Less polluting, but diesel is far from being clean

By Lorraine Mallinder

Date: 24/03/05

The diesel boom continues apace. Sales of cars fitted with direct injection diesel engines, which combine high fuel efficiency with low emissions, have been on the increase in recent years. In 2004, the proportion of newly registered cars fitted with diesel engines hit 48% and future prospects for expansion of this technology are looking good. Diesel is now a credible alternative to petrol.

"There can be no doubt that we have profited from the diesel boom," said Bernd Bohr, chairman of car parts manufacturer Robert Bosch at the Geneva Motor Show earlier this month. "This is reflected in the growing unit sales of our high-pressure diesel injection systems. In 2004, we produced 7.2 million systems for passenger cars. This year, we expect this figure to be 8.4m."

Bosch, which is a privately owned company, is the world's biggest car parts manufacturer and has more than half the market in diesel fuel injection pumps. The extent to which the car industry relies on Bosch was painfully exposed at the beginning of this year, when the company announced quality problems that halted production lines both at Mercedes and BMW and also affected Volkswagen's Audi production. BMW was obliged to recall thousands of cars.

Bosch has high hopes for its latest direct injection system, the so-called third generation of Common Rail, which is compatible with a wide range of vehicle and engine types, from mid-range four-cylinder to premium class eight-cylinder engines. Large-scale production of the system started in 2003 and was first fitted to Audi's three-litre six-cylinder engine.

Bosch claims the new generation means "even fewer pollutants, greater fuel economy, more engine power and quieter running diesel engines".

Diesel's advantages of fuel economy over petrol are off-set by difficulties with emissions from what is basically a dirtier fuel. Ordinarily, when emissions are reduced in diesel engines, the trade-off is higher fuel consumption. The new generation injection system, however, has the potential to reduce pollution emissions by up to 20% while reducing fuel consumption by 3%.

While Bosch believes it has made a breakthrough, there is still room for improvement. While CO2 emissions are reduced with use of such diesel engines, high levels of harmful nitrous oxides (which contribute to the formation of acid rain and ozone) and cancer-causing soot are still released into the atmosphere.

Low sulphur fuel, which will be compulsory in the EU from 2009, can help to reduce such emissions, but the real breakthrough technology needed to overcome this problem has yet to be found.

• Lorraine Mallinder is a freelance journalist based in Brussels.