Thursday, 24 March 2016

Volvo opts for turbocompounding

Volvo Trucks North America has launched the group’s MY2017 engines offering customers increased power, performance and fuel efficiency.
In addition to various engine improvements aimed at extending fuel efficiency benefits, including those affecting the D11 and D13 engines, Volvo has launched its D13 with turbo compounding.
Turbocompounding appears to defeat the laws of physics by creating energy out of nothing. It recovers energy that might otherwise be lost, or wasted but, unlike a turbocharger it puts the ‘wasted’ energy back into the engine mechanically.
Perhaps the most complex example of turbocompounding was the Napier Nomad aero engine which had a ‘gas turbine’ slung beneath the piston engine, the two connected by a Beier infinitely variable disc-type gearbox.
In addition to Napier (in WW2) turbocompounding used by Scania and Detroit Diesel as well as previously aero engine maker Wright in the US. In Volvo's case, the technology adds 50bhp back into the engine, which might seem to be a modest amount considering the additional cost and added technology.
                      Securing worthwhile fuel economy gains
Even so, according to Volvo the gains are reflected in worthwhile gains as the technology results in improved fuel efficiency compared with previous engine models.
In the case of the Scania engine, there is a second turbine, the turbocompound turbine, and this spins at 55,000 rev/min. This motion is passed through gearing and a hydraulic coupling, then through the timing gears to the crankshaft. Stepping down the speed produces a boost in torque, which adds momentum when it reaches the flywheel.
Overall, Volvo is claiming between 2.2 to 6.5 per cent better fuel efficiency with the 2017 engines compared with previous generation power. However, it is likely the figure of 6.5 per cent is acieved only on long-haul operation in the US on those routes which do not require many changes in gear.
"Volvo's 2017 lineup of engines is the most fuel-efficient we've ever offered in North America," says Göran Nyberg, president of Volvo Trucks North America. "Volvo engineered multiple engine enhancements to provide customers with the needed fuel savings without sacrificing power and performance."
The D13 with turbo compounding can be specified with Volvo's XE – eXceptional Efficiency – powertrain packages or in super direct drive. Through down-speeding, XE allows the engine to cruise at up to 300 rpm less than the average truck sold today – significantly improving fuel efficiency. The D13 with turbo compounding is available on an XE driveline with a 2.47 rear axle ratio.
In addition to the new D13 with turbo compounding, Volvo also updated its 11-liter D11 and standard 13-liter D13, already two of the industry's most fuel-efficient engines.
                           Using proven Delphi common rail 
Designed for improved reliability, the engines feature a proven common-rail fuel system for reduced engine and cab noise, providing drivers a more comfortable ride. The common-rail fuel system also contributes to fuel efficiency improvements through finer control of the fuel injection, allowing for quicker, more accurate injection and a more efficient way to control fuel pressure. Although the company makes no mention of suppliers it is likely that Volvo continues to use unit injectors from Delphi which intensify the pressure of the fuel in the common rail.
An updated EGR flow sensor has a new double-wall casing that reduces condensation and soot buildup in cold weather, preventing downtime. A low-pressure fuel system features an improved after-treatment dosing module that is integrated into the fuel filter housing for easier serviceability. Upgrades to the two-speed coolant pump for both engines also improve fuel efficiency as a result of reduced parasitic losses. The new intake throttle enables a faster warmup when the engine is started.
The 2017 Volvo D11 offers up to 425 bhp and 1,550 lbft torque, an increase of 20 bhp. The engine also delivers up to a 2.2 per cent fuel efficiency improvement compared with the previous D11 engine.
The D11 is available in Volvo VN daycabs, VNM 430 and VNL 430 sleeper models, VAH and VHD models.
The D13 also features a new wave piston, which allows the compression ratio to be increased and improves flame propogation to reduce sooting while also increasing cylinder efficiency.
                                  Technology from Europe
The updated D13, available in VN, VHD and VAH truck models, offers a fuel efficiency gains up to 2.5 per cent compared to the previous D13. These engine enhancements were also included in the 2017 Volvo D13 with turbocompounding.
In the context of turbocompounding, it would be interesting to know if Volvo's re-examination of the technology - remember the company briefly flirted with turbocompounding some years ago - is the result of quiet market research that has been conducted by Volvo Trucks North America. More than likely, executives will have initiated studies to tout the opinions of rival long-haul operators using Daimler AG's Freightliner trucks powered by the DD15 engine.
This Detroit Diesel DD15 carries turbocompunding technology but althoough based in Detroit, Michigan and owned by Daimler AG, more than likely the Detroit Diesel-branded technology was developed some three or more years ago alongside the engine in Mannheim, Germany. There, engineers will no doubt have minutely studied the turbocharging systems adopted by Scania and Volvo and possibly taken a leaf out of their book.
Turbocompounding is not an attractive option on European roads where hills on many cross-country routes require constant gear-changing. Hence its non-arrearence in the rion. But in the US, where truckers can take advantage of long, straight stretches of Interstate Highways, the full benefits of having a turbcompoiunded-engine can be realised. And no doubt Volvo executives have tapped into this, otherwise there would be little point in going to the expense of developing a more complex engine which no doubt will provide some additional headaches for Volvo service engineers on the roadside In passing, it would be interesting to know the on-costs of turbocharging for a standard D13 engine.
As to another technology - compacted graphite iron (CGI)  - Volvo powertrain planners clearly considered turbocompounding a more worthwhile option in preference at this stage for their 'new' engines. No mention of the material is made in the Volvo press releases or company statements.
Meanwhile, Freightliner managers will be carefully monitoring the emergence of this new turbocompounded engine from Volvo - developed in Sweden - to assess user reaction and, if possible, quantify any reliability issues attributable directly to the technology as opposed to peripheral causes of problems, such as faulty sensors and the like which, although small items in their own way, can cause long delays for operators at the roadside.
The 16-litre Volvo D16, the largest engine in its class, offers power output from 500 to 600 bhp with 1,650 lbft to 2,050 lbft torque. The engine is available in the VNL and VNX models, and Volvo suggests the D16 is "the perfect choice" for line-haul and heavy-haul operations.


1 comment:

Alan Bunting said...

Heavy truck manufacturers have blown (no pun intended) hot and cold on turbocompounding. Scania first had a go in 1991 with a prototype 11 litre engine. Several examples were produced and trialled by Swedish hauliers. The concept proved only moderately successful. The expectation of a significant improvement in thermal efficiency - translatable into either a significant fuel saving or performance boost was not realised, when viewed against the formidable initial cost. There were also problems with the deep-reduction gearing necessary for the drive from the (Holset) secondary turbine, revving at up to 55,000rpm, to be inputted to the flywheel.
Those early Scania trials, as well as those undertaken by the company a decade or so later with an upgraded installation - and a parallel turbocompound development at around the same time by rival Volvo - were a little more promising.
But it was concluded by both Swedish companies that the principle was not best suited to most European heavy truck operations.
Fluctuating road speeds imposed by traffic conditions and gradients meant correspondingly varying engine loads, which seriously eroded the turbocompound's efficiency.
About three years ago, Daimler's 15 litre engine, designated DD15 in North America, became the first turbocompound truck diesel available on the US market (in class 8 Freightliner chassis). It has enjoyed some success as a fuel saver, but significantly in long-haul operations, typically on interstate highways where hour after hour of near constant-speed running is often possible.
Volvo has clearly taken note of the DD15's positive operational feedback, prompting the effective resurrection of its own turbocompound involvement - but only for North America, where the technology can bring worthwhile benefits.