In search of the perfect burn

The simultaneous downward pressures on NOx and PM continue to make research into higher injection pressures and alternative combustion solutions such as homogenous-charge compression ignition attractive.

The European Commission's recently published proposals for Euro VI on-road emissions limits are not likely to persuade engine designers in Europe to change direction. The new limits will only confirm what they thought was likely to be coming their way. The proposals target an 80% reduction in NOx and a 66% reduction in particulate matter (PM) compared with Euro V limits. The new limits-0.01 g/kW·h (0.007 g/hp·h) for PM and 0.04 g/kW·h (0.03 g/hp·h) for NOx-are scheduled for implementation in 2013 to 2014.

Meeting the PM limits will require particulate filters, much as expected. Since the gap between on- and off-highway emissions limits will have more or less closed by this stage, the new on-road limits will have some relevance to off-highway applications. Given that some off-highway engines are developed for use on highway as well, engine designers will need to meet the limits even if other, less stringent limits apply to the end application. And if it is possible to meet the limits with reduced aftertreatment, that could represent a big cost saving for OEMs and customers.