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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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