Transport and sustainability
Transport and sustainability

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Transport and sustainability

5 Cleaner conventional car technologies

Vehicle emission legislation has been one of the strongest factors stimulating car manufacturers and their suppliers to develop less-polluting engines. Technology improvements to date include more efficient engine designs, new tail-pipe emission controls and electronic management systems, together with improved sensing devices to monitor the state of the engine and exhaust.

Up to around 2007, the main focus was on meeting the increasingly stringent EU emission standards (and the parallel air-quality emission standards in the USA and Japan). In addition to development of the three-way catalytic converter, much work has been conducted to develop new exhaust emission control systems for petrol and diesel engines. Hover your mouse over the different areas of the diagram in Figure A.5 to learn more about the functions that have been implemented in each area.

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Source: based on Piock, 2011
Figure 5 Functions to minimize particulate emissions
Interactive feature not available in single page view (see it in standard view).

A crucial technology is the diesel particulate filter (DPF). This has been used to meet the substantial cuts in particulate matter required under the Euro 4 and 5 regulations for diesel engines, as well as programmes in other countries (e.g. Mexico City started a programme for particulate filters to be retrofitted to diesel lorries in 2003).

A particulate filter is a complex system containing a filter to trap the soot, an active fuelling strategy that helps burn the trapped particles and a control system to monitor the soot level, initiating combustion of the particulates when required. For heavy-duty engines, particulate emission control devices include oxidation catalysts ('one-way' catalysts) and continuously regenerating traps (CRTs). A CRTs is a diesel particulate filter system which traps the particulate and then combusts the particulate completely under controlled circumstances. The combustion (or regeneration) is carried out by a reactive gas or agent in the presence of oxygen. These devices are now fitted as standard and are proven to reduce particulates by up to 90%. Other 'after-treatment' units that are designed to reduce NOx are also being fitted to meet the latest heavy-duty diesel standards (Euro 5 and 6); these include exhaust gas recirculation [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] (EGR) systems and selective catalytic reduction (SCR) systems.

Activity 5 (self-assessment)

Using the data shown in Figure 6 (which is a repeat of Figure 4), calculate the percentage improvement in test CO2 emissions between:

  • a.1997 and 2007
  • b.2007 and 2010.

Note any particular contrast in the rate of change.

Source: redrawn from SMMT, 2011, p. 5 (Chart 2)
Figure 6 UK average new car test CO2 emissions, 1997–2010


  • a.For the ten years between 1997 and 2007, the percentage improvement was (190 − 165)/190 × 100 = 13%.
  • b.For the three years between 2007 and 2010, the percentage improvement was (165 − 144)/165 × 100 = 13%.

Up until 2007, there was only a gradual improvement in new car test CO2 emissions (and also fuel economy). In the ten years from 1997 to 2007, test CO2 emissions were cut by 13%. Yet in only three years to 2010, CO2 emissions were cut by a further 13%. The change from the poorly enforced voluntary agreement of the 1990s to the EU regulations and prospective fines of the 2009 regulations seems to have spurred real action from the car industry to improve fuel economy and cut CO2 emissions.


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