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, writes Matthew Beecham.

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.”

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.”

Q&A with Katcon

In June 2008, Delphi put its global exhaust systems business up for sale which consisted of mainly hot-end exhaust components, including design and manufacture of the front-end module with catalytic converters and exhaust manifolds. A few months later, Mexico’s Bienes Turgon stepped forward to buy the business. Bienes Turgon officially took over operations on 1 May 2009 under the name, Katcon Global.  In this interview, Matthew Beecham talked with Jose De Nigris, executive vice president, sales and engineering, Katcon Global, and Bob Houtschilt, vice president, business development, Katcon Global.

just-auto: How has your business shaped-up over the past two years?

Jose De Nigris: Less than two years after seamlessly absorbing Delphi’s exhaust business globally, Katcon has already seen bright prospects for the future of our company and the industry in general. We are convinced that exhaust and aftertreatment is a growth industry and are prepared to help our customers face the challenges that lie ahead in this field for gasoline and diesel vehicles, and engines in general. From very small engines and light duty applications, all the way into enormous heavy duty and industrial applications, our global, experienced and diverse team, with a presence in the United States, Mexico, Venezuela, Luxembourg, Poland, South Africa, India, Australia and China, as well as in Korea through our alliance with industry-leader KDAC, reaffirms our commitment to the industry and our readiness to become one of the key suppliers in the industry.

We have been able to grow not only our manufacturing capabilities worldwide, but also our team’s abilities and competencies, from analysis, design, engineering and development, to specific R&D initiatives; we continue to expand our testing capabilities and have strengthened our relationships with the supply chain, a key element of our business.

In short, Katcon is already working on projects that address concerns in vehicle size reduction; this brings not only packageing concerns for customers, but additional thermal and durability factors that need to be solved. We are focused in providing technical and practical solutions from manifold to tail pipe to a variety of customers and applications around the world.

The current trend on gasoline engine, 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. In what ways has this trend affected the exhaust system?

Jose De Nigris: Downsizing is a trend forcing exhaust system suppliers to adapt their systems since the engines will deliver exhaust gases with high flow rates. The hot-end attached to the engine turbocharger needs advanced modeling tools to be optimized in terms of structure and flow. A special focus will be given to flow in order to optimise the catalyst usage and reduce PGM loadings. Noise treatment will be also treated accordingly since the high flow rate and the turbocharger will introduce different tuning needs.

Bob Houtschilt: Packaging more content under the hood also brings challenges for thermal management.  This will also change the way in which exhaust systems and modules are manufactured.

The economic crisis 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?

Jose De Nigris: It mainly forces exhaust suppliers to use modern and sophisticated analytical prediction tools in order to optimise the designs along with downsizing. Looking for more compact and lighter designs goes well together with downsizing.

Bob Houtschilt: 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.

Although a lot has been said about the prospects for PEVs, the IC engine will be around for the foreseeable future. How do you see the powertrain market over the next 5–10 years?

Jose De Nigris: The exhaust system will mainly...

For the rest of this interview and much more: Global market review of automotive exhaust systems - forecasts to 2026