22nd January 2008

CO₂ emissions are currently hot on the political agenda in Europe and in North America. In December 2007, the European Commission proposed legislation to reduce the average carbon dioxide (CO₂) emissions of new passenger cars to 120 grams per kilometre (g/km) by 2012, an improvement in fuel economy of about 25 per cent from current levels¹. In the same month, a new energy bill was approved in the US, which stipulates an improvement in corporate average fuel economy (CAFE) to 35 miles per gallon (mpg) by 2020, 40 per cent higher than the current CAFE standards². Automakers in both regions are working on a number of strategies to improve the fuel economy of vehicles to meet these new targets. There are a number of potential CO₂ reducing technology options, including the use of biofuels and advanced, but not market ready, combustion systems, but three engine technologies are currently seen to be crucial in improving fuel consumption and thus lowering CO₂ output; Diesel engines, hybrid gasoline-electric vehicles, and downsized turbocharged gasoline engines combined with direct injection. Each of these three technologies will have a different impact on pgm use.

• Diesel engines offer fuel efficiency gains of 20-30 per cent over similar sized conventional gasoline engines and therefore produce less CO₂. On average, diesel vehicles use more pgm than their gasoline counterparts since they produce higher amounts of particulate matter (PM) and nitrogen oxides (NOx), boosting the need for catalytic aftertreatment. PM emissions can be controlled with a diesel particulate filter (DPF), many of which contain pgm, and NOx emissions are reduced via one of two methods; the use of a NOx trap (containing pgm), or Selective Catalytic Reduction (SCR) using urea (no pgm). Diesel vehicles already account for over half of new vehicles sold in Europe, and this share is expected to grow to around 60 per cent over the next decade.
  
• There is vast potential for the use of diesel vehicles in the US, where diesel penetration is currently low at around 5 per cent of overall light vehicle sales. However, the main focus for automakers in the region is currently on hybrid powertrain development. Hybrid vehicles generally have have smaller engines than their conventional gasoline counterparts, although as the engine does not run continuously, it tends to run at cooler temperatures. In these conditions, more pgm is required to meet the same emissions limits - hybrid vehicles can therefore broadly be considered as pgm neutral when compared to conventional gasoline engines.
  
• Downsized gasoline engines (a.k.a. turbo and super charged engines), particularly when combined with gasoline direct injection (GDi), provide similar (or even improved) performance at reduced engine size and hence the potential for greater fuel economy. It has been estimated that GDi engines could take up around 25 per cent of the gasoline vehicle market in Europe by 2010³. Catalyst volumes tend to be smaller in these exhaust systems and thus require less pgm.

References

1 http://ec.europa.eu/environment/co2/co2_home.htm

2 http://www.nhtsa.dot.gov/cars/rules/cafe/overview.htm

3 ‘New emissions rules will boost GDI sales’ Automotive news Europe, May28th 2007