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Chuck Husick: Techno-Talk, March 2004, BoatUS Magazine -

Diesel Engines
With new federal diesel engine emissions rules coming down the pike in 2006, manufacturers are moving ahead with production and the diesel engine in the next boat you buy may well meet the 2006 specifications. The new rules cover marine diesels producing more than 37 kW (50 hp) and will be phased in from 2006–2009. Existing engines will be “grandfathered” and can continue in service without alteration.

The new engine emission rules impose lower limits on the amount of hydrocarbon (HC), nitrous oxides (NOx) and particulate matter (PM) permitted in the exhaust, leaving the already low carbon monoxide and carbon dioxide requirements virtually unchanged. The greatest challenge imposed by the new rules is a 22% reduction in combined HC+NOx. (More stringent limits are specified for highway diesels due to their far more substantial numbers and vastly greater operating hours.)

Although all manufacturers are now or soon will be offering products complying with the new standards, Volvo Penta led the way with the introduction of 2006 specification engines last summer. The Volvo Penta engines I evaluated at their test facility in Gothenburg, Sweden, in June 2003 are impressive examples of how technology can simultaneously protect the environment while providing performance advantages.

Our experience with these new engines will be very different from the highly negative results we remember from initial efforts to clean up our car engines — hard starting, poor acceleration, generally poor fuel economy and unreliability. The new diesels will start more easily, idle much more quietly and smoothly, deliver superior acceleration and provide a small increase in fuel efficiency.

The new technology engines will be totally computer controlled and therefore benefit from the extensive performance monitoring and diagnostic capability of the powerful microprocessors and sophisticated software that manages every aspect of their operation. Virtually any required troubleshooting will be done via computer, and will be far more precise than is possible with current engines, saving the owner money to hopefully offset the increased cost of the engine.

Meeting the new specifications required a number of technical changes in engine design, primarily in how diesel fuel is burned in the cylinder. A diesel engine’s fuel is injected into the cylinder at high pressure beginning just before the piston reaches its most upward position during the compression stroke. In today’s engines, the injection pressure is usually about 3500 psi and the flow of fuel is continuous once the fuel pressure is high enough to force the fuel injector’s valve open.

In the new engines the injection pressure can be 1600 bar (1600 times atmospheric pressure – 23,500 psi) creating a fuel aerosol much finer than can be attained at today’s much lower injection pressures. The new fuel injectors are electrically controlled by the engine’s computer and deliver fuel in multiple bursts, each lasting perhaps 1/1000th of a second.

The quiet, almost gas engine-like idle sound on the new diesels is a result of beginning the combustion cycle by injecting a small amount of fuel to initiate combustion in the cylinder without causing the very fast pressure rise, which creates the characteristic diesel “rap” sound. The initial puff of fuel is followed by injection of however much fuel is needed to meet the load imposed on the engine.

When you inspect one of the new engines you may notice the absence of the familiar fuel injection pump and the individual high-pressure fuel lines that connect it to each fuel injector. In its place, usually under a protective metal cover, you will find a single highly pressurized fuel reservoir, the “common rail” with fuel supply pipes connected to each electrically controlled fuel injector.

The engine control computer manages fuel injection to a precision not attainable with the mechanical controls used on current production engines. The engine can achieve maximum rate acceleration under load without spewing clouds of black smoke (unburned fuel) from the exhaust. The characteristic soot stained transom of some diesel powered boats will be come an increasingly rare sight. The computer will protect the engine from overloading, extending its life.

The introduction of these new engines presents us with a rare coincidence: enlightened environmental rule making coinciding with advanced technology to produce a clearly superior product.


By Chuck Husick

Chuck Husick is a pilot, engineer, sailor and former president of Chris Craft Boats.

© Copyright BoatUS Magazine 2004





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