Abstract :
The radial
engine is an internal combustion engine configuration in which the cylinders point
outward from a central crankshaft like the spokes on a wheel. This configuration
was very commonly used in aircraft engines before being superseded by turboshaft
and turbojet engines. It is a reciprocating engine.
The cylinders
are connected to the crankshaft with a master-and-articulating-rod assembly. One
cylinder has a master rod with a direct attachment to the crankshaft. The remaining
cylinders pin their connecting rods attachments to rings around the edge of the
master rod (see animation). Four- stroke radials almost always have an odd number
of cylinders, so that a consistent every-other- piston firing order can be maintained,
providing smooth running.
DEBATE OF USE
The debate about
the merits of the radial vs. the inline continued throughout the 1930s, with both
types seeing some use. The radial was more popular largely due to its simplicity,
and most navy air arms had dedicated themselves to the radial because of its improved
reliability for over-water flights and better power/weight ratio for aircraft carrier
takeoffs. Although inline engines offer smaller frontal area than radials, inline
engines require the added weight and complexity of cooling systems and are generally
more vulnerable to battle damage.
The vast majority
of radial-engined aircraft designed since the 1930s were also were fitted with NACA
cowlings to reduce drag & to also enhance forward thrust by virtue of its airfoil
effect.
PISTON
In general,
a piston is a sliding plug that fits closely inside the bore of a cylinder. Its
purpose is either to change the volume enclosed by the cylinder, or to exert a force
on a fluid inside the cylinder There are two ways that a piston engine can make
power. These are the two-stroke cycle and the four-stroke cycle. A single cylinder
two-stroke engine produces power every crankshaft revolution, while a single cylinder
four-stroke engine produces power every other crankshaft revolution. Older designs
of small two-stroke engines produced more pollution than four stroke engines, however
modern two-stroke designs, like the Vespa ET2 Injection utilise fuel-injection and
are as clean as four-strokes.
Large diesel two-stroke engines, as used in ships
and locomotives, have always used fuel injection and produce low emissions. One
of the biggest internal combustion engines in the world, the Wärtsilä-Sulzer RTA96-C
is a two-stroke; it is bigger than most two-story houses, has pistons nearly 1 meter
in diameter and is one of the most efficient mobile engines in existence. In theory,
a four stroke engine has to be larger than a two stroke engine to produce an equivalent
amount of power. Two stroke engines are becoming less common in developed countries
these days, mainly due to manufacturer reluctance to invest in reducing two-stroke
emissions. Traditionally, two stroke engines needed more maintenance, even though
they have fewer moving parts and tended to wear out faster than four stroke engines,
however fuel-injected two-strokes achieve better engine lubrication and cooling
and reliability should improve considerably.
PISTON RING
Is an open-ended
ring that fits into a groove on the outer diameter of a piston in an internal combustion
engine. Piston Rings The three main functions of piston rings in internal combustion
engines are:
1. Sealing the
combustion chamber.
2. Supporting
heat transfer from the piston to the cylinder wall.
3. Regulating
motor oil consumption.
The gap in the
piston ring compresses to a few thousandths of an inch when inside the cylinder
head. Most automotive pistons have three rings: The top two whilst also controlling
oil are primarily for compression sealing (compression rings); the lower ring is
for controlling the supply of oil to the liner which lubricates the piston skirt
and the compression rings (oil control rings). Typical compression ring designs
will have an essentially rectangular cross section or a keystone cross section.
The periphery will then have either a barrel profile (top compression rings) or
a taper or taper napier form (second compression rings.
There are some taper faced
top rings and on some old engines simple plain faced rings were used. Oil control
rings typically are of 3 types. Single piece cast iron, helicoil spring backed cast
iron or steel, multipiece steel. The spring backed oil rings and the cast iron oil
rings have essentially the same range of peripheral forms which consist of 2 scraping
lands of various detailed form. The multipiece oil control rings usually consist
of 2 rails or segments (these are thin steel rings) with a spacer expander spring
which keeps the two rails apart and provides the radial load.
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