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Auto Parts / UNDER PRESSURE

High injection pressures are helping to meet tougher emission
standards, but they also mean that fuel filters require more attention.

It is said timing is everything, and the fuel injection system and its ability to
injection of fuel has always been a atomize the fuel. In general, the
matter of timing. Add the proper higher the injection pressure, the finer
amount of atomized diesel into a the atomization and the greater the
cylinder at just the right moment, and fuel economy,” explains Ed Saxman,
the engine responds with the cleanest product manager, drivetrain, with
burn and the best performance. Volvo Trucks North America. “High-
pressure fuel injection minimizes the
This explains why engineers have
soot… low soot formation means that
been investing so much of their time on 100 percent of the soot can be
systems that deliver well-timed shots of
regenerated from the (diesel
fuel at extremely high pressures.
particulate filter) passively, without
The injection process has certainly the use of additional fuel.”
come a long way.
To suggest that modern injection
The performance of traditional pump systems are dealing with historically
line nozzle systems was always high pressures would be an
directly dependent on the speed of the understatement. The 35,000 psi
engine. At 0 rpm, the engine did not pressures that are generated for
generate the pressure for an injection today’s Volvo engines are 20
of fuel. Conversely, the top forces were percent higher than the 29,000 psi
only created at the top engine speed. that was generated for the engines
built between 2002 and 2006.
If the two points were plotted on a
graph, there would be a straight line Cummins is generating similar
pressures, through the XPI fuel
between the two, notes Tim Shick,
director of business and product system that was produced for big-
bore, on-highway engines in a
strategy for Navistar’s engine group.
At lower engine speeds, it meant that partnership with Scania.
the fuel was more likely to be delivered But manufacturers have taken two
in the form of a slug of diesel rather distinctly different approaches to
than a fine mist, generating the puff of modern fuel systems, either refining
smoke that would spill from the stack. existing electronic unit injectors, or
adopting common rail systems that
Enter electronic unit injectors that
could deliver higher pressures pressurize a supply of fuel within the
rail that feeds the injectors. Rather
across a wider range of operating
speeds, regardless of whether the than generating pressure with the
barrel and plunger on a unit injector,
truck was accelerating or lugging.
a common rail system includes a
Those higher pressures are more high-pressure pipe and piston pump
important than ever before. that has enough capacity to maintain
pressures at lower engine RPMs.
“The solution to meeting EPA ’10
(2010) emissions with good fuel There are some differences in the
economy is all about a high pressure systems, of course. Detroit Diesel’s
1263 / Auto Parts

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