Urine and diesel reduce toxic emissions in traffic

As of October 1 this year the EU requires that emissions of nitrogen oxides be reduced by 30 percent in trucks and 50 percent in diesel-powered cars. In 2008 these regulations will be become more stringent in Europe, and even more so in the US. The technical solution chosen by nearly all automakers to meet the requirements was originally developed by the Lund University in Sweden. Now these researchers are working on methods to reduce nitrogen oxide emissions even more.

Emissions of nitrogen oxides from heavy trucks account for 40 percent of nitrogen oxide emissions in traffic. This is seen as a major environmental problem. Thanks to the so-called three-way catalytic converter, exhaust from gasoline-powered passenger cars is relatively clean. On the other hand, it has been more problematic to clean up the exhaust from diesel-powered vehicles.

To come to grips with the problem, scientists at Lund University have developed the so-called Urea Method. This entails injecting a urine substance, NH2(CO)NH2, into the exhaust fumes in a catalytic converter in the exhaust pipe. This is the method that is now to be used.

“The urine substance is converted to ammonia, which reduces the nitrogen oxide to innocuous nitrogen gas, which occurs naturally in the air. It also reduces the amount of smaller, but harmful, residual particles such as diesel soot, carbon, and hydrocarbons,” says Ingemar Odenbrand, professor of chemical engineering and one of the prime movers in the project.

For the last few years the research team has been working instead with a method of NOx storage, which reduces emission levels even further. This method is expected to become the future standard.

The method is based on storing nitrogen oxides, NOx, in the catalytic converter and successively reducing them by repeated injections of hydrocarbons, often diesel fuel, every 60 or 90 seconds. The hydrocarbons are broken down into smaller hydrocarbons and carbon monoxide, which then reduces NOx to plain nitrogen.

“In our latest experiments we have managed to reduce emissions from 7 g of NOx per kWh to 3 g,” says Ingemar Odenbrand.

Using the full-scale exhaust and engine system constructed at LTH, the researchers are busy tweaking the variations in temperature, flow, and consistency that arise in authentic exhaust. The aim is to meet the environmental requirements that will take effect in the US from 2008, a reduction of 94 percent from today’s levels. That same year Europe will ratchet up its requirements to 2 g, a further reduction from the 3.5 g taking effect this autumn.

This work is being done in association with Volvo, Scania, and the catalytic converter manufacturer Johnson Matthey, as well as the Chalmers Institute of Technology in Göteborg when it comes to modeling and lab trials. Today Lund University is nearly the only actor, apart from the EPA in the US, publishing studies in the field with trials run on authentic exhaust.