Clean diesel in the USA – part of the air pollution solution?

Reductions in NOx and particulate emissions from diesel vehicles in the USA shows how the technology can be part of the solution to air quality problems, writes Alan Schaeffer, executive director of the Diesel Technology Forum.

Allen Schaeffer - Diesel Technology Forum

Allen Schaeffer – executive director of the Diesel Technology Forum

Friend or foe? Problem or solution? Diesel has been cast into these and other roles both in Europe and the U.S. for over a decade. Loved for its fuel efficiency or the scapegoat for all air pollution and health problems, any discussion about diesel is bound to bring out strongly held views, including this one: there is no question that diesel is a part of the air quality challenges we all face and there is also no question that it is part of the solution.

As parts of Europe emphasized low-carbon dioxide (CO2) emissions and efficiency, car buyers were propelled toward diesels by both policy and technology. In the U.S., emissions control was the order of the day through a fuel and technology neutral approach. And whether in London or Los Angeles, growing economies and populations have led to major traffic congestion, with vehicles of all types and fuels often stuck idling or running in less efficient modes.

In the U.S., pollution concerns of the diesel were driven by visible smoke emissions from commercial trucks and buses painting a very visible and negative diesel image. It also created a regulatory emphasis toward eliminating particulate emissions, which met their fate in 2007 with the advent of the diesel particulate filter (DPF) that removed over 90% of the solid particles from the exhaust. Today DPFs are standard fare in diesels large and small. Some gasoline engines emit more fine particles today than a modern diesel.

Nitrogen oxides

A focus on NOx emissions (including nitrogen dioxide or NO2) reduction followed and was until recently a major challenge. Inside the diesel engine, strategies to reduce formation of particulates tended to increase the formation of nitrogen oxides and reduce fuel efficiency, and vice-versa. Today’s two-pronged solution minimises NOx formation through precision control of the combustion process, and then uses selective catalytic reduction (SCR) technology to scrub out the remainder in the exhaust. SCR is near standard fare for all on-highway trucks and most all passenger cars as well. Today in the U.S., heavy duty diesel trucks achieve near zero emissions performance (0.20 g/BHP-hr) for nitrogen oxides, compared to 6.0 g/BHP-hr some eight years ago. They are also achieving gains in fuel efficiency of 3-6%.

What we call ‘clean diesel’ in the U.S. is new technology that has reduced NOx and PM by 98% and ultra-low sulfur diesel that has removed 97% of the sulfur from diesel fuel.

Complex air

In the U.S. some science questions further reductions in NOx emissions because of a counter-intuitive finding – that lowering NOx emissions can actually increase smog formation, at least in some cities. It is clear that air is a complex mixture of things including emissions from many sources and that air emissions chemistry and local atmospheric and environmental conditions can play a big role.

“We find ourselves today with the situation of having made great advances in new technology diesel engines achieving near zero emissions. But it will take time before we fully see the benefits from these advancements.”

We find ourselves today with the situation of having made great advances in new technology diesel engines achieving near zero emissions. But it will take time before we fully see the benefits from these advancements. About 38% of all big-rigs in operation here are 2007 or newer technology and the average car ownership lasts more than 11 years.

The whirlwind lifecycle of smartphones and computers has driven new expectations of technology turnover that unfortunately do not apply to the amortisation period for work trucks or a passenger car loan or lease. One thing they do share in common is that unless we buy that new phone (or car or truck), we (or society) don’t get to experience its benefits.

Manufacturers are counting on the very high efficiency of the diesel to help achieve the increasingly more stringent CO2 requirements in both the U.S. and EU. They are also committed to addressing disconnects in certification testing and real world driving; a problem shared in both the U.S. and EU. Older technology vehicles of any kind met the requirements and regulations of their time, but today they are more polluting than new ones, and traffic congestion only makes it all worse.

To achieve the aggressive near and long term goals of cleaner air along with reductions in greenhouse gas emissions, electric and hybrid vehicles and the new generation of clean diesel technology are the best team to get us there.

The Diesel Technology Forum, based in the Washington, D.C. region, is a non-profit organisation dedicated to raising awareness about the importance of diesel engines, fuel and technology.