Real driving emissions tests prompt development of new fuels

Real driving emissions (RDE) tests are being phased in by the EU to stipulate the range of driving conditions under which a car must be tested for emissions. New fuel and lubricant formulations will be needed to meet the challenge of reducing emissions further without causing engine problems. Engine, fuel and lubricant will need to be designed to work together.

After the controversy over the gap between lab emissions results and real-world emissions results, the EU is phasing in real driving emissions (RDE) tests for new vehicles over the period until 2020. Cars will be fitted with a portable emission measuring system for the test. This equipment has flow meters to measure the exhaust, a weather station, a GPS system, and gas analysers. The system must be used to monitor emissions in real time while the car is driven under normal road conditions.

Those road conditions will need to include different altitudes, loads, temperatures and hills, and must feature urban, rural and motorway driving.

The RDE tests will supplement the existing light vehicles test procedure (WLTP), which measures fuel economy and CO2 emissions. The new tests will concentrate on pollutants such as nitrogen oxide (NOx) and particulates.


Bringing down CO2, NOx and particulates

The mix of air and fuel that is burnt by the engine has a considerable influence on the amount of pollution produced. The technical term ‘stoichiometric’ is used to describe mixtures in which just enough air is provided to burn all the fuel.

A mixture lower than this is called ‘rich’. These mixes are not as efficient, but they can make more power and burn more coolly, helping to preserve the engine; however, they also produce more CO2. Why is this important? To keep real driving emissions down, the engine needs to avoid combustion outside the stoichiometric range; therefore, we could well see the advent of real driving emissions fuels specifically developed to help deliver this.

To bring nitrous oxide (NOx) emissions down, engines will have to avoid ‘scavenging’. This can degrade the efficiency of the motor, affecting both petrol and diesel engines.

This leaves particulate numbers (PN), which are emitted by the exhaust. It is likely that cars are going to have to be fitted with a particulate filter over their exhaust to deal with this, which is a fairly cheap and low-tech fix.

Engines, fuels and lubricants will need to work together

When it comes to engines, the tests are likely to drive development towards more efficient engines, better catalysts, the use of filters for particulates, and nitrogen traps. Engine hardware, lubricant and fuel will be designed to work together to achieve lower emissions while protecting the engine. There will be a number of technical challenges to overcome, and new formulations of both lubricants and fuels will be needed.

The changes will almost certainly prompt new issues to arise, so fast-response testing and fuel development facilities will be an important resource for automotive manufacturers. For now, Volkswagen’s head of engineering development has announced that the NOx emissions problem is solved in its new engines, including under RDE conditions; however, this is very unlikely to be the last word in this ongoing and fast-developing story.

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