Headquartered in Lummen, Belgium, Bosal develops and manufactures complete exhaust systems for passenger cars, trucks and industrial applications and catalytic converters. In this interview, Matthew Beecham talked with Dr. Ing. Jean-Paul Janssens, Director Advanced Research, Bosal Research nv about technical trends in exhaust systems

just-auto: 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. In what ways has this trend affected the exhaust system?

Jean-Paul Janssens: This is correct. The high performing engines equipped with one or double stage turbochargers require exhausts with as low as possible backpressure. The reason is, of course, 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.

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?  

Smaller vehicles do not necessary mean technical challenges. What is of importance is that the limitations imposed -- such as weight and space limits and cost reductions -- require technical solutions to meet those challenges. So a continuous technical challenge is present.

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?

In the next five to ten years, a further hybridisation will be seen. Also, pure electrical cars will gradually gain share in short distance transport applications.

I guess, in future, the IC engine will be supported by various degrees of electrical components?

The evolution of embedding the engine and exhaust into a web of sensors and electrical control devices will not stop. They are not only required for the improved control systems in the engine management but also to ensure the functionality of all emission related components as required by law.

Despite some people saying the IC could be in sharp decline in 15 – 20 years’ time, I guess there is still considerable scope for its development?

It is clear that in 15 to 20 years time, there will be a shift to other prime movers. However, other prime movers will need a different kind of base material for which scarceness can hamper the introduction of such technologies. For this reason, IC engines will still last some time.

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.  What do you see happening with respect to gasoline engine after-treatment systems these days?

Thermal management can be seen in a broad spectrum. 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 utilization 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.

For some time, we seen how carmakers have paid close attention to exhaust sound in order to maintain and enhance its “brand”. How do you set about supporting the carmakers achieve the right note?

Acoustical sound engineering and shaping is an important activity that is well under control over the processes of measuring techniques, simulation techniques and numerical quantification techniques. 

I guess because of the increasing cost and price volatility in the precious metal markets, this is forcing manufacturers to squeeze more performance out of smaller catalysts.  Is that how you see it?

Emission control elements are more and more designed to reach the specifications with as low as possible exposure to precious metal price fluctuations. The use of virtual tools is a must. 

What is happening to catalysts these days?

Lay-out of catalyst systems are optimised, multiple substrates, optimized cell density, optimised thermal inertia, all to minimise weight and cost.

Is there a trend toward using multiple exhaust gas sensors in order to deliver the performance improvements and reduced catalyst size?

It is certainly in the direction to optimise performance, not necessarily to reduce catalyst size, but in any case the cost.

For some time, we’ve seen increasingly stringent emission legislation introduced leading to the exhaust after-treatment system becoming more complex, particularly for diesel engines. What lies ahead for diesel after-treatment systems?

The diesel engine exhaust of the future will contain typically the following components: a diesel oxidation cat, a diesel particulate filter, a deNOx system such as a SCR, followed by a slip cat to avoid smell from ammonia or H2S, and downstream from all this, a heat recuperation system to generate additional power. All these components need to interact properly in order to reach optimal performance and cost.  

Finally, in terms of developing increasingly complex exhaust systems, how do you manage the delivery of those systems yet keep lead time and costs under control?

More and more virtual developments need to be performed to ensure the short lead times. So this means validated simulation techniques for acoustics, endurance, emissions and thermal management.