1. In the first of a new series covering the
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run-up to Euro-6, we begin by reviewing the journey from Euro-1 to -6. It hasn't been plain sailing...
Words: David Wilcox It's been quite some journey. After 20 years, and billions of euros spent on research and development, the truck engine has gone from pariah to shining example of environmental engineering. Terms like 'barely measurable' and 'near zero' are being used to describe Euro-6 truck exhaust emissions. The scale of the improvement is evident in the two accompanying charts, showing how maximum limit values of the two key pollutants, particulates and oxides of nitrogen (NOx), have been whittled away with each successive tier of Euro emission regulation.
The neatly stepped reductions suggest this has been an orderly, well-controlled programme Far from it. Truck manufacturers have been frustrated by European legislators' prevarication in fixing limits, complaining that the delays robbed them of crucial development time. And implementation of each Euro limit has led to feast and famine for truck production, as operators adjust vehicle replacement programmes to defer purchase of the cleaner but more expensive trucks.
More importantly, the new limits have all too often failed to produce the real-world improvements expected. For example, back in 2003 Graz University of Technology in Austria published results of a four-year study that found Euro-2 truck engines on average emitted 10% more NOx than Euro-1 engines, despite Euro-2's NOx limit being 12.5% lower than Euro-1's. The Graz engineers attributed this to the fact truck manufacturers had moved up to electronically controlled fuel-injection for Euro-2 and were using its precise management to jump through the legislators' hoops. In a nutshell, injection timing was retarded during steady-state running at the 13 test points on the certification procedure, minimising NOx production to hit the Euro-2 limit. However, injection was advanced for normal transient operation, optimising fuel consumption at the expense of NOx emissions, which ended up higher than at Euro-1 for in-service trucks.
The German environment ministry, the Umweltbundesamt (the UBA, which, together with Swiss and Austrian environment authorities, commissioned the Graz study) accused truck manufacturers of conforming to the letter of emission legislation rather than its spirit. This was a deliberate strategy, motivated by commercial pressure to achieve the best fuel consumption, according to the UBA. This so-called 'cycle-beating' continued at Euro-3; the UBA calculated that by the time Euro-4 was implemented in 2006, total NOx emissions from trucks and buses in Germany would be 50% higher than forecast. This effect was replicated throughout Europe.
Similar cycle-beating had already occurred in the US in the mid-1990s, when the US government's Environmental Protection Agency (EPA) accused seven truck and engine manufacturers, including Volvo Trucks, Cummins and Detroit Diesel, of using electronic defeat devices in their engine management to circumvent US NOx limits. The EPA was prepared to prosecute the companies for violating the US's Clean Air Act, but agreed to settle the matter out of court in 1998. It was reported to have cost the seven companies around $1bn one way or another, including rectification of the engine management of all the trucks in question.
Unlike the EPA, European legislators decided not to mount a legal challenge against truck makers about cycle-beating on this side of the Atlantic.
Euro-3 was not just a disappointment in terms of NOx reduction: evidence suggests that it did little to reduce particulates too, even though the limit was 33% lower than Euro-2's, down from 0.15hg/kWh to 0.10g/kWh. This time, it had nothing to do with cycle-beating. Scania data from 1999 shows particulate emissions of its Euro-2 engines were typically 0.07g/kWh, just half of the Euro-2 limit. As Scania's engineers sought to cut NOx to meet the tougher Euro-3 limit, the particulate emissions of its Euro-3 engines actually rose to 0.09g/kWh, compromised by the usual trade-off between particulates and NOx. This was not an isolated case; data from Volvo Trucks also indicates that its Euro-3 engines emitted more particulates than some of its Euro-2 engines. Truck makers were complying with the rules but actual emissions were not necessarily tracking downwards in line with the limits, suggesting that legislators and truck makers were not on the same page.
Reduced Pollution Certificate scheme It was the surprisingly low particulate emissions of some Euro-2 engines that allowed thousands of standard trucks to take advantage of the UK government's Reduced Pollution Certificate (RPC) scheme, cutting their annual vehicle excise duty (VED) by £1,000 a year. The RPC's qualifying threshold had been set in 1999 at well below Euro-2's particulate limit, in the mistaken belief that operators would need to fit expensive diesel particulate filters (DPFs) to achieve it — hence the VED incentive. It proved a costly misjudgement for the government, with 44,000 trucks qualifying for the RPC scheme before the qualifying criteria were tightened and the RPC's value was halved in January 2001. Around 80% of them had no DPE Although Euro-2 and -3 did not produce all the air-quality improvements expected, at least their on-cost for truck operators was negligible. The deterioration in fuel consumption between Euro-2 and -3 was tiny in most cases and forecasts of premiums of £2,000 or so for Euro-3 engines turned out to be exaggerated.
Euro-4 called for substantial reductions in both NOx and particulates, so for most trucks that entailed the addition of SCR exhaust after-treatment systems. That added around £3,500 to tractor unit prices in most cases, plus the on-cost of buying AdBlue. There was a weight penalty too, around 140kg for a typical tractor's SCR system. Operators could now feel the cost of cleaner exhausts.
Another sizeable cut in NOx was all that was required for Euro-5, easily handled on an SCR engine by increasing the AdBlue dosing rate, so there was no justification for a price hike. EGR engines needed to recycle a greater proportion of their exhaust gas to meet Euro-5, and that was not quite so simple. Scania and MAN both added a second stage of EGR cooling; Scania changed the fuel-injection system and moved to variable geometry turbocharging, while MAN opted for two-stage turbocharging But once again, real-world testing, carried out in the Netherlands and Germany, shows that Euro-4 and -5 engines fail to achieve all the expected NOx reductions. The problem lies in urban areas where slow running leads to low engine loads and thus cool exhausts, restricting the NOx conversion rate of heatcritical SCR systems (trucks using EGR rather than SCR do not suffer from this). This time, it is flawed legislation that must carry the blame. Euro-4 and -5 emissions test cycles do not include cold starts and under-represent low engine-load conditions, and so fail to model the cool exhausts of urban operations.
And so we arrive at Euro-6, arguably the least costeffective of European emissions legislation. It delivers another sizeable NOx cut but only a tiny reduction in particulates, and carries a high penalty in terms of added complexity, higher capital cost, deterioration in fuel consumption and additional weight.
Fuel consumption suffers because of the back pressure generated by the small chemical plant in a Euro-6 exhaust system — diesel oxidation catalyst, DPF,AdBlue injection, SCR catalyst and ammonia anti-slip catalyst — and the possible need to burn extra fuel to regenerate the DPE Truck manufacturers claim their Euro-6 models will be at least as fuel-efficient as their Euro-5 counterparts, but that is because fuel savings are coming from elsewhere, such as revised gearing, improved aerodynamics, smarter control of auxiliary components or even an entirely new engine design. It is a similar story on kerb weight. The addition of EGR and a hefty exhaust after-treatment box adds around 200kg to most tractor units and 100kg-150kg on two-axle rigid chassis. Once again, truck makers have sought to mitigate this by finding weight-savings elsewhere on the chassis, with Daf, for example, claiming its Euro-6 XF tractor is just 140kg heavier than the Euro-5 model.
Money, money, money The extra cost of Euro-6 gets lost among the upgrades and model revisions, but sums of between £5,000 and £10,000 are mentioned in relation to tractor units. It's not just the extra hardware, the catalysts and the plethora of costly emissions sensors: billions of euros spent on R&D have to be recouped too. Although Euro-6 has a poor bang-for-buck ratio, its salvation is that it promises to actually deliver the anticipated emissions improvements. Legislators have come up with robust test methods and implementation rules, determined to make sure that none of the air-quality benefits will go missing between engine test cell and the high street.
Particulates are now measured in terms of their number as well as their mass, thus limiting emissions of the tiniest of particles that penetrate the deepest part of lungs and so are most injurious to health. This compels fitment of highly effective wall-flow DPE Second, there are new test cycles, resistant to cycle-beating and designed to accommodate cool exhaust conditions that catch out SCR systems. Third, new 'in-service conformity' testing means truck manufacturers will be responsible for testing a sample of in-service trucks up to seven years old, using PEMS (portable emissions measurement systems) to measure emissions in real-world conditions.
These 'off-cycle' results must not be too far away from type approval values, leaving little scope for deterioration of emissions equipment and preventing use of cycle-beating engine-management strategies. And NOx control systems must be protected by new anti-tamper safeguards, so disabled or reduced AdBlue injection results in an initial dashboard warning, followed by a 25% torque reduction and then a speed restriction to just 20km/h (12.4mph).
This dash through two decades shows European truck emissions legislation has travelled a surprisingly tortuous route. Euro-6 rules appear to be so thoroughly constructed that the chances of yet another surprise twist look remote. •