The acceptability of diesel as a fuel for the UK’s urban buses now hangs in the balance, with a few locally-elected politicians likely to decide its fate. However, asks Richard Simpson, can they be trusted to make the right choice when history shows their predecessors have often got it so badly wrong in the past?
Historically, the bus industry has used a variety of fuels to power its vehicles. In the 1830s, coal-fired steam-buses were the height of technical innovation. Running primarily between towns on routes not covered by railways, they slashed running costs in half when compared to horse-buses or stagecoaches, did far less damage to roads, and offered enhanced safety thanks to their progressive brakes and greater stability.
However, and not for the last time, the British Government of the day was swayed away from progress by a very vocal lobby who won the day not by presenting logical argument but by[wlm_nonmember][…]
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Turnpike Trusts, which were in most cases controlled by local landowners, imposed very high tolls on steam vehicles using the country’s main road network, although tests by civil engineers of the day proved that they did far less damage to the highway surface than horse-drawn vehicles did. While horse-drawn vehicles ran on narrow metal tyres and cut through the road surface, steam-vehicles featured wide wheel-rims that actually consolidated the roadway by ironing out the indentations left by horse hooves.
In 1861, the landowners who dominated Parliament introduced the Locomotive Act (singular), which restricted steam vehicles to speeds of just 5mph in town and 10mph on open roads. This was followed by the Locomotives Act (plural) of 1865 (better known as the Red Flag Act) which reduced rural speeds to just 4mph and town speeds to half that.
Furthermore, local authorities were given the power to regulate the hours within which powered vehicles were permitted to operate on ‘their’ roads.
Faced with such a barrage of hostile legislation, steam buses were forced off the road, to only return when the Red Flag Act was repealed in 1896. Steam buses, some fired by oil which allowed a far quicker warm-up to operating pressure than coal did, continued in use until around 1923, but the hiatus in development caused by the two Acts had effectively stalled technical progress for too long for steam to recover.
Electricity vs petrol
Two new power technologies were now in the ascendency: electricity and petrol. The first petrol-engined vehicles to run a UK bus service that we would recognise as such today appeared in Edinburgh in 1898. Hybrid drivelines were very popular in the early days of the motor bus: W A Stevens built a practical petrol-electric hybrid in 1906, and after successful installations of the Stevens driveline in Halford and Dennis chassis, the technology was taken up by one of the biggest bus operators of the time: Thomas Tilling; to produce the Tilling-Stevens chassis which was also supplied in large numbers to other operators at home and abroad. Drivers and passengers often preferred the smooth drive of the hybrid to the jerky crash gearboxes found in mechanical transmission vehicles of the time.
The outbreak of the First World War effectively killed the early hybrid. The War Department rejected petrol-electrics as unsuitable for operation in harsh front-line conditions, and thousands of men (and some women) were trained to drive vehicles with mechanical transmissions in the service of their nation. Manual gearbox technology itself was greatly improved in response to the needs of mechanised warfare, and the post-war release of thousands of ex-WD chassis and men with the skill to drive them meant hybrid technology was pretty much sidelined by 1930.
This didn’t signal the end for electric traction though. Trolleybuses had been first demonstrated in Berlin in 1882. Leeds and Bradford both got trolleybuses running in 1911. Tilling-Stevens was able to transfer its electric technology to trolleybus application in 1923, when Wolverhampton Corporation decided to remove the tram rails which were causing problems to other road users on one of its main routes, but retain the overhead power supply for trolleybuses. As the Corporation was already an operator of Tilling-Stevens petrol-electric motor-buses, it made sense to ask the company to produce a chassis that drew its electrical power from an overhead external source. A hybrid trolleybus: capable of running either from overhead wires or on its own petrol engine-generator pack; was also developed, but saw little uptake.
Meanwhile, the march of pure petrol buses continued apace from its pre-war beginnings. Automotive technology pioneer Maudslay Motor Co had already produced the world’s first double-decker motor bus in 1905, which was notable for its advanced overhead cam 6.44-litre four-cylinder engine. London General Omnibus Company built and operated the B-type bus with a conventional petrol driveline from 1910. Arguably the first mass-produced standard bus in the world, in addition to their normal service, vehicles of this type famously operated in a variety of roles in France during the First World War with nearly 1,000 examples being requisitioned for service. The successor post-war model K-type featured a 30 hp 4.4-litre four-cylinder engine, and, trolleybus routes aside, firmly embedded petrol as the fuel of choice for the bus industry.
This was only for a short while. In 1923, the first farm tractor with what we would recognise as a modern diesel engine appeared in Germany. German truck manufacturers launched diesels at the IAA Show in 1924, and in 1927 Robert Bosch started making injection pumps and injector nozzles specifically for truck and bus engines.
It looked like diesel would take over the world as applications spread from agriculture and heavy-duty road-going engines to some passenger cars and even aircraft. AEC, the rebranded spin-off of London General’s bus manufacturing operation, rapidly switched to the new power source, along with the rest of the rest of the British bus industry.
‘Producer gas’
Until World War II, that is, when the old petrol-engined buses underwent something of a temporary renaissance. Spark-ignition engines could be persuaded to run, badly, on a horrible confection called ‘producer gas’ which consisted of carbon monoxide, hydrogen, nitrogen and carbon dioxide, that was given off when damp coal or wood was partially combusted.
The opportunistic Frederick Heaton, who had ousted all members of the Tilling family from the Thomas Tilling board to become company chairman, knew a potential money-maker when he saw one, and convinced the war time Government that significant amounts of valuable fuel could be diverted to the front-line if the UK’s bus operators could be made to convert 10% of their fleets to run on producer gas, which would be generated in trailers (which, conveniently, his company was in a position to manufacture) towed behind the vehicles.
Purely coincidentally, Thomas Tilling won a lucrative contract to build 2,500 producer gas trailers at its Bristol works, and Heaton was awarded a knighthood by a grateful nation. The only problem was, the technology didn’t work very well.
The engines had to start up on petrol. When they switched to gas, power dropped by 40%, and the engines had to be kept running fast to draw enough air through the convoluted pipework linking trailer to engine air intake to stop the fire going out. Bus conductors understandably refused to have anything to do with the trailers and their lethal output, so re-stoking on the move was impossible. After 80 miles, the supply of primary fuel on the trailers was exhausted, so arrangements had to be made to pick up refreshed trailers during the shift.
There is also evidence that some diesel buses were converted to producer gas, presumably with a small amount of diesel still being injected to act as an ignition medium.
Hated and feared by passengers, crew, managers, and the poor unfortunates who lived alongside the routes that they operated alike, the producer gas buses are typical of what can happen when a clever if unscrupulous businessman wins the ear of politicians with a solution to a perceived problem. The reality was that with private motoring tightly restricted, the UK never faced any serious shortage of oil-based fuels for war purposes. Indeed, various inventive and spectacular ways to consume the generous supplies of petrol being landed in the UK were continually being devised throughout the duration of the war. The real constraint on wartime bus operation was the provision of replacement tyres, as many rubber plantations were in the hands of the Japanese.
Diesel dominates
Peace and sanity returned in 1945: and with it the diesel engine rose to absolute domination of the British bus market. Where the infrastructure could be put into place, trolleybuses had a significant role to play too, but as diesel engines improved, the advantages of electric traction (quiet, fume and vibration-free operation) were eclipsed by their seemingly ever-growing performance and operational flexibility. Local politicians backed diesel against electricity.
The last trolleybus line in the UK, in Bradford, closed in 1972 – ironically just before the world’s first ‘oil shock’ of 1973, when OPEC nations slashed crude output to force the USA to pull Israel back into line during the Yom Kippur War. No doubt the bus bosses of the time consoled themselves with the prospect of North Sea oil being available to calm any price instability in the future.
Diesel has reigned pretty much unchallenged as the ‘one fuel for all purposes’ ever since. Issues over pollution have been countered by improvements in technology which saw emissions of particulates and NOx slashed by progressive European legislation. At Euro 1 (1992) emissions of 8g/kWhr of NOx and 0.612g/kWhr of particulates were permitted. When Euro 6 was introduced in 2013 the limit for NOx was reduced to 0.4g/kWhr and 0.01g/kWhr for particulates. There was also an actual limit on the number of particulates emitted, the engines constantly monitored their own performance to ensure the limits were adhered to, and the test cycles were very broad and reflected the wide range of actual operating conditions.
Euro 6 buses worked: urban bus routes which switched exclusively to Euro 6 operation saw a rapid improvement in roadside air quality. However, more generally, the good work done by the bus and truck manufacturers was undermined by the politically very powerful car industry, which persuaded European Governments that global warming concerns could be addressed by switching private motorists from petrol to the more economical diesel, and that the new generation of light-duty automotive diesels were both clean and green.
Testing
Of course, it didn’t turn out that way. Unrealistic test cycles produced artificially low levels of NOx from car exhausts, and some manufacturers ruthlessly ‘gamed’ the system with engines specifically programmed to downrate combustion temperatures (and hence NOx production) when the engine control unit sensed it was going through a test cycle.
The situation was further exacerbated by private motorists removing the PM filters from their vehicle exhausts, because they frequently clogged when diesel cars were operated in heavy traffic. Urban air quality suffered as a consequence.
Once the full ramifications of the ‘dieselgate’ scandal became apparent, it was open season on diesels of all size, even though it was accepted that heavy-duty Euro 6 diesel actually had cleaned the air up in many urban locations and that real-life tests on Euro 6 vehicles revealed that modern diesel buses and trucks produced less NOx on a vehicle vs vehicle basis than small diesel cars.
Roadside tests in Norway on a range of vehicles showed that, on average, the seven diesel cars tested emitted four times the amount of NOx than the average for trucks and buses. NOx, the testers concluded, had been “effectively removed” from the exhausts of heavy-duty diesels.
By then, any hope of proportionality had been thrown out of the window. A figure of 40,000 UK deaths from diesel fumes each year was widely quoted, but was in fact produced by the addition of two over-lapping and fairly arbitrary estimates for deaths from air pollution generally. A leading expert in respiratory health described it as “a zombie figure that will not go away,” but its proponents continued to advance it regardless.
The inconvenient truth is that London, with the worst air quality in the south-east of England, also has the lowest death rate, and Westminster, with the worst air quality in London, has the longest life expectancy in the country. In contrast, Scotland, with the UK’s cleanest air, has the UK’s highest death rate. Incidents of cancer per 1,000 head of UK population are lowest in London and highest in Scotland.
In short, it’s difficult to discern any impact from air quality on the population as a whole, although there is no doubt that a small number of people do suffer respiratory problems because of it.
Future fuels
Labour London Mayor Sadiq Khan, himself the son of a London bus driver, has pledged to stop buying diesel-only double-deckers for London from next year and make all new single-deckers zero-emission. In practice, this will mean a policy of hybrid or non-diesel double-deckers and electric or hydrogen single-deckers.
With elected mayors in Cambridgeshire, Greater Manchester, Liverpool, Tees Valley, the West Midland and the West of England all having been granted transport responsibilities, it would be a foolish bus company manager that did not bet on at least some of them going for headline-grabbing initiatives similar to Khan’s.
In truth, the London hydrogen initiative predates Khan’s election. Hydrogen buses using fuel cell technology which converts the chemical energy in hydrogen into electricity by combining it with atmospheric oxygen to produce water, started regular operations on London’s RV1 route back in 2010, after an earlier trial finished in 2007. While the fleet was temporarily taken out of use a year later following a fire on one vehicle that was unrelated to its hydrogen system, the buses are continuing in service.
Speaking at a recent conference organised by Shell, Michael Copson, the company’s Hydrogen Business Development Manager said that critics had often unkindly dubbed hydrogen as “the fuel of the future…and it always will be.”
However, there were now 15 hydrogen filling stations in the UK and, he said: “Costs are coming down, and political and environmental pressures are driving the acceptance of hydrogen as a road fuel forwards.
“There are advantages in reducing local air pollution as well as global carbon output,” he argued. “But to achieve these with hydrogen we need cooperation between the vehicle manufacturers, Governments and ourselves.”
Scott Macgregor, Shell’s UK Commercial Fleet Sales Manager, said: “In future, fleet managers are going to need a diverse energy portfolio which may include hydrogen, CNG, and electric vehicles.
“To a certain extent, the choice becomes a chicken and egg situation: which comes first: the infrastructure or the vehicles?”
He added that the fuel of choice would be driven very much by the application of the vehicle: hydrogen fuel cell, battery electricity or similar zero-emission technology in cities, natural or biogas in the suburbs and on medium distances, and diesel on longer journeys.
What are the pros and cons of hydrogen as a fuel for city buses?
The first myth to knock on the head is that hydrogen is dangerous. Properly handled, it is not. Hydrogen was unfairly demonised by the spectacular crash of the Hindenburg air-ship back in 1937, which occurred for reasons that have never been absolutely determined but, in reality, it is far less dangerous than oil-based fuels if properly handled. Gas tanks are stronger than diesel tanks and are designed to vent upwards. Hydrogen will not ignite on its own, it needs to be mixed with oxygen or dispersed into air before it will burn.
Unlike oil fuels, which puddle when released, spilled hydrogen will disperse rapidly up and away from any crash site. It has an auto-ignition temperature of 500°C: the equivalent temperature for diesel is 256°C.
The real problem with hydrogen is making enough of it. Its proponents point out that it is the most common element in the universe: what is not so often acknowledged is that here on Planet Earth it has combined with oxygen to form water, and our nearest source of large quantities of pure hydrogen is the sun.
It can be produced from methane, but this releases carbon dioxide to the atmosphere and effectively just turns one fuel into another, or it can be produced by electrolyzing water. Would we compromise water supplies by turning large quantities of it into hydrogen?
It takes just over nine litres of water to produce a kilogramme of hydrogen, which co-incidentally is about the same as the amount of water needed to refine an energy-equivalent amount of petrol or diesel, so it would seem not.
The bigger issue is compromising current electrical supplies. At 100% efficiency, you need almost 40 kW/hr of electricity to produce a kilo of hydrogen. Current equipment runs at 60-70% efficiency. If hydrogen is electrolysed using energy direct from the national grid then this will clearly put an unsustainable load on an already creaking system: increasing the generating capacity of the national grid is a highly problematic issue and whichever way you look at it, using electricity to produce hydrogen means inputting more energy than can be recovered when the hydrogen is passed through a fuel cell and turned back into water.
Proponents for hydrogen argue that this is looking at the problem the wrong way. Renewable energy sources such as wind and solar are unpredictable and largely uncontrollable. Conventional electric vehicles may not be in a position to make the most of occasions when renewable power generation peaks: a recent announcement by a small ‘green’ UK operator that their electric bus would be charged up by solar energy when it returned to the depot at night indicates just where the problem lies!
Hydrogen offers a workaround, in that excess peak power generation capacity can be used to electrolyse hydrogen, which can be stored until it is required. As such, it could form a useful component of the palette of fuels which may be required to operate buses in large conurbations.
It is by no means the only solution. Scania and Cummins both offer conventional diesel bus engines that, today, will run on a renewable fuel of tomorrow: hydrogenated vegetable oil (HVO). HVO is a clean-burning synthetic diesel that can be made from virtually any organic waste, including slaughterhouse waste. The downside is slightly lower power outputs and higher fuel consumption than mineral diesel as its calorific density is lower. There is also methane, which can be used in compressed or liquid form (CNG or LNG), and is available as a renewable in the form of bio-gas. Methane is probably the next attainable step in cleaning up exhaust emissions beyond Euro 6.
Conclusions
At the moment, the future of fuelling the bus industry hangs in the balance. Heavy-duty diesels have been tainted by the poor performance of their automotive cousins: even 70% of the new Euro 6 diesel cars exceed their NOx limits by 100% in real life conditions according to the latest report from respected independent testers Emissions Analytics, and the uninformed bystander is likely to conclude that ‘bigger is badder’.
History, as outlined in the first part of this article, shows how the bus industry has repeatedly suffered from wrong decisions made by politicians who paid too much attention to vested interests, since its inception.
Today’s bus operators must do what they can to counter the latest barrage of misinformation coming from those whose true motivation is more political than environmental and ensure that future fuel choices are made on the basis of something other than blind prejudice.[/wlm_ismember]
