Soil microbiology

 

Introduction

How combustion leads to pollution

Other factors that lead to pollution

Probing the combustion process

Engineering lighter cars

Devices that capture emissions

Fine-tuning the fuel-air mixture

Rethinking engine designs and materials

Powering cars of the future

Sources

 

 

As the human population growth, pollution from human activity also increases. Many activities - such as driving automobiles, farming, manufacturing, and power generation - release pollutants into the air, water, or soil. Common results of such pollution are changes in the chemistry of the environment. It is wide-known fact that transport is the biggest contributer to air pollution. That is why, for example Designers of the cars of the future new in 1991 that they would begin taking some dramatic turns. In November 1990, United States President George Bush had signed into law the Clean Air Act Amendments, which challenged automakers to concentrate harder than ever on styling cars that offered not only mechanical muscle and slick bodies but also engine systems that dirtied the air far less than did cars already on the road. Bush described the law a «the most significant air pollution legislation in our nation’s history.»

The legislation targets all source of air pollution. It requires that by 1994 many new cars - and by 1996 all new cars - be designed to produce significantly fewer emissions, the by-products and pollutants they release into the air. The vehicles must also be able to meet these new emissions standards for 10 years or 100,000 miles, twice as long as required before.

The automotive industry has been modifying car engines, exhaust systems, and controls since the 1950’s, when experts first realized that automobiles contributed to air pollution and smog. The newest laws will require the most extensive changes in engine designs to date. They also challenge the oil industry to develop fuels that will be less polluting as we drive into the year 2000.

In order to create cleaner-operating cars and better fuels, scientists and engineers study every detail of the workings of the internal-combustion gasoline engine. This engine design, which was first created in Germany in the late 1800’s, has propelled American automobiles since they first pulled onto the road near 100 years ago. It is a clever device for using fuel to produce heat, which in turn produces mechanical work to move the car.

Combustion, the process of burning fuel in the presence of oxygen, breaks the chemical bonds of the fue1, releasing energy in the form of heat. To achieve combustion, air is drawn into the engine and mixed with a fine spray of fuel - usually gasoline - in a combustion chamber, a closed region at the top of a cylinder. One wall of the chamber is the head of a piston, a metal rod that moves up and down inside the cylinder. The piston moves up to compress the mixture of fuel and air. Then a small spark from a spark plug ignites the mixture. An explosion follows in which the gasoline is burned, producing hot, expanding gases that force down the piston. The piston is attached to a crankshaft, which the piston’s movement turn. This motion is the primary movement that makes the car go. So a car engine can be thought of as an energy transformer, converting chemical energy to thermal (heat) energy to mechanical energy, all in one neat package.

Combusted gas exerts enormous force on the typical piston - equivalent to having the defensive line of a professional football team stand on the piston head. The attractive feature of gasoline engines is that such great power is produced in a fairly small space.

Compactness of this sort is due t the nature of gasoline, which packs more energy per pound that does dynamite. Although gasoline is a convenient, powerful fuel, it can pollute the air. Some gasoline pollutes the atmosphere simply became the fuel evaporates at the gas-station pump or through small leaks in the car’s fuel tank or fuel line connections. Gasoline combustion also pollutes.

 

 

Most efforts at creating cleaner cars focus on limiting emissions formed as by-products of gasoline combustion. These emissions come out of the car’s exhaust system an are among the major factors contributing to air pollution in urban areas. Scientists trying to solve these pollution problems study what happens to the fuel when it is burned and what can influence the outcome of the combustion process.

Gasoline is made through the refining of crude oil or petroleum. Like all petroleum products, the gasoline used in automobiles is composed of hydrocarbons, molecules consisting primarily of atoms of hydrogen