Renault is likely to stop offering diesel engines in most of its cars sold in Europe. The move by the French major, according to a September 6 Reuters report, is a result of the increase in the anticipated cost of ensuring that diesel engines comply with tighter emissions regulations following the crackdown on diesels launched after last year’s emissions scandal involving German carmaker Volkswagen.
Diesel models accounted for more than 60% of the 1.6 million cars Renault sold in Europe last year, and this step could dent the company’s topline badly. But tougher emissions norms and testing standards would make diesels unviable — and Renault had already removed the diesel option in its smallest cars such as Twingo well before the Volkswagen scandal hit. By 2020, when more stringent EU emissions standards come into force, larger models such as Clio and Megane could also have their diesel variants shelved.
Renault’s move could deal a decisive blow to Europe’s powerful diesel car lobby, and potentially shake up the continent’s auto industry. Europe had been a proponent of diesel until very recently, a position influenced by the diesel car lobby, most of whom are leaders in diesel technology — led by Renault and PSA Peugeot Citroën in France, Volkswagen in Germany, and Fiat in Italy.
So is this the end of the road for diesel?
Volkswagen’s chief executive, Matthias Mueller, had in June, in the aftermath of the emissions scandal, said that his company was now wondering “whether it still makes sense to invest a lot of money in further developing diesel”. As the scandal’s fallout continues, Renault too is being investigated by French authorities for publishing suspected fraudulent emissions figures. According to French road tests on 100 vehicles, Renault and Nissan cars emit more than 8 times the current limits for nitrogen oxide. Other diesel engine manufacturers, including Japanese and American carmakers, are on tenterhooks in anticipation of possible regulatory action.
For all vehicles with big engines, diesel is the default choice of fuel. The diesel engine is more efficient; the diesel combustion cycle yields a leaner fuel-air mixture to operate at optimal efficiency as compared to petrols. Measured by volume, diesel is more energy-dense than petrol. The combustion cycle itself works best at leaner mixtures, and diesels deliver a torque curve that works better for bigger cars and trucks as compared to petrol. Plus, most diesels are equipped with a turbocharger, which offers a sudden surge in power delivery after a certain RPM, a popular feature in bigger cars and SUVs. Modern diesels also emit less carbon dioxide than petrols, something that has pushed them in markets such as Europe.
Basic chemistry, however, runs counter to the narrative of ‘clean’ diesel built up by European carmakers over the years. Diesel engines also emit higher levels of nitrogen oxides, and over 7 times more particulates as compared to petrols — pollutants that cause respiratory ailments. In 1998, California identified diesel exhaust particulate matter as a toxic air contaminant based on its potential to cause cancer, premature death, and other health problems. The turning point has been the VW scandal that has cast a shadow over all diesels, prompting the EU to reassess it testing process, and announce plans to introduce new real driving emissions tests (which are considered far more accurate than the current lab tests) from September 1, 2017.
The big reason for the higher efficiency of diesels boils down to the engineering design. In a petrol engine, fuel and air is injected into small metal cylinders, and then a piston compresses the mixture, making it explosive. A small electric spark from a spark plug sets fire to it, which makes the mixture explode, generating thrust. This then pushes the piston down the cylinder, and through the crankshaft, turns the wheels.
In diesel engines, air is let into the cylinder and the piston compresses it, but much more than in a petrol engine. (In petrols, the fuel-air mixture is compressed to about a tenth of its original volume; in diesels, it is compressed 15-25 times.) Compressing a gas generates heat, and once the air is compressed, a mist of fuel is sprayed into the cylinder by an electronic fuel-injection system, which works like an aerosol spray. The air is so hot that the fuel instantly ignites and explodes — without the need for a spark plug. This controlled explosion pushes the piston back out the cylinder, producing the power that drives the vehicle.
The absence of a spark-plug ignition system is among the reasons diesels tend to be up to twice as efficient as petrols. Because the fuel is compressed more, it burns more completely in combination with the air in the cylinder, thereby releasing more power. Also, in a petrol engine that is working at less than full power, more fuel (less air) needs to be supplied to the cylinder to keep it running, while diesel engines actually consume less fuel when they are working at lower power. This lowers fuel usage while idling.
Plus, measured by volume, diesel is more energy-dense than petrol, and thereby offers more energy per litre. Diesel — which is a lower grade, less refined product of petroleum made from heavier hydrocarbons — is also a better lubricant than petrol, with the result being that a diesel engine runs with less friction, thereby generating better efficiency.
But because it is full of longer and heavier hydrocarbon chains, it has a number of chemicals interspersed that do not burn fully when combusted, including sulphur and NOx, which got Volkswagen into trouble.
A higher compression ratio — the result of the squeezing of the air in the chamber — means that parts of a diesel engine have to withstand far greater stresses than those of a petrol engine, with the result that they need to be sturdier and, therefore, heavier. Diesels are also noisier, and they produce a lot of unburnt soot particles and nitrogen oxides. However, since diesels are more efficient, they typically use less fuel, and thereby produce lower CO2 emissions. Due to their better build quality, diesels also tend to cost more initially than petrols, though their lower running costs and longer operating life offsets that cost over time. In India, where diesel is priced lower than petrol, this price tradeoff is reduced, resulting in a rush for diesel cars.