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DOUBLINGTECHNOLOGY: COMPOUND TURBOCHARGING UP

The recent debut of Volvo’s D13TC engine proves at least one European truck maker is still keen to use compound turbocharging to harness wasted exhaust gas energy

Start your engines: compound turbo gear and fluid coupling on Volvo D13TC

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Back in black: latest Volvo it at the time: “The ingenious turbo-compound design I-Save drivetrain in FH includes has fallen out of favour for the foreseeable future.” And The principle behind compound 500hp turbo-compound that appeared to be that, at least as far as Volvo and turbocharging is simple enough. Add D13TC engine compound turbocharging were concerned. Or was it? a second turbocharger downstream This is not of the first, but instead of using the PROMISED LAND exhaust energy to power another Fast-forward to the 2012 launch of Next Generation the turbo- compressor, it drives a second turbine FH (“an icon reborn” as the marketing men had it) compound which, via a mechanical system of and tucked away inside the press kit was an intriguing gears and couplings, feeds power story about a new, ‘coming your way’ Euro-6 drivetrain engine of the back into the flywheel and crankshaft. called ‘I-Torque’. Said to offer “superb” driveability In short, it’s the classic waste heat and potential fuel consumption savings of as much as past. It’s been recovery system. 10%, I-Torque production was promised to get under completely The tricky part is transferring way in autumn 2013 in Europe. But what exactly was the power from a turbine, typically it? Beyond the fact that it featured a 460hp 13-litre redesigned spinning at speeds in excess of diesel, dual-clutch I-Shift auto, high-efficiency rear 50,000rpm, to a crankshaft rotating axle and Volvo’s I-See predictive cruise control, we to provide at 900rpm to 2,000rpm, without were none the wiser. maximum fuel- incurring heavy mechanical losses. As the months went by, references to I-Torque The solution invariably involves a became noticeably thin on the ground. Finally, in the efficiency transfer gear train using step-down summer of 2014, word came back that it had been gears of between 20:1 and 30:1, and quietly shelved. Further probing by CM did, however, some form of extra fluid

uncover some unexpected nuggets. I-Torque’s NOT NOT WANT WASTE coupling. D13 engine would have featured compound

WORDS: BRIAN WEATHERLEY Compound turbocharging is a bit like a boomerang. Just when you thought Europe’s truck makers had thrown it away, back it comes. And just like the curved stick that circles back to its thrower, compound turbocharging returns otherwise wasted exhaust gas energy back into an engine, boosting its power and torque, all for free. It’s an obvious example of a virtuous circle. Compound turbocharging has certainly returned to Volvo. Its latest 13-litre D13TC turbo-compound six-pot, launched in March, is described by its advocates in Gothenburg as the manufacturer’s “most efficient long-haul engine to date”. Rated at either 460hp or 500hp, it sits at the heart of Volvo’s new I-Save FH drivetrain, which boasts up to 300Nm more torque than an equivalent single-turbo D13K diesel. That, says the company, “means less acceleration and fuel are needed to keep a steady speed in highway traffic. It is the ideal solution for long-haul customers”. Former glory: Volvo’s first turbo-compound version of the original 12-litre engine While the D13TC features a number of innovations attempt at compound used in its FH chassis. Yet despite its many adherents, including wave-shaped piston crowns that guide heat turbocharging, the D12D500, within four years the D12D500 had been sidelined, first and energy back into the centre of the cylinders, thereby launched in 2000 but was in 2003 by the arrival of Volvo’s mighty D16C, a 16-litre improving combustion efficiency, it’s by no means quickly surpassed by big banger with more power and torque thanks to its Volvo’s first attempt at compound turbocharging. Back alternative technology considerably greater displacement; then in 2005 by its in 2000 it unveiled the D12D500, a 500hp/2,400Nm 13-litre range which included a 520hp rating. As CM put Sitting pretty: side view of D13TC showing compound turbo unit

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turbocharging, while the dual-clutch I-Shift was to Stateside debut: Volvo’s ensure it operated within a very narrow torque band. turbo-compound 13-litre Whatever the facts, the demise of I-Torque suggested engine appeared in US turbo-compounding had finally slipped off the radar models first of Volvo’s product planners for good.

LIVING IN AMERICA Then, in March 2016, what should land on CM’s desk but a press release from Volvo Trucks North America trumpeting the arrival of new, model year 2017 heavy truck engines including “the Volvo D13 with turbo- compounding”. Huh? Clearly, VTNA’s engineers and marketing men were happy to embrace turbo- compounding technology, especially as the release declared: “Turbo-compounding… results in a 6.5% improvement in fuel efficiency compared with previous engine models.” Equally important, it delivered an consumption was nothing to write home about. additional 50hp that didn’t come from fuel going in, So how did the Americans square the circle but from captured exhaust gas energy going out. between the D13TC’s requirement for low-speed Prior to the D13TC’s arrival, early turbo- ‘grunt’ and the need to deliver good fuel economy? compound engines had one major shortcoming: their John Moore, VTNA’s product marketing manager, highest efficiency was delivered when under full load insists: “This is not the turbo-compound engine of the and maximum power. That was fine if you operated past. It’s been completely redesigned to work at low most of the time at maximum weights and over tough engine rpm and provide maximum fuel-efficiency terrain, like a 60-tonne logging rig in Scandinavia, through extreme [engine] down-speeding. We’ve but when the engine revs dropped, as they inevitably taken the technology that’s been tried in the past would on easy roads or when unladen, their fuel and we’ve tweaked it with our own innovations in

The first European But by far the most impressive drive chassis on the grounds and high-pressure fuel Nineties knowhow: Scania was manufacturer to offer a stat was that its brake thermal that potential buyers “may injection… hold great the first truck maker in Europe to turbo-compound engine in efficiency (BTE) was up from choose not to wait until 1993 potential for further offer a turbo-compound engine with a heavy truck was Scania. 44% to 46%, similar to what and will spend their money on emissions reductions, its 400hp 11-litre unit Four years after unveiling a typical Euro-6 big diesel something else – and there’s no while preserving fuel a prototype to the press in achieves today. guarantee that it will be a Scania efficiency. These engines for Euro-5, it dropped 1987, it officially launched its That summer, we took a with a V8”. new systems are vital compound turbocharging in DTC1101 400hp/1,750Nm left-hand-drive R113.400 By early 2001, the DTC1101 elements in Scania’s favour of alternative routes to 11-litre compound turbo diesel around our demanding had been superseded by an environmental strategy.” Only if we were improved engine performance as an option in its 3 Series at European test route at 40 all-new Euro-3 470hp 12-litre When our road testers regularly running under and lower emissions, including the 1991 Brussels Show. A tonnes where it delivered a compound turbo diesel finally got their hands on extreme conditions, or had an its XPI common rail injection compact gearbox bolted to the respectable 7.0mpg overall. featuring an HPI fuel injection a right-hooker R124.470, image to maintain at all costs, and own in-house engine offside of the in-line six engine’s We reckoned: “The compact system developed jointly they weren’t disappointed would we be tempted to spend management software, a flywheel housing used two power of the new turbo- with Cummins. Adding the by its performance. Indeed, our own money on those two combination that allowed sets of spur gears and a fluid compound engine, together second turbo reclaimed 3% of we thought it gave Scania’s [extra, V8] cylinders.” Next, engine characteristics to be

COMPOUND INTEREST coupling to feed the power with its pleasing driveability the power otherwise wasted venerable V8 a real run for its with the advent of Euro-4, tuned for low-rev torque as well recovered by the second turbo and all round suitability for though the exhaust, while money. Under the heading Scania’s turbo-compound as cruising economy. back into the crankshaft. Not high-speed long-haul work, Scania’s then boss Leif Östling “Meet the six that thinks it’s a 12-litre gained an extra 10hp It says: “The in-house only did the DTC1101 deliver makes the R113.400 a strong declared: “With the 470, Scania V8!” we concluded: “ Nice as to become the 480, while a electronics and injection 44hp more than a regular contender in the TIR tractor is a strong contender in the it might be to have a socking more modest alternative 420 TC technologies helped greatly 356hp DSC 11 six-pot, it was stakes.” However, we cautioned segment of straight-six cylinder great V8 at your beck and call, rating was also offered. in the development of Euro-6 also 200kg lighter than the Scania (Great Britain) not to engines above 450hp.” He the 470 option is close to being However, when Scania engines, which Scania was first

SCANIA’S equivalent 14-litre 400hp V8. delay in bringing in right-hand- added: “Turbo-compounding the ideal choice for the world. introduced its all-new 13-litre to offer to customers in 2012.”

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COMPOUND TURBOCHARGING NOT JUST THE SWEDES CM’s archives record various attempts by diesel engine manufacturers over the past 50 years to apply compound turbocharging. In 1972, Cummins set up a compound turbo development programme in the US that saw prototype units based on its 14-litre NTC 400 engine field-tested from 1978. In 1991, it also revealed it was running operator not only further reduces the amount of NOx created trials with a pre-production 10-litre turbo- during combustion but reduces AdBlue costs too. compound engine. However, neither So what made the Swedish truck maker come back project led to large-scale production. to compound turbocharging after 18 years? In late 1987, DAF confirmed it had also “done a lot of work FIGHTING TORQUE on turbo-compounding” though Volvo Trucks’ director of powertrain strategy Mats it reckoned the second turbine’s The long game: Mats Franzén responds enthusiastically: “The reason for power would be better used to Franzén, right, Volvo Trucks using the turbo-compound unit is simply that it drive engine auxiliaries, not the director of powertrain saves fuel.” Indeed, according to Volvo, the D13TC crankshaft. strategy, says the D13TC and I-Save can together deliver savings of up to 7%. In the same year, Detroit Diesel can cut fuel use by 7% when Equally noteworthy is the fact that, unlike earlier claimed it had built a turbo- coupled with I-Save generation turbo-compound engines, the D13TC and compound version of its Series 60, while I-Save are at their most effective between 1,000rpm the chief engineer for Perkins’ advanced and 1,100rpm. “The improved torque level allows projects insisted: “The issue is no longer a the use of a faster rear axle while still maintaining technological one, but more concerned with economics and market demands.” our integrated driveline, and we’re making it work.” Naturally, the stateside debut of the D13TC driveability and traction,” explains Franzén. “The By 2003, IVECO was said to be trialling a 620hp turbo-compound version of Moore continues: “In the past, turbo-compound begged an obvious question on this side of the savings created by the I-Save package balance its Cursor 13 engine in Australia. designs were set up to run on performance only. You pond: if the US has got a turbo-compound well with the additional cost, resulting in a positive In 2007, Detroit Diesel launched its 14.8-litre DD15 in-line six with a really didn’t see much in fuel efficiency. This engine is 13-litre engine, why hasn’t Europe? Well it has business case for long-haul operators.” compound turbo that transferred power to the crankshaft via a hydrodynamic designed to do both. We designed the D13TC engine now, thanks to the adoption of D13TC in Volvo’s For the moment, the European compound coupling. Its fuel consumption was said to be 5% lower than an equivalent Series to run at low rpm for maximum fuel efficiency, and latest optional I-Save drivetrain package for turbocharging flag is being flown solely by Volvo. 60 engine. However, three years ago turbo-compounding on the DD15 was to be able to run at 1,400-1,500rpm to give us the the FH. In the D13TC, the energy generated But given the nature of ‘shared drivetrain platforms’ discontinued in favour of a single, asymmetric turbo. performance we need when we do find ourselves in by the second turbine is transferred back to the within the Volvo Group, it’s not inconceivable that more aggressive terrain.” crankshaft by a series of gears, together with a fluid coupling which ensures good damping of any crankshaft torque fluctuations. the D13TC could find its way into other heavy truck chassis offered by Renault, Mack or UD. Likewise, LIGHT FANTASTIC as diesel manufacturers look to boost the efficiency Spec for spec, the 500hp D13TC has a number of of their engines and cut CO2 emissions further, attractions. For starters, it’s 238kg lighter than an compound turbocharging arguably offers a less equivalent 16-litre 550hp D16K without giving too complicated route to waste heat recovery than, say, a much away in performance, while its peak torque Rankine Cycle generator. of 2,800Nm is just 100Nm below the D16K550’s We’ve already experienced Volvo’s turbo- 2,900Nm. What’s more, regardless of whether it’s compound 13-litre in the US in a bonneted VNL a 500hp or 460hp rating, the D13TC’s compound tractor (CM 1 February 2018), and more recently turbo system only adds around 100kg to a ‘regular’ tried the I-Save option with D13TC out in the D13K Euro-6d engine. And in addition to its SCR FH 460 and FH 500 in Europe (CM 25 July), and emission control system, the D13TC also features we’d like to think that this time, turbo-compounding cooled exhaust gas recirculation (EGR) which is here to stay.

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