Internal Combustion Engines

Introduction

Internal Combustion Engine, a heat engine in which the fuel is burned (
that is, united with oxygen ) within the confining space of the engine itself.
This burning process releases large amounts of energy, which are transformed
into work through the mechanism of the engine. This type of engine different
from the steam engine, which process with an external combustion engine that
fuel burned apart from the engine. The principal types of internal combustion
engine are : reciprocating engine such as Otto-engine, and Diesel engines ; and
rotary engines, such as the Wankel engine and the Gas-turbine engine.
In general, the internal combustion engine has become the means of
propulsion in the transportation field, with the exception of large ships
requiring over 4,000 shaft horsepower ( hp).
In stationary applications, size of unit and local factor often
determine the choice between the use of steam and diesel engine. Diesel power
plants have a distinct economic advantage over steam engine when size of the
plant is under about 1,000 hp. However there are many diesel engine plants much
large than this. Internal combustion engines are particularly appropriate for
seasonal industries, because of the small standby losses with these engines
during the shutdown period.

History

The first experimental internal combustion engine was made by a Dutch
astronomer, Christian Huygens, who, in 1680, applied a principle advanced by
Jean de Hautefeuille in 1678 for drawing water. This principle was based on the
fact that the explosion of a small amount of gunpowder in a closed chamber
provided with escape valves would create a vacuum when the gases of combustion
cooled. Huygens, using a cylinder containing a piston, was able to move it in
this manner by the external atmospheric pressure.
The first commercially practical internal combustion engine was built by
a French engineer, ( Jean Joseph ) Etienne Lenoir, about 1859-1860. It used
illuminating gas as fuel. Two years later, Alphonse Beau de Rochas enunciated
the principles of the four-stroke cycle, but Nickolaus August Otto built the
first successful engine ( 1876 ) operating on this principle.

Reciprocating Engine

Components of Engines

The essential parts of Otto-cycle and diesel engines are the same. The
combustion chamber consists of a cylinder, usually fixed, which is closed at one
end and in which a close-fitting piston slides. The in-and-out motion of the
piston varies the volume of the chamber between the inner face of the piston and
the closed end of the cylinder. The outer face of the piston is attached to a
crankshaft by a connecting rod. The crankshaft transforms the reciprocating
motion of the piston into rotary motion. In multi-cylindered engines the
crankshaft has one offset portion, called a crankpin, for each connecting rod,
so that the power from each cylinder is applied to the crankshaft at the
appropriate point in its rotation. Crankshafts have heavy flywheels and
counterweights, which by their inertia minimize irregularity in the motion of
the shaft. An engine may have from 1 to as many as 28 cylinders.
The fuel supply system of an internal-combustion engine consists of a
tank, a fuel pump, and a device for vaporizing or atomizing the liquid fuel. In
Otto-cycle engines this device is a carburetor. The vaporized fuel in most
multi-cylindered engines is conveyed to the cylinders through a branched pipe
called the intake manifold and, in many engines, a similar exhaust manifold is
provided to carry off the gases produced by combustion. The fuel is admitted to
each cylinder and the waste gases exhausted through mechanically operated poppet
valves or sleeve valves. The valves are normally held closed by the pressure of
springs and are opened at the proper time during the operating cycle by cams on
a rotating camshaft that is geared to the crankshaft . By the 1980s more
sophisticated fuel-injection systems, also used in diesel engines, had largely
replaced this traditional method of supplying the proper mix of air and fuel;
computer-controlled monitoring systems improved fuel economy and reduced
pollution.

Ignition

In all engines some means of igniting the fuel in the cylinder must be
provided. For example, the ignition system of Otto-cycle engines , the mixture
of air and gasoline vapor delivered to the cylinder from the carburetor and next
operation is that of igniting the charge by causing a spark to jump the gap
between the electrodes of a spark plug, which projects through the walls of the
cylinder. One electrode is insulated by porcelain or mica; the other is grounded
through the metal of the plug, and both form the part of the secondary circuit
of an induction system.
The principal type of high-tension ignition now commonly used is