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CPT, TU Wien study finds 48V mild diesel hybrid cuts engine-out NOx 9%, 4.5% fuel economy improvement

A joint study by Controlled Power Technologies (CPT) and Austria’s Technische Universität Wien (TU Wien) into 48V diesel mild hybrid technology verified a 9% reduction of NOxin raw engine-out emissions, while retaining the fuel economy and CO2 benefits of diesel engine technology.

The cost effectiveness of this approach is further underscored by its impact on lean NOx trap (LNT) and selective catalytic reduction (SCR) aftertreatment systems, which have less raw NOx emissions to process, potentially allowing for a reduction in exhaust system cost and complexity, and a longer service life.

The result of our research programme, incorporating e-motor characterization, simulation and engine emission dynamometer testing was a clear benefit in terms of raw NOx reduction of a premium saloon with a 3-liter V6 engine. The decrease in NOx emissions, moreover, was achieved with a near 5 per cent fuel economy improvement and corresponding CO2 reduction, delivered simultaneously by the SpeedStart starter-generator.

—Paul Bloore, CPT’s manager responsible for applications engineering and strategic projects

Belt-integrated starter-generator (BISG) systems have already been successfully applied by the industry to reduce CO2 emissions by the simple expedient of stop-start. In principle, the same low voltage technology can be used to modify the load on the engine and optimize its performance for minimal NOx and particulate emissions. The challenge is having a fast-enough response time for real world driving conditions.

CPT’s switched reluctance technology is by its very nature fast acting as well as highly controllable, and well-suited to optimizing diesel and gasoline engines for minimal NOx and particulate emissions, the company said.

Not only does lower raw emissions of NOx reduce the load on an SCR system—and hence the continuous consumption of ammonia (AdBlue) used as the reducing agent—but also has the potential to reduce the active catalytic components, which are usually precious metals.

A switched reluctance machine might even allow the use of an LNT solution rather than requiring the more expensive SCR system. Diesel exhaust systems can also include a diesel particulate filter (DPF), which may also require less frequent purging.

The CPT-TUW study evaluated the switched reluctance technology to the Worldwide Harmonised Light Vehicles Test Procedure (WLTP)—the latest compliance requirement for any new cars launched onto the EU market from September 2017 onwards. WLTP defines a globally harmonised standard for determining the levels of pollutants and CO2 emissions, as well as fuel or energy consumption.

Being closer to real world driving conditions, WLTP offers a more dynamic test profile. It’s more helpful therefore in demonstrating the ability of an SRM to very rapidly supply torque to the engine, which is delivered to the crankshaft via the front pulley belt system, thereby adapting the level of electric assist to the traffic conditions and style of driving.

—Paul Bloore

The CPT-TUW study not only considered elements such as the belt ratio, but also the thermal efficiency of the water-cooled BISG, as well as vehicle operational patterns over additional test cycles. The boosting provided by the BISG came only from energy recovered during recuperation events, with a balanced battery state- of-charge and a constant vehicle electrical load applied of 300W.

It is well understood that real world driving conditions can typically increase the load on an engine with a corresponding increase in exhaust emissions compared with laboratory test cycles. The precision and repeatability of laboratory test cycles, however, makes them invaluable for vehicle back-to-back and technology comparisons.

—Paul Bloore

CPT is further validating its technology over the Real Driving Emissions (RDE) test cycle, which being even more robust should demonstrate the potential for further improvements of its SRMs.

An SRM offers consistent high power and high efficiency over a wide speed range, and unlike some alternative motor technologies, energy sapping electromagnetic field weakening is not an issue. The precise torque control enables a swift response within milliseconds to changes of load on the machine—and that’s one of our unique advantages against other types of electrical machine.

—Paul Bloore

Like mild hybrid systems generally, CPT’s SpeedStart technology harvests kinetic energy when the vehicle decelerates, which is then reapplied as torque by the switched reluctance machine during accelerations to offset fuel burn in the combustion engine. The advanced electronic control offered by an SRM, however, can further influence the engine operating point by absorbing or supplying electrical energy to move the combustion engine into a more favorable operating region. The benefits are achieved, because an SRM machine can respond swiftly to fast changing and transient road conditions.

The control strategies being developed and refined by CPT are based not only on this latest study, but also numerous other R&D programs, as well as extensive real world driving and vehicle systems simulation work. This enables interrelated systems, such as battery management, exhaust aftertreatment and complementary thermal energy recovery, to be operated seamlessly, while also providing a valuable computer-aided engineering capability to explore further potential avenues of development through 48V electrification.

Not only applicable as original equipment in cars, CPT’s switched-reluctance technology is also being tested in trucks and buses and off-highway vehicles.



In Dublin you see lines of cars, about 50-70% diesel stopped in traffic with their engines running.
It would be very nice if these did not run their engines while stopped.
It would be even nicer if they could run on electric up to 30 mph, but that would be another story.

Thomas Pedersen

9% reduction is 90% short of what is really needed.

The real-life health costs of NOx are actually quite high.


9% is better than nothing.

Normally, increases in fuel economy trade off against other factors (think of everybody's diesel timing strategy hacks which force massive recalls).  Cutting emissions 9% while boosting fuel economy 4.5% is a coup.

Maybe there's more to be had.  Using a SRM-driven supercharger to boost the air charge at low speed and cut combustion temperatures should also lower NOx.  Cooled EGR limits temperatures further, but you need the supercharger to avoid losing power.  A TIGERS can feed recovered exhaust energy back to the BAS which kicks fuel economy up again.  So far they're only doing the first bit of this.


this recent article claimed "60% reduction in real-world NONOxx emissions and a simultaneous 2% reduction in CO2 emissions"


They found lots of emissions from take off, so the hybrid helps reduce those. I am not a fan of start/stop, but if it helps go for it.


If it was still year 2005 I would think that mild-hybrid would be great, but now it is too little too late. We need plug-in hybrids that can drive >50 km on a charge, so all city-driving can become electric.


There's what we need, and what we can get in the near term.

I'll take the mild hybrid that we can convert everything to by 2020.  THEN we can worry about making everything PHEV or better.


The big potential for reducing NOx by hybridization is in improving aftertreatment efficiency, which this study has not addressed. The 9% cut in NOx is just engine-out NOx. This explains the big difference compared to the Continental article, as mentioned by “dursun”. For once, you should also try to think like a car manufacturer. If you can meet Euro 6 limits in the new WLTP cycle and, in addition, also in the (coming) real-driving test cycle (RDE) for on-board measurements, what is then the motivation for further reduction of NOx? Our emission standards do not demand more. Customers will not pay more for a car that has even lower emissions. The authors indicate that they can meet those limits even with simplification of the exhaust aftertreatment. This will cut costs. Technical measures not implemented can then be postponed until Euro 7, whenever this standard will come. Finally, the incremental cost for 48 V hybrids is relatively moderate (compared to full hybrids). If this hybridization can cut costs in aftertreatment and other areas, it is a further improvement of the cost-effectiveness.

For once, I can also agree with Engineer-Poet. Mild hybrids have greater potential to replace conventional cars on short-term horizon than PHEVs. The incremental cost is prohibitive for the latter category.



The senselessness of traffic idle qualifies as a form of systemic madness IMO.

I really lose my rag on the rare occasions when people leave the air con - esp diseasels running in supermarket underground carparks.

I could understand or sympathise if they had an oxygen mask over the face or on life support.. but really.

I reluctantly must agree a poke in one eye is better than a poke in both and stop start is a step in the right direction even if kicking and screaming.

And yes ~ 20KW or so on a serpentine belt( and decompressor) is more than enough for the majority fleet of peak hour captives.

Some would say two options doen't count.

I find it pretty lame for clever people to be apologising for obsolete offerings on a forum that offers the opportunity to share and critique next G.

Any number of manufactures offer 'look at me' 'I'm so green' 'last years' lowball efforts.

I know we are better than that.

Much prefer to be mistakenly accused as fantasist than abandon aspiration.


By 2025 Paris, Athens, Madrid, London and Mexico City plan to ban diesel cars from city center. A mild-hybrid diesel will not qualify. Search for "Mayors of Madrid, Mexico City and Paris pledge to remove diesel cars from their cities by 2025"

Oslo plans to also ban gasoline cars by 2025. A mild-hybrid gasoline car will not qualify. I think we more European cities do the same.

Mild-hybrid has no plug, all energy still has be loaded as gasoline / diesel.

We need plug-in and 50 km range, then the car can do all city driving electric and can also be used in cities after 2025.

If you answer to my post, please write my name to make it clear.


Presently, our household is supplemented with two cars, a Yaris diesel and a Nissan Leaf. With two exceptions - range and design - my preference is definitely for the Leaf. With the market launch expected for September this year, the new gen. Leaf will replace both present vehicles. I can't understand why so many bank on fossil fuel guzzlers; as far as I am concerned, those vehicles belong to the stone age and that is history.

Mild-hybrid has no plug, all energy still has be loaded as gasoline / diesel.

And even with the next step up, the full hybrid.  (Disclosure:  I've been driving a plug-in hybrid since 2013.)

This doesn't matter.  The batteries of mild hybrids are too small to make grid charging worthwhile.  But getting rid of idling losses, converting belt-driven accessories to electric (which instantly makes them compatible with electric vehicles), and the other advantages appear to be worth it.


At a time when, as E-P. points out, belt drive is almost completely obsolete today these machines are extremely inefficient in terms of simplified and integrated design.

Indeed they are only physically possible because most if not all other belt drives have been discontinued.

vvvvv or serpentine belts are possibly the most time consuming and expensive high maintenance item on today's vehicles and that is why they are obsolete in every other application.

As for power transfer they fail here on every level require heavy idler pulleys and bearings a lot of space and then ~ 5 times less efficient than chain drive according to pushbike studies. The numbers quote
towards 20kW but don't mention the more important torque limit.
Cog belts are known to be an improvement in some ways especially power transfer they have their own set of maintenance and installation limitations.

The use of stop start suggests a questionable but cheap to manufacture work around to soften up it's power train through slippage and or stretch.


@ 8 am. eastern standard time. Disappointing way to start the day.
The "spoilt ranga" escapes the asylum yet again.
life goes on

For decades( even since the health benefits of smoking) we hear glowing reports of the benefits of some or other technology breakthrough.

The facts have been known and it's fair to say covered up for a century.
Industry interests have a lot of money invested in junk product and have no exit plan.

This is another aspect relevant to the topic.
Notice the ineffectiveness of SCR at low temperatures in stop start city and short haul suburban.

it reads in part:

"In 2015 the UK Government estimated that exposure to NOx and particulate matter emissions from diesel engines lead to around 52,000 additional deaths in the UK. NOx emissions are also the primary cause of smog in major cities around the world and a growing public health concern. This has led to growing pressure on vehicle manufacturers to reduce engine emissions.
most impossible to meet.

Currently almost all new diesel vehicles are fitted with a Selective Catalytic Reduction (SCR) system to try and remove NOx produced by combustion. This system uses AdBlue to safely provide the ammonia required to reduce NOx into harmless nitrogen and water.

The drawback is that AdBlue only functions well at high exhaust temperatures, typically in excess of 250 ˚C. Therefore, the SCR does not necessarily operate at all engine conditions, for example, during short, stop-start commutes, particularly in urban areas or on construction sites.

Further, use of AdBlue at these problematic lower temperatures can result in severe exhaust blockages and subsequent engine damage.

ACCT is an AdBlue conversion technology that uses waste energy to modify AdBlue to work effectively at these lower exhaust temperatures. By greatly extending the temperature range at which SCR systems can operate the new technology significantly enhances existing NOx reduction systems. ACCT is the only technology of its kind in the world, the researchers said."


"I've been driving a plug-in hybrid since 2013."

Yes, it has been possible to make plug-in hybrids for already many years now. E.g. BMW, GM, VW etc. have already done it.

"This doesn't matter. The batteries of mild hybrids are too small to make grid charging worthwhile."

That is the problem, mild-hybrid by 2020 is too little, to late.

With plug-in hybrids you can charge by power or fuel. That will spur consumer to ask for charge-points at public and residential parking.

Plug-in hybrids will make city driving electric and that is what is needed. Mild-hybrid is too little. A mere distraction from what has to be done.

If you answer to my post, please write my name to make it clear.

That is the problem, mild-hybrid by 2020 is too little, to late.

It's what we're going to get (as well as 500,000 Teslas a year more or less).  The micro-hybrids are going to accomplish more in aggregate than the Teslas.

With plug-in hybrids you can charge by power or fuel. That will spur consumer to ask for charge-points at public and residential parking.

Tell me something I didn't already know before I got my Fusion.  The problem is what to do about it?  I see charging points disappearing even where they were put in under DOE grant.

Plug-in hybrids will make city driving electric and that is what is needed. Mild-hybrid is too little. A mere distraction from what has to be done.

Then that's going to have to require measures such as prohibiting ICEVs (or a severely restricted set of fuels, like CNG only) in city centers.  Otherwise people will drive what appeals to them and they can afford.  We are already seeing prohibitions of diesels inside cities.

[Ad hominem comments excised by editor as not in keeping with policy. -MM ]

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