Soil microbiology

 

 

To control the production of pollutants, scientists must first understand what is occurring in the combustion chamber and related areas before, during, and after combustion. Scientists at research centers such as Sandia National Laboratories in Livermore, Calif., and Southwest Research Institute in San-Antonio try to measure such factors as the flame speed and temperature during combustion and the quantities of fuel and oxygen present. Obtaining such data presents a great challenge because the combustion process takes place in a small chamber, under hostile condition of extreme pressure and temperature, during time frames that are measured in thousandths of a second,

Two major technological advances aid scientists studying automotive engine combustion: the laser and the computer. Both came into widespread use in the mid-1970”s and now are the mainstays of combustion research,

The laser, a device that emits an intense beam of light, allows scientists to «probe» into the very heart of the combustion process without inserting any instruments the might react with the hot gases. The laser light is pulsed in flashes that last only millionths of a second or less. In effect, this technique allows scientists to observe the chain of chemical reactions as if they were a slow-motion film.

To see the combustion process, scientists developed combustion chambers with windows made of quartz or sapphire. They also used transparent pistons. Researchers at the General Motors Research Laboratory in Warren, Mich. even developed a totally transparent cylinder to allow them to view every angle of the combustion process.

Typically, researchers shine a laser through one of the clear areas of the combustion chamber. Through another window, they capture the laser’s light and analyze how it passes through the gases. This enables the researchers to determine the temperature of the expanding gases, the speed at which they are traveling, and the types of molecules and number of particles present to each stage of the combustion process.

A computer scans and processes this data rapidly. Computer graphics also can be used to reconstruct the various stages of the combustion process from the data the last analysis provides. Cray Research Incorporated in Eagan, Minn., has developed a computer model that can simulate the flow and mixing of the fuel and air, the valve and piston movements, and the resulting emissions. In addition, chemists can compute the rates of the individual chemical reactions that make up each step of the combustion process. Powerful supercomputers aid these studies.

Such tools have enabled scientists t understand combustion in greater detail and helped them to develop engines that run better yet pollute less. Research advances have ranged from changing the size and construction of cars, to chemical changing the composition of emissions, to redesigning both the fuel and the engine.

 

 

Because a lighter car uses less fuel and one way to reduce carbon dioxide and other emissions is to reduce the amount of fuel burned - auto engineers have created lighter, smaller cars. A 1975 federal law initiated the trend toward smaller car It required automakers to increase average fuel efficiency from 6 kilometers per liter (14 miles per gallon) to 11.7 kilometers per liter (27.5 miles per gallon) by 1985.

In response to this law, engineers put automobile engine parts on a diet of high-strength, low-weight materials, such as aluminum alloys. Many composite materials, such as fiberglass, graphite epoxy, and kevlar aramid, have found their way into engine components and accessories as well.

Although lighter cars reduced fuel consumption and, therefore, the total amount of emissions, they did not change the types of emissions leaving the car. Consequently, engineers have devised a number of ways to prevent many of the emissions from entering the atmosphere.

 

 

Because the piston must move up and down in the cylinder, there is a slight space between the piston and the cylinder wall. Although piston rings encircle the piston and fill the space between the piston and the cylinder wall, some combustion by-products «blow by» the piston rings and enter the crankcase of the engine. Until the 1960”s, cars were equipped with only a tub that allowed these gases to escape out of the crankcase and into the atmosphere. Then engineers introduced the positive crankcase ventilation system (PCV). In a PCV system, a hose and valve direct the vapors in the crankcase back into the engine’s intake manifold (a pipe that carries fuel and air to the cylinder) where they are returned to the combustion chamber to be recycled. This keeps all the combustion gases in the exhaust system, where the heat produced by