American dream?

The top carmakers are all launching diesel models into the US. But what technologies can help diesel to shed its image there as the noisy, slow, smoky option? David Fowler reports.

Look back 10 or 20 years, and the only reason for buying a diesel car was fuel economy. A diesel would cost less to run than a petrol-engined car, if you could put up with it being noisy, smoky and slow.

In the past 10 years the situation has been transformed. Diesel technology has advanced rapidly. Today’s engines bear little resemblance to their predecessors and are the equal of petrol in most respects. Some of the most desirable models in the ranges of luxury car makers such as BMW, Mercedes and Audi are diesel. In the European passenger car market compression-ignition engines are expected to break through the 50 per cent market share barrier by 2008.

The US is different. Economy was never the issue there, as it was in Europe; the diesel car market has experienced a long, slow decline; and most drivers think diesels are still noisy, smoky and slow.

Yet next month Mercedes launches a diesel version of its E-Class executive saloon in the US, having had no similar car in the market for a number of years. It’s following on the heels of Volkswagen, which has been introducing its latest TDI models. Ford has also indicated it may launch a diesel Focus there.

There’s a big job to do in overturning perceptions across the Atlantic, and neither company is making wild predictions of the numbers they might sell. But if they succeed, there’s an immense market there for the taking. And with Europe at the forefront of diesel development, it’s European companies that stand to benefit most.Diesel peaked in the US in 1981, in the wake of the 1970s oil crises, with a six per cent share of the passenger car market there. At that time the equivalent figure for Europe was only 10 per cent. But in contrast to Europe, improved economy was not enough to offset the disadvantages of diesel-engined cars, and by the late 1980s US diesel passenger car sales had fallen from 500,000 to under 10,000.

Moreover, legislation in the US has concentrated on reducing toxic and smog-forming emissions such as carbon monoxide and oxides of nitrogen, rather than carbon dioxide, which is related to fuel consumption. By contrast, Europe has taken a more balanced approach which gives more recognition to diesel’s inherent economy. Fuel economy and carbon dioxide emissions are becoming even more important as European fleet average economy rules are phased in.

The only significant market for light-duty diesels in the US recently has been in pick-ups, which are hugely popular there. In 2001 283,000 diesel-powered pick-ups were sold, giving diesel a market share of 3.2%. These all had V8 engines of five litres or more.

Nevertheless, in the same year VW managed to sell 31,000 diesel Jettas, Golfs and Beetles, though this was still well below one per cent of the market. It has launched its TDI Passat and most recently the Touareg SUV.

Mercedes-Benz has a long history of diesel in the US. During the oil crises 80 per cent of the cars it sold were diesels. By 1999, the last year of the previous E-Class model, this had dwindled to an annual figure of 3,000. When the face-lifted E-Class was launched the diesel version was dropped – until a new engine became available. Next month the new E320 CDI goes on sale, equipped with the latest technology. The Jeep Liberty 2.8 CRD, the first light off-roader to be powered by a diesel engine in the US, will follow.

The company is not trying to sell the new E-Class by virtue of its fuel economy, though. In fact it’s not even calling it a diesel. ‘It’s important to put over to the customer that it’s a completely new-generation technology. We refer to it as CDI and we want to get across the message that it’s fun to drive. The low end torque is perfect for the US market and the acceleration is even better than the petrol E320,’ said Bernhard Glaser, product manager for passenger cars with Mercedes-Benz USA. And though customers may not be bothered one way or the other about economy, they may be attracted by the diesel’s impressive range of 700-800 miles.

The company will be aiming at two sets of customers. Former diesel buyers, who Glaser said remain very loyal, will be contacted by direct mail. ‘We’re confident of getting many back,’ he said. Meanwhile, a launch campaign will try to attract new customers by emphasising the performance and driveability and, to use the planned tagline, the car’s ‘fun to fuel factor’.

On sales Glaser will only say, ‘We’re confident we can reach the old figure of 3,000 in a full year.’ But it’s clear the company is hoping sales will build well beyond that, over a few years.

One snag is that the car will be available in only 45 states. California, because of its smog problem, and four other states have more stringent emissions regulations than the rest of the US and because, unlike in Europe, low-sulphur fuel is not widely available, even with the new technology the TDI and CDI can’t meet the requirements. Nonetheless, there are people in California who are big enough fans of diesel to be prepared to go out of the state to buy secondhand Volkswagen TDIs. And legislation is in place to make low-sulphur fuel widely available by 2006, at which point the cars should meet the requirements everywhere – at least for a while.

Germany’s Robert Bosch is the world’s leading supplier of diesel-injection systems. It has around 50 per cent of the European market, supplying both VW and Mercedes, and it makes common-rail systems locally in the US for heavy-duty pick-up trucks.Dr Bernd Bohr, chairman of Bosch’s automotive group, said: ‘We see diesel having good possibilities in the US. Our vision is that there’s a possibility for a 20 per cent market share. Some say this is an exaggeration. We’re not so sure.’

He adds that there are two main challenges: ‘First is image – it’s still on the level where diesel was 20 years ago in Europe.’

Second is a technical challenge. New regulations to take effect in 2007 will impose stringent requirements for emissions of particulates and oxides of nitrogen. Successfully meeting this challenge is crucial if diesel is to break out from its current niche in European imports to the US and be widely adopted in cars produced in the US by General Motors, Ford and Chrysler.

‘The feedback from the big three is that they have a high interest in diesel on condition that we can take the hurdle of the US 2007 legislation,’ said Bohr. ‘If we can demonstrate a viable solution, then we expect more than one high-volume project being started in the US.’

The requirements, known as Tier 2, are considerably tougher than the forthcoming Euro IV standards, which third-generation common-rail systems, introduced last autumn on the Audi A8, can already meet. Steve Gregory, product line manager for Delphi Diesel Systems, said: ‘The legislation’s objective was explicitly to bring in after-treatment devices [such as particle filters and NOx catalysts]. But Tier 2 is so stringent it’s proving extremely difficult for everybody to find robust and cost-effective solutions. It could drive an even bigger gap between diesel and gasoline.’

Bohr said Bosch is attacking the problem from two angles: the injectors and after-treatment systems. Bosch’s fourth-generation system will use higher fuel pressure for more precise control, and variable nozzles: a fine nozzle, as in today’s system, to get a fine spray of fuel at low loads and a bigger one to get more fuel through at high loads. This requires ‘an intricate mechanism’, said Bohr.

For after-treatment, the latest particulate filters have the capacity to last the lifetime of the vehicle, or 250,000km. Alternatively, after-treatment for oxides of nitrogen could be added in the form of either a NOx storage catalyst or a selective reduction catalyst. The SCR or AdBlue system, which involves adding urea in an after-treatment catalyst to reduce the NOx, requires an additional injection system for the urea which has to be topped up at filling stations by the driver. For this reason it is likely to remain restricted to heavy-duty diesels.

To complement development on injection systems, for the past five years Bosch has been building up its technical capabilities in combustion process design: that is, looking at the engine itself and how the geometry of the injector and combustion chamber can be improved to make the fuel burn as cleanly as possible. In the past it left this area for the most part to its customers.

Bohr said Bosch is making progress towards meeting the requirements: ‘We don’t have it in the bag yet. But we’ve made great strides forward in the last couple of years – if we continue at that speed I’m reasonably confident.’

If the US car makers’ interest bears fruit, there’s a wide consensus that their primary area of interest initially will not be cars as we know them in Europe. Instead the focus will be ‘light heavy-duty’ vehicles: SUVs, pick-ups and people carriers with a gross weight of 3.5-6 tons – the sort of vehicle that only exists in the US. Diesel versions of vehicles bigger than this already exist, and below 3.5 tons foreign car makers could import them from elsewhere.

That view is borne out by a report by consulting engineers Ricardo, which lists the benefits of diesels as driveability and towing capability deriving from their high torque: ‘US light truck engines have relatively high torque output with lower rated power, so diesels fit naturally into the premium offering of vehicle ranges. The diesel variant will generally be sold as the premium powerplant, not at the low cost end of the vehicle ranges.’

If Bohr’s goal of 20 per cent of the passenger car market can be achieved, that would represent three to four million vehicles annually. With the hardware of a common-rail system costing over $200 (£111) even without the electronic controls, that’s a market of well over half a billion up for grabs between, at present, four competitors. Of these, Bosch and Siemens VDO are European; Delphi, the second-biggest producer, is US-owned but developed its common-rail systems in Europe; and Denso is Japanese.

Those who argue that this is too optimistic point out that it is not just a question of improving the image of the cars. Owners will still have to contend with the fact that in many filling stations diesel pumps are stuck round the back where the heavy trucks refuel. Meanwhile, there remains the open question of what resale value a diesel car will have when the first owner wants to sell it.

Delphi’s Gregory said: ‘Not so long ago we were in the same position in Europe. The two aspects – improved performance and driveability, and accessibility of fuel – need to be brought on together at the right pace.’

Meanwhile, Bohr also expresses the hope that the future approach to emissions in the US will be more like Europe’s, which, he argues, has been prepared to take a slightly more relaxed view of diesel’s higher emissions of particles and NOx because of its better fuel consumption and hence lower carbon dioxide output. ‘If the market plays freely there will be a bigger share for diesel,’ he said.

Ron Cogan, editor of US magazine Green Car Journal, said: ‘I think we’re about to turn a corner. It will take a pretty good educational effort on the part of the automakers but they really want to bring diesel to the States. They’re striving to reduce corporate fleet averages without downsizing. SUVs and large vehicles need whatever help they can get.’

Ricardo senior technology manager Nick Owen sums up the situation: ‘No one knows where the US market for diesel passenger cars is going, but Volkswagen and Mercedes are making a significant offer. It’s an exciting prospect for European industry because we have the technology. People are waiting with bated breath.’

Sidebar: Today’s Diesel engines bear no resemblance to predecessors

Diesel technology has vastly improved in the past 10-12 years, helped by advances in electronic control systems, which allow the control of the fuel injection to be integrated with the vehicle’s engine-management system, and by improved manufacturing tolerances needed for the latest injectors.

Modern direct-injection diesels have 20 per cent better fuel efficiency than their indirect-injection predecessors, and 30 per cent better than petrol. Meanwhile, in the past 10 years emissions of particles have decreased by 90 per cent and of NOx by 95 per cent, even without adding NOx catalysts or particulate filters.

Common-rail injection, introduced in the late 1990s, was a major leap forward. Fuel is supplied to a pressurised tube or rail running along the top of the cylinder block. From this tube the fuel is precisely metered to each cylinder through individual injectors.

Second-generation common-rail injection, introduced on the Ford Focus TDCi, improved combustion quality by more precise control of the injectors, allowing the fuel to be cut off cleanly. Refinement was improved by making possible pilot injections at idling revs: that is, a small injection of fuel takes place milliseconds before the main one, which helped to remove the characteristic idling diesel ‘knock’ by making combustion of the fuel more even. Ford initially offered it on only top-of-the-range Ghia models because of the limited availability of facilities capable of meeting the tolerances and carrying out manufacture in essentially clean-room conditions.

First and second-generation common rail used solenoid technology for the injectors. Bosch’s recently introduced third generation uses piezo-electronic actuators which can be mounted very close to the injector needles, improving speed of operation and precision. It allows the Audi A8 to meet forthcoming Euro IV emission regulations without after-treatment, even in the four-wheel drive automatic version.

Rival supplier Delphi said it can achieve the same effect by sticking with cheaper solenoid technology in its third-generation system, but it is also working on piezo actuators for future versions.

VW uses a different system called pumpe-düse technology. This employs unit injectors in which fuel is delivered directly to the injector, dispensing with the common rail. Unit injectors can operate at pressures of up to 2,050 bar compared with common rail’s 1,600 bar, which VW says provides finer atomisation of the fuel, improving emissions and efficiency. Again pilot injections are possible.

New US regulations will be challenging especially for NOx emissions, according to consulting engineers Ricardo. It expects solutions to include NOx traps and reduction of NOx formation in the combustion chamber by using exhaust gas recirculation to reduce combustion temperatures.

Sidebar: Rise of the diesel

Diesel’s onward march continues – at both ends of the car spectrum. Fiat claims the 1.3-litre 16-valve 70bhp MultiJet diesel offered in the Punto and Idea is the smallest second-generation common-rail turbodiesel in the world.

Later this year BMW launches the 535d, with two-stage turbocharging, developing 272bhp, 569Nm of torque at 2000rpm and accelerating from 0 to 62mph in 6.6 seconds.

In 2002, 42 per cent of passenger cars sold in Europe were diesels. They were most popular in France and Belgium, both with over 60 per cent of sales.

The fastest-growing market segments for diesels were small hatchbacks, where the Peugeot 206 is the bestselling model, and the family saloon and executive saloon classes, which accounted for 28 per cent of the diesel market and where the VW Passat and the Mercedes C-Class were top sellers.

Diesel accounts for 58 per cent of sales in the Passat class. In the executive class nearly 70 per cent of the Mercedes E-Class sold are diesels.