Step off the gas: Alternative fuel

Compressed natural gas and electric power are making inroads into the bus market, but what is there in the way of alternative fuel for coaches? Richard Simpson finds out

An unfortunate consequence of the Dieselgate scandal is that the opprobrium which was (rightly) heaped on the heads of those diesel car manufacturers who gamed emissions testing processes has spread to the manufacturers and operators of generally compliant heavy-duty diesel vehicles.

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Whilst operators may protest that Euro VI coaches, buses and trucks actually produce less in the way of NOx per vehicle kilometre than many modern diesel cars, there is increasing pressure on city authorities to be seen to be ‘doing something’ about local air pollution curtailing the access of diesel vehicles to sensitive areas. And non-compliant coaches and trucks are usually expected to pay much more by way of a toll for access to a Low Emissions Zone (LEZ) than vans and cars, even though engine size is a poor determinant of the actual level of emissions produced.

Non-compliant cars will pay just £9 to access the proposed LEZ in Bath, while all but Euro VI coaches, buses and trucks will have to pay £100 a time. It’s a similar story in many other towns and cities where LEZs
are proposed.

The problem is that the UK’s longest-running LEZ in London, has apparently had little beneficial effect on the very things it was supposed to protect: children’s lungs.

Researchers at Kings College, London investigated the respiratory health of more than 1,800 children attending primary schools near pollution hot spots in the East End, from 2008 to 2011. The researchers expected to see a decline in traffic pollution-related respiratory and allergic symptoms. When the figures came in, however, they found that the “LEZ has had no beneficial effect on these symptoms, up to three years after
its implementation.”

Now a rational person might conclude that there might be other causes than diesel engines for the poor respiratory health of London children. These could include a lack of exercise, high levels of air pollution indoors from frying food and aerosol sprays (both far worse than diesel engines), or the horrendous levels of particles, NOx and other toxins produced by urban hipsters’ wood burners.

But no. Diesels are now apparently not just one source of air pollution. They are the only source in the eyes of many prominent campaigners. And the insanity is not confined to the UK. Paris has introduced its own restrictions on diesel engines, with the objective of banning them from the capital altogether by 2020.

Late in 2016, in what could be seen as a precursor to the present Gilets Jaunes protests, over 300 touring coaches from France, Germany and elsewhere conducted a protest drive-through in Paris, with banners pointing out that ‘Pollution: Les autocars sont la solution, pas le probleme’ or Pollution: Coaches are the solution, not the problem, and ‘Pas de cars, pas de Touristes’ or ‘Without coaches, without tourists’ but to no avail.

Perhaps if the coach operators had burned down the Eifel Tower, someone might have listened.

Other sectors of the heavy-duty market have developed solutions including battery-electric and natural gas, but while these are readily adaptable for city buses and increasingly so for trucks, the unique construction constraints of touring coaches preclude their use in these vehicles for the present at least.

Challenges with biodiesel

So, instead, a less complex technical solution needs to be found. The industry at one time had high hopes for fatty acid methyl ester (FAME), commonly marketed as biodiesel. This can be manufactured from vegetable oils and animal fats (high molecular weight oils), which react with a short molecular-chain alcohol (methanol) in the presence of a catalyst (potassium hydroxide) to produce acidic lower molecular weight esters with glycerol (soap) as a by-product.

Blends of up to 7% FAME can be found in pump diesel, and fuels with content of  up to 100% are available, but its use can be problematic.

One significant issue is that methyl esters are hygroscopic, which is to say that they absorb water and hold it in suspension. Combine this characteristic with the biodegradable qualities of FAME and you can create a perfect breeding ground for moulds and bacteria to grow in the fuel. In contrast, when mineral diesel suffers water contamination, it sheds it to the bottom on the tank where it can be separated if necessary.

FAME supplier Crown Oil suggests users carry out regular visual inspections of their fuel storage tanks, plus looking for tell-tale signs such as poor or impossible starting after refuelling, erosive damage to vehicle fuel tanks and visible water droplets in the fuel. It also recommends a yearly professional check on fuel storage tanks and stocks.

Another issue is FAME’s suitability for use in high concentrations in modern vehicles. According to Mercedes-Benz, problems can include fuel filters being clogged by glycerol residues or microbe culture, fuel gelling in low ambient temperatures, acidic corrosion attacking pumps and injectors, sludge forming in the engine oil, and combustion deposits forming on piston-rings, oxygen sensors and in exhaust gas recirculation systems.

The problems don’t end there. Metallic contamination because of poor fuel production processes which can wreck fuel injectors has also been noted, and, unlike mineral diesel which tends to vaporise, unburned FAME will accumulate in the engine oil, potentially raising it to the level where a catastrophic and unstoppable diesel runaway occurs.

Engines with diesel-fired PM trap regeneration are particularly prone to this, and PM trap regeneration on high concentrations of FAME is unlikely to be as effective as on conventional fuels.

All major coach engine manufacturers will accept diesel with up to 7%(B7) FAME content. Beyond that, the situation becomes more complex. The French now allow B10 (10%) diesel to be sold at the pumps, but this should only be used in vehicles with the appropriate blue sticker around the fuel filler neck. If you are heading for France and need to buy fuel, you can check by downloading this guidance from European auto industry body ACEA: bit.ly/2WoXoye

Be aware that while some manufacturers will accept B10 fuel, they may also stipulate shorter engine service intervals, with early changing of fuel and oil filters and engine oils to mitigate the problems outlined above.

Environmental concerns

If that wasn’t enough, there are further environmental and ethical issues that were raised. Environmental campaigners Greenpeace point out that if rain forests are cleared to make way for palm oil production, and that palm oil is then used as a feedstock for FAME, the CO2 emissions are worse than if mineral diesel is used. There are also obvious questions regarding the damage done to wildlife habitats and the ethics of replacing food with fuel if agricultural land is used to grow crops as feedstocks.

While the EU Parliament has responded by voting to ban palm oil as fuel from 2030, Greenpeace is not impressed and said: “Chopping down rainforests in South East Asia to grow palm oil for ‘biofuels’ in Europe is completely nonsensical and does nothing to help stop climate change. 2030 is still 12 years away. Deforestation is causing havoc with our climate now, and will make iconic animals like the orangutan extinct.”

About the only environmental positive that may emerge is that NOx emissions can be reduced by around one-third if high concentrations of FAME are added to diesel, because it burns cooler and less efficiently than mineral diesel. However, the lower energy yield will result in increased fuel consumption.

On balance then, while the benefits of FAME as ‘renewable fuel’ may seem initially attractive, the downsides make it little more than green window-dressing.

So, are there any more beneficial alternatives?

Gas-to-liquid

One is gas-to-liquid (GTL). Currently, and very wastefully, installations such as oil rigs and refineries flare off methane gas that cannot be recovered on site. The quantities wasted globally are estimated at an annual 150 billion cubic metres…or 30% of the European Union’s natural gas consumption. Using gas to liquid processes, this resource can be converted into a liquid fuel suitable for diesel engines.

Shell, which is pioneering the fuel on a global basis, first partially oxidises methane, which creates so-called synthesis gas: a mix of hydrogen and carbon monoxide. This is purified and then converted into a liquid by a catalytic reaction. If left to cool to room temperature at this stage it forms a wax-like substance.

This forms the raw material for further cracking and isomerisation processes which tailor molecule chains to form precise and very pure products. Depending upon the processes selected, the final product can be a range of high-quality liquids, including synthetic base oils for lubricants, and diesel fuel of far more consistent quality than that derived from
crude oil.

With contaminants found in mineral diesel such as sulphur, aromatics and nitrogen almost completely absent, this synthetic fuel clearly has great potential for clean operations in an urban environment.

Promising trials

The fuel is currently being trialed by a coach operator in East Anglia, but no results are available yet. However, in the world of urban food distribution the fuel has been used by wholesaler Brakes to fuel a fleet of 50 DAF LF 230 fridge trucks, which use a Paccar-badged Cummins engine.

A nine-month trial of Shell GTL yielded a 47% reduction in NOx emissions, which was verified by independent testing at Millbrook Proving Ground. Engine particulate emissions were also much reduced, as drivers noted the periodic requirement for static filter generation was virtually eliminated–saving fuel and reducing CO2 output.

The work cycle of these vehicles is not too dissimilar to that of an urban commuter coach.

Unlike FAME, there is no technical downside to using GTL. The purity and consistency of the fuel could even extend engine life, and users report quieter running after switching to the fuel.

Potentially, the fuel could meet up to 30% of the UK’s demand for diesel. It could either be blended with conventional diesel to provide a smaller but more widespread benefit, or supplied exclusively as a ‘pure’ fuel to users in areas where air quality is critical.

Shell GTL Fuel is distributed throughout the UK by Certas Energy. Current supply locations include Ellesmere Port, Thames Port, Ashford in Kent, Horsham and the Peel Port Liverpool bunker sites. Certas Energy reports that its supply network is expanding as demand for the fuel grows. A further outlet will open at Kings Lynn in the New Year, and a feasibility study is being carried out for Immingham.

Pricing is an issue. GTL is sold as a ‘premium’ fuel, much like super unleaded petrol, and no duty rebates are available. It is likely to remain as a premium given the limited supply of surplus gas.

Utilising waste

Good as it is, synthetic diesel would be even better if we could make it from rubbish which would otherwise be difficult and expensive to dispose of.

Well, the good news is that we can do that with Hydrotreated Vegetable Oil (HVO).

This is not biodiesel as we know it. Biodiesel was seen as a fuel of the future a couple of decades ago, but it poses both practical (short ‘shelf’ life and increased vehicle maintenance requirements) and ethical (either displacing food production or destroying natural habitat) issues that cannot be easily resolved.

HVO is different. It is made from waste products from the food chain, which can include everything from crop residues to butchery waste. Not only does it share the engine and environmentally-friendly properties of GTL fuel, it can also yield a 90% reduction in CO2 emissions in comparison to fossil diesel.

Like FAME, it is made from plant material. But the process requires a feedstock of far lower quality, meaning that virtually all food waste can be used, including crop residues and fatty butchery waste.

The production process is also different: rather than using methane as a catalyst and producing glycerine as a by-product, the catalyst is hydrogen, and this removes the oxygen from the feedstock to form water. Free of oxygen and water, the resultant product has a far longer shelf-life than FAME products, and is also resistant to cold filter plugging problems. Indeed, it can be used in jet engines operating at very high altitudes and hence low temperatures. It has been tested at temperatures as low as – 50°C without issues. Other by-products from the process are naphtha (used in oil refining) and propane gas (a useful fuel).

The only real issue is that it is less dense than conventional diesel, so fuel consumption measured in litres/km (as it is in road vehicles) will go up. For aviation, where consumption is measured in kg/km, it goes down!

In terms of quality and properties, HVO is very similar to GTL, but with the added advantage that, if made from plant waste, it can reduce well to wheel CO2 emissions by an order of 90% compared to mineral diesel.

Backing for HVO

Neste Oil leads the European market, with production at two plants in its home country of Finland and one in Holland. Fuel made from waste cooking oil and imported from Neste’s Dutch facility by Green Biofuels was used in a trial by Lucketts Coaches of Fareham. Seven coaches were run on pure HVO for three months on the National Express service from Portsmouth to London, with data also being harvested from seven similar coaches running on conventional diesel on the same route. Scania remains tight-lipped about the results of this exercise, but approves the fuel at up to 100% concentrations on all its Euro V and VI engines, while tests on buses at Millbrook conducted on behalf of TfL apparently show ‘significant reductions in emissions.’

DAF, which supplies engines to VDL, Irizar and others, is also enthusiastically backing the fuel, arguing that there is little need for more elaborate replacements when HVO can simply be poured into an existing vehicle with no modification to the engine or change to the maintenance schedule.

It fuels its truck demonstrator fleet with HVO supplied by Green Biofuels of London. Green Biofuels markets two synthetic diesels: Green D and Green D+. It claims Millbrook tests show that the former can reduce NOx by 9% and the latter by 29%, with a 77% reduction in PM over standard diesel in addition.

But there must be a catch, and there is. There is a high capital cost in building HVO production facilities, although this can be recovered reasonably quickly because the feedstock is cheap and the by-products (naphtha and LPG) are valuable.

Capital costs can be reduced by carrying out HVO production using the same ingredients as part of the process of refining mineral oil, a process which liberates hydrogen. The HVO product is automatically blended into the mineral diesel, so ‘pure’ HVO cannot be produced.

Total in France, Preem in Sweden, ConocoPhillips in Ireland, Cepsa and Repsol in Spain and Galp in Portugal are using this technique in Europe. The technique gives refineries that might otherwise be struggling with economic and environmental issues a new lease of life.

Besides DAF and Scania, other manufacturers are prepared to approve these synthetic diesels. Cummins has approved them across its current on-highway engine range, while Mercedes-Benz will accept them on OM934, OM936, OM470 and OM417 engines from February 2016 production onwards. Volvo Group approves HVO on ‘a full range of engines from 210 to 750 hp’.

MAN approves D20, D26 and D38 engines built from 2017 for GTL and HVO fuels.

However, all manufacturers caution that the fuel used must meet the EN15940 standard if warranty cover and service schedules are not to be compromised. It would be wise to seek advice from the manufacturers concerned to ensure that the fuel you intend using is indeed suitable for the vehicles on your fleet.

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