Emissions tests for diesel vehicles ‘meaningless’?

While only a few years ago, the diesel seemed to hold the answer to lower CO2 emissions and was hailed vastly superior to the “old fashioned” gasoline engine and the clunky electric vehicles, several things now have changed. Modern spark ignited engines have caught up the technology advantage – introduced in the 90’s with the turbocharged direct injection diesel – of the compression ignition engine by equally resorting to turbo-supercharging and direct injection.

Super Diesel?


While the diesel engine can – in principle – be more efficient than a gasoline engine by burning a leaner air-fuel mixture, increased economy comes at the cost of pollutant emissions. As damaging to the environment CO2 might be particulate matter (PM) – a recognised carcinogen – and nitrogen oxides (NOx) – responsible for numerous respiratory illnesses – are the real show stoppers. What is more: Over the lifecycle (emissions from prospecting, drilling and transport in addition to the emissions from the fuel itself), scientists working for the European Commission have calculated CO2-emissions for diesel fuel to be in fact around 2% higher than for gasoline and a whopping 30% higher than for Autogas.

A studies conducted by the World Health Organisation WHO has confirmed that diesel particles “cause cancer”. Other recent studies have shown that nitrogen dioxides (NO2) cause or worsen respiratory health conditions leading to asthma, bronchitis, heart attacks and strokes as well as leading to weaker infants. Many European cities regularly exhibit NO2 levels more than double World Health Organization guidelines.

Particulate matter has been identified as the principal contributor and carmakers consequently outfit all modern cars with particle filters. Filters which quite effectivley block over 98% of all particles emitted.


So much for the theory. Mr Archer points to a “significant problem with tampering with filters”, because as these filters capture particles they begin to clog up and need to be regenerated. A process controlled by the car’s electronics which is initiated under certain conditions. Conditions difficult to reach if you only drive around town. Problems with the filters have led to different “solutions”, from “baking” the filters in ovens for cleansing to simple removal which renders them useless. Filters are no guarantee nor do they help with secondary particulate matter formed from NOx.

Over 400,000 people die prematurely in Europe due to the effects of road transport and diesel in particular. Diesel vehicles clearly being the single largest contributor.

We’re being duped

To add insult to injury, recent tests conducted by the International Council on Clean Transportation (ICCT) have revealed that real world NOx emissions can be up to 20 times higher than tested in the lab. Despite a number of technologies to reduce NOx emissions, such as catalysts with urea injection and exhaust gas recirculation, the high cost and complexity of these systems, already being used to clean truck exhaust fumes, will need an additional push to find their way into a passenger car.

According to an ICCT representative, “the technologies for real-world clean diesels already exist, but they are not being employed consistently by different [carmakers]”.

Even when available they don’t work as well as they should, expecially after the car has aged somewhat. Just how ineffective these systems become can be mind-boggling. On average “clean Euro 6” diesel cars emit seven times the EU limit for NOx. Another test showed that certain models will emit even more. Audi’s A8 leads the field with real emissions 22 times the actual limit.

Actual diesel emissions vs EU limits* CarmakerNumber of models testedLowestAverageHighest Audi 3 0.9 times EU limit 8.2 times EU limit 21.9 times EU limit BMW 7 0.9 4 9.9 Citroen 3 3.2 3.9 5.4 Mazda 2 2.5 2.9 3.2 Mercedes 3 3 4 4.9 Peugeot 1 3 3 3 Vauxhall 1 9.5 9.5 9.5 VW 3 0.7 2.6 6.1 Volvo 1 2.2 2.2 2.2 Total 23 0.7 4.5 21.9 Source: Transport & Environment think tank.*NOx emissions

The millions of customers buying diesel cars in the conviction that they emit fewer harmful pollutants into the environment are ill-advised.

In order to come clean, future diesel engines will need to burn a richer mixture to avoid NOx or have expensive and sensitive exhaust aftertreatment systems.


The reason carmakers are allowed to keep selling these cars is that EU limits are set according to tests conducted in a laboratory, where conditions bear little relation to real-world driving out on the open road. This extraordinary situation, which has effectively rendered current emission limits meaningless, has not escaped the attention of the EU. It wants to introduce limits based on real-world testing by 2017, but needs the agreement of all member states.

Carmakers agree real-world tests are needed, but would prefer more time. Discussions are ongoing, but the likelihood is that new limits will be higher than the current 80mg/km.

Given that this limit was first agreed in 2007, we may well end up with new limits for harmful diesel emissions that are less stringent than those agreed more than a decade earlier – an absurd situation that carmakers and policymakers must do more to address.

Only in Europe

While at the global level only one in seven passenger cars are diesel powered, 7.5 diesel cars were sold in Europe alone. This makes diesel related air pollution a European “anomaly”. While an interesting academic excercise would be to research the exact reason for Europe’s enamoured relationship with diesel, the hard facts speak for themselves. Diesel is a highly subsidised fuel, often not even paying half the excise duty for gasoline. A great favour to the agricultural and transport sectors.

Carmakers argue similarly and comment nonchalantly that the industry was merely following government incentives. According to ACEA, the European Automobile Manufacturers Association, “All manufacturers followed this political direction.”

Learning Lawmakers

Local politicians and authorities have begun to realise the attempt to dupe them and are putting measures into place, which will effectively ban diesels or at least make their life more difficult, by, for instance, increasing the cost of monthly parking permits. In France a new classification method has been introduced, which places diesels of the same Euro emissions class in fact one step behind its gasoline powered cousins. Carmakers were quick to voice their “surprise and disappointment” as the newly introduced colour coding schem in France did not include the brand new “clean” diesels to the highest emissions category. A snide comment may slip from the unprepared as the very same industry was equally quick to add the support for the more realistic testing scheme Real Driving Emissions, RDE. Claiming the vehicles tested according to this scheme, shall meet the requirements “not just in the laboratory, but also on the road”. Seriously?

Transport&Environment (T&E) has repeatedly pointed their finger at the emperor’s new clothes not really being there, highighting logical breaks in the information on diesel emissions but also on so-called “bio-fuel”. T&E’s Greg Archer sums it up: “The car industry is fighting to keep selling diesel because it has invested so heavily in the wrong technology”.