INTERNAL-COMBUSTION ENGINE 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. Fig. 1, Component of Piston Engines. 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 fu! el 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 the battery-and-coil system.
The current from the battery flows through the low-tension coil and magnetizes the iron core. When this circuit is opened at the distributor points by the interrupter cam, a transient high-frequency current is produced in the primary coil with the assistance of the condenser. This induces a transient, high-frequency, high-voltage current in the secondary winding. This secondary high voltage is needed to cause the spark to jump the gap in the spark plug.The spark is directed to the proper cylinder to be fired by the distributor, which connects the secondary coil to the spark plugs in the several cylinders in their proper firing sequence.
The interrupter cam and distributor are driven from the same shaft, the number of breaking points on the interrupter cam being the same as the number of cylinders. Cooling System Because of the heat of combustion, all engines must be equipped with some type of cooling system. Some aircraft and automobile engines, small stationary engines, and outboard motors for boats are cooled by air. In this system the outside surfaces of the cylinder are shaped in a series of radiating fins with a large area of metal to radiate heat from the cylinder.Other engines are water-cooled and have their cylinders enclosed in an external water jacket. In automobiles, water is circulated through the jacket by means of a water pump and cooled by passing through the finned coils of a radiator. Some automobile engines are also air-cooled, and in marine engines sea water is used for cooling.
Starter Unlike steam engines and turbines, internal-combustion engines develop no torque when starting, and therefore provision must be made for turning the crankshaft so that the cycle of operation can begin. Automobile engines are normally started by means of an electric motor or starter that is geared to the crankshaft with a clutch that automatically disengages the motor after the engine has started. Small engines are sometimes started manually by turning the crankshaft with a crank or by pulling a rope wound several times around the flywheel. Methods of starting large engines include the inertia starter, which consists of a flywheel that is rotated by hand or by means of an electric motor until its kinetic energy is sufficient to turn the crankshaft, and the explosive starter, which employs the explosion of a blank cartridge to drive a turbine wheel that is coupled to the engine.The inertia and explosive starters are chiefly used to start airplane engines. Otto-Cycle Engines The ordinary Otto-cycle engine is a four-stroke engine; that is, its pistons make four strokes, two toward the head (closed head) of the cylinder and two away from the head, in a complete power cycle.
During the first stroke of the cycle, the piston moves away from the cylinder head while simultaneously the intake valve is opened. The motion of the piston during this stroke sucks a quantity of a fuel and air mixture into the combustion chamber. During the next stroke the piston moves toward the cylinder head and compresses the fuel mixture in the combustion chamber.At the moment when the piston reaches the end of this stroke and the volume of the combustion chamber is at a minimum, the fuel mixture is ignited by the spark plug and burns, expanding and exerting a pressure on the piston, which is then driven away from the cylinder head in the third stroke. At the end of the power stroke the pressure of the burned gases in the cylinder is 2.8 to 3.5 kg/sq. cm (40 to 50 lb.
/sq. in). During the final stroke, the exhaust valve is opened and the piston moves toward the cylinder head, driving the exhaust gases out of the combustion chamber and leaving the cylinder ready to repeat the cycle. Fig.2, Otto-Cycle Engines.
The efficiency of a modern Otto-cycle engine is limited by a number of factors, including losses by cooling and by friction. In general the efficiency of such engines is determined by the compression ratio of the engine. The compression ratio (the ratio between the maximum and minimum volumes of the combustion chamber) is usually about 8 to 1 or 10 to 1 in most modern Otto-cycle engines. Higher compression ratios, up to about 12 to 1, with a resulting increase of efficiency, are possible with the use of high-octane antiknock fuels. The efficiencies of good modern Otto-cycle engines range between 20 and 25 percent (in other words, only this percentage of the heat energy of the fuel is transformed into mechanical energy). Diesel Engines Theoretically the diesel cycle differs from the Otto cycle in that combustion takes place at constant volume rather than at constant pressure.Most diesels are also four-stroke engines, but operate differently than the four-stroke Otto-cycle engines.
The first or suction stroke draws air, but no fuel, into the combustion chamber through an intake valve. On the second or compression stroke the air is compressed to a small fraction of its former volume and is heated to approximat …