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Allan Sager

Thu, Sep 11, 2003 9:11 AM

I saw a reference to the "optimum" 80% power figure, and I was not
successful in finding any reference to that number in the diesel books I
have in my marine library. Can someone point me to a reference that
explains what and why 80% rpm is important? And, is it 80% of WOT, or 80%
of the continuous rpm rating?

TIA,
Allan
Avatar
Mainship Pilot 34

I saw a reference to the "optimum" 80% power figure, and I was not successful in finding any reference to that number in the diesel books I have in my marine library. Can someone point me to a reference that explains what and why 80% rpm is important? And, is it 80% of WOT, or 80% of the continuous rpm rating? TIA, Allan Avatar Mainship Pilot 34

JD

Joe DellaFera

Thu, Sep 11, 2003 12:59 PM

All: A while ago someone mentioned the article in the Oct 2003 issue of
"National Fisherman " concerning the dangers of running the engine at too
low a speed.

On the topic of fuel dilution they said "... the unburned fuel goes down
past the cylinder's piston rings. thinning the oil with fuel
which reduces the oil's viscosity, along with its protective
qualities. The fuel prematurely fills ( I guess they mean clogged) the
engine oil filter, which causes the filter bypass valve
to open. ... results in the engine being lubricated with unfiltered oil"

I understand the "fuel dilution" , but does anyone know why the filter
would be clogged prematurely ? ...jd

Joe DellaFera / Margaret Murray
36' Prairie DC "Prairie Star"
Kitching Cove (Port St Lucie) Fl.
Waypoint 000 = 27.14.930 80.19.200

All: A while ago someone mentioned the article in the Oct 2003 issue of "National Fisherman " concerning the dangers of running the engine at too low a speed. On the topic of fuel dilution they said "... the unburned fuel goes down past the cylinder's piston rings. thinning the oil with fuel which reduces the oil's viscosity, along with its protective qualities. The fuel prematurely fills ( I guess they mean clogged) the engine oil filter, which causes the filter bypass valve to open. ... results in the engine being lubricated with unfiltered oil" I understand the "fuel dilution" , but does anyone know why the filter would be clogged prematurely ? ...jd Joe DellaFera / Margaret Murray 36' Prairie DC "Prairie Star" Kitching Cove (Port St Lucie) Fl. Waypoint 000 = 27.14.930 80.19.200

LH

Leo Hill

Thu, Sep 11, 2003 5:28 PM

--- Joe DellaFera samakijoe@adelphia.net wrote:
[snip]

I understand the "fuel dilution" , but does anyone
know why the filter
would be clogged prematurely ? ...jd

If there is diesel dilution of the oil, then there are
other issues happening too. It is my understanding
that it isn't >just< fuel that is making it past the
rings - there are some (microscopically) large
particles of carbon from incompletely burned fuel that
also get into the oil and are filtered out by the oil
filter.

Why incompletely burned fuel? Something in the
injector system - the pump or injectors - is either
squirting too much fuel into the cylinders, the timing
is off or the injectors are not atomizing the fuel
correctly. Too many large drops from an injector
means that the fuel doesn't get burned cleanly and
that causes carbon and the continued supply of either
excess fuel or too large droplets washes some of the
carbon off the head &/or piston top and the whole
sludgy mixture gets forced past the rings.

If enough carbon gets past the rings - and the filter
isn't changed as recommended - then it clogs and goes
into its bypass mode.

Regards,

Leo

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--- Joe DellaFera <samakijoe@adelphia.net> wrote: [snip] > I understand the "fuel dilution" , but does anyone > know why the filter > would be clogged prematurely ? ...jd If there is diesel dilution of the oil, then there are other issues happening too. It is my understanding that it isn't >just< fuel that is making it past the rings - there are some (microscopically) large particles of carbon from incompletely burned fuel that also get into the oil and are filtered out by the oil filter. Why incompletely burned fuel? Something in the injector system - the pump or injectors - is either squirting too much fuel into the cylinders, the timing is off or the injectors are not atomizing the fuel correctly. Too many large drops from an injector means that the fuel doesn't get burned cleanly and that causes carbon and the continued supply of either excess fuel or too large droplets washes some of the carbon off the head &/or piston top and the whole sludgy mixture gets forced past the rings. If enough carbon gets past the rings - and the filter isn't changed as recommended - then it clogs and goes into its bypass mode. Regards, Leo __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com

MM

m/v MOJO

Thu, Sep 11, 2003 8:40 PM

Why incompletely burned fuel? Something in the
injector system - the pump or injectors - is either
squirting too much fuel into the cylinders, the timing
is off or the injectors are not atomizing the fuel
correctly.

My Cummins operation and maintenance manual (Cummins 6BTA5.9) states that
"if the cylinder chamber temperatures drop to low the fuel will not burn
completely. This will cause carbon to clog the injector spray holes and
piston rings, and can cause the valves to stick. If the engine coolant
temperature becomes too low (140 F), raw fuel will wash the lubricating oil
off the cylinder walls and dilute the crankcase oil;"

This section is referring to idling the engine for long periods of time
(defined as greater than 10 minutes). The manual does not mention how much
load is required when operating, it just discusses the need to keep the
coolant temp above 140 F. The Cummins factory tech that surveyed the engine
when I purchased the boat used an exhaust gas pyrometer to check and make
sure the EGT was in the normal operating range at the speed (1500-1600 rpm -
max engine rpm is 2500) we cruised. It was. He was not concerned that we
were operating it under too little load or at too low rpms - just that the
engine was running hot enough.

Ray B.
m/v MOJO
Bebe design #112 Passagemaker 49-10 in steel
www.mvmojo.com

> Why incompletely burned fuel? Something in the > injector system - the pump or injectors - is either > squirting too much fuel into the cylinders, the timing > is off or the injectors are not atomizing the fuel > correctly. My Cummins operation and maintenance manual (Cummins 6BTA5.9) states that "if the cylinder chamber temperatures drop to low the fuel will not burn completely. This will cause carbon to clog the injector spray holes and piston rings, and can cause the valves to stick. If the engine coolant temperature becomes too low (140 F), raw fuel will wash the lubricating oil off the cylinder walls and dilute the crankcase oil;" This section is referring to idling the engine for long periods of time (defined as greater than 10 minutes). The manual does not mention how much load is required when operating, it just discusses the need to keep the coolant temp above 140 F. The Cummins factory tech that surveyed the engine when I purchased the boat used an exhaust gas pyrometer to check and make sure the EGT was in the normal operating range at the speed (1500-1600 rpm - max engine rpm is 2500) we cruised. It was. He was not concerned that we were operating it under too little load or at too low rpms - just that the engine was running hot enough. Ray B. m/v MOJO Bebe design #112 Passagemaker 49-10 in steel www.mvmojo.com

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TWL: Optimum 80% Figure