INTERNAL-COMBUSTION ENGINE Essays - Piston Engines, Free Essays

INTERNAL-COMBUSTION ENGINE Essays - Piston Engines, Free Essays 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

Habits and Traits of the Ant Family

Habits and Traits of the Ant Family Ask any insect enthusiast how they became so interested in bugs, and hell probably mention childhood hours spent watching ants. Theres something fascinating about social insects, especially ones as diverse and evolved as the ants, the family Formicidae. Description Its easy to recognize ants, with narrow waists, bulbous abdomens, and elbowed antennae. In most cases, when you observe ants you are only seeing the workers, all of which are female. Ants live underground, in dead wood, or sometimes in plant cavities. Most ants are black, brown, tan, or red. All ants are social insects. With few exceptions, ant colonies divide labor between sterile workers, queens, and male reproductives, called alates. Winged queens and males fly in swarms to mate. Once mated, queens lose their wings and establish a new nest site; males die. Workers tend to the colonys offspring, even rescuing the pupae should the nest be disturbed. The all-female workforce also gathers food, constructs the nest, and keeps the colony clean. Ants perform important tasks in the ecosystems where they live. Formicids turn and aerate the soil, disperse seeds, and aid in pollination. Some ants defend their plant partners from attacks by herbivores. Classification Kingdom – AnimaliaPhylum – ArthropodaClass – InsectaOrder – HymenopteraFamily – Formicidae Diet Feeding habits vary in the ant family. Most ants prey on small insects or scavenge bits of dead organisms. Many also feed on nectar or honeydew, the sweet substance left behind by aphids. Some ants actually garden, using gathered leaf bits to grow fungus in their nests. Life Cycle The complete metamorphosis of an ant may take from 6 weeks to 2 months. Fertilized eggs always produce females, while unfertilized eggs yield males. The queen can control the sex of her offspring by selectively fertilizing the eggs with sperm, which she stores after a single mating period. White, legless larvae hatch from eggs, completely dependent on worker ants for their care. The workers feed the larvae with regurgitated food. In some species, pupae look like colorless, immobile adults. In others, pupae spin a cocoon. New adults may take several days to darken into their final color. Special Adaptions and Defenses Ants employ a fascinating variety of behaviors to communicate and defend their colonies. Leafcutter ants cultivate a bacteria with antibiotic properties to keep unwanted fungi from growing in their nests. Others tend aphids, milking them to harvest sweet honeydew. Some ants use a modified ovipositor to sting, like their wasp cousins. Some ants function as little chemical factories. Ants of the genus Formica use a special abdominal gland to produce formic acid, an irritating substance they can squirt as they bite. Bullet ants inject a strong nerve toxin when they sting. Many ants take advantage of other species. Slave-making ant queens invade colonies of other ant species, killing the resident queens and enslaving her workers. Thief ants raid neighbor colonies, stealing food and even young. Range and Distribution Ants thrive throughout the world, living everywhere except Antarctica, Greenland, Iceland, and a few isolated islands. Most ants live underground or in dead or decaying wood. Scientists describe nearly 9,000 unique species of Formicids; almost 500 ant species inhabit North America. Sources Insects: Their Natural History and Diversity, by Stephen A. MarshallAnt Information, University of ArizonaFormicidae: Information, Animal Diversity Web