Concentrating on Catalytic Converters
The widespread introduction of catalytic converters, almost a decade ago, has had a dramatic effect on vehicle pollution. Harmful emissions from petrol cars have been reduced by an average of 75 per cent. The effectiveness of ‘cats’, combined with vast improvements in the quality of fuels, means that today it is estimated that it would take up to approximately 100 new cars to produce the same emissions as just one made 20 years ago.
The hazardous by-products produced as petrol or diesel is burnt in an engine, are primarily responsible for vehicle pollution. Hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) are three elements among the main pollutants.
Concentrations of hydrocarbons and nitrogen oxides react with oxygen in the presence of sunlight to form smog, which can cause difficulties in breathing, and can aggravate such conditions as bronchitis and asthma. This smog also interferes with plant growth and can damage buildings. Nitrogen oxides are also a component of low-level ozone, another respiratory irritant, and are a major contributor to acid rain.
90 per cent of the highly toxic gas carbon monoxide comes from road vehicles. Which is highly disturbing considering its harmful affects on a person’s central nervous system, vision, and reflexes. CO is also a major factor in global warming.
The widespread introduction of catalytic converters, almost a decade ago, has had a dramatic effect on vehicle pollution. Harmful emissions from petrol cars have been reduced by an average of 75 per cent. The effectiveness of ‘cats’, combined with vast improvements in the quality of fuels, means that today it is estimated that it would take up to approximately 100 new cars to produce the same emissions as just one made 20 years ago.
The technological developments in catalytic converters have had a major impact on the strength of the replacement market, which now stands at around 1.2 million units per annum in the UK alone and is expected to double by 2010. European demand for replacement cats has grown by around 10 per cent to create an aftermarket of circa 2.9 million units in 2003. Industry experts estimate that cat equipped cars currently account for 84 per cent of the car parc and predict that the high value catalytic converter market will continue to show impressive growth over the next five years. In Europe the number of vehicles fitted with a catalytic converter is rising by around 12 million a year.
How a cat works
A catalytic converter is a vehicle’s primary emissions control device. Its function is to convert the hydrocarbons, carbon monoxide and nitrous oxides produced by an engine into less harmful products – namely water vapour, carbon dioxide and nitrogen.
The steel casing containing an interam mat made of ceramic fibre holds a monolith in place to protect it from damage. The monolith is the core of the converter, where the harmful gases are converted. It is made up of a ceramic material or stainless steel, coated with precious metals such as platinum, palladium and rhodium. The monolith is constructed in the same way as a honeycomb and provides a high surface area about the size of a football field, through which the exhaust gases pass.
The emissions produced by the engine flow into the catalytic converter via a lambda sensor, which measures the air and fuel mix and provides feedback to the engine control unit in order to ensure the best and most efficient combustion.
When the gases come into contact with the precious metals coating the substrate, they act as the catalyst and convert the poisonous gases. The cat starts operating once the gases have attained a temperature of 250-270°C, which is reached no later than 200 seconds after start up. The time in which the monolith reaches this operating temperature is known as the ‘light-off’, an important parameter for emission control, because during this time the exhaust gases come out of the stack untreated. The exact amount of light-off time depends on the driving and position of the cat in the exhaust line, the closer the cat is to the engine, the quicker the light-off time. To meet the demands of the new Euro 3 emission standards, the catalytic converter is located as close to the engine outlet as possible.
Technological developments
There are three basic types of automotive catalytic converters, two-way, three-way and three-way plus air. Early models of converters used a pelletised catalyst, but today most use the free-flowing honeycomb ceramic catalyst. Each type uses a slightly different method and chemistry to reduce the harmful elements in exhaust emissions. The type of converter required on a particular vehicle varies with model year, engine size and vehicle weight. Some vehicles even make use of more than one type of converter or a pre-converter to meet emission reduction standards.
Oxidation (two-way) converters represent the early generation of converters that were designed to oxidize hydrocarbons and carbon monoxide. Although these units represent the most basic form of catalytic converter technology, they remain a viable pollution reduction option in some areas. Oxidation converters usually contain platinum or palladium.
In the early 80s, most vehicle manufacturers began using converters designed to reduce nitrogen oxides (NOx), in addition to oxidizing HC and CO. These three-way converters, which were used in conjunction with computer controlled engine systems and oxygen sensors, were employed to enable a more precise control of the air to fuel ratio. This type of converter does exactly what the name suggests and deals with three compounds: HC, CO and NOx.
Three-way converters that have a reduction and an oxidation catalyst together in one housing are called three-way-plus-oxidation converters. The difference is the addition of secondary air between the two internal catalyst substrates that improves the oxidation capabilities of the converter. Put simply they oxidize and reduce pollutants. The secondary air is pumped into the middle of the converter between two separate catalyst coated ceramic substrates. The front ceramic performs the reduction and the back ceramic performs the oxidisation. Essentially it’s like having two converters in one.
Today’s catalytic converters represent the highest level of technology and advanced materials available. The result is reduced pollution emission levels combined with high engine performance.
Continuing in Catalytic Converters
In theory a catalytic converter is designed for the service life of the vehicle. But because it is invariably exposed to extreme levels of thermal and mechanical stress, it is likely that on average the cat will need to be replaced once during the vehicle’s service life.
Walker engineers from leading catalytic converter manufacturer, Tenneco Automotive, explain the symptoms of a failing ‘cat’ as the infamous, rotten egg smell lingering long after the engine has warmed up, difficulty in starting the car, sluggish acceleration, a loss of power from about 80 km/h, and higher petrol consumption. Problems with a catalytic converter can stem from a number of causes; it may have been physically damaged, for example by a speed bump or it may have been contaminated, if unleaded fuel has been used by mistake. Some of these problems can be rectified quickly and inexpensively; a simple check of the injection system can resolve the problem within 15 minutes. Others may mean that the catalytic converter needs to be replaced.
A well-known brand of Tenneco Automotive, Walker, has had a dominant presence in the automotive exhaust market for decades. The company claims to have developed the world’s first catalytic converter over 40 years ago and continues to invest in both cats and emission control technology.
The company launched its lambda sensor program last year and is currently revising its product line to enable it to offer a wider coverage. The company believes its lambda sensor program gives installers “a fast, safe way to replace worn out lambda sensors without cutting any wires.” Its ‘easy click’ solution comprises of a lambda sensor and a connection wire. With four universal sensors, 30 connection wires and two extension wires Walker is marketing its product as the “safe method” for over 2000 car applications.
Frank Plas, of Tenneco Automotive, producer of Walker products, said, “As the European market for catalytic converters grows, we will continue to introduce new products to meet the increasing demand. Our range helps installers generate more business, as they can offer high-quality replacement ‘cats’ for a wider range of vehicles. To further benefit installers, we’ve streamlined the whole part identification and ordering process, while the Lambda sensor program has given them the opportunity to generate even more business while working quickly and more safely.”
As well as these developments it now offers some 450 cat references for 3000 applications, including Ford Focus and Peugeot 307. On top of this it has an exhaust range that includes 3500 references for over 10,000 applications, including Citroen C3, Fiat Stilo, Ford Fusion and VW Polo.
The manufacturer has also carried out a review of the tools installers need to manage their stock control. The Walker Addendum, a book that supplements the 2003-2004 catalogue, and details 317 new items and 139 parts under development, has also been launched.
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