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Emission testing

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EMISSIONS TESTING

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In emissions testing, technology is king. It plays the leading role in ensuring legislation targets are achieved, while enabling engineers to face increasingly difficult challenges.

One of the leading suppliers of systems and equipment facing these challenges is Horiba Automotive Test Systems. Les Hill, leader of the

company’s global product planning group, says, “Nowadays, having a successful test facility is not just a simple question of accurate emissions measurement capability. You also need an accurate and repeatable engine or chassis dynamometer to simulate the loading during operation, the test cell environmental conditions and their control, and the test automation system. Only when you put all these together can you produce data that’s realistic, repeatable and reproducible.”

Also vital for precise emissions measurement is the means by which gas from the exhaust is extracted, conditioned and processed. Enter the

sample handling system (SHS), which must eliminate unwanted components, such as contaminants, that affect an analyzer’s performance, while keeping the components that need to be measured intact. “The required combination is analyzer technology with an effective SHS, and a controller with an easy-to-use operator interface as well as a comprehensive interface to test the automation system,” says Hill.

To this end, the company has developed flow controllers and system controllers, and recently launched its Horiba One Platform, which enables the integration of a greater number of instruments, analyzers (between 5 and 30) and SHS modules, organized into multiple lines of analysis – for example, tailpipe, engine out, mid-bed or diluted exhaust streams.

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A fully equipped Horiba emissions test cell including an ADS-7000 Automatic Driving System. When integrated with appropriate measuring equipment, a chassis dynamometer and the test cell computer, ADS-7000 allows automatic laboratory operation

Comments Hill: “The system controller has to be flexible to handle a multiplicity of configurations within the system, and that’s what we’ve managed to achieve. It will enable us to fulfill future OEM requirements, which will be for more components with a greater capacity for customization.”

Meanwhile at UK-based Cambustion, engineering manager Chris Nickolaus highlights the move toward normalization of drive cycles, as part of the world harmonized light-duty test procedures (WLTP), as one of the industry’s current challenges.

“I’m running a WLTP on a chassis dynamometer,” says Nickolaus. “It’s more transient than NEDC, so it’s more demanding in terms of getting the robot or human to drive it accurately. But also in terms of optimizing the vehicle and the engine calibration, it needs a lot more time spent on optimizing the transient operation because you encounter a wider range of engine speeds and load operating conditions.”

In addition, Cambustion recognizes an increase in the use of automated mapping – placing an engine on a dynamometer and using a test matrix, while a computer optimizes all considerations. “For example,” says Nickolaus, “we have instruments running in test cells for three shifts a day, and the engine is being run at different steady-state and transient conditions to map all the emissions. Then you can choose different operating conditions or strategies to optimize. Automated mapping enables you to get a lot of data in as short a time as possible.”

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Horiba’s chassis test cell features a chassis roller dyno for the emissions testing of passenger cars and other light-duty vehicles

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The flexible engine test systems in Horiba’s Titan series offer extensive test functionality

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Catagen’s first Maxcat unit has been bought by Mahle Powertrain

Dr Dean Tomazic, executive VP and CTO at FEV, argues that the most effective emissions testing takes into equal consideration the engine, transmission, vehicle integration and chassis development. “You have to work all technologies together,” he says. “In simulation you need to go through lots of scenarios to identify the best configuration that will enable you to meet your targets. There’s a lot of upfront work to configure the overall system and then optimize each component. The rest is calibration and application work, and from an algorithm development perspective, with new software in the controller, we look at airpath models to minimize engine-out emissions, as well as different direct-injection strategies and warm-up strategies to optimize the catalyst operations.”

Eric Watel, engine expert at Critt M2A, agrees that mastering huge product diversification is a major challenge in powertrain development: “To improve fuel efficiency and minimize engine-out pollutant emissions, the turbocharger matching must be perfectly optimized for each application. It requires a consistent application of simulation models and, therefore, thorough testing of the turbocharger to feed those models.”

Critt M2A’s turbocharger testing facilities comprise four development gas stands. “We are improving our experimental setup to extend the

turbocharger characterization,” says Watel. “The challenge is to implement industrial measurements that fit with advanced simulation models, only used in the academic world at the moment.”

Like turbochargers, aftertreatments have become increasingly important to passenger-car engines in recent years. Pi-Innovo, a services company based in the UK and the USA, has developed a range of one-dimensional mathematical models of common aftertreatment system components, such as DOC and DPF, taking input from conventional sensors and creating virtual sensors to understand what goes on inside components, including catalysts and filters. The models enable accurate control by predicting parameters such as temperatures, pressure drop, soot load and emissions in real time.

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Chris Nickolaus and director Bruce Campbell with a test vehicle on chassis rolls at Cambustion. The company is based in Cambridge, UK

“Estimating gas species, temperatures and pressures inside the middle of the cat is necessary, says CTO David Price. “You can easily put in the temperature probes, but trying to get an undistorted sample of gas out of the middle is almost impossible without disturbing the flow. We use temperature samples at various points inside, and immediately in front of and behind each element of the cat.”

With the stringent Euro 6c legislation scheduled for full implementation in passenger cars by September 2018, the future will bring greater demands to measure particle numbers and small size particles for particulate matter. Price foresees further challenges: “The particles are so small, the question is how to trap and count them. Plus, they have a habit of coalescing and then breaking down along the exhaust.”

He also predicts that their impact on the public’s health will come to the fore: “There will be studies that show they have even more effects on health than thought. But the health problems they cause aren’t necessarily related to what comes from the tailpipe; the problem is when they get into the air and react with other things.”

Another expected trend – perhaps still five years away – is onboard measuring of real driving emissions (RDE) through portable emissions monitoring systems (PEMS). Cambustion’s Chris Nickolaus believes this will happen because “there are concerns that diesel NOx might not have fallen as much in the real world as hoped for. With RDE, you do all the usual development and certification, and then you’re checked up on in the real world against certain limits – but nobody knows what those limits are yet.”

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Thermal testing of turbochargers at Critt M2A. Like Horiba, Critt will be exhibiting at Automotive Testing Expo in Stuttgart

He continues, “Getting any piece of equipment that’s used to working on a test bench to work onboard a vehicle is difficult. When you run on a test bench, you’ve got all the electrical power you want, but onboard you don’t want to load the vehicle with electrical systems because it skews the results if you start drawing power from the alternator. That means running off batteries, which means traditional vacuum pumps that produce a lot of heat are out of the question because they’ll flatten batteries very quickly.”

Pi-Innovo has already trialed this kind of testing, fitting analyzers into the back of a pickup truck. Price says the test was useful because it was

possible to have a range of drivers employ random driving styles while monitoring emissions. The measurements weren’t as accurate as in labs, but Price adds, “It’s better than simulation, because drivers do all sorts of things that can’t be anticipated in simulation.”

And Horiba’s Les Hill concludes, “To cater for the future trend of RDE using PEMS, our system solutions need the ability to integrate and exchange data with other test cells, such as chassis, powertrain, and engine. The test cells themselves already have a much wider range of environmental control – from sub-zero to above 40°C, for instance – and these will increase in number in the future.”

New kid on the block

Catagen made quite a splash at last year’s Automotive Testing Expo North America in Novi when it unveiled Maxcat, its first 200g/sec

flow-rate test rig for catalyst aging. The company has now sold the first Maxcat to Mahle Powertrain but it is currently at Catagen’s base in Belfast, Northern Ireland, running correlation studies and contract testing.

“Aging catalysts is a headache for the OEMs and this technology opens up opportunities for them to reduce costs, but gives them greater

flexibility in their testing as well,” explains Professor Roy Douglas of Queen’s University of Belfast, one of Catagen’s co-founders and a former

Ford and GM engineer.

The appeal of Catagen’s equipment lies in the energy savings offered over traditional engine-based catalyst aging methods. According to another of the founders, Andrew Woods, the company’s technology – based on Woods’ own PhD research – is up to 90% more energy-efficient

than using an engine to do the same test, resulting in operating costs up to 85% lower than engine-testing a cat, and produces 98% less CO2

at source. Catalyst characterization testing, such as light-off tests, can also be performed on the same equipment.

Correlation studies to demonstrate the capabilities and savings that are possible are now being performed on the Maxcat, which is flexible enough to reproduce the engine exhaust gas composition, flow rates and temperatures of OEMs’ individual aging cycles. The studies will complement similar data from the smaller, lower flow-rate Labcat unit. On completion of the studies, the Maxcat will be delivered to Mahle in Farmington Hills, Michigan.

International variations

“At the base level of equipment, there is a great deal of commonality,” says Horiba’s Les Hill about the global emissions-testing picture. “But it changes higher up in the process, such as when you look at the type and number of test cells in use. Some OEMs like to do as much testing as possible before the real vehicle is used – at the engine or powertrain level. Other OEMs tend to do less upfront and more at the vehicle level on chassis dynamometers. In addition, the type of analytical and SH systems you supply can depend on alternative fuel initiatives in certain countries, such as the use of CNG in Brazil.”

FEV’s Dean Tomazic adds, “Regulatory requirements dictate in many cases the use of specific equipment. An example of different measurement methods are those used for heavy-duty gaseous emissions, which are governed by 40 CFR Part 1065 in the USA. These highaccuracy requirements exceed the levels that European and Asian measurement systems have to demonstrate.”

And Chris Nickolaus of Cambustion highlights a Russia-specific manufacturer test that demonstrates some practical differences: “Because

of low ambient temperatures, there’s a test conceived around a parked vehicle with a gentle tailwind. Customers idle their cars to provide cabin heat, often for prolonged periods. They want to check that the combination of the engine and the aftertreatment system are capable of tailpipe emissions that couldn’t cause CO poisoning, if the tailwind blows the exhaust gas toward the cabin air intake, for example.”

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A natural gas test cell at FEV North America. FEV has seven engineering centers across four continents