The pressure on bus and coach operators to cut exhaust emissions is unrelenting. So how should they go about it? John Lewis considers the options
MAN is European market leader so far as gas buses are concerned and has been selling hybrid buses since 2010, says MAN Truck and Bus worldwide Chief Executive Officer, Joachim Drees. He is convinced however that pure electric buses are likely to dominate in the coming years, at least so far as big-city transport is concerned.
“Because cities want to go zero-emission, the only choice for urban buses in future will be electric drive – and that will certainly be the case from 2025 onwards,” he told transport journalists at a recent press conference in London. [wlm_nonmember][…]
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“As a consequence an MAN electric city bus will be in series production from the end of 2019. I believe that the future of urban transport will be very much electric and that this will be true for the transport of people as well as goods,” he said.
Rival manufacturers such as BYD, which has enjoyed success in London in particular, would doubtless agree with him – and would point to the low pence-per-mile running costs enjoyed by electric transport as well as the absence of tailpipe emissions; battery buses are now being seen in increasing numbers outside the capital. To take an example at random, Go North East has been trialling a Chinese-built electric Yutong single-decker on its X66 route between the Gateshead Interchange and the vast Metrocentre shopping complex. Yutong’s UK distributor is Castleford, West Yorkshire-based Pelican.
Not that the dash to battery power is without its challenges, Joachim conceded, not the least of them being the still-steep front-end price of the vehicles concerned. If the weather is wintry and a diesel-fired heater is not fitted, then 50% of the battery pack’s output will go on keeping the passengers warm, he observed – and that shortens the distance between recharges. “Then there is the question of how long the batteries will last,” he said. “At present we’re looking at a life of about six years and you then have to decide what you are going to do with them afterwards.”
To all the foregoing can be added the mechanics of charging up, say, 100 buses when they return to the depot after a day’s work. Where exactly do you plug them in, to what degree will the local electricity infrastructure need to be upgraded to cope with the current draw, and who is going to pay for it?
A further concern surrounds the safety of vulnerable road users. Electric buses run silently, so some degree of deliberate noise generation is required to ensure that cyclists and pedestrians crossing the road hear them coming. That assumes, of course, that they are not wearing headphones.
Dash for gas
As MAN’s own involvement with gas buses indicates, battery power is by no means the only solution. That is certainly the view taken by Nottingham City Transport (NCT) and by MAN’s sister company Scania; both manufacturers are owned by Volkswagen. NCT can claim to have the world’s biggest fleet of biogas-fuelled double-deckers in service, now that the 53rd ADL-bodied biogas Scania it ordered has arrived. They represent a total investment of £16.8m, with £4.4m contributed by the Office for Low Emission Vehicles (OLEV); switching to alternative fuels invariably involves a contribution from the taxpayer at some stage.
Biogas is a natural gas that can be produced through anaerobic digestion which consumes sewage and food and agricultural waste. They are all, of course, eminently renewable. The process generates methane which can then be turned into fuel. The biogas fleet will help cut NCT’s annual CO2 output by over 3,500 tonnes, NOx output by 35 tonnes and particulates by 0.75 tonnes.
“With carbon dioxide emissions reduced by up to 84%, the introduction of this fleet represents an important milestone for NCT and Scania,” said Scania UK Bus and Coach Fleet Sales General Manager, Mark Oliver. “We’re sure that many other public transport operators around the country will now look to follow Nottingham’s lead.” The city is one of several scheduled to introduce a Clean Air Zone in a bid to improve local air quality.
Choose gas and you need appropriate refuelling facilities. Nottingham-based biogas infrastructure specialist, Roadgas, has built NCT’s facilities at its Parliament Street garage – with the OLEV funding referred to earlier helping to cover the cost. Specialists such as Gasrec can deliver liquefied natural gas (LNG) – which can also be dispensed as compressed natural gas (CNG) – to operators by tanker. Meanwhile, Roadgas can construct a station that will supply CNG direct from the local gas pipeline.
Gasrec argues that a dedicated CNG engine produces up to 99% fewer particulates and 70% fewer NOx emissions than a Euro VI diesel. Iveco adds that CNG’s CO2 output is 10% below that of diesel, while biogas’ is more like 80% to 90% lower – the sort of figures NCT and Scania also have in mind.
Methane slip – the loss of unburned methane – can be an issue for LNG, but doesn’t affect CNG or biogas. LNG and CNG are approximately 25% cheaper than diesel, but the engines that burn them are around 10% less efficient than their diesel equivalents. Plus, gas vehicles can cost approximately 20 to 25% more than diesel models, although as indicated earlier the premium can be offset by government subsidies.
There are various ways of ensuring biogas is included in the gaseous fuel mix. In the case of NCT, biogas is withdrawn from the closest national gas grid point to the Parliament Street depot, where it is compressed and stored until the buses are refuelled at night. Designed for future expansion, the refuelling facility is available for use by third parties.
LNG, CNG and biogas are not the only gaseous fuels that can be employed. Ten hydrogen fuel cell buses built by Van Hool are in operation in Aberdeen, and 40 should be plying the streets of Cologne and Wuppertal in Germany come 2019.
Shape of water
The sole emission produced by hydrogen fuel cell buses is water vapour. They are painfully pricy however – the 40 destined for Germany are being funded by the country’s government – and the CO2 that can be generated by hydrogen production may place question marks over their environmental credentials.
Birmingham City Council hopes to rub out those question marks as part of a £13.4m project it is backing to put 22 hydrogen buses onto the streets in 2019. The hydrogen they use will be produced using renewable electricity from a gasification plant at Tyseley Energy Park, which burns waste wood. Again, OLEV funding is involved; and despite an ongoing age of austerity, there appears to be no shortage of government largesse for low-emission buses. Earlier this year, Transport Minister Nusrat Ghani announced a new Ultra-Low Emission Bus Scheme for England and Wales. Operators and local authorities can bid for a share of a £48m fund, which they can use to acquire hundreds of new ultra-low- emission buses as well as the infrastructure required to support them. The application window closes on June 30, although interested parties should have signalled their intention to submit an application by April 30 says the Low Carbon Vehicle Partnership.
So will much-criticised diesel soon be consigned to the dustbin of road transport history? Despite his espousal of battery power, Joachim does not think so – at least so far as transport outside congested urban areas is concerned: “Euro VI diesel engines are very clean and fuel-efficient and we have to keep explaining to politicians that they are part of the solution, not part of the problem,” he observed.
He does not believe that retrofitting Euro IV or Euro V bus engines with the equipment required to bring them up to Euro VI standard – an approach chosen by Transport for London – is a desirable course of action to take; hardly a surprising view from a manufacturer given that it means that fewer new Euro VI vehicles will be sold. “You get something similar to Euro VI but such systems are not subject to the same testing procedures,” he claimed.
Such criticisms are refuted by the companies involved in the TfL retrofit programme. Eminox points out that its SCRT (Selective Catalytic Reduction Technology) was the first retrofit system of its type to meet the requirements of the government’s Clean Vehicle Retrofit Accreditation Scheme run by the Energy Saving Trust. It certifies technology that complies with real-world Euro VI emission levels.
Other businesses that are programme participants include Amminex – now working closely with Eminox in the UK – Proventia, which is represented by Excalibre of Mitcheldean in Gloucestershire, Baumot and HJS. None of them are short of technical expertise. Amminex has cut NOx emissions from Euro V buses operated by Metroline to Euro VI levels, while Proventia has slashed Euro V NOx and NO2 output by nearly 99%.
Alternative view
An alternative approach to retrofitting a new emission control system is repowering. This can involve retrospectively installing a fully-electric zero emission drivetrain from a supplier such as Magtec, installing a diesel-electric hybrid system from Vantage Power or swapping an old Euro IV or V diesel for a cleaner Euro VI diesel from Cummins. Move from Euro IV to Euro VI and you will enjoy a near-90% cut in particulates and halve the vehicle’s NOx output, Cummins contends.
Showing a commendable ability to re-invent itself, at least in part, Cummins has developed a bus powertrain configurable for either a fully-electric or a range-extended electric vehicle. The latter is likely to employ a 2.8-litre diesel rather than the up-to-6.7-litre diesel that would have to be deployed in a conventionally-powered city bus model.
At the start of the year, Cummins revealed that it had acquired Johnson Matthey’s UK automotive battery business. Several months previously it announced that it had bought Brammo, which designs and develops battery packs for both mobile and stationary applications.
Selecting the right transmission when buying a new bus or coach can bring CO2, fuel consumption and emission cuts too.
Striking a balance
Allison has made a number of changes to its automatic transmissions, which it says could lead to potential fuel consumption improvements of up to 6.3%. It is the consequence of enhancements to its FuelSense software combined with DynActive Shifting, which it says make an infinitely-variable combination of shift points possible.
This in effect means that the transmission is constantly looking for just the right balance of fuel economy and performance, taking into account factors such as whether a vehicle is ascending or descending a hill or whether it is full or empty.
Opt for the Plus edition and you benefit from an improved version of Neutral at Stop. This cuts the load on the engine by shifting the transmission to neutral when the vehicle is stationary, thereby reducing fuel consumption and exhaust emissions. It comes with a locked output at stop to help prevent the vehicle from rolling backwards. A derivative is available which allows low-speed coasting – a fuel and CO2 saver.
Go for the Max variant and you get an enhanced version of Acceleration Rate Management as well. It limits the scope for aggressive and potentially risky driving by automatically controlling the engine’s torque, and allows acceleration to be restricted in line with a rate pre-determined by the operator.
Allison’s rivals ZF and Voith have both headed down the stop/start route. Voith’s DIWA.6 automatic box is available with it, and the resulting package has now been installed in well over 1,000 buses. Operators can enjoy fuel savings of between 10% and 12% as a consequence says the manufacturer.
Whichever direction the passenger transport industry heads in its ongoing battle to minimise its environmental impact and comply with ever-tighter emissions restrictions – often imposed by local authorities – one thing is certain: the journey won’t come cheap.
“In 2017 MAN invested around €640m in research and development, which is double what we spent in 2011 and 2012,” Joachim observed. He does not appear to be unduly concerned by this rising level of expenditure however.
“What with digitisation, electrification and autonomous driving, it’s the most exciting time for our industry since we replaced horse-drawn carriages with vehicles,” he remarked. “We are on the brink of radical change, and we are looking at this major turning point with confidence.”
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