Article
Articles, Issue 47 - Winter 2012

Future Powertrain Technology

Reflecting on the Frankfurt and Paris motor shows of 2011 and 2012, respectively, I detected two significant trends that in the future could prove to be seminal in the development of the car in this second decade of the new millennium. Ian Adcock (just-auto.com).

Hybrid and electric vehicles?

At a Bosch press conference held somewhere within the vastness of the IAA exhibition site, the company’s chairman, Franz Fehrenbach, told the assembled analysts and journalists “…there is no immediate likelihood of electric cars flooding on to the streets,” and that in these economically challenging times neither did he expect governments to intervene with fiscal incentives for them, at least, not “until the middle of the next decade.”

On a more personal level, during my visit to the Paris Salon last year the only electric vehicles (EVs) I encountered were in the show grounds or exhibited on various stands. I checked with colleagues and not one of us had seen an EV on the streets of Paris.

Whilst these events don’t spell the end of the industry’s flirtation with EVs it does, I think, have a bearing on the future direction of powertrain developments. Spurred on as it has been by the 2015 regulations, now less than two years away, and, arguably, more significantly by the 95 g/km CO2 target set for 2020, the industry across the board has been working feverishly to ensure it isn’t hit by swingeing fines of EUR 95 for every gram over that target.

EU targets

A report conducted by the European Federation for Transport and Environment (T&E) says the industry as a whole cut its average CO2 emissions by three percent in 2011 to an average of 136 g/km, just 6 g/km beyond the 2015 limit.

Some OEMs, Toyota, PSA Peugeot-Citroën and Fiat, hit their targets four years ahead of schedule whilst Mazda with its 12 percent deficit has the farthest gap, claims the group. Assuming this to be the case then 2020’s 95 g/km target should be easily attainable, with the European industry in a better position than its Asian rivals.

Based on recent improvements and current positions, the report estimates that the European OEMs only need an annual improvement in fuel efficiency of 3.8 percent to achieve 2020’s target, which seems realistic enough given the technological developments we have seen of late and which are in the pipeline.

What might be more difficult to achieve are the proposed fleet averages of 94 mpg for petrol and 108.6 mpg for diesel by 2025 which, in all probability, will involve some form of hybridisation.

Downsizing

Downsizing is the most obvious route to achieving improved emissions and fuel economy and whilst in the past this resulted in asthmatic performance, the latest smaller capacity engines have power and torque figures that, a decade ago, would have only been feasible in engines twice their capacity. Arguably the most sophisticated of this latest generation of small capacity engines is Ford’s one-litre EcoBoost. With a footprint no bigger than a sheet of A4 paper, it produces 100 or 120 PS at 6,000 rpm and an impressive 170 Nm from 1,300 to 4,500 rpm with transient overboost capability of 200 Nm. A key enabler for this performance says powertrain development manager, Andrew Fraser, is its tiny Continental turbocharger which runs at peak speeds of 248,000 rpm and is capable of withstanding temperatures of 1,030 ºC.

In what should be an inherently out of balance engine, Ford has adopted the novel approach of carefully unbalancing the front pulley and flywheel to offset most of the shaking forces so it’s closer to a five-cylinder, with the rest of the vibrations countered by precisely designed and tuned mounting systems. It’s feasible that Ford will stretch the engine to 1.2 litres and 150 PS at some point in the future for applications in larger bodied cars or, simplify the unit to run it as a range extender.

Launched at the last Frankfurt show, this EcoBoost engine was just one example of downsizing, others coming from Kia (diesel) and VW’s more conventional three-cylinder for the Up (or up!).

Similarly Volvo is planning a new range of two-litre four-cylinder engines for 2014 to replace its current mix of four, five, six and eight cylinder units. They will be available in a variety of power outputs achieved by employing turbocharging, hybrid drive and even flywheel technology based on Formula One kinetic energy recovery (KERS) system.

AUDI 4.0 TFSI Engine

AUDI 4.0 V8 TFSI Engine

But, perhaps, the most dramatic example of downsizing whilst not sacrificing performance came from Audi and Bentley. The VAG siblings revealed a jointly developed four litre twin-turbo V8 featuring cylinder deactivation, a technology that Bentley uses with effect on its 6.75 litre V8, albeit with a central camshaft and pushrods, rather than the new engine’s quad-cam layout. With power outputs ranging from 313 kW and 549 Nm in the base Audi application to 373 kW and 660 Nm for Bentley this is hardly a planet saver, even so Bentley’s director of powertrain, chassis and motorsport, Brian Gush predicts 40 percent fuel saving over the company’s W12.

Cylinder deactivation

Although cylinder deactivation is a relatively complex and costly solution, economies of scale within VAG have enabled it to be applied to the group’s 1.4 litre TSI four-cylinder engine with the aim of reducing consumption in low and medium load conditions by 0.4 litres per 100 km in the NEDC combined cycle and 0.6 litre when allied to stop-start. Dr Ulrich Hackenburg, Volkswagen’s research and development director, is even suggesting it could be installed on the prototype three-cylinder turbodiesel, as seen on the XL1 concept, where an electric motor would drive the car up to an engine speed of about 1,400 rpm, thereafter the combustion engine would take over.

Forced induction

A key enabler to downsizing will be forced induction, either turbocharging or supercharging, especially when the latter is combined with an electrical motor or similar device as seen in the Controlled Power Technologies system it acquired from Visteon and sold onto Valeo for further development and industrialisation last year.

There are two schools of thought emerging for this solution to downsizing: Valeo has a prototype Renault turbocharged 1.2 pfi running with a 25 percent increase in gear ratios that would normally cripple the car’s performance. However, with the electric compressor spooling up from an idle speed of 4,000 rpm – at an engine speed of 800 rpm – to 70,000 rpm in a matter of milliseconds (Valeo refuse to declare a time, but Visteon originally claimed it took 0.3 milliseconds to reach 50,000 rpm), turbo lag is eliminated until the engine reaches an operating speed of 1,800 rpm by which time the turbo is fully boosted.

Utilising a separate 48 V system that harvests energy under braking to drive a generator to charge a capacitor ensures the supercharger isn’t a drain on the car’s 12 V network.

Whereas Audi, which is trialling three electric supercharging systems including Valeo’s, is employing it to boost top end and mid-range performance on its three-litre TDI V6; series production is predicted within the next two to three years timeframe.

The challenge meeting all OEMs is that the big gains have virtually all been realised, it’s now about chipping away at the margins to gain an extra percentage point, or fraction thereof, that will steadily accumulate to deliver a meaningful saving.

Federal Mogul's advanced Corona Ignition System (ACIS)

Federal Mogul’s advanced Corona Ignition System (ACIS)

Ignition system

Federal Mogul, for instance, has a new take on the humble spark plug that, claims director Kristapher Mixell, allows manufacturers to run higher levels of exhaust gas recirculation (EGR) resulting in up to 10 percent fuel savings. Its Advanced Corona Ignition System (ACIS) features a four-pointed star transmitting a low current 25,000 volt discharge. Running at 1 MHz the high intensity plasma stream excites the air-fuel molecules into combusting whereas a conventional sparkplug relies on ignition.

One of the main challenges going forward to Euro 6 is meeting particulate numbers in gasoline engines which are likely to be the same as for diesels, says

Delphi GDi Spray Stratified Injection Illustration

Delphi GDi Spray Stratified Injection

Delphi’s engineering director Europe, Dr Sebastian Schilling: “Stratified Gasoline Direct Injection (GDI) can deliver up to 20 percent CO2 improvements and even homogenous GDI can deliver 15 percent compared multi-point fuel injection (MPFI).”

The Delphi technology differs in that it runs an outboard opening injector and a solenoid rather than the more costly Piezo system, yet it’s still capable of controlling the injector stroke between fully opened and closed.

Schilling believes that stratified GDI will “dominate” in the future “as you can inject the fuel in the same position every time to achieve a really lean mixture and fuel atomisation.”

Technical challenges 

But downsizing brings its own technical challenges, especially when combined with stop-start. Whilst typical cylinder pressures of 180-190 bar for diesel and 120 bar for petrol, combined with higher engine speeds, aren’t in themselves problematical, Federal Mogul’s director application engineering bearings, Gerhard Arnold, does see challenges when the engine is started. As the engine is started there’s a high coefficient of friction which changes to mixed lubrication at 100-200 rpm to full hydrodynamic conditions at around 800-900 rpm (the Stribeck curve).

Before the advent of stop-start, explains Arnold, an engine would start “30,000-40,000 [times]”, that could now increase more than ten-fold with stop-start to half a million and double that for a full hybrid, he claims.

Federal Mogul has developed a new series of polymer IROX coated bearings that combine a Pal (PolyAmidelmide) overlay

Federal Mogul has developed a new series of polymer IROX coated bearings that combine a Pal (PolyAmidelmide) overlay

To cope with this, Federal Mogul has developed a new series of polymer IROX coated bearings that combine a Pal (PolyAmidelmide) overlay that contains a number of additives dispersed through the matrix for wear resistance, mechanical strength etc. but still resulting in a CO2 saving of 1 or 2 g/km.

Euro 6 legislation 

It’s generally agreed that the forthcoming Euro6 legislation will impact on diesel engines and, predicts the managing director of Ford’s European Research Centre, Andreas Schamel, shift the balance towards diesels being used more in heavier, commercial vehicles rather than passenger cars – well, at least in their current format.

Ford is seriously looking at 42 V and 48 V systems for diesels. The attraction being that, we can recoup the energy from braking and use it to power a 10-15 kW electric motor for low-speed manoeuvres and city driving,” says Schamel. The diesel engine would take over for motorway cruising, for instance, where its flatter efficiency map delivers minimum fuel consumption.

Ricardo’s chief technical officer, Neville Jackson is in agreement, adding that diesels will almost certainly require closed-loop particulate traps in the exhaust system to meet future demands.

Whilst Professor Hongming Xu, chair of the Energy and Automotive Engineering at Birmingham University considers the benefits of Homogenous Charge Combustion Ignition (HCCI) better suited to petrol rather than diesel engines. He goes further, in fact, by suggesting that future generations of ‘smart’ fuel injectors, somewhat analogous in operation to an ink jet printer, would minutely control the combustion process allowing both port and direct fuel injection that could lead to multi-fuel engines capable of identifying and then running on diesel, petrol, biofuel or some form of fuel property modifier.

Alternative fuels

The possibility of running multi-fuel engines at some point in the future might be Professor Xu’s ‘dream’ but closer to reality is compressed natural gas (CNG) as an alternative to renewables. Toyota showed a new one-litre DI twin cylinder engine at last year’s Geneva Salon that could run on CNG and emit only 38 g/kms whilst Ford’s Schamel admits to “Watching the uptake of natural gas…with interest,” adding “Because CNG is very knock resistant, you can get to diesel – or better – levels of efficiency.” The downside being it’s a dry fuel lacking any lubricity which makes it tough on the valve train and other reciprocating engine components.

Nevertheless Audi is committed to launching a TCNG version of its third generation A3 Sportback this year. In the longer term, its joint venture with US start-up, Joule Unlimited expects limited production of synthetic e-ethanol and e-diesel to start in May 2013 and 2014, respectively. By using a combination of sunlight, CO2 and waste water to feed cyanobacteria to generate continuous streams of ethanol or long-chain alkanes, which are important constituents of diesel, it can then be added to fossil gasoline or as a basis for E10 or E85.

Summary

Clearly the emission targets being set for the industry are going to get ever more stringent. But, with increasingly powerful electronics to monitor and control combustion strategies, new materials and a raft of yet to be fully developed and matured combustion strategies then whatever legislation is laid down before the industry, the probability is that OEMs and suppliers will rise to meet them. 

Ian Adcock (just-auto.com)

About lotusproactive

Lotus proActive is an e-magazine published quarterly by Lotus Engineering, covering engineering articles, industry news and articles from within Group Lotus (Cars, Engineering, Originals and Racing).

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