汽车尾气的危害与治理的英文资料还要翻译好的

【专家解说】：http://www.epa.gov/oms/consumer/05-autos.pdf http://everything2.com/index.pl?node_id=1707379 Automobile emissions control covers all the technologies that are employed to reduce the air pollution-causing emissions produced by automobiles. Exhaust emissions control systems were first required on 1966 model year vehicles produced for sale in the state of California, followed by the United States as a whole in model year 1968. the overall reduction in pollution has been much slower. The emissions produced by a vehicle fall into three basic categories: Tailpipe emissions: This is what most people think of when they think of vehicle air pollution; the products of burning fuel in the vehicle's engine, emitted from the vehicle's exhaust system. The major pollutants emitted include: Hydrocarbons: this class is made up of unburned or partially burned fuel, and is a major contributor to urban smog, as well as being toxic. They can cause liver damage and even cancer. Nitrogen oxides (NOx): These are generated when nitrogen in the air reacts with oxygen under the high temperature and pressure conditions inside the engine. NOx emissions contribute to both smog and acid rain. Carbon monoxide (CO): a product of incomplete combustion, carbon monoxide reduces the blood's ability to carry oxygen and is dangerous to people with heart disease. Carbon dioxide (CO2): Emissions of carbon dioxide are an increasing concern as its role in global warming as a greenhouse gas has become more apparent. Particulates. Particle of micron size. Sulphur oxide (SOx) General term for oxides of sulphur, mostly sulfur dioxide and some sulfur trioxide, from coal or unrefined oil. Tailpipe emissions control Tailpipe emissions control can be categorised into three parts: Increasing engine efficiency Increasing vehicle efficiency Cleaning up the emissions Increasing engine efficiency Engine efficiency has been gradually improved with progress in following technologies: Electronic ignition Fuel injection systems Electronic control unit Increasing vehicle efficiency Contributions to the goal of reducing fuel consumption and related emissions come from lightweight vehicle design minimized air resistance reduced rolling resistance improved powertrain efficiency increasing spark to the spark plug (this topic should be under the ignition system) regenerative braking Each of these items breaks down into a number of factors. Increasing driving efficiency Significant reduction of emissions come from driving technique (some 10-30% reduction) unobstructed traffic conditions cruising at an optimum speed for the vehicle reducing the number of cold starts Cleaning up the emissions Advances in engine and vehicle technology continually reduce the amount of pollutants generated, but this is generally considered insufficient to meet emissions goals. Therefore, technologies to react with and clean up the remaining emissions have long been an essential part of emissions control. Air injection A very early emissions control system, the Air injection reactor (AIR) reduces the products of incomplete combustion (hydrocarbons and carbon monoxide) by injecting fresh air into the exhaust manifolds of the engine. In the presence of this oxygen-laden air, further combustion occurs in the manifold and exhaust pipe. Generally the air is delivered through an engine-driven 'smog pump' and air tubing to the manifolds. Exhaust Gas Recirculation Many engines produced after the 1973 model year have an exhaust gas recirculation valve between the exhaust and intake manifolds; its sole purpose is to reduce NOx emissions by introducing exhaust gases into the air/fuel mixture, lowering peak combustion temperatures. Catalytic converters The catalytic converter is a device, placed in the exhaust pipe, which converts various emissions into less harmful ones using, generally, a combination of platinum, palladium and rhodium as catalysts.They make for a significant, and easily applied, method for reducing tailpipe emissions. The lead emissions were highly damaging to human health, and its virtual elimination has been one of the most successful reductions in air pollution. Evaporative emissions control Efforts at the reduction of evaporative emissions include the capturing of vented vapors from within the vehicle, and the reduction of refuelling emissions. Capturing vented vapors Within the vehicle, vapors from the fuel tank are channelled through canisters containing activated carbon instead of being vented to the atmosphere. These are known as carbon canisters. The vapors are adsorbed within the canister, which feeds into the inlet manifold of the engine. Emission Testing In 1966, the first emission test cycle was enacted in the State of California measuring tailpipe emissions in PPM (parts per million). The Environmental Working Group used California ASM emissions data to create an Auto Asthma Index that rates vehicle models based on emissions of hydrocarbons and nitrogen oxides, the chemicals that create smog. Some cities are also using a technology developed by Dr. Stedman,of University of Denver which uses lasers to detect emissions while vehicles pass by on public roads, thus eliminating the need for owners to go to a test center. Stedman's laser detection of exhaust gases is commonly used in metropolitan areas. ----------------------------------------- Emission control systems in automotive applications can trace their beginnings to the smoggy skies that were noted over the city of Los Angeles after the end of World War II. There were of course cars before the war and air pollution problems as a result of the activities of steelmaking, oil refining, and coal burning power plants were well known by then. Air Pollution in those days was for the most part written off as the price of progress, but as automobiles streamed onto the nation's ever-expanding highway system in unprecedented numbers in the 1950s, the pollution problems caused by their use, along with pollution caused by industrial sources could no longer be dismissed as an annoyance. Tailpipe emissions from automobiles fall into 5 major categories: Unburned Hydrocarbons Oxides of Nitrogen Carbon Monoxide Sulfur Dioxide Compounds of Lead In addition, automobiles also generate several secondary sources of pollution. These Include: Evaporative Emissions from fuel vapors, which find their way into the air Water pollution, from fluids that leak from cooling systems, engines, and transmissions. Hazardous Waste from discarded fluids, tires, batteries, and the like. Asbestos fibers from brake linings and clutches. A bit about the nature of automotive air pollutants Unburned Hydrocarbons are the result of incomplete combustion of fuel in an engine. Theoretically, if an engine burns its fuel perfectly, there should be little or no unburned hydrocarbons. Skipping all the chemistry equations, if there is one part gasoline vapor by volume to 15 parts air, the fuel should burn perfectly, producing only carbon dioxide and water vapor as byproducts. In practice, this is difficult to do with a carbureted engine operating over a wide variety of temperatures, fuel formulations, and load conditions. Blowby, which is combustion gasses escaping past piston rings (or Apex Seals for you Wankel buffs) is also a major source of unburned hydrocarbons. Carbon Monoxide is formed when combustion takes place when there is a shortage of oxygen. Carbon Monoxide wants to be Carbon Dioxide, but can't find another oxygen atom combine with. This makes it very reactive, and will bind with Hemoglobin, rendering it useless to transport oxygen in the blood. Small amounts of breathed CO cause headaches and fatigue, but Carbon Monoxide can kill if breathed in large enough amounts. In the Steel industry, Carbon Monoxide is used to pull the oxygen out of Iron Oxide to form pure Iron, but it is bad news in your bloodstream. CO can form in large amounts if too much fuel is allowed into the cylinders, or there are pockets of too rich a fuel-air mixture in the cylinders. Oxides of Nitrogen form Smog when exposed to sunlight, and form when combustion temperatures exceed 2,300 F, forcing Oxygen and atmospheric Nitrogen (N2) to combine in a sort of chemical shotgun wedding. Like the human kind of shotgun weddings, these types of bonds are unstable and form reactive compounds under the right conditions. They form when preignition occurs, but also form under conditions of normal operation as well, particularly in high performance applications. Sulfur Dioxide is a byproduct of burning sulfur, a common impurity in many fuels. Sulfur Dioxide can combine with water to form Sulfuric Acid, a very corrosive chemical which can corrode metals, etch paint, and render lakes too acid to support aquatic life. Control primarily consists of removing sulfur from fuel at the refinery. A Timeline of Automotive Emission Controls 1966: California implements the first emissions standards in the nation. Early emission controls consisted of a PCV Valve, which provided positive crankcase ventilation while routing blowby gasses back into the air intake to be reburned in the engine. This was a great help in reducing emissions from unburned hydrocarbons, but did little to reduce Nitrogen Oxide emissions or Carbon Monoxide emissions. California cars also got fixed high-speed carburetor jets, and saw other tweaks to engine tuning to reduce other emissions. California, then and now served as a laboratory for nationwide deployment for more advanced emission controls. 1968: Emission Controls were implemented Nationwide Nationwide crankcase emission controls were implemented in new cars, and were similar to 1966 California cars. Light Trucks started to get emission controls a few years later. For a long time, emission standards for light trucks tended to lag those of automobiles, but the gap has narrowed over time. Air injection was introduced into California vehicles, in an effort to reduce CO and Unburned Hydrocarbons. 1969-1971: A gradual tightening of standards: Compression ratios were dropped to reduce Nox emissions, and carburetion was leaned out to lower CO and HC emissions. This was the beginning of the end of the muscle car, at least in its original raw form. Air Injection and Exhaust Gas Recirculation made its way into more vehicles. 1971: The Clean Air Act was passed The Clean Air Act mandated drastic reductions in emissions over the next decade. The Clean air Act also mandated the eventual removal of tetraethyl lead from automotive fuels. Detroit's Big Three howled in protest, complaining that the new standards at best would be hugely expensive, or impossible to meet. In the automaker's research and development laboratories, a number of approaches were developed, and were the forerunner of modern emission controls. Ford had a program called Programmed Combustion, Honda developed the Stratified Charge Engine, and technologies such as electronically controlled carburetors, electronic ignition, catalytic converters, and the beginnings of computerized engine management systems were developed over the next several years. 1972 to 1975: Emission Controls and the Energy Crisis take a bite out of Detroit The early to mid `70s were the darkest years for Detroit. Work on new technologies was feverishly going on in the lab and on the test track. What found its way into the average car however, was lowered compression ratios to allow operation on 87 octane unleaded gas, lean tuning to reduce unburned hydrocarbons, air injection, and exhaust gas recirculation to reduce peak combustion temperatures. An energy crisis followed the arab oil embargo of 1973, forcing gas prices up and prompted implementation of the much hated 55 mph speed limit in the United States. American cars of this era for the most part ran terribly, hobbled by lean tuning, low compression ratios, and an increasingly crowded engine compartment featuring a rats nest of new plumbing and wiring. They ran even worse when these quickly designed systems became balky. Stalling and hesitation were common problems, and people forced to drive them often resorted to removing emission controls in an attempt to restore some driveability. Emission controls of the time had a negative effect on fuel economy, aggravating an already bad fuel supply situation. 1975 saw the widespread introduction of the Catalytic Converter, which allowed automakers to restore at least some driveability to their offerings, but performance was still a shadow of its late 1960s levels. An informal comparison of vehicles our family owned during the late `70s shows how much performance dropped. We owned a 1970 Chrysler Town and Country with a 383 cubic inch engine with a 2-barrel carburetor, which would run on regular gas. It got about 13 mpg around town, 17 on the highway, and had a top speed of about 110 miles per hour, even loaded to the roof. We also had a 1976 Ford LTD Wagon with a 400 cubic inch engine and a 2-barrel carburetor, and in most other respects they were very similar cars. The LTD got 10 mpg around town, 14 on the highway, and had a top speed of barely 100 mph. As performance dropped through the `70s, carmakers also limited the top indicated speed on the speedometer to 85 mph on most cars. Performance became a four letter word, and instead automakers chose to emphasise styling and accessories in their large cars, and fuel economy in their smaller models. 1976-1980: Downsizing and the introduction of electronics under the hood The dark years for Detroit continued, though sales perked up for a while as gas prices stabilized from 1975 through 1978. Detroit engineers also faced the challenge of improving the fuel economy of their fleets, while also meeting stricter safety standards. General Motors trimmed nearly 1,000 pounds and about 100 cubic inches from their full size cars. Ford's new LTD in 1979 looked suspiciously like their old Ford Fairmont, a much smaller vehicle. The new "premium" LTD Landau was still over a foot shorter, and had an engine 100 cubic inches smaller than the 1978 model. Catalytic Converters, combined with air pumps, exhaust gas recirculation, lean tuning, and electronic ignition on most vehicles allowed most cars to meet increasingly strict emissions standards, but many of the larger engines could not meet the newer standards. The second energy crisis in 1979, combined with emissions problems with many larger V8 engines made engines over 400 cubic inches nearly extinct by the end of the decade, except in the Cadillac Sedan de Ville and 3/4 ton and larger pickups. Technology by the end of the 1970s for most vehicles made in North America consisted of Catalytic Converters, combined with air pumps, exhaust gas recirculation, lean tuning, and electronic ignition on most vehicles. The end of the decade also saw the beginning of electronic engine management systems. My 1978 Plymouth Horizon had a spark control computer to control ignition timing and my brother's 1979 Plymouth Horizon TC3 had an electronically controlled carburetor in addition to the ignition timing. Overseas, emissions standards were getting stiffer as well, particularly in Western Europe and Japan. Honda, Mercedes-Benz, and Volkswagen were able to meet US and even California emissions standards without needing a catalytic converter. Diesel Engines and other technologies Mercedes-Benz and Volkswagen were able to meet the standards for emissions by using diesel engines in their cars. Diesel Engines tend to produce pretty low emissions without extra equipment, though they do produce a fair amount of soot which was not a pollutant of concern at the time. Diesel Engines also allowed for greater fuel efficiency, a Volkswagen Rabbit Diesel was able to get nearly 50 miles a gallon, at the time. Mercedes Benz had built diesel vehicles since the `30s, and by the late `70s, they had developed an almost legendary reputation for design, durability, and fuel economy as well. A late `70s 240D got 25 miles per gallon, not bad considering that a similarly sized American car of the time got about 17 mpg. General Motors got into the diesel act in 1978 with a diesel engine option in full-sized Oldsmobiles, Buicks, and Cadillacs. A 4 cylinder diesel Chevette was also sold for a few years as well, which got nearly 50 mpg. In the fuel-starved days of 1980, they were a popular option, despite their slower acceleration, noise, and $1,000 premium compared to the gasoline powered model. What the buyer got in return was a full-sized car that got nearly 30 miles per gallon on the highway. What the buyer didn't get was an engine designed from the ground up as a diesel, but a converted gasoline engine based on the proven 350 cubic inch small-block V8. Diesel Engines operate at very high compression ratios, up to 22 to 1, and the extreme stresses placed on the engine internals caused many of these engines to self-destruct before they even had 50,000 miles on them. If the engines had managed to get a diet of high-quality fuel, the stiffened internals of the GM Diesels compared to their gasoline counterparts would have been adequate to hold up. The root of the problem turned out to be the fact that the injector pumps corroded from exposure to moisture and acids present in the poor quality of diesel fuel commonly available at the time, combined with an inadequate filtration system to remove these impurities. A damaged injector pump would cause improper timing and amount of fuel to be injected, causing the cylinder pressures to go sky-high eventually blowing the head gasket. once the head gasket blew, it usually didn't take long for the rest of the engine to self-destruct. General Motors had to replace many of these engines under warranty, and within 5 years the diesel engine option was dropped. Regrettably this gave not only GM a black eye, but gave diesel engines as viable automobile powerplants a black eye as well, at least in the eyes of most Americans. Diesels gained wider acceptance as alternatives to big-block V8 gasoline engines in medium duty trucks, delivery vehicles, and school busses, but have not seen a rebirth in domestic cars, though they outnumber gasoline cars in Western Europe today. Honda was able to meet 1975 standards by use of a novel gasoline engine called a Stratified Charge Engine, which Honda dubbed the CVCC. The engine featured a cylinder head with 3 valves per cylinder, and a special carburetor. The carburetor featured a main section which provided a lean fuel-air mixture for most of the volume in the cylinder, and a section which provided a richer mixture in the area near the spark plug. The enriched layer of mixture ensured reliable ignition, while the main charge was lean enough to suppress formation of unburned hydrocarbons, oxides of Nitrogen and Carbon Monoxide. The carefully designed combustion chamber promoted swirling combustion, which ensured complete burning of the fuel-air mix. Honda was able to avoid putting Catalytic Converters on their vehicles until well into the 1980s. 字数超限了。。。。