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| Tony's Tips |
ARTICLE DATE: 10/01/2000 |
| What is white smoke? |
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What causes white smoke? What is white smoke? What
can we do about white smoke? Why does white smoke seem to be more of a problem
now than it was fifteen years ago? Why is it that most of the popular marine
diesels of today are all certified "IMO Compliant" or "EPA
Certified" and still may have white smoke issues? These are tough questions
to answer, although some of them can be answered with some science. But
other times, some will still have "gray" answers, as the answer
may or may not solve the problem.
White smoke occurs as a result of combustion temperature being so low that
only partial combustion occurs and the partially burned fuel that exits
the exhaust is in the form of a white vapory smoke. Technically, the white
color is caused by the light-scattering characteristics of the re-condensed
droplets of fuel (unburned or partially burned) larger than one micron.
Many factors contribute to this unsociable condition and it can be one or
more of the following:
1. Poor fuel quality (low cetane rating).
2. Low inlet air temperature.
3. Low coolant temperature.
4. Low compression ratio.
5. Retarded (incorrect) ignition timing.
6. Incorrect/failed fuel injection components.
Since this is a boat and marine diesel forum, and, white smoke seems to
come with the territory, I'll first start by giving you about twenty years
of personal experience with white smoke.
Cummins released the 6BTA 250 around 1987 and this was an upgrade of the
6BT 210. Within a few months after the release of the 250, "white smoke"
suddenly became a thorn in my side. The engine would start to suffer from
slow start-up with one or two cylinders initially firing. Finally, after
what seemed like an eternity (actually, about thirty seconds or so) all
six cylinders would finally catch and the engine was running. Of course,
during the first few minutes of running, the operator wished it wasn't running,
as clouds of white smoke would billow from the exhaust. This would last
for five to ten minutes while idling out of the harbor and, just all of
a sudden, it seemed to disappear and the engine would be fine for the remainder
of his fishing trip. This would reoccur after 24-48 hour shut-down and the
sequence of this obnoxious white smoke would slowly get worse over the next
few hundred hours. It took a couple of years for Cummins to fully address
the issue and finally cough up the fix. The CAV pump that was used on the
210, which could last 10,000 hours or so, was now only lasting a hundred
to 500 hours before excessive wear on the cam plate was sending metal particles
throughout the injection system causing very poor injection properties which
led to incomplete fuel burn.
The added fuel pressure for the higher HP rating was wearing out the pump
way before its time. The reason the problem went away after five to ten
minutes was that sufficient temperature within the engine itself allowed
enough (complete) combustion to make the problem go away. Talk about a couple
of years of my company making excuses.
Obviously, the above scenario starts with item 6, "failed components."
But, as you can see, temperature comes into this as a "fix-all".
Since my initial experiences with white smoke in the late eighties, I can
honestly say that I haven't seen any direct failures of components that
have led to any white smoke issues that always seemed to be a concern. Within
the last few years, I've seen and been directly involved with white smoke
concerns with Yanmar, Cummins, Ford, and Volvo engines. In none of these
cases have I been able to ascertain exactly what has been causing the white
smoke. But in all cases, the one remedy for all of these complaints is temperature.
So, why does Seaboard install block heaters? Because white smoke can still
be an issue with these modern "low-emission diesels".
I consider this particular engine to be the flagship of the Cummins marine
diesels offered today in this horsepower range. There is no doubt in my
mind that within ten years, I will see many of these engines with 20,000+
hours on them and the heads will have never been off.
So why is white smoke still a problem? Temperature, plain and simple.
Of all the possible causes and, from my experience, the lack of temperature
at which the fuel is burning within the engine is the single biggest cause
of white smoke. So to me, the simple solution is to increase the temperature
at start up. It doesn't matter if the engine's yellow, green,silver-gray,
or white. They all can suffer the same, and YES, some individual engines
are worse than others. The particular engine in a group that is having some
very serious white smoke issues, such as the Yanmar 4LH in this thread,
probably has some mechanical components that are not up to spec which may
need to be fixed. In the meantime, the owner can mitigate this problem by
adding temperature to the engine through a block/coolant heater, oil pan/pad
heater, or an air heater. Just about every Yanmar 300 LP that I've come
in contact w/ has the owner questioning the cold start-up. And yet this
engine is a beauty in all other modes of operation.
On the new Cummins engines that I install, like the 350 C, white smoke at
start-up can be of concern in many circumstance. These engines have "
state of the art" seawater after-cooling, piston cooling nozzles, and
are optimized for full power output. The design limitations of a mechanical
fuel injection system limit this "optimization" somewhat, although
do offer some other advantages. These are the design features that make
the engine fuel efficient, give it a longer life due to superior thermal
control, and lower NOx levels to meet emission requirement. But these are
the very reasons that, before the temperature comes up to a certain level,
can cause an unacceptable level of "white smoke".
You've got air feeding the engine that's being cooled by seawater (after-cooler),
you've got cold engine oil being sprayed at high volumes to the underside
of the piston crown slowing it's heating process, and you've got a mechanical
fuel delivery system that is designed to be at optimum efficiency at WOT
or close to it. Other than the fuel system, it's the temperature again that
is the common denominator.
Now, we can bring in the new full authority electronic diesels that can
give complete control to the fuel system to allow only the most perfect
balance of fuel- to-air ratios, fuel pressures, and timing sequences to
overcome even the temperature problem.. Even w/ cold air, cold oil, or a
cold engine, the engineers at Cummins, Detroit, Caterpillar, Volvo, etc.,
have been able to modify/control this fuel delivery in such a way that these
"fly by wire" diesels have not only increased power and efficiency,
they have solved the cold start-up smoke problem to where they will become
the "engines of choice" within the next decade. But, increasing
start-up temperature by adding block/pan heaters to these engines will still
offer many benefits. You'll still get improved start-up and oil circulation,
less moisture build up in the engine room spaces, and a much nicer environment
for the engine to live in (warm and cozy).
So, as you can see, white smoke is an issue with many of the engines today
that are in perfect mechanical condition. The simplest and most effective
way to control this is by using heat to solve the problem. Block and oil
pad heaters are an inexpensive and sure solution to this reoccurring problem.
I haven't found a single engine yet that couldn't benefit from a couple
of hundred watts from Mr. Edison. |
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