Vehicle emissions control

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Vehicle emissions control is the study of reducing the emissions produced by motor vehicles, especially internal combustion engines.


Types of emissions

Emissions of many air pollutants have been shown to have variety of negative effects on public health and the natural environment. Emissions that are principal pollutants of concern include:


Throughout the 1950s and 1960s, various federal, state and local governments in the United States conducted studies into the numerous sources of air pollution. These studies ultimately attributed a significant portion of air pollution to the automobile, and concluded air pollution is not bounded by local political boundaries. At that time, such minimal emission control regulations as existed in the U.S. were promulgated at the municipal or, occasionally, the state level. The ineffective local regulations were gradually supplanted by more comprehensive state and federal regulations. By 1967 the State of California created the California Air Resources Board, and in 1970, the federal United States Environmental Protection Agency (EPA) was established. Both agencies, as well as other state agencies, now create and enforce emission regulations for automobiles in the United States. Similar agencies and regulations were contemporaneously developed and implemented in Canada, Western Europe, Australia, and Japan.

The first effort at controlling pollution from automobiles was the PCV (positive crankcase ventilation) system. This draws crankcase fumes heavy in unburned hydrocarbons – a precursor to photochemical smog – into the engine's intake tract so they are burned rather than released unburned from the crankcase into the atmosphere. Positive crankcase ventilation was first installed on a widespread basis by law on all new 1961-model cars first sold in California. The following year, New York required it. By 1964, most new cars sold in the U.S. were so equipped, and PCV quickly became standard equipment on all vehicles worldwide. [3]

The first legislated exhaust (tailpipe) emission standards were promulgated by the State of California for 1966 model year for cars sold in that state, followed by the United States as a whole in model year 1968. Also in 1966, the first emission test cycle was enacted in the State of California measuring tailpipe emissions in PPM (parts per million). The standards were progressively tightened year by year, as mandated by the EPA.

By the 1974 model year, the United States emission standards had tightened such that the de-tuning techniques used to meet them were seriously reducing engine efficiency and thus increasing fuel usage. The new emission standards for 1975 model year, as well as the increase in fuel usage, forced the invention of the catalytic converter for after-treatment of the exhaust gas. This was not possible with existing leaded gasoline, because the lead residue contaminated the platinum catalyst. In 1972, General Motors proposed to the American Petroleum Institute the elimination of leaded fuels for 1975 and later model year cars.[ citation needed ] The production and distribution of unleaded fuel was a major challenge, but it was completed successfully in time for the 1975 model year cars. All modern cars are now equipped with catalytic converters, and leaded fuel is no longer sold at filling stations in most First World countries. Leaded racing fuel is available in small quantities from some suppliers, but it is legal for off-road use only.

Leading up to the 1981 model year in the United States, passenger vehicle manufactures were faced with the challenges in its history of meeting new emissions regulations, how to meet the much more restrictive requirements of the Clean Air Act (United States) per the 1977 amendment. For example: to meet this challenge, General Motors created a new "Emissions Control Systems Project Center" (ECS) first located at the AC Spark Plug Engineering Building in Flint, Michigan. Its purpose was to "Have overall responsibility for the design and development of the carborated and fuel injected closed loop 3-way catalyst system including related electronic controls, fuel metering, spark control, idle speed control, EGR, etc. currently planned through 1981." [4] [5] [6]

Regulatory agencies

The agencies charged with implementing exhaust emission standards vary from jurisdiction to jurisdiction, even in the same country. For example, in the United States, overall responsibility belongs to the EPA, but due to special requirements of the State of California, emissions in California are regulated by the Air Resources Board. In Texas, the Texas Railroad Commission is responsible for regulating emissions from LPG-fueled rich burn engines (but not gasoline-fueled rich burn engines).

North America



The European Union has control over regulation of emissions in EU member states; however, many member states have their own government bodies to enforce and implement these regulations in their respective countries. In short, the EU forms the policy (by setting limits such as the European emission standard) and the member states decide how to best implement it in their own country.

United Kingdom

In the United Kingdom, matters concerning environmental policy are "devolved powers" so that some of the constituent countries deal with it separately through their own government bodies set up to deal with environmental issues:

However, many UK-wide policies are handled by the Department for Environment, Food and Rural Affairs (DEFRA) and they are still subject to EU regulations.

Emissions tests on diesel cars have not been carried out during MOTs in Northern Ireland for 12 years, despite being legally required. [8]

Emission control system design

It was very important to system designers to meet the emission requirements using a minimum quantity of catalyst material (platinum and/or palladium) due to cost and supply issues. The General Motors "Emissions Control Systems Project Center" was "to follow the operational plans established by previous (GM) Project Centers. Items unique to the "Emissions Control Systems Project Center" (were):

The ("Emissions Control Systems Project Center") (had) seven tasks to perform, such that an emission system, which passes all existing Federal Emission and Fuel Economy legislation is put into production.

These are to work with the car divisions to:

  1. Define hardware and system requirements.
  2. Develop design specifications for all hardware all hardware required.
  3. Review alternative designs and systems.
  4. Arrange to test and validate systems, which best suits the needs of all concerned.
  5. Monitor component design and release.
  6. Follow progress of divisional certification work.
  7. Keep management and divisions apprised of progress status.

The system iplementation (was to) be phased in over three years. In the 1979 model year. California vehicles with 2.5, 2.8 and 3.5 liter engines will have a CLCC system. In 1980 model year, vehicles sold in California and 3.8 and 4.3 liter engines sold federally will have CLCC, and finally in the 1981 model year all passenger cars will have the system. California light and medium duty trucks may also use the c-4 system. While 1979 and 1980 systems are very similar, the 1981 system (2nd generation) will differ in that it may include additional engine control systems (i.e., electronic spark timing, idle speed control, etc.)

The Emission Control System under development has been designated C-4.This stands for Computer Controlled Catalytic Converter. The C-4 System encompasses Closed Loop Carburetor Control (CLCC) and Throttle Body Injection (TBI) systems."" [4] [9] [10]

Emissions control

Engine efficiency has been steadily improved with improved engine design, more precise ignition timing and electronic ignition, more precise fuel metering, and computerized engine management.

Advances in engine and vehicle technology continually reduce the toxicity of exhaust leaving the engine, but these alone have generally been proved insufficient to meet emissions goals. Therefore, technologies to detoxify the exhaust are an essential part of emissions control.

Air injection

One of the first-developed exhaust emission control systems is secondary air injection. Originally, this system was used to inject air into the engine's exhaust ports to provide oxygen so unburned and partially burned hydrocarbons in the exhaust would finish burning. Air injection is now used to support the catalytic converter's oxidation reaction, and to reduce emissions when an engine is started from cold. After a cold start, an engine needs an air-fuel mixture richer than what it needs at operating temperature, and the catalytic converter does not function efficiently until it has reached its own operating temperature. The air injected upstream of the converter supports combustion in the exhaust headpipe, which speeds catalyst warmup and reduces the amount of unburned hydrocarbon emitted from the tailpipe.

Exhaust gas recirculation

In the United States and Canada, many engines in 1973 and newer vehicles (1972 and newer in California) have a system that routes a metered amount of exhaust into the intake tract under particular operating conditions. Exhaust neither burns nor supports combustion, so it dilutes the air/fuel charge to reduce peak combustion chamber temperatures. This, in turn, reduces the formation of NOx.

Catalytic converter

The catalytic converter is a device placed in the exhaust pipe, which converts hydrocarbons, carbon monoxide, and NOx into less harmful gases by using a combination of platinum, palladium and rhodium as catalysts. [11]

There are two types of catalytic converter, a two-way and a three-way converter. Two-way converters were common until the 1980s, when three-way converters replaced them on most automobile engines. See the catalytic converter article for further details.

Evaporative emissions control

Fuel vapor storage canister for a Peugeot 205. Aktivkohlefilter 205.JPG
Fuel vapor storage canister for a Peugeot 205.

Evaporative emissions are the result of gasoline vapors escaping from the vehicle's fuel system. Since 1971, all U.S. vehicles have had fully sealed fuel systems that do not vent directly to the atmosphere; mandates for systems of this type appeared contemporaneously in other jurisdictions. In a typical system, vapors from the fuel tank and carburetor bowl vent (on carbureted vehicles) are ducted to canisters containing activated carbon. The vapors are adsorbed within the canister, and during certain engine operational modes fresh air is drawn through the canister, pulling the vapor into the engine, where it burns.

Remote sensing emission testing

Some US states are also using a technology which uses infrared and ultraviolet light to detect emissions while vehicles pass by on public roads, thus eliminating the need for owners to go to a test center. Invisible light flash detection of exhaust gases is commonly used in metropolitan areas, [12] and becoming more broadly known in Europe. [13]

Use of emission test data

Emission test results from individual vehicles are in many cases compiled to evaluate the emissions performance of various classes of vehicles, the efficacy of the testing program and of various other emission-related regulations (such as changes to fuel formulations) and to model the effects of auto emissions on public health and the environment.

Alternative fuel vehicles

Exhaust emissions can be reduced by making use of clean vehicle propulsion. The most popular modes include hybrid and electric vehicles. As of December 2020, China had the world's largest stock of highway legal plug-in electric passenger cars with 4.5 million units, representing 42% of the world's stock of plug-in cars. [14] [15]

See also

Related Research Articles

<span class="mw-page-title-main">Catalytic converter</span> Exhaust emission control device

A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually used with internal combustion engines fueled by gasoline or diesel, including lean-burn engines, and sometimes on kerosene heaters and stoves.

<span class="mw-page-title-main">Exhaust gas</span> Gases emitted as a result of fuel reactions in combustion engines

Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack, or propelling nozzle. It often disperses downwind in a pattern called an exhaust plume.

An oxygen sensor (or lambda sensor, where lambda refers to air–fuel equivalence ratio, usually denoted by λ) or probe or sond, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analysed.

<span class="mw-page-title-main">Diesel exhaust</span>

Diesel exhaust is the gaseous exhaust produced by a diesel type of internal combustion engine, plus any contained particulates. Its composition may vary with the fuel type or rate of consumption, or speed of engine operation, and whether the engine is in an on-road vehicle, farm vehicle, locomotive, marine vessel, or stationary generator or other application.

Lean-burn refers to the burning of fuel with an excess of air in an internal combustion engine. In lean-burn engines the air:fuel ratio may be as lean as 65:1. The air / fuel ratio needed to stoichiometrically combust gasoline, by contrast, is 14.64:1. The excess of air in a lean-burn engine emits far less hydrocarbons. High air–fuel ratios can also be used to reduce losses caused by other engine power management systems such as throttling losses.

<span class="mw-page-title-main">Exhaust system</span> Part of the internal combustion engine

An exhaust system is used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes. Depending on the overall system design, the exhaust gas may flow through one or more of:

<span class="mw-page-title-main">Diesel exhaust fluid</span> Standardized aqueous urea solution for exhaust aftertreatment

Diesel exhaust fluid is a liquid used to reduce the amount of air pollution created by a diesel engine. Specifically, DEF is an aqueous urea solution made with 32.5% urea and 67.5% deionized water. DEF is consumed in a selective catalytic reduction (SCR) that lowers the concentration of nitrogen oxides in the diesel exhaust emissions from a diesel engine.

In atmospheric chemistry, NOx is shorthand for nitric oxide and nitrogen dioxide, the nitrogen oxides that are most relevant for air pollution. These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone.

<span class="mw-page-title-main">Diesel particulate filter</span> Removes diesel particulate matter or soot from the exhaust gas of a diesel engine

A diesel particulate filter (DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine.

BlueTEC is Mercedes-Benz Group's marketing name for engines equipped with advanced NOx reducing technology for vehicle emissions control in diesel-powered vehicles. The technology in BlueTec vehicles includes a selective catalytic reduction (SCR) system that uses diesel exhaust fluid, and a system of NOx adsorbers the automaker calls DeNOx, which uses an oxidizing catalytic converter and diesel particulate filter combined with other NOx reducing systems.

A NOx adsorber or NOx trap (also called Lean NOx trap, abbr. LNT) is a device that is used to reduce oxides of nitrogen (NO and NO2) emissions from a lean burn internal combustion engine by means of adsorption.

Secondary air injection is a vehicle emissions control strategy introduced in 1966, wherein fresh air is injected into the exhaust stream to allow for a fuller secondary combustion of exhaust gases.

An air-fuel ratio meter monitors the air–fuel ratio of an internal combustion engine. Also called air–fuel ratio gauge, air–fuel meter, or air–fuel gauge, it reads the voltage output of an oxygen sensor, sometimes also called AFR sensor or lambda sensor.

United States vehicle emission standards are set through a combination of legislative mandates enacted by Congress through Clean Air Act (CAA) amendments from 1970 onwards, and executive regulations managed nationally by the Environmental Protection Agency (EPA), and more recently along with the National Highway Traffic Safety Administration (NHTSA). These standard cover common motor vehicle air pollution, including carbon monoxide, nitrogen oxides, and particulate emissions, and newer versions have incorporated fuel economy standards.

The BMW M56 is a 2.5 liter 184 PS straight-six engine. It is a re-engineered version of the BMW M54B25 engine, manufactured in order to meet SULEV regulations in 4 US states.

Carl Donald Keith was a chemist who was inventor of the three-way catalytic converter, which has played a dramatic role in reducing pollution from motor vehicles since their introduction in the mid-1970s.

John Joseph Mooney was an American chemical engineer who was co-inventor of the three-way catalytic converter, which has played a dramatic role in reducing pollution from motor vehicles since their introduction in the mid-1970s.

<span class="mw-page-title-main">Cerium(III) oxide</span> Chemical compound

Cerium(III) oxide, also known as cerium oxide, cerium trioxide, cerium sesquioxide, cerous oxide or dicerium trioxide, is an oxide of the rare-earth metal cerium. It has chemical formula Ce2O3 and is gold-yellow in color.

<span class="mw-page-title-main">California Smog Check Program</span>

The California Smog Check Program requires vehicles that were manufactured in 1976 or later to participate in the biennial smog check program in participating counties. The program's stated aim is to reduce air pollution from vehicles by ensuring that cars with excessive emissions are repaired in accordance with federal and state guidelines. With some exceptions, gasoline-powered vehicles, hybrid vehicles, and alternative-fuel vehicles that are eight model-years old or newer are not required to participate; instead, these vehicles pay a smog abatement fee for the first 8 years in place of being required to pass a smog check. The eight-year exception does not apply to nonresident vehicles being registered in California for the first time, diesel vehicles 1998 model or newer and weighing 14,000 lbs or less, or specially constructed vehicles 1976 and newer. The program is a joint effort between the California Air Resources Board, the California Bureau of Automotive Repair, and the California Department of Motor Vehicles.

<span class="mw-page-title-main">Mobile source air pollution</span>

Mobile source air pollution includes any air pollution emitted by motor vehicles, airplanes, locomotives, and other engines and equipment that can be moved from one location to another. Many of these pollutants contribute to environmental degradation and have negative effects on human health. To prevent unnecessary damage to human health and the environment, environmental regulatory agencies such as the U.S. Environmental Protection Agency have established policies to minimize air pollution from mobile sources. Similar agencies exist at the state level. Due to the large number of mobile sources of air pollution, and their ability to move from one location to another, mobile sources are regulated differently from stationary sources, such as power plants. Instead of monitoring individual emitters, such as an individual vehicle, mobile sources are often regulated more broadly through design and fuel standards. Examples of this include corporate average fuel economy standards and laws that ban leaded gasoline in the United States. The increase in the number of motor vehicles driven in the U.S. has made efforts to limit mobile source pollution challenging. As a result, there have been a number of different regulatory instruments implemented to reach the desired emissions goals.


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