Natural gas (methane) engines have been around for almost a century. However, despite some notable uptake in a few niche bus and truck applications, in the UK they have languished, perhaps unfairly, in the transport equivalent of football's League One. Could their low-cost, clean, low-emissions credentials yet propel them to the Champions League? Maybe not quite and not soon, but make no mistake, the wind of change is blowing through the underlying commercial, operational, political and technical drivers. Add the improving LNG/CNG (liquefied/compressed natural gas) refuelling infrastructure, and the argument for gas vehicles is becoming more compelling.
So what's happening? First, commercially, there is the guaranteed 10-year fuel duty differentiator which, depending on the vehicle application and the price of diesel, can easily mean a two-year payback from cheap fuel, despite gas trucks' higher capital cost. Second, operationally, not only is LNG/CNG becoming more widely available around major UK routes, but also, as OEMs see the potential for market growth, Euro 6 gas vehicles are emerging, and dealer workshops are being equipped (and technicians trained) to handle gas vehicle maintenance and repair. Thirdly, politically, with the government now under pressure from the Supreme Court to cut transport-related emissions in line with EU demands, there is surely the prospect of a return to financial incentives in the form of something like the former RPCs (reduced pollution certificates).
Sounds interesting? How about technical developments? Excluding dual-fuel participants (see next month for detailed coverage), Iveco, Mercedes-Benz, Scania and Volvo lead the gas truck presence in the UK. All now offer Euro 6 LNG/CNG-engined vehicles. However, although there are striking similarities, there are also differences, in terms of the engineering execution, power and torque ranges, as well as the transport sectors addressed and these companies' visions for the future.
Kicking off with Iveco, product director Martin Flach explains that its Daily panel van (3.5 to 7 tonnes) is fully Euro 6 gas enabled, with the 3.0 litre engine delivering 136bhp and broadly matching the diesel equivalent for torque. "Gas Daily vans have been available for sale since the CV Show, and next up will be Euro 6 Eurocargo gas rigids [200bhp, 12- and 16-tonners], although not before early next year," he states.
That said, spark-ignition (Otto cycle) gas variants of Iveco's heavy-duty Stralis (4x2 and 6x2 rigids, and 4x2 tractors) are already available at Euro 6, with Cursor 8 engines offering 270 to 330bhp and, again, torque closely matching the equivalent diesel. From the emissions perspective, comparatively speaking, they're a doddle: being virtually soot free, they don't require a DPF (diesel particulate filter), even at Euro 6, and, as with any spark-ignition engine, NOx control is via a three-way catalytic converter. As for the transmission, they drive through manual boxes or Allison fully-automatics (not the preferred AS-Tronic: see panel overleaf) and are being pitched at the light end of heavy – 26 tonne rigids up to 32-tonne urban artics, fitting the 10bhp per tonne sweet spot.
But there's more to come. Iveco seems set to mirror Cummins Westport's development, which last year saw its 11.9-litre spark-ignition ISX12G gas engine launched at 400bhp. "When we can offer larger displacement, higher horsepower CNG engines – say 420, 450 or 480bhp – and a conventional two-pedal AMT, this could become mainstream. We're actively looking at that development now," states Flach.
Moving on to Mercedes-Benz, the German giant launched its Euro 6 Econic NGT (natural gas technology) at 18 and 26 tonnes in Sweden last August. This vehicle uses Mercedes' six-cylinder M936G engine, based on its OM936 7.7-litre BlueEfficiency single-stage turbodiesel engine, delivering 302bhp and 1200Nm torque. In brief detail, you're looking at a near identical cylinder block and head, but with a new asymmetric turbocharger, modified piston combustion cavity, and new charge-air ducting, spark ignition and fuel mixing systems, including exhaust gas recirculation – all in the same footprint.
Again, the Econic NGT drives through a six-speed Allison auto box, albeit with new eco software (Fuelsense) for fuel optimisation. However, since we're only talking Econic, Mercedes is clearly targeting the low-entry cab, stop-start RCV (refuse collection vehicle) market where fully automatics are standard fare. That said, with the potential for 8/6 x 4/2 city-based tippers and similar trucks under CLOCS (Construction Logistics Cycle Safety) thinking, pus the emissions and noise advantages of gas, uptake could yet spread.
As for Scania, it takes the title for the world's first Euro 6 CNG/LNG-powered truck, which entered service with Swedish operator Bring Logistics in June 2013. Power is delivered by Scania's 9-litre, spark-ignition 280 or 340bhp (1,350, 1,600Nm torque respectively) engine, driving through a manual or Allison fully automatic. Like Iveco, Scania sees its current gas trucks as fulfilling roles in light heavy-duty return-to-base distribution (range crica 450km), and its gas trucks are available as P and G series 18—26 tonne rigids and urban tractors (4x2) up to 28—32 tonnes.
Argos was famously the first taker in the UK, taking delivery of five 340bhp 4x2 Scania CNG tractors last March, each plated at 40 tonnes gtw, as part of Innovate UK's (formerly the Technology Strategy Board) Low Carbon Truck Trial. "A key aim of the project has been to introduce gas vehicles into service at Magna Park in the run-up to a publicly-accessible gas refuelling station," states John Baldwin, managing director of CNG Services, which is leading the Innovate UK consortium with Gasrec, Argos, DHL Supply Chain, Culina Logistics and Eddie Stobart. And referring to the 70% carbon saving claimed for running on biogas, he adds: "Argos's new gas-powered Scania trucks will be transformational in terms of CO2 emissions and their impact on air quality in the coming years."
However, according to Scania specialist sales executive David Burke, Scania's aspirations for gas trucks go much further than the current 340bhp cap. "We're looking to develop six-cylinder, 13-litre 410—460bhp Euro 6 CNG/LNG variants for long-haul next year," he reveals. "They will run on our R-Series two- and three-axle tractors." He also suggests that construction vehicles could well follow – and that the expensive Allison box and retarder will be complimented by Scania's Opticruise two-pedal transmission both in the existing 9-litre and future larger engine variants.
How about Volvo Trucks? Well to date this Swedish OEM has followed the Mercedes model, launching the FE CNG low-entry chassis cab last August, and targeting RCV and stop-start local distribution operations. Speaking at last year's launch, John Comer, product manager for Volvo Trucks, said: "The Volvo FE CNG is primarily aimed at centrally-operated municipal and refuse operators, working from transfer stations where there is a renewable source of methane."
Its existing rendition, now in series production, is based on a 9-litre, Wesport spark-ignition Euro 6 CNG-powered engine, delivering 320bhp and 1,356 Nm maximum torque, yet again mated to a six-speed Allison automatic. Truck options are 19-tonne 4x2 or 19-5—26 tonne 6x2 rigids.
However, all eyes remain on Volvo for its much delayed diesel-initiated (not spark ignition) Euro 6 gas truck, widely expected to be pitched at the 450bhp mark – ideal for trunking. Tony Owen, Volvo's key account manager for low-entry cabs and gas trucks, concedes that this much trailed development has taken far longer than expected, but adds: "Volvo FH and FM rigids and tractors are in field trials in Sweden now." He's coy about engine sizes, truck variants and a release date – save for saying it won't be this year – but confirms that it is based on new, high gas substitution injector and engine technology.
That said, it seems certain the technology partner is Westport, well known for its work on a system that injects gas direct into the cylinders, instead of the plenum, along with a circa 5% diesel charge. The engine then runs on a compression ignition cycle which, in turn, initiates the gas burn – much as current dual-fuel conversions, but with a far higher gas ratio. As a result, Volvo's new beast will harness what amounts to a fairly conventional diesel engine married to a heavily-modified top end.
In short, when it comes, it looks set to offer the best of all worlds: proven, robust diesel technology, heavy-duty diesel power and torque, but low gas prices and emissions. "We're definably bringing out this gas engine and it will be world beater," insists Owen. "If CNG/LNG availability is good, then I'd like to think we'll be selling thousands of them. They'll be similar to diesel but much cheaper to run." And asked about the likely transmissions, he adds: "There is no reason why we can't use our I Shift." So there's another significant revolution.
How do you feel about gas trucks' viability now? Well consider this: "If you're currently spending, say, £60,000 a year on diesel, the gas equivalent would be about £45,000," sys Iveco's Flach. "So, if your vehicle costs, say, £25,000 more than a diesel equivalent [which depends largely on the required range and hence gas tank sizes and numbers], payback is just under two years." And they offer obvious emissions and noise advantages. Not bad, eh?
The transmission conundrum
What about gearboxes on pure gas spark-ignition engined heavy vehicles? To date, virtually all the vehicle OEMs have offered only manual or Allison fully automatic transmissions – fine for RCVs (refuse collection vehicles) and buses, but not to all truck operators' tastes. Why that choice? Fundamentally, it's because of the way gaseous fuel is injected. To date, that's into the charge air stream in the intake manifold or plenum, some distance from the cylinders – as opposed to diesels' direct head injection. As a result, there is nothing like the precision torque response available with modern multi-injection diesel engine control systems.
That, in turn, makes it difficult to synchronise gas engines to the requirements of industry-preferred AMTs (automated manual transmission), and hence their absence from the options list. As Allison marketing director Manlio Alvaro explains, AMTs typically require a shift phase of some two seconds, during which time engine torque has to be reduced twice (before and after shifting) along with speed control for synchronisation. That's no problem for a diesel, but it's not feasible on most current gas engines.
Allison full-power shift auto boxes, however, don't require any torque or speed control during shifts. And there's another factor: gas engines typically deliver lower clutch engagement torque than diesels, as well as lower torque density, which, incidentally, also reduces the effectiveness of engine braking. "That's the other advantage of our torque converter," explains Alvaro. "First, it allows the vehicle to be launched at higher engine speed and hence torque. But second, it multiplies that torque at launch, because of the geometry of the pump-turbine-stator hydraulic coupling, which transmits engine energy to the driveline as reduced speed but higher torque."
Allison also argues that its Continuous Power Technology maximises CNG engine efficiency, because higher average drive power equates to improved fuel efficiency. Indeed, it applies the same logic to diesel engines. It's a moot point, particularly when it comes to stop-start operations encountered in city and urban environments where torque converters are widely accepted as thirsty beasts. That said, when the box locks up in top gear for trunking, fuel efficiency becomes comparable to that of AMTs. Either way, if you want automatic on a spark ignition gas truck, then for the time being you're going to have to rethink your attitude to fully automatic.
Hence Allison's spectacular success with high-profile developments such as: Spain's Aucar-Trailer Policar 16 tonne urban distribution artic-cum-rigid demounts, which run with Allison-equipped Iveco EuroCargo 300bhp gas tractors; the Turkish Konya Metropolitan Municipality bus fleet transformation, where 60 Allison-equipped 280bhp TCV Karat CNG vehicles now cover the city; and the Berliner Stadtreinigung project, where 150 Allison-equipped Mercedes-Benz Econic CNG RCVs now run on plentiful biogas.
Reading Buses has been using gas-powered Scania/Alexander Dennis Enviro 300 buses since April 2013. Indeed, it was one of these that beat the world land speed record for a service bus in May this year. Reading Buses' Bus Hound 'powered by cow poo' gas bus was clocked at 80.78mph on the Millbrook high speed circuit.