Hybrid engines are claimed to be the next big thing, yet diesels outsell petrol vehicles in parts of Europe andmeet emissions objectives. Julia Pierce reports as two top car makers strengthen their backing for diesel.

Changing the transport infrastructure to run on hydrogen rather than hydrocarbons has long been seen as the blueprint for combating global warming and lowering carbon dioxide emissions.

However, last week two of Europe’s largest car makers appeared to be turning their backs on hybrid and hydrogen power and championing diesel engines as the most effective way to meet the EU’s CO2 emissions targets.

Since 1998 a partnership between PSA Peugeot Citroën and Ford has produced three common rail (HDi) diesel engine families with capacities from 1.4 to 2.7 litres. These feature technologies including a high-pressure fuel-injection system to improve the efficiency of the combustion process and an electronically controlled Exhaust Gas Recirculation system that reduces combustion temperatures and eliminates black smoke. Fuel consumption and CO2 emissions have been cut by 20 per cent, exhaust particulates by 60 per cent and carbon monoxide emissions by 40 per cent.

Last week the companies appeared to complete the range, launching a 2.2-litre HDi diesel dedicated to the light and medium commercial vehicle market, as well as a 2.2-litre premium, high-output diesel for medium, large and executive passenger vehicles.

The engines’ green credentials are impressive — they can also run on a blend of up to 30 per cent bio-diesel, five times the EU objective for 2010.

All over Europe sales of diesel vehicles are increasing, particularly in the UK where they are popular owing to their low running costs.

According to the Vehicle Certification Agency, for conventional powertrains the top 105 most fuel-economic cars on sale in the UK are all diesels, based on combined fuel consumption figures. Diesels also provide increased levels of vehicle torque, giving drivers a more exciting ride.

In 1998 diesels accounted for 25 per cent of cars sold in Europe. By the end of last June this figure had doubled. In Austria, France and Belgium over 55 per cent of new car sales are diesel powered.

‘The number of hybrid cars in use across Europe is tiny compared to the millions of diesels,’ said Lewis Booth, executive vice president for Ford. ‘Hybrids are very expensive to produce and to purchase. We believe that encouragement should be given to those cars that meet environmental goals.’

Diesels can produce higher quantities of other pollutants such as nitrogen dioxide and fine particles than petrol models with the same CO2 output. In 1992 exhaust emission limits (referred to as the Euro I standards) were introduced for new cars which resulted in the fitting of advanced emission-control techniques such as catalysts. Further tightening of the emissions limits (Euro IV) began on 1 January and will be fully in force by 1 January 2007.

According to Jean-Martin Folz, chief executive of PSA Peugeot Citroën, though regulations are getting tighter it is unlikely that even the next round of European emissions legislation, Euro V, would have a negative effect on the saleability of diesels.

‘The EU is sensible and realises that an increase in the cost of diesels will reduce demand for them and so create a rise in the use of petrol vehicles with a rise in CO2 emissions. After signing the Kyoto agreement this is the opposite of the EU’s goals. The way to meet the targets is to reduce the number of petrol vehicles and increase diesels. Hybrids are expensive niche products with less than one per cent of the UK market, but diesel vehicles account for over 50 per cent. They represent an affordable solution to CO2 emissions.’

‘The number of hybrids on the road is small because so few people can afford to buy them,’ added Ford’s Booth. ‘Diesels are the most cost-effective solution to the legislation that is in place today which calls for us to reduce the amount of CO2 produced.’

Some countries have recognised the trend towards diesel ownership and have introduced environmental programmes reflecting this.

The Dutch government is particularly concerned about nitrogen dioxide and particulate levels. As of June 2005 it introduced a subsidy consisting of a reduction of 600 euros from the purchase tax of new diesel cars with a carbon filter, making the Netherlands the first European country to offer financial incentives for the use of carbon filters.

‘The question of nitrogen dioxide output is being discussed as part of the framework for the Euro V legislation,’ said Folz. ‘However, this pollution isn’t diesel specific and there are many other sources. Targeting diesel engines is not the best way to reduce global nitrogen dioxide emissions. It does need to be reduced, but so does carbon dioxide and the two must be balanced.’

Support for the use of low-emission diesel vehicles in the UK comes in the shape of changes to the Energy Saving Trust’s PowerShift register. To be registered and gain benefits such as a reduction in price for London’s congestion charge, a vehicle must use an alternative fuel source showing a reduction in emissions.

However, the list has been scrapped in favour of a new low-carbon car programme, currently awaiting EC approval. The EST hopes this will be given by the end of the year. Under this, a car will be eligible for an EST grant if its CO2 output is below a certain level. The level of eligibility is likely to be around 115g per kilometre, though this has yet to be confirmed.

The scheme will operate on a sliding scale with cleaner cars receiving a larger grant. By 2012 the EST aims to have 10 per cent of new vehicles emitting less than 120g of CO2 per km.

The EU is also sponsoring development of technologies that will make diesels cleaner. The IMITEC project, based in Greece, has succeeded in producing a sensor platform that calculates the build-up of particulates on exhaust filters then triggers their removal by oxidation, regenerating the filter exactly when necessary.

According to vehicle manufacturers, this concentration on diesel rather than hydrogen power is the most logical way forward, even if opposition from the green lobby is likely to be fierce.

‘At the end of the day we must offer something that the customer wants,’ said Booth. ‘Diesels are a much less expensive solution than hydrogen and the number of real sales proves this. But hydrogen is unfortunately very well publicised.’