What does Euro 4 really mean?

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If you’ve read anything about new bikes over the last couple of years the chances are that you’ve heard the term ‘Euro 4’ bandied about.

You probably know it’s a set of tougher emissions rules, but meeting them is far more complex than simply sticking a more sophisticated catalytic converter in the exhaust and leaving it at that.

Euro 4 has been in the news because it affects almost all new bikes sold throughout Europe after 1 January 2017. Anything sold under previous regulations will still be totally legal and won’t be forced to meet harder rules. The new regulations are being applied only to new bikes, and over two stages. The first stage applies to newly-designed machines that first went on sale after 1 January 2016 – so things like Kawasaki’s 2016 ZX-10R and Triumph’s new water-cooled Bonnevilles are already compliant. The second stage, in force from 1 January 2017, applies to existing models, which will have to be updated and retested to prove they pass the new rules.

Compared to the Euro 3 emissions rules that have been in place for the last decade, Euro 4 represents a massive step forward. Not only are the absolute limits hugely reduced but the testing methods are becoming tougher and addition durability rules are coming into force to ensure that bikes remain emissions-compliant even as they get older.

Although there are different restrictions depending on a bike’s capacity and performance, the most important numbers are the ones that apply to unrestricted bikes over 125cc. They see CO (carbon monoxide) levels dropping from 2.0g/km (grams per kilometre) to 1.14g/km. Hydrocarbons will be cut from 0.3g/km to 0.17g/km and oxides of nitrogen (NOx) are cut from 0.15g/km to 0.09g/km.

To find out more, we spoke to engineers Paul Etheridge and Franz Berndt of Ricardo.

Ricardo might not be a name that’s familiar to everyone, but it’s a British firm that’s been developing engines for a century. Most of the firm’s work is bound in secrecy but there’s a strong chance that you’ve ridden a bike that’s had input from Ricardo, regardless of the badge on the tank.

Right from day one, emissions were key – the firm started when engineer Harry Ricardo was asked to reduce the amount of smoke coming from the engines of tanks used in WW1, resulting in him designing a completely new tank engine that was introduced in 1917.

You can't afford to lose a single horsepower. No one wants to buy a bike that's less powerful than last year's

Franz Berndt, Head of Thermodynamic Development at Ricardo
Franz Berndt

The numbers give a clue to the amount of work involved, as they clearly show that limits are close to being halved in most key emissions areas.

But that’s just the start. Berndt (pictured right) who is Head of Thermodynamic Development at Ricardo Motorcycle, explains: “Looking at the legislation and the numbers it’s an emissions reduction of 50 to 60%, plus the introduction of deterioration factors, which add another 30% of emissions reduction requirement.”

Those ‘deterioration factors’ are one of the key difficulties, as the 2017-on bikes need to be designed to beat emissions limits by a wide margin just to ensure they can still be under the limit when they’ve got several years’ worth of mileage under their belts. Etheridge adds: “For Euro3 you only need to pass the test when the bike is new, or after 1000km. Now you have to show emissions compliance after 20,000 or 35,000km depending on the size of the machine. So you have to engineer so that in a new condition you’re about 30% lower than the standards so that deterioration over time won’t put you over the limit at the specified mileage.”

Given the small average annual distances covered by bikes, it means Euro 4 motorcycles still need to be compliant after close to a decade’s worth of miles. How much catalytic converters deteriorate over that time depends on how well their emissions systems are developed in the first place. Etheridge said: “If the temperatures in the catalyst are reasonable and you don’t have things like oil poisoning or nasty things in the fuel to poison the catalyst, they are very durable. It’s application-specific and if you’ve done a poor application and got very high temperatures you can destroy a catalyst relatively quickly.”

Making catalysts more durable isn’t difficult, but it can be expensive. Berndt said: “A lot of oxygen and unburnt fuel in the coast-down region does a lot of harm to the catalyst. On the other hand, with some different chemical formation in the precious metal coatings of the catalyst can make them more durable. It’s nothing you’d see from the outside.”

Etheridge elaborated: “But the more precious metal you have, the more expensive it is. For Euro 3 there wasn’t a need to have very high quality or expensive catalysts in the exhaust because they weren’t legislated to last 20,000km or more. But now there is a requirement so they have to prove durability over this long period.


Getting older engines up to standard

New engines are terrifyingly expensive to develop. There’s no coincidence that firms will often build a wide range of bikes around relatively few basic engines. Just look at the number of BMW’s using the 1200cc boxer motor, or how many different models Honda has spun from the NC750 twin.

So firms are keen that even their older engine designs should be able to be modified to pass the new regulations.

“We focus on three things,” said Berndt, “The after-treatment system, the calibration and the combustion system itself. So there are some activities to cut the raw emissions by just having a better, more stable combustion. For Euro 4 the biggest part comes from the catalyst. When it comes to Euro 5 we will have to look at everything, but for Euro 4, even though the numbers show quite a large reductions of emissions, it’s still easier to achieve.”

Etheridge (pictured below) said: “The biggest update for the base engine, if you like, is the combustion system. There’s always been a bit of a trade-off between achieving maximum power and achieving good combustion stability at part load. When you’re riding through town you don’t want the bike to be misfiring or jerking. That trade-off is something that requires very detailed development of the combustion system to achieve the right compromise. That’s where a lot of effort is focussed, both with updating existing engines and developing new ones. We’ve done a lot of work on those problems in the recent past.

Paul Etheridge

“I’ve got a Hayabusa – a very early one – and it’s got a very early fuel injection system on it, it is open loop, it’s got no lambda control, it’s got a fairly rudimentary combustion system. And it does misfire a bit in town, it’s a bit jerky and the driveablity is not that good even though the performance is really good. If you look at the later Hayabusas they’ve got a much more sophisticated fuel injection system with more sensors and controls, the combustion system is better, and it’s a different animal. It’s much better in town, and it’s got more power than the old one. That’s evolution and development. That will continue and Euro 4 and Euro 5 won’t change that. The development of improved combustion systems will continue.”

How the testing is done?

There’s been a huge amount of publicity in recent months over the Volkswagen emissions scandal, where many of the firm’s diesel cars were designed to go into a special emissions-reduction mode when they sensed they were being put through tests.

That’s led to a demand for more real-world testing. It’s one area where bikes are already a step ahead.

Motorcycle emissions testing is done using the World Motorcycle Test Cycle (WMTC), which is designed to replicate the way a bike is used on the road, but in controlled conditions to allow comparative tests to be made.

Etheridge explains: “WMTC is now becoming globally accepted as the emissions standard test procedure. The old (ECE 40) test was just a step cycle, with a maximum speed of 50km/h, which is not at all representative of how you ride a motorcycle on the road. Later, for high performance motorcycles there was also a higher speed phase up to 120km/h added, but the average speed is now higher for WMTC and even more important the cycle is much more transient. WMTC is generally much more dynamic, with higher speeds, and is more real-world representative. There’s a relatively simple set of criteria that decide which cycle you use depending on the bike that’s being tested.”

Franz Berndt: “The complete cycle consists of three main parts. There’s a cold start part, which is quite slow, a medium part and a high-speed part up to 125km/h. There are also other variants where only 115km/h applies, depending on vehicle top speed. If you have a small-capacity vehicle you only do part one – once cold, once hot – and if you have a more powerful vehicle above 125cc and a certain power, you do them all.”

Electronic throttles. Are they the key to passing the tests?

Although ride-by-wire was introduced more than a decade ago on Yamaha’s R6, there’s been an explosion in its use over the last couple of years as manufacturers scramble to make their bikes Euro 4 compliant.

“For Euro 4 it’s not forced on them, you don’t have to use them. It’s a natural requirement, making it easier to meet the emissions tests. Ride by wire also has a lot of the furniture for the control strategy itself.”

“A lot of these technologies aren’t being forced on the motorcycle world,” said Etheridge, “It’s just how things are evolving. Ride by wire, for instance, has a lot of other advantages, like for instance you can smooth the torque curve of an engine. The rider will demand a certain requirement from the throttle, and the ECU can decide how best to give him that. So you don’t necessarily have a direct connection between what the intake throttle is doing and what the rider is demanding on the twist grip. That can give you driveability advantages, it can smooth the torque curve, it can give emissions advantages as well because you can optimise these settings independently of what the rider is demanding.

“As a general point of motorcycle technology, there are a lot of examples where it’s followed the automotive world – with some years of delay – and not every technology has read across from automotive to motorcycle but some have. And there’s a clear trend of how that’s happened over the years. It’s happened with fuel injection, with variable valve timing, with ride by wire, and these things give real improvements on motorcycles when it comes to the riding experience, not just to meet the legislation. But these things cost money, and that’s why it’s slow on motorcycles because the technology has to be mature, it has to become affordable and at that point it can start to be adopted and really to give a benefit.”

With electronic throttles becoming commonplace, traction control and multiple riding modes have also spread. Those riding modes add an extra layer to the complexity, as it’s not clear whether there’s a requirement to select a specific mode when a bike goes through the WMTC that is used to test a bike’s emissions. It’s likely that a bike will simply be tested in whatever mode is selected by default.

Franz adds: “Different bikes use different strategies. Some bikes, if you put them in sport mode they stay in sport mode. Other bikes might revert to another mode [when they’re turned off and on again]. In our opinion it’s not that critical and as far as we know all of them are homologated to meet the emission requirements. But that is not so difficult because at the moment it is still much easier for a motorcycle to meet the emission requirements in the low WMTC zone because you don’t use the complete engine map in the test cycle. If a bike can do 200km/h or 300km/h and is being tested at 125km/h, you use a low load, low speed zone [of the map].”

If that changes, and it appears that bikes are using technologies where different maps will lead to wildly different emissions performance, it’s likely the test will be updated to reflect that. Berndt said: “If you look at the passenger car world, they use turbochargers, VVT, scavenging, other technologies. You can do a lot of different stuff that has a large impact on emissions. Some countries, like Japan for example, require that a car is tested in the worst engine mode.”

At the moment, though, the alternate maps aren’t thought to impact emissions. Etheridge said: “For a bigger bike, even if you’ve got different modes, it’s quite likely that the speed and loads that you’ll drive over the WMTC, that part of the map will be the same across all modes anyway, so it may not apply." 


Are emissions limits killing 600cc supersports bikes?

Not long ago we wrote about the impending demise of the once-dominant 600cc supersport class and the Ricardo guys confirmed that they’re a category of engine that’s particularly hard-hit by Euro 4 emissions rules.

Etheridge said: “That’s probably one of the most difficult engines to make emissions compliant.” Berndt added: “You’re looking at really high engine speed, which requires high valve overlap. This makes a difference for sure.”

“You can’t afford to lose a single horsepower when you go into a new emissions regime,” explained Etheridge, “Nobody wants to buy a bike that’s less powerful than last year’s model. That’s a particular issue for bikes in that sector and those are probably the most difficult ones to make meet the regulations.

“In those sorts of engines there’s a real benefit in something like variable valve timing but that’s a real tear-up of design. For sure it’s a new cylinder head design and probably other changes as well, and also it’s very much a packaging issue as well. Those supersports bikes are so tightly packaged that you can’t fit an awful lot of exhaust emission control technologies that are out there and available.”

Yamaha YZF-R6

Throw in the fact that supersports 600s are now selling in such small numbers that it will be near-impossible to justify the expense of the all-new engine designs needed to lever them through the Euro 4 and later Euro 5 tests and it’s increasingly clear that they’re likely to disappear from showrooms altogether.

The packaging problems aren’t limited to supersports bikes, though, as Etheridge explains:

“As emissions get more severe up to Euro 4 and then to Euro 5, the contribution of cold start emissions becomes much more significant. The emissions produced in the first 60 seconds from cold become a much larger proportion of the total emissions over the cycle. The obvious thing to do is to move the catalyst further forward because you need to get the catalyst alight and working as soon as possible. Look at cars and you’ll see the catalyst right up by the exhaust manifold. You can’t do that on a motorcycle – it kills the performance, it kills the look of the vehicle and then you’ve got thermal problems to deal with as well. So it’s not so easy on a motorcycle. You want to do it, you want to move the catalyst forward. It’s no good having an enormous catalyst in the muffler if it doesn’t light off for three or four minute – you’ve failed the test before you’ve even got the catalyst alight. There are a lot of technologies being applied to making catalysts light off as soon as possible by other strategies, other than just putting the catalyst as far forward near the engine as you can. It’s a particular problem with motorcycles.”


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