How it Works: Pollution

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How It Works: Pollution

Car Pollution
There was, a few decades ago, a joke in the USA automobile industry that some American cars expel air from their exhausts cleaner than that which went into the engine in the first place. Emission controls really started to bite in the 1970s, and as with all highly emotive subjects there were two camps - one which believed that the car emitted harmful gases to a rate of a crisis of world-wide proportions, the other one which believed that traffic fumes were not a serious threat to health. Rightly or wrongly, the same occured here in Australia in 1975 when the first emission controls took effect, and motorists would look under the bonnet to discover plenty of extra plumbing, with its resultant loss in horse power.

What is Pollution?

Many urban and industrial areas experience air pollution from time to time in varying degrees of intensity, from barely discernible to highly objectionable. There are many different types of air pollution, including smoke from domestic chimneys, gases from industrial processes, dust from many sources and photochemical smog. The amount of pollutant in the air at any one time is governed by such man-made phenomena as population density, industrial activity, traffic density and fuel consumption and such natural phenomena as climate and weather.

Photochemical Smog

Concern with a special type of air pollution known as 'photochemical smog', first recognised as a problem in the Los Angeles Basin of California during the late half of the 1940s, was the prime motivator of today's concern with pollution of all kinds. As the phenomenon of smog gradually increased in intensity and frequency of occurrence in the Los Angeles area, it became the object of much investigation and research. During the early 1950s the theory became accepted that this Los Angeles smog was formed by a complex chemical reaction which took place in the atmosphere, rather than being something just dumped into the air, like dust or smoke.

Hydro-Carbons (HC) and Nitrogen Oxides (NOx)

It was accepted that the ingredients necessary to form photochemical smog in sunlight were hydro-carbons (HC) and nitrogen oxides (NOx). Both these gases exist in many forms and come from a variety of sources. In metropolitan Los Angeles, one of the major sources of air-polluting hydrocarbons was found to be cars. Legislative action in California was quickly copied at national level and gave rise to stringent controls on emission levels, at relatively short notice. The American automobile manufacturers then joined together in an extensive research programme to help resolve the problem. One of the first questions to be investigated was the precise source from which each air pollutant was emitted from an automobile. It was found that hydro-carbons (there are over 200 types) were emitted from the exhaust system, the engine crankcase ventilation system, vents in the fuel tank filler cap and the carburettor. Nitrogen oxides in several forms were also found in exhaust emissions.

Carbon Monoxide (CO) and Leaded Petrol

Carbon monoxide (CO), a toxic gas but not an ingredient of photochemical smog, was found in both exhaust and crankcase emissions. The original source of these pollutants is, of course, the fuel on which the car runs and it was this which led to the discovery that lead from the petrol was also being emitted, mainly as a dust. The motor vehicle also contributes to overall pollution in other, though far less significant ways, such as tiny rubber particles from tyres and asbestos from brake linings and clutches. How damaging were these pollutants to health? Again the camps were divided - one believed that there is no medical evidence to show that the human body was affected by the emissions from cars, while the other believed that there was. While the former pointed to the fact that the only concrete evidence was that lead emitted from cars did have an effect on the blood stream's lead level and that even then it was less than that which most people have in their teeth in the form of fillings, the others pointed to the circumstantial evidence.

Carbon Monoxide Poisoning

Unless you have been hiding under a rock, you will be well aware that more than one person has committed suicide by enclosing themselves in a confined space with their motor car and switching on their engine to eventually die of carbon monoxide poisoning. Basically what happens is that the gas combines with the blood's haemoglobin to form carboxy haemoglobin which makes the blood less capable of carrying oxygen which in turn leads to drowsiness etc, and, in confined spaces, eventually death. Lead is a cumulative poison and known to be toxic to humans but concentrations sufficiently high to produce this effect have been found only in isolated cases, usually the result of occupational hazards.

Measuring Carbon Monoxide Output
Measuring carbon monoxide output from a cars exhaust .

Mexa Exhaust Measurement System
A Mexa exhaust measurement system - a fast-response analytical system targeted for raw exhaust emissions from diesel or gasoline (4-cycle) engines

Nitrogen Oxides and Global Warming

Nitrogen oxides are major participants in photochemical reactions and the most significant is nitrogen dioxide which provides the yellow-brown colour of smog. Although generally toxic to man, the low concentrations in the atmosphere here in Australia have yet to be specifically identified as damaging health. Ozone and peroxyacyl nitrates are other oxidising agents found in car exhausts and they have been found to cause damage to plant life in city areas and they also attack many minerals including rubber, textiles and dyes. Carbon dioxide (produced by all fossil fuels) is not toxic except in undiluted form, but its infra-red absorption properties cause outgoing heat from the earth to be retained near the surface, resulting in an increase in the temperature of the atmosphere - and thus the dreaded 'Global Warming'.

Legislating Against Emissions

By the mid 1970s world governments set various standards to legislate control of exhaust emissions. American and Japanese regulations were the most difficult ones for car manufacturers to meet as they included controls on fuel evaporation and required vehicles to be certified over 50,000 miles without attention. The 1977 / 1979 American Federal Emission limits were:

  • Hydrocarbon: 1.5 grams per mile
  • Carbon Monoxide: 15.0 grams per mile
  • Oxides of Nitrogen: 2.0 grams per mile
  • Fuel Evaporative Hydrocarbons: 6.0 grams per test.
To complicate matters even further, the California state controls were more stringent:
  • Hydrocarbon: 0.9 grams per mile
  • Carbon Monoxide: 9.0 grams per mile
  • Oxide of Nitrogen: 1.0 grams per mile
  • Fuel Evaporative Hydrocarbons: 1.5 grams per test.
Things got even tougher in 1983 when limits were set at:
  • Hydrocarbon: 0.41 grams per mile
  • Carbon Monoxide: 3.4 grams per mile
  • Oxides of Nitrogen: 1.0 grams per mile
  • Fuel Evaporative Hydrocarbons: 2.0 grams per test.
The test cycle used in the American emission control tests involved an initial 4000-mile vehicle pre-conditioning process, a 12-hour soak period, then a cold-start, 1372-second, drive cycle, followed by an additional 50-second hot-start test cycle restart after a 10 minute soak period. This was repeated during and at the completion of a specified 50,000-mile durability test, during which no work was allowed to be carried out on the engine.

Japanese Emission Controls

Given that Japanese cars are so popular in Australia, it is also worth looking back at the evolution of their own domestic pollution control regime. For Japan there was a different set of standards and two different test cycles. The evaporative test in Japan was similar to that in the USA, but the driving cycle involved incremental six-mile vehicle pre-conditioning, followed by one warm up test cycle and then a 135-second, 10 mode, cycle repeated five times, total test time being 810 seconds, compared with the US Federal 1372-second time. Additionally, an 11 mode cold start test with different measuring methods could be used.

The Economic Commission for Europe

In Europe the Economic Commission for Europe (ECE) laid down test standards for emission control which were adopted individually by member countries on different dates. In the UK controls on crankcase emissions were applied from July 1971 and on carbon monoxide at idle from 1972. Since 1973 there were also limits on the carbon monoxide and hydrocarbon emissions during a driving cycle. Certification was by test prototype approval, all vehicles produced being required to display a small EIS sticker in an accessible place to identify the ECE 15 regulation with which they complied. The actual limits which applied in Europe were governed by the weight of the vehicle which was being tested. The total exhaust volume emitted was collected and analysed to give results in grams per test.

Tamper Proof Carburettors

By 1972 limits were set at between 8.0 and 12.8 for hydrocarbons and 100 to 200 for carbon monoxide. From 1st October, 1975, these were reduced by 15 and 20 per cent respectively and from 1st October, 1976, it was a requirement that carburettors should be tamper-proof (i.e. the percentage of carbon monoxide at idle should not exceed 4.5 per cent by volume, as in 1975, but over the full range of idling adjustment possible). For vehicles to comply with the ECE regulations there were incremental 1800-mile vehicle pre-conditioning, followed by a six-hour soak and a cold start 400-second idle period.

Then followed a 195-second, 15 mode, driving cycle repeated four times without interruption. Total test time was 780 seconds and the total exhaust volume was assessed to give results in grams per test. Carbon monoxide measurements were made with a tailpipe sampling probe immediately after the fourth cycle. By the late 1970s American cars, when compared with cars of the early 1960s, averaged a 90 per cent reduction in hydrocarbons (in 1968 it was a 58 per cent reduction) an 83 per cent cut in carbon monoxide (50 per cent in 1968) and 38 per cent less oxides of nitrogen (no 1968 figure is available as control was not begun on oxides of nitrogen until 1971).

Meeting Emission Targets

The control of crankshaft emissions was relatively straightforward because the technology for a recirculating ventilation system had been developed for application on military vehicles required to operate underwater or in dusty areas. As a result all new cars sold in California in 1961 were equipped with this ventilation system. Nationwide installation began with 1963 models and as a result emissions from this source were immediately cut by 20 per cent and further improvements to the system have cut these even more. Control of exhaust emissions, however, proved to be the major problem with the exhaust pipe emitting all of the oxides of nitrogen, most of the carbon monoxide and more than half of the hydrocarbons.

Most motor manufacturers throughout the world experimented with methods to reduce exhaust emissions, some more satisfactorily than others. Ford, for example, developed two methods - supplemental air injection and engine modification - and applied one or the other to all new cars being sold in California as early as 1966, extending this nationwide in 1968. To control fuel evaporative emissions the same company developed the fuel seal which was first employed on the 1970 Maverick, and achieved an 85 to 90 per cent reduction in evaporative emissions.

REAPS - Rotary Engine Anti-Pollution System

In Japan, Mazda (Toyo Kogyo) have developed an exhaust control system for the rotary engine (REAPS - Rotary Engine Anti-Pollution System), employing a similar thermal reactor to the Ford supplemental air injection system, which enabled them to meet the 1981 Japanese emission standards. Their system consists of three main parts, the rotary engine itself, which helps in itself to block the formation of nitrogen oxides, a thermal reactor which re-burns the noxious elements present in the exhaust gas, and a mini computer, which controls the reactor. This system was incorporated in all the rotary engined Mazdas sold in Japan and on certain models which are exported. Subsequent to the development of the REAPS system, the company developed an anti-pollution system for use with reciprocating engines - CEAPS (Conventional Engine Anti-Pollution System). This system also employed a thermal reactor, a vaporised fuel control device (a charcoal canister with condenser tank) and a blow-by gas recirculation device with a PVC valve. It was fitted on all of the conventionally engined Mazdas sold in Japan and enabled them to also meet the 1981 Japanese emission standards.

The Catalytic Converter

Here in Australia, the catalytic converter and switch to unleaded petrol occured in 1986. The role of the catalytic converter (colloquially, "cat" or "catcon") is to convert toxic exhaust emissions into non-toxic substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction in which noxious byproducts of combustion undergo a chemical reaction. The type of chemical reaction varies depending upon the type of catalyst installed, for example current North American gasoline powered Light Duty Vehicles are fitted with a Three-way Catalytic Converter, which reduces carbon monoxide(CO), unburned hydrocarbons(HC), and oxides of nitrogen(NO, NO2, & N2O) to produce carbon dioxide(CO2), nitrogen(N2), and water(H2O).

And even though there was plenty of controversy when it was introduced, Australia had delayed the introduction for many years, much like the introduction of colour TV. The first widespread introduction of catalytic converters was in the United States in 1975, these being two-way models, combining carbon monoxide(CO) and unburned hydrocarbons(HC) to produce carbon dioxide(CO2) and water(H2O). Two-way catalytic converters of this type are today considered obsolete except on lean burn engines. Since most vehicles at the time used carburettors that provided a relatively rich air-fuel ratio, oxygen (O2) levels in the exhaust stream were in general insufficient for the catalytic reaction to occur. Therefore, most such engines were also equipped with secondary air injection systems to induct air into the exhaust stream to allow the catalyst to function.

Some early converter designs greatly restricted the flow of exhaust , which negatively affected vehicle performance, driveability, and fuel economy. Because they were used with carburettors incapable of precise fuel-air mixture control, they could overheat and set fire to flammable materials under the car. Illegal it may have been, but many car enthusiasts removed the converter and replaced it with a welded-in section of straight pipe, or a flanged section of "test pipe" legal for off-road use that could then be replaced with a similarly fitted converter-choked section for legal on-road use, or emissions testing. For many reasons, including not voiding insurance and remaining street legal, you best option is to install a high-flow converter or install an exhaust system with larger-than-stock capacity.

The Smoky Car Syndrome

It is fairly typical for older cars to emit some smoke - but if there is a larger than normal volume, there are a few areas you neexd to check:

  • spark plugs may need replacement or cleaning
  • ignition timing needs adjustment
  • worn piston rings, pistons or cylinder bores
  • worn valve stem guides or seals
  • sump over-filled with engine oil
  • blocked air cleaner
  • faulty electronic or mechanical controls in parts such as the choke
  • poor, contaminated or incorrect density or grade of fuel
  • blocked or damaged fuel filter
  • incorrectly set or damaged fuel injectors or fuel pump
  • incorrectly set or damaged turbo or super charges.

Remember, this list is just a guide and might not be relevant to both diesel and petrol cars.

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