Walker - a pioneer of catalytic converters
Walker, founded in 1888 in Racine, WI., USA, began making exhausts in the early 1930s. It soon established a reputation for innovation, patenting the first louvered tube silencer. In 1963 Walker continued breaking new technological ground, working on the development of a device to convert the harmful gases produced by a vehicle's engine into less harmful emissions - a catalytic converter

Although catalytic converters soon began to be introduced in American cars, it took almost 15 years before 'cats' were generally regarded as an acceptable emission treatment, and concerns about safety, capability and costs had to be overcome. Cars in Germany, Sweden and Switzerland were first fitted with catalytic converters in 1985, the year in which Walker became one of the very first companies selling catalytic converters in Europe

Today, Walker makes 220 catalytic converters for some 1300 applications, and this number is growing all the time

Vehicle Pollution
Catalytic converters were developed in response to growing concern about environmental pollution. As early as 1947, vehicle pollution was deemed to be a serious health hazard in California, USA, where smog had increased dramatically as the population and number of cars on that state's roads rose

Vehicle pollution is primarily caused by the dangerous by-products produced as petrol or diesel is burnt in an engine to provide the energy necessary to power the car. Among the main culprits are hydrocarbons (HC), carbon monoxide (CO) and nitrous oxides (NOx)

Concentrations of hydrocarbons and nitrous oxides react with oxygen in the presence of sunlight to form smog, which causes irritation of the mucous membranes, difficulties in breathing, and can aggravate such conditions as bronchitis and asthma. Smog also interferes with plant growth and can damage buildings. Carbon monoxide is highly toxic, and 90% of it comes from road vehicles. It affects the central nervous system, impairs vision, slows reflexes and causes headaches. It is also a factor in global warming. Nitrous oxides are a component of low-level ozone, another respiratory irritant, and are also a major contributor to acid rain

Since the widespread introduction almost a decade ago of catalytic converters, which reduce harmful emissions from petrol cars by an average of 75%, vehicle pollution has decreased dramatically. The effectiveness of 'cats', combined with vast improvements in the quality of fuels, means that today it would take up to 100 new cars to produce the same emissions as just one made 20 years ago

However, the number of vehicles on our roads continues to grow, and 70% of Europeans now cite air pollution as their main environmental concern (source: the European Commission Eurobarometer). The automotive industry is investing heavily in response.

A large part of the estimated £2 billion the industry spends on research and development across Europe every year is committed to researching technology to further reduce vehicle emissions

In heavy traffic, the air quality inside a car can be three times as polluted as the air outside (source: Environmental Transport Association)

Legislation
In 1968 the USA introduced the first restriction on vehicle emissions, followed, in 1971, by emission limits in Europe. Legislation has continued to be passed by governments around the world, setting stricter and stricter limits

In 1992 catalytic converters became compulsory on all new cars sold in Europe. The impact has been dramatic - in the UK alone, harmful road transport emissions have fallen by 45%. This figure is set to fall yet further as older cars are gradually replaced with newer ones which meet the higher EU emissions standards

1992 also saw the formation of the Auto Oil Programme, a cooperative project of the European Commission and the oil and auto industries. This led to the most stringent emissions laws to date in Europe, which began with the introduction of a new, mandatory European vehicle emission standard, Euro I, in which an emission level for carbon monoxide was set at 2.72g/km and the combined level for hydrocarbons and nitrous oxides was set at 0.97g/km

Euro I was followed by even tougher legislation - Euro II (1997), which reduced these levels to 2.2g/km and 0.5g/km respectively and Euro III (2000), which has set levels of 2.3g/km for CO, 0.2 for HO and 0.15 for NOx

At first glance, it may appear that levels actually increased under Euro III. However, this is the first time that the period before light-off has been included in the standard test driving cycle used to check emission levels. For both previous Euro standards, the 40-second lead-up to light-off was not included, which gave a distorted picture, as at least 90% of a vehicle's emissions over the whole test driving cycle are produced before light-off is reached. Euro III, therefore, represents a significant reduction over the limits set in Euro II

Euro IV, due to come into effect in 2006, sets dramatically higher standards, with CO emissions to be reduced to 1g/km and HC/NOx to just 0.15g/km

Tenneco Automotive with its Gillet and Walker products is continuously striving to meet and exceed the increasingly stringent standards to manufacture products that will preserve health and the environment. Currently Tenneco Automotive is producing systems meeting Euro III legislation requirements for models such as the Ford Focus C170, the Ford Transit, the Opel Astra, the Porsche 911, the Porsche Boxster, the Peugeot 406 and 605, VW Galaxy and VW Sharan.

Catalytic converter technology
A catalytic converter is a vehicle's primary emission 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

It comprises a stainless steel casing containing an interam mat made of ceramic fibre, which holds the monolith in place and protects it from damage

The monolith is the core of the converter, where the harmful gases are converted. It comprises a ceramic or metal substrate, coated with precious metals - platinum, palladium and rhodium. The structure of the substrate, which is similar to a honeycomb, provides a very high surface area, some 20,000m2, or about the size of two football fields

The emissions produced by the engine flow into the catalytic converter via a lambda sensor, which measures the air/fuel mix and provides feedback to the engine control unit to ensure efficient combustion

When the gases come into contact with the precious metals coating the substrate, they are converted, once the monolith has reached 250-300°C. The time in which the monolith reaches this operating temperature is known as the light-off

A heat shield, located under and/or above the converter, protects the surrounding area from the heat

Catalytic converter maintenance
According to Juan Carlos Diez, Product Manager for Walker Catalytic Converters, "symptoms of a failing 'cat' include 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, perhaps by a speed bump or excessively rough terrain. It can be contaminated (usually if leaded fuel is used by mistake), or the monolith can literally melt down if it comes into contact with unburned fuel. This can occasionally happen when the car is run on empty, push or tow-started, or has a defect in the ignition or carburetion system. In addition, the lambda sensor may have failed, causing the catalytic converter to operate inefficiently"

Some of these problems can be rectified quickly and inexpensively (Britain's Department of the Environment, Transport and the Regions estimates that 90% of badly polluting vehicles can be retuned within 15 minutes). Others may mean that the catalytic converter needs to be replaced

Once a catalytic converter has a clean bill of health, Walker recommends some simple steps can help keep it that way. They include:

• Never push or tow-starting the car
• Not running the car on empty
• Using unleaded fuel only
• Avoiding very short journeys - which result in exhaust gas condensation which corrodes the metal parts
• Slowing down when driving over speed bumps
• Carrying out a regular visual inspection for broken welds and air leakages in the manifold pipes into the cat
• Keeping the vehicle regularly serviced. A nationwide free emissions programme operated in the UK in 1999 showed a higher failure rate for cars which hadn't been serviced in the past 12 months. Only 9% of cars serviced by franchised dealers failed emissions checks, compared to 20% of those serviced by their owners