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The more miles you put on a Diesel the better un like Gas (long )
below is comparison to Gas and Diesel. Bottom Line, if you want your
work truck to last - get a Diesel. See below
Technically speaking, the compression ratio of an engine is the
comparison of the total volume of the cylinder at the
bottom of
the piston's stroke divided by the volume of the
cylinder
remaining at the top of the piston's stroke. Since we
are familiar
with gasoline engines, let's quickly discuss their
compression
ratios and a condition that spells disaster in a
gasoline engine,
detonation or "pinging."
GASOLINE RATIOS.
Serious damage to gasoline engines can result if you
attempt to
run a high compression ratio with low-octane fuel.
Detonation
or "pinging" is the ignition of the fuel due to the high
temperature caused by a high compression ratio/high
pressure
developed by a given design. The fuel is ignited prior
to the
spark of the spark plug resulting in rapid uncontrolled
burning.
The appropriate maximum compression ratio for a gasoline
engine in race trim is 14:1. Most "non-racing,"
low-octane
compression ratios used in automobiles are less than
9:1.
DIESEL RATIOS.
Remember, the diesel is a "heat engine," using heat
developed
from the compression of air. High compression ratios
(ratios
ranging from 14:1 up to 20:1) are possible since air
only is
compressed. The hot compressed air is sufficient to
ignite the
diesel fuel when it is finally injected near the top of
the
compression stroke. A high compression ratio equals a
greater
expansion of the gases following ignition and a higher
percent of
the fuel's energy is converted into power! The diesel
compression ratio is higher, there is more power!
THE INJECTION SYSTEM.
"It's in the injection system."
Diesel designed the "heat engine" using the injection of
fuel at
the last moment to ignite the compressed air.
Understanding the
heart of the diesel, the fuel pump, is another key to
answering
the fuel-efficiency question.
THE GASOLINE ENGINE.
A gasoline engine is stochiometric. Stochiometric: the
quantitative relationship between two or more
substances,
especially in processes involving physical or chemical
change.
With a gasoline engine there is a stochiometric equation
of 14
parts of air to one part of fuel. Remember, always 14:1;
whether at idle or full throttle, the fuel and air are
mixed outside
the cylinders in a carburetor or injection manifold and
the
mixture is introduced via the intake valve. 14:1 always.
THE DIESEL ENGINE.
Fuel and air in the diesel design are not premixed
outside the
cylinder. Air is taken into the cylinder through the
intake valve
and compressed to make heat. Diesel fuel is injected
near the
top of the piston's stroke in an amount or ratio
corresponding to
the load on the engine. At idle, the air-to-fuel ratio
can be as
high as 85:1 or 100:1. At full load the diesel still
boasts a miserly
25:1 or 30:1 ratio! It is in the injection system.
THE FUEL PUMP.
The fuel pump currently used on the Dodge Turbo Diesel
pickup is a Bosch P7100 in-line fuel pump. Think of it
as a mini
in-line six-cylinder engine and it's easy to understand
its
principle of operation. Six plunger pumps actuated by
the pump
camshaft send fuel pulses through six high-pressure fuel
lines to
the injectors. The pressure opens the injector valve
allowing fuel
to pass into the combustion chamber.
Metering of the fuel (at idle 65:1 or full load 25:1) is
controlled
by a fuel rack and gears which rotate a metering helix
to allow
fuel into the six plunger pumps.
The fuel pump on pre-'94 trucks was a Bosch VE
rotary-style
fuel pump. Think of this pump like a mini automobile
spark
distributor. A rotary "head" sends fuel pulses through
the
high-pressure fuel lines to the injectors. Just like the
in-line fuel
pump system, the pressure opens the injector valve and
fuel is
injected.
FUEL BTUs.
"The btu value of diesel is greater."
Quite true, the btu, or British thermal unit, for diesel
fuel is
130,000 btu's per gallon and a weight of 7.0 lb/gal. The
value
for gasoline is 17,000 btu's and a weight of 6.0 lb/gal.
If we go
back to our basic physics rules for energy, you'll note
the fuel in
the tank has potential for work if it is injected into
the cylinders
and, combined with the compressed heated air, ignited.
The
piston is forced downward, the crankshaft rotates, the
wheels
turn.
The diesel design (the "heat engine"), compression
ratios (the
"heat engine"), the fuel injection system (allowing 85:1
down to
25:1 air-to-fuel versus gasoline at 14:1) and fuel btu's
(diesel
fuel has more power), all these diesel attributes add up
to more
miles per gallon of fuel!
HEAVY-DUTY STRUCTURE.
Final notes: We've covered the principle of diesel
operation and
the high compression ratios needed to make the heat for
diesel
engine combustion. The high compression ratio causes the
engineers to design, test and manufacture the block,
heads, head
bolts, crankshaft, connecting rods, rod bolts, pistons,
piston
pins, etc., with greater structural capacity. In other
words,
diesels are inherently heavy in relation to their
gasoline brothers.
Take for example the B Series engine used in the Dodge
pickup.
It is 970 lb for the 359 cubic inch turbo diesel engine
versus 540
lb for the 380 cubic inch Dodge Magnum V-8 gasoline
engine.
Looking back at the first engine designed by Clessie
Cummins in
the 1920s, it was a monster at 400 lb per horsepower
produced.
Although diesels still tend to weigh more than gas
engines, it's
obvious we've made a lot of progress in 70 years.
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