What comes after Euro 6?

Euro 6’s approach was accompanied by scare stories about adverse fuel consumption and inflated maintenance costs. The reality is different, but it still posed a challenge to engine manufacturers. What next? Cummins has given its predictions. Tim Deakin reports.

Euro 6 was one of the biggest challenges ever faced by the engine manufacturing industry, and it poured billions into developing products that comply with the legislation not only in the test laboratory, but also under various operating conditions.

Among the first to bridge the gap to Euro 6 was Cummins. Its offering in the bus market is the four- and six-cylinder ISB range.

One of the key differences between earlier legislation and Euro 6 is that under the latter, engines must be proven to comply throughout ‘real world’ usage cycles, which in buses can be very demanding. That includes at various temperatures and under different load conditions. While earlier models performed well on test rigs, results in reality were often different.


In the real world

“The focus for Euro 6 is on ‘real world’ air quality control,” says Pete Williams, Cummins Product Environmental Group Director. “It really is more stringent than Euro 5. We count particulates now rather than weigh them, for example.”

“Euro 4 and 5 were great when tested, but there were questions over performance in the real world. That’s why there have been additional conditions added to Euro 6 legislation,” adds Communications Director – Europe, Middle East, Africa, CIS, Steve Nendick.

To ensure that these are met throughout the useful life of a Euro 6 engine – which in bus applications Cummins regards as seven years or 700,000km – continual monitoring takes place. When defined levels are exceeded a warning appears on the dash, and when NOx levels fail to conform, an engine torque reduction and vehicle speed limit are imposed.

That, says Mr Williams, “is about restricting people’s ability to tamper with the SCR system. The mission is to prevent journey completion in cases of tampering.”

He stresses that torque derating and speed limiting only occur when problems are detected with NOX emissions. That could be down to either AdBlue quality – indicating watering down, for example – or unusually low consumption, suggesting that the line has either been blocked or disconnected. Unrelated problems will merely drive dash warnings.


The next step: Euro 7?

Euro 6 is now established. What will follow is not yet completely clear, although a progression to Euro 7 is unlikely, say Cummins’ engineers. Instead, they predict legislation more focused on the vehicle as a whole, with CO2 emissions the most important consideration.

“There is a good feeling from manufacturers that there is no need for a Euro 7 if Euro 6 is successful at controlling air quality,” says Mr Williams. “We see no discussion around Euro 7. It’s important to demonstrate that Euro 6 products are complying throughout the seven-year useful life, but the focus will shift to fuel economy and CO2 going forward.”

Central to CO2 calculations will be VECTO, the Vehicle Energy Consumption Calculation Tool. VECTO will factor in other elements such as rolling resistance, drag and transmission efficiency to develop an overall vehicle efficiency rating, potentially leading to vehicle ‘labelling’ as already seen on tyres.

“Calculations will be whole-vehicle based, although [in its current form] VECTO could be improved,” continues Mr Williams. “It gives an opportunity to integrate engines with the whole vehicle, but we are concerned about optimisation of the whole configuration as one unit.”

Instead, Cummins favours adoption of methodology which considers two separate standards: the engine’s CO2 emissions and a vehicle element, including aerodynamic aids. This method would be less complicated than attempting a whole vehicle measurement, it says, and would also help drive engine improvements.

“Under VECTO, engine gains may be ‘buried’ under easier wins such as aerodynamic aids. The EU regulation can be made more effective by adding a [separate] engine element,” adds Mr Williams. As an illustration, Cummins is working on stop-start engine technology which will be compatible with non-hybrid buses. It is expected to debut in 2016, and in testing has delivered around a 5% improved fuel consumption.

The EU’s regulation concerning VECTO is due to be issued in late 2016, with roll-out beginning a year later. Initially it will apply to three segments, including coaches.

Buses are expected to come under VECTO from mid-2018 onwards; validating the process on “more transient operations” – among which are buses – will prove difficult as there is more variation of CO2 emissions in ‘real world’ bus work than in largely steady state testing.


Cutting consumption

Regardless of whether CO2 scoring includes a separate engine consideration, reduced fuel consumption will be vital under VECTO, and fully understanding duty cycles will enable engine optimisation post-Euro 6. Manufacturers now have the tools to accurately characterise real world operation, and this data will be central to some potentially big decisions on future policy.

“In terms of reducing emissions, Euro 6 has done the job very effectively,” says Bill Lamb, Programme Leader Darlington Technical Operations, and ongoing mandatory ‘real world’ testing of Euro 6 engines’ emissions means that they must still comply when at the end of their useful lives.

It’s because of this requirement that Cummins has used both EGR and SCR at Euro 6. Stringent NOX limits have impacted fuel consumption at low power outputs, and a catalyst working at higher temperatures is more efficient, says Mr Lamb.

Cummins’ view is that if optimum fuel consumption is to be achieved then operators must look very closely at engine selection.

“It is critical to specify the right engine for a particular situation, and match its size and rating to the application. A smaller or lower-powered engine comes with a smaller catalyst, which warms up more quickly. The aftertreatment unit is worked harder, which gives better fuel economy.

“We don’t advocate extreme downsizing, but it is worth looking at whether a lower-rated or smaller engine would be more suitable. It may deliver equal performance but better fuel economy.”

Cummins calls this ‘rightsizing’, and despite its 6.7-litre ISB currently being the largest engine offered in Euro 6 double-deckers, it believes that displacements will continue to reduce as understanding of buses’ duty cycles, and their impact on catalyst performance, grows.

Nevertheless, its engineers are also aware that a bus may work under more than one set of circumstances during its life. It uses the example of a double-decker spending its earlier years in London followed by cascade to higher-speed duties in the provinces as an example.

“The second life of a bus must be considered, but vehicles will become more specific to an individual task,” says Mr Lamb. Questioned on whether it would be possible simply to plug in a laptop and electronically uprate the engine’s output, he says that it’s unlikely. Some individual components within the power unit are dependent to its rated output.

Reduced fuel consumption, and more onus placed on packaging the engine and associated components within the bus as effectively as possible, may mean that VECTO will come as a breath of fresh air for coach and bus operators.