Nitro Engines
Nitro engines used for
R/C models are highly advanced engines that can turn in excess of 50,000
RPMs. With this much movement, a lot of friction is generated and the
fuel used for these engines usually contains between 12-18% oil content
depending in the nitro-methane percentage. Most engines in R/C cars
today are 2 stroke engines, which means that it takes 2 strokes of the
piston to complete the engine cycle.
A nitro engine generally refers to an engine powered with a fuel that
contains some portion of nitro-methane. Nitro-methane is highly combustible
substance that is generally only used in very specifically designed
or modified engines.
On the first stroke as
the piston travels downward, a mixture of nitro and oxygen is sucked
into the crankcase, from the carburetor and travels into the induction
port and finally into the combustion chamber. As the piston travels
upward the mixture is compressed and ignited by the glow plug which
causes the fuel to explode forcing the piston down. As the piston travels
downward the spent exhaust gases escape out of the combustion chamber
through the exhaust port, and the cycle starts over by the fuel mixture
being again sucked into the induction port.
Nitro engines use a carburetor
to mix the nitro and air together. The carburetor can either be sliding
or rotary. On a rotary carburetor, the slide is opened as the arm is
turned by the servo. On a slide carburetor the slide is opened by sliding
the arm out by the servo. Both are held open slightly by an idle screw
which allows the engine to receive a very small amount of fuel to keep
the engine running when the vehicle is at a stop. The carburetors usually
feature 2 needles used to tune the mixture. A high speed needle tunes
how much fuel is allowed into the carburetor at mid to high RPMs, and
a low speed needle determines how much fuel is allowed into the carburetor
at low to mid range RPMs. Turning either needle in a clockwise motion
will lean the engine out. Lean describes the amount of oil the engine
is being lubricated with.
To a point this will make
the engine run faster with better performance, but once too lean the
engine will overheat, and wear out prematurely due to too little lubrication.
Turning either needle counterclockwise will richen the engine. Rich
is the opposite of lean, it means more oil is entering the engine. If
the engine is too rich, it will run poorly. The engine will run very
slow and seem to have no power and possibly cut out from being flooded
with fuel. Although, being too rich is better than being too lean, because
being too rich just means the engine is getting too much oil which is
perfectly fine, although performance may not be as good as if the engine
were lean. A properly tuned engine will last a long time with good performance
throughout its life.
There are several different
types of R/C engines. There are onroad, offroad, aircraft, marine, and
monster truck engines. Onroad engines are designed to come into their
powerband from mid to high RPM. These engines are can be used in offroad
vehicles but are normally used in onroad sedans where very high rpms
and high speed is required. Offroad engines have a less abrupt power
curve compared to onroad engines. Offroad engines have a powerband that
extends through most of the rpm range.
Offroad engines do not
rev as high as onroad engines, but they do have more torque that can
easily propel the vehicle it is in to impressive speeds. Offroad engines
are usually used in 1/8 scale buggies where high speeds and good acceleration
are required. Aircraft engines are manufactured to be able to sustain
high RPMs. The biggest difference between all other nitro engines and
aircraft engines is the ability to sustain RPMs. Other nitro engines
tend to break if run at full throttle for a full tank of fuel. Marine
engines are cooled with water rather than air like other nitro engines.
Monster truck engines are generally very large compared to onroad and
offroad engines. Where an offroad engine may be .21ci size, a monster
truck engine may be as much as .32ci. Monster truck engines generate
much of their torque and horsepower at low to mid range RPMs. They are
usually used in large and heavy trucks where all that power is needed
to get good performance out of the vehicle.
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