Diesel is essential to combat climate change, say IMechE experts

The average CO2 of the fleet would go up by about 16g/km if all diesel cars were taken off the road

The ‘death of diesel’ being predicted as a result of the Volkswagen emissions scandal would represent an enormous technological setback and would significantly increase CO₂ emissions from transport, leading figures within the IMechE have warned. 

While condemning obvious wrongdoing emerging from the diesel emissions scandal engulfing VW, IMechE president Professor Richard Folkson said that knee-jerk calls for an outright ban on all diesel engines would be a disaster for climate change.

“There’s a really big problem with banning diesels,” he said. “This is because diesels are much better at reducing CO₂ than their petrol equivalents. If we took all the diesels off the road the average CO₂ of the fleet would go up by about 16g/km. That increase is absolutely massive and it would push back the steps to address climate change by decades. 

“Then we have a much bigger problem of faster average climate increase.”

Folkson, an automotive engineer who worked in product development at Ford for 30 years, said that diesel engines were not inherently incapable of meeting strict emissions laws in the US and Europe. He added that technological developments in the pipeline would reduce their NOx emissions to virtually zero within a few years.

“Because of their thermal characteristics we are likely to see cleaner diesels that are very close to zero noxious pollutants and with better CO₂ performance than equivalent petrol cars,” he said. 

“Diesel engine makers are lowering the turbocharging pressures going into the engine, and de-speeding the engine so that the combustion temperatures are reduced. That means that in the longer term we will have diesels that are still powerful and refined, but because they have lower combustion temperatures they will produce less NOx in the combustion chamber. Then technologies similar to particulate filters can trap the NOx, converting it during the regeneration mode to nitrogen and oxygen.

“We are getting closer to absolute zero NOx – we are almost there. The technology is coming. We should not write off diesels.”

Philippa Oldham, head of transport and manufacturing at the IMechE, also called for diesel to remain a key part of the fuel mix in the UK. She said that technologies to reduce emissions, including engine optimisation through turbocharging and fuel injection, oxides of nitrogen reduction through active NOx storage catalysts and selective catalytic reduction, as well as particulate matter filtration systems (in the form of closed filters that have a typical particulate filtration efficiency of greater than 95%), were all going to be needed. 

Meanwhile, the VW scandal has led to calls for improved emission testing procedures which are more representative of on-road conditions, initially through the implementation of the Worldwide Harmonised Light Test Cycle in 2017. Alongside this, Real Driving Emissions criteria are being developed which could be fully integrated by 2025 to offer an even truer picture of on-road emissions. 

Oldham said that future testing scenarios should be developed to consider full lifecycle emissions. “If this re-examining of automotive emission testing is occurring perhaps we should take stock and see if more can be done in terms of future proofing this test? What about looking at the lifecycle emissions? If we are looking towards a future that has a large percentage of the fleet made up of plug-in hybrids and electric vehicles should the emissions created by electricity generation be considered?”

Oldham said that improved testing procedures, rather than outright bans on certain engine types, should be used as the template for reducing emissions. “With all the negativity surrounding diesel vehicles, an important message is being lost,” she said. “Globally we need to meet our emission targets and to do this we need to find an approach to decide how we phase out old vehicle types, based on real-world emissions and not fuel type, to help significantly improve air quality. We need to make sure that there is a robust policy framework to ensure that these targets are delivered.”