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19th May 1994, Page 32
19th May 1994
Page 32
Page 32, 19th May 1994 — VANS
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Which of the following most accurately describes the problem?

EMISSIONS

Vans have had it easy for far too long. Emissions laws have added to the cost and complexity of cars and heavy commercials for 20 years, but have not been so rigorously applied to LCVs. In a few months' time, new European legislation will shake up the market, removing a loophole that excused light commercials from the latest emissions requirements; some manufacturers will have to drop some of their engines, some will tweak them to keep them going, while others have introduced completely new ranges.

• Legislation

Euro-1 (properly called Directive 91/542/EEC) and Euro-2 apply to heavy vehicles, while petrolengined passenger vehicles now need catalytic converters and engine management systems to comply with Directive 91/441/EEC. The most obvious result of this is that fuel injection no longer has much cachet.

The impending Directive 93/ 59/EEC brings light commercials more into line with passenger vehicles, and applies to new registrations from the 1 October 1994 (and vehicles Type Approved since 1 October 1993). It specifies emissions levels (for spark-ignition or diesel vehicles) for each of three weight bands of commercials (see table): The limits in the lightest weight band correspond directly with car requirements. The legislation concerns three aspects of emissions: carbon monoxide (CO), hydrocarbons plus nitrogen oxides (HC+NOx) and particulate emissions (PM). Carbon monoxide is itself poisonous, while nitrogen oxides and hydrocarbons encourage the formation of poisonous ozone, and ultimately smog. Particulates are the subject of most alarm at the moment: they have been implicated in cancers, though there is no conclusive proof of such a link.

Emissions are measured in grammes per kilometre (g/km) over a set driving cycle, including transient conditions. Such figures cannot be directly compared to the heavy duty diesel requirements: these are measured in grammes per kilowatt-hour (g/kWh) over a different cycle of steady-state conditions.

• Technology

Diesel engines are inherently more efficient than Otto-cycle spark-ignition engines, so they have some advantages in the battle against emissions. A small diesel should produce far less carbon monoxide and fewer unburnt hydrocarbons than an uncatalysed petrol engine, as combustion is more complete. A petrol engine with an oxidation catalyst (a "two-way" catalyst) has levels of CO and HC reduced more than ten-fold, but CO levels are still higher than for a diesel. The high temperatures that a catalyst requires are more quickly achieved in a diesel, and may not be achieved at all by a petrol engine during a typically short urban journey.

Nitrogen oxides are more difficult to de z: with: improved oxidation cuts CO and HC lev els, but it results in more NOx—a reduction process is needed. Petrol engines can employ a "threeway catalyst" to cut NOx by up to 95%, but a diesel's excess air mixture makes this impractical. Exhaust gas recirculation (EGR) lowers combustion temperatures and cuts NOx, but at the same time reduces efficiency.

Particulate emissions are a thorny problem for diesel engineers: they are improved by better combustion and an oxidation catalyst, but research continues on practical particulate traps to reduce emissions drastically, in line with proposed future legislation. Another consideration is fuel quality: low-sulphur fuel discourages the formation of acids that reduce the effectiveness of an oxidation catalyst.

For the time being, the ideal combination of features is a direct-injection charge-cooled diesel (for efficiency) with a twoway catalyst (for low CO and HC) and EGR (to reduce NOx levels); electronic engine management would ensure the correct mixture, improving combustion and reducing maintenance needs. This is now available. Particuiates (Om) 0.14 0.19 0.25

• Manufacturers

LDV (formerly Leyland Daf Vans) has had to rethink its range: the 200 Series' Perkins Prima 2.0-litre DI diesel engine is efficient, but will not satisfy the new requirements. Its October replacement will almost certainly be the Peugeot XUD9A 1.9-litre unit. The LDV 400 Series will continue with a larger Peugeot-derived diesel and turbodiesel—it may get the new DJ5 engine.

Ford has recently revised its range of car-derived vans, dropping the carburetted petrol models and making EGR standard on 1.8-litre diesels. The Transit too has EGR on all versions of its 2.5-litre DI diesel, including the catalyst-equipped, electronically controlled 84hp turbodiesel.

Volkswagen has long emphasised environmental policy and one of the first European firms to fit catalytic converters to petrol

cars, VW also pioneered the catalyst-equipped diesel. Its Umwelt ("Environment") turbodiesel was claimed to be the "cleanest" car engine in the world: it has been superseded in the Golf Van by a naturally aspirated version, said to meet 1996 regulations—as do VW's other diesels. A DI diesel should be on its way for the Transporter, and this may benefit from electronic control.

Fiat has thrown every feature currently available into the top-ofthe-range engine for its new Ducat(); this 2.5-litre SOFIMsourced turbodiesel incorporates direct injection with EDC (Electronic Diesel Control), a charge-cooler, EGR and a twoway oxidation catalyst. PM levels are claimed to be half the EC limit. The 1.9-litre diesel is also available with EGR and a catalyst. The new Fiorino, too, has the choice of an EGR-equipped diesel or a catalysed petrol engine.

Peugeot and Citroen, Fiat's Sevel partners, have taken a different approach to their own flagship 2.5-litre diesel for the Boxer and Relay. The indirectinjection PSA DJ5 has three valves per cylinder for improved combustion, while the turbocharged DJ5T variant also has a catalyst. Both have mechanical fuel injection, as do the smaller XUD9 models.

Vauxhall's car-derived vans already comply with EC 93/59, but the Japanese-derived Midi and Brava may need modification. GM fits its passenger turbodiesels with two-way catalysts—this could become standard on LCVs and has traditionally absorbed the cost of new emissions legislation.

Nissan's Sunny Van is fitted with EGR, and the 2.0-litre Vanette will comply with the new rules, but the position of the 2.5litre engine used in the Cabstar, Urvan and D21 pick-up is uncertain.

Rover has the biggest change of all to its commercial range: the Maestro van, powered by the MDI diesel (the Perkins Prima by another name) is to be dropped, and will not be replaced.

LJ by Toby Clark

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