Peugeot & Citroen: 3m clean diesels and counting

In January, PSA Citroen chalked up its three millionth diesel engine fitted with the company's patented diesel particulate filtration (DPF) system -- a technology making them not just clean by diesel standards but what PSA says are the world's cleanest internal combustion engines.

DPF has been a part of all Citroen and Peugeot diesel products since 2000, meaning the two marques have met the stringent Euro V emissions standards since before they were drafted -- which make particulate filters mandatory in all new diesel vehicles after September 2009 -- for nearly a decade.

Now in its second generation, the additive-based technology destroys enough particulate matter to reduce emissions almost below measurability (0.004g/km). The company claims this makes its HDi oilers the world's cleanest internal combustion engines.

Today, the group's Citroen and Peugeot brands have DPF as standard across their HDi ranges.

Next up: Euro VI. More specifically, to work on NOx abatement levels. Hitting or bettering the 0.08g/km NOx directive, set to take effect in September 2014, is considered the primary challenge set for manufacturers by Euro VI. PSA says an important element in winning this is lowering the cost of NOx reduction systems.