20
MARINE TECHNICIANTODAY | SUMMER 2015
This can cause hot spots in the combustion chambers, increased cylinder
misfiring and disrupt the flow of air coming through the intake manifold
and past the intake valve. These conditions will increase the amount of
unburned fuel in the combustion chambers. When the intake valve opens
during the intake stroke, it can come in contact with the unburned fuel,
and unlike the exhaust valve, the gases passing by are not hot enough to
burn off. These un-burned gasses collect on the intake valve stem, further
disrupting the airflow by the valve and creating even more deposits. It is
important to note that it is imperative that misfires be avoided at all costs,
and customers must be educated how to maintain their fuel systems.
Some GDI engines with variable valve timing can expose the valve to
combustion byproducts as the valves adjust, which creates a scavenging
effect to either pull or leave behind a small amount of exhaust gases
in the chamber to control NOX emissions. Also some turbocharged GDI
engines will leave the intake and exhaust valves open at the same time in
order to keep the turbo spinning to reduce turbo lag time.
With variable valve timing, the engine management system can control
when, how long and in some cases how deep the valve goes into the
combustion chamber. If the intake valve is dropping to deep into a
combustion chamber filled with unburned fuel, the valves will be very
prone to carbon build up. Other areas of concern are the PCV (Positive
Crankcase Ventilation) systems, as they can leave an oily film on the
intake valve which can bake on and turn into thick carbon deposits over
time. Proper maintenance is now more important than ever. Periodic
chemical intake cleaning can help keep internal components clean, but
must be performed early enough to be effective and carefully enough
to avoid damaging the engine and associated downstream components
like the catalyst system, and the very important O2 sensors.
Proper maintenance must be stressed to our customers, it is more
important than ever so the engine can keep running properly and
efficiently. Timely engine oil and filter changes are needed to keep
the variable valve timing camshaft actuators working at their optimal
performance. This helps control the exposure of intake valves to
damaging carbon deposits. Spark plug replacement is important
to protect against deposit creating misfires. Regular fuel injector
cleaning can help injectors maintain the correct spray geometry. This
helps atomize the fuel in the combustion chamber so it gets burned
properly. Also, in my opinion, fogging procedure ratios for winterization
will have to change to a lighter mixture similar to that of a two stroke
oil and fuel mixture.
So why have the automotive manufactures, and now the marine engine
manufactures begun the move from EFI engines to GDI engines? The
biggest reasons are the efforts to meet increasingly stringent fuel
consumption and emission regulations worldwide.
Beginning about 5 years ago, the inboard/sterndrive industry had to
begin to meet tougher EPA regulations. This is just the beginning of
these more stringent requirements as more are sure to come. GDI is
one way that can help meet these tougher emissions standards. Testing
shows a decrease in cold start emissions up to 25%, and a reduction in
the overall carbon footprint of an engine, especially for carbon dioxide.
And not only does it help with emissions problems, but offers more
power compared to an equal MPI engine, and greater fuel economy.
Direct fuel injection engines, especially for the marine industry, present
a new array of diagnostic challenges. It is up to us to turn those
challenges into opportunities. We as marine service professionals
need to take the time to study and fully understand these new systems.
We need to know this new technology’s strengths and weaknesses,
and invest in the proper training, tooling and equipment to be well
positioned to begin servicing and repairing these new engines. Those
who do will become leaders in the marine hi-tech field.
For more information about marine engine development contact Bob Madara,
Marine Kinetics 114 Woodward Ave. Rochester, NY 14609. Phone 585-654-8583
email;
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Aluminum block V-8
direct injection engine
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2015 Volvo Penta
V-6 direct injection
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