaust is forced to flow through the porous ceramic walls to adjoining channels, which are open at the outlet end. This filter can remove up to 99 percent of particulates.
This type of catalyst makes a great deal of difference in filter performance. Precious metal catalysts, such as platinum, permit low-temperature regeneration or burn-off of soot but are inactivated by sulfur in the fuel. Base metal catalysts require higher exhaust temperatures but are resistant to higher sulfur content fuel.
Many generators operate at low loads and low exhaust temperature, which prevents passive DPFs from regenerating, and leads to rapid filter clogging. Electrical or burner-type exhaust heaters produce active regeneration but make for a more complex installation. Active exhaust heating systems provide longer filter service life and can be retrofitted to existing passive systems.
A quality active DPF system will include continuous data logging of exhaust pressure before and after the filter, exhaust gas temperature, electrical power input, a backpressure alarm, and permit modification of system operation to match changes in power demands. Data collected by the treatment system should be easily downloaded and analyzed by the engineer and the system manufacturer to provide a valuable troubleshooting tool for generator and exhaust system maintenance.
This column originally ran in the April 2018 issue of Dockwalk.