VW emissions scandal: Is this the death of diesel?

Volkswagen emblems in a box at a scrap yard in Berlin, Germany, on Sept. 23, 2015. (Michael Sohn / AP)

Over the past 20 years diesel's image has experienced an extreme makeover of the kind usually associated solely with US reality TV shows, going from the dirty, industry fuel used to power polluting trucks and buses to a potential short-term solution to preserving current oil supplies without compromising on performance, driving dynamics and crucially, air pollution.

But that was before Monday, when the current situation at Volkswagen -- the world's largest carmaker is accused of using software to cheat on US emissions tests on its TDI diesel powerplants -- became front-page news around the world.

In a statement issued Tuesday, the group's CEO, Martin Winterkorn, said: "The irregularities with these engines contradict everything for which Volkswagen stands. We want to continue to work closely with the relevant state departments and authorities."

Although diesel is a niche market in the US, accounting for just 2% of new car sales, VW was the biggest player and its cars were developing a loyal, environmentally-conscious following.

VW and consequently the current system of emissions certification will be investigated by the US Congress's Oversight and Investigations Subcommittee. "Strong emissions standards are in place for the benefit of public health," said House Energy and Commerce Committee Chairman Fred Upton and Oversight and Investigations Subcommittee Chairman Tim Murphy in a joint statement. "Manufacturers throughout the United States, and across the world, have developed leading technologies to reduce airborne emissions within the limits set by EPA and state environmental agencies. However, reported EPA allegations that certain Volkswagen models contained software to defeat auto emissions tests raise serious questions."

The allegations also led to the UK's Society of Motor Manufacturers and Traders releasing a statement regarding testing procedures. "The EU operates a fundamentally different system to the US -- with all European tests performed in strict conditions as required by EU law and witnessed by a government-appointed independent approval agency," said its CEO, Mike Hawes.

Diesel more efficient than petrol -- it has a higher energy content per liter and more of that energy is converted successfully during combustion resulting in 20% less CO2 emissions than an equivalent petrol car. However, diesels emit more NOx (Nitrogen Oxide) which is a potentially life-threatening of air pollutant.

The Clean Air Act in the US and the new Euro 6 standard in the EU are meant to tackle that issue by ensuring new cars emit NOx levels almost on a par with petrol, but if US testers can be tricked, how can European consumers be sure that they're not being "green washed" too?

The ACEA, which represents all European carmakers, on Wednesday moved to reassure drivers and to underline that European testing standards are the strictest in the motoring world and are about to become even more comprehensive.

"Soon, Euro 6 will also require for the first time emissions testing of diesel cars under realistic driving conditions, making Europe the only region in the world to implement such real world testing for cars," it said in a statement.