As each new emissions regulation swings into force, more and more content is added to the exhaust in order to comply. Matthew Beecham talks with executives from Katcon Global, Tenneco Automotive, Bosal and BASF Catalysts about the ways in which they are meeting each regulation.
Finding the right note
Go deeper with GlobalData
Discover B2B Marketing That Performs
Combine business intelligence and editorial excellence to reach engaged professionals across 36 leading media platforms.
Exhaust sound used to be simply a by-product of engine and vehicle development, but for today’s sports and luxury cars, it is a carefully-manipulated ‘product’ that must fit in with the car’s character and the brand’s image.
Tenneco Automotive executives told us: “The whole sound pattern, especially the tailpipe noise of the exhaust system, plays an important role in the subjective impression of the car. There are two sound classifications: the limousines with a harmonic, quiet and discrete sound whereas for sports cars a more rough and powerful sound is requested. The degree of freedom for sound design is mainly determined by the number and arrangement of the cylinders. In addition to the number of cylinders, tuning of the valve control timings represents an efficient power driven possibility for a sound design.”
Katcon Global believes that the overall noise and second order noise are very important to customers. Jose De Nigris, executive vice president, sales and engineering, Katcon Global, told us: “We are already supporting the carmakers using analytical tools, vehicle measurements and subjective noise assessment.” His colleague, Bob Houtschilt, vice president, business development, Katcon Global, added: “Other than performance cars, most auto makers have settled on “quiet”. Achieving a quiet exhaust with low back pressure for engine performance with more and more crowded under body space is the challenge. Our advance modelling and advanced laboratory equipment enable us to optimise sound, performance and value.”
Engine trends
The current trend on gasoline engines, at least in Europe, is the downsizing linked with introduction of turbochargers. For example, a 1.6-litre North America gasoline becomes a 1.2-litre turbo gasoline.
Bosal reckons that the high performing engines equipped with one or double stage turbochargers require exhausts with as low as possible backpressure. The reason, says Dr Jean-Paul Janssens, director of advanced research, Bosal Research nv, is the turbo sensitivity for backpressure. “This means that the optimal acoustical design needs to be combined with optimal flow conditions. Given the presence of emission elements, flow uniformity must also be guaranteed. The competence of designing the exhaust system using fluid dynamics modeling is becoming more and more important.”
As far as gasoline engines are concerned, after-treatment systems appear to be on a level although we understand that there is some development work underway to control thermal management. “Thermal management can be seen in a broad spectrum,” adds Janssens. “Within the functionality of after-treatment systems, thermal management is very important to ensure that every component functions within its required temperature window, for performance and life. Thermal management can also mean the utilisation of the remaining heat in the exhaust for additional power generation. Such techniques are under development and seem to be the most promising techniques by far to improve fuel economy.”
Catalyst trends
The increasing number of catalytic converters inevitably leads to an increasing demand for noble metal. Yet the limited resources and correspondingly high prices are prompting the development of converters with higher efficiency and lower catalyst ageing. Manufacturers say that tendency continues today and can be read from the past where closed couple converter, thinner walls and high cell densities have significantly increased efficiency and thus lowered even cost. Today, rising noble metal prices is supporting further investment by manufacturers into SCR (selective catalytic reduction) technologies.
As we see it, manufacturers are working toward positioning the catalytic converter as close to the manifold as possible thereby making the catalyst smaller. Catalytic converters are also becoming more and more integrated into the manifold.
“Many vehicles use a catalytic converter system consisting of a close-coupled catalyst and an under-floor catalyst,” said Dr Thomas G Droege, global marketing director, BASF Mobile Emissions Catalysts. “The close-coupled catalyst is placed as close to the engine as possible to handle the emissions when the engine first starts up. The exhaust system is cold at this point and so the catalyst must be specially engineered to operate at low temperatures. Placing the catalyst near the engine helps increase the temperature that the catalyst sees, especially during this cold start period. The under-floor catalyst is placed under the vehicle near the muffler. Once the engine has been running, the exhaust system is warm and the under-floor catalyst can function effectively.
“Space around the engine is limited. In general, larger engines do not have the space in the engine compartment for the required catalyst volume. Placing the catalyst close to the engine exposes the catalyst to higher temperatures during demanding driving conditions. To prevent excessive deactivation of the catalyst during this high temperature exposure, catalyst suppliers have incorporated innovative materials with higher stability into their catalysts.”
Finally, the economic crises has led to a change in customer behaviour and switching to smaller and smaller vehicles. In terms of exhaust and catalytic systems, does that pose technical challenges?
De Nigris believes that it mainly forces exhaust suppliers to use modern and sophisticated analytical prediction tools in order to optimise the designs along with downsizing. He said: “Looking for more compact and lighter designs goes well together with downsizing.”
Houtschilt concluded: “Customers have been down pricing their vehicles, as well as downsizing. Lower price vehicles still need long lasting exhaust systems to meet emissions legislation and customer expectations but with greater value in terms of useful life, acoustic quality and engine performance.”
