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“If you’re in the emissions game, heat is your friend,” says Tenneco’s Chief Technical Officer, Dr. Ben Patel. (image: Ryan Gehm)

Tenneco takes active (and passive) approach to thermal management

At the inaugural North American Commercial Vehicle (NACV) Show in Atlanta this past September, Tenneco executives detailed the company’s latest system solutions developed to address two key goals for commercial trucks: reducing criteria pollutants and improving fuel economy.

Chief Technology Officer Dr. Ben Patel shared Tenneco’s underlying strategy for how it develops products: “When you think about ‘clean air,’ and think about emission control in general, there is one primary rule—the lowest cost of compliance is always going to win.” And cost is more than just dollar signs, he noted; it includes cost of complexity, value of packaging advantages, weight and other considerations.

Patel gave Truck & Off-Highway Engineering a tour of the company’s mobile technology display at NACV, discussing industry trends and technology concepts that will likely hit the market in the near term. Active and passive thermal management solutions were a big part of the discussion.

“People like to mix all emissions when they talk about emissions, but you've got to think about NOx and PM separately from how you think about CO2. That said, there are product solutions that [can address both],” Patel said. “Waste heat recovery is going to play a role, because efficiency is so critical. Think about the end customer, the fleet owner, and how the biggest number on the page for them is very often fuel on the total-cost-of-ownership (TCO) model. So anything we can do to help fuel economy, and a big thing we can do is help harvest back some of that free heat that's about to be thrown out the tailpipe.”

Many believe solving for NOx and CO2 is not compatible. So you feel differently?

That's a paradigm that I reject; that you solve for one or the other. If I want to solve for fuel economy (CO2), whether it's in a commercial truck or off-highway piece of equipment, I want to set a calibration which is going to run an extremely hot engine cycle, because I want the maximum energy in my combustion process. That's going to be great for fuel economy, but it's going to be terrible for NOx. The outcome of that is my engine-out NOx is going to be higher. So if I have traditional SCR (selective catalytic reduction) capability, I may not be able to abate all of that NOx and still hit the tailpipe requirement.

But what happens if I develop really efficient SCR conversion, and I go from let's say 95% conversion to 98% conversion. Now I don't mind that I'm making a whole bunch more NOx, because downstream of that my aftertreatment can manage it. Then I've got the best of both worlds...Now, it's very application specific, but the methodology to get there is defined, and the tools and subsystems that you would put together are there. So I may choose a different advanced mixer design depending on an engine calibration, but the fundamental approach will be the same.

What are you working on related to ultra-low NOx?

We’ve developed a Beyond Euro VI concept that’s meant to be a demonstration of what is possible—the conversation with Euro VII, there's conversation about nationalizing what's going on in CARB (California Air Resources Board) right now with the low NOx program. In this solution, we've got all the conventional components—DOC (diesel oxidation catalyst), DPF (diesel particulate filter) and SCR—we’re taking advantage of the fact that our aftertreatment system is also one of the richest spots for extracting heat. So we’re starting to build into that design the potential to have an evaporator, which could be the lead component to a Rankine system. We’re thinking about what we can do all the way from the manifold to the tailpipe. Our historical real estate has been the aftertreatment component, but now what we’re asking ourselves is how can we help our customers have more options, so they can decide what are the trade-offs they want to make as they go after that TCO model.

A couple of components that fit in this Beyond Euro VI concept are upstream from the aftertreatment. So thermal management—if you're in the emissions game, heat is your friend. Every 10°C doubles the kinetic rate of a reaction. So if you think about all the chemical reactions that are happening from the moment the exhaust enters the aftertreatment—whether it's oxidation, whether it's reduction of NOx to N2—all these chemical transformations are benefitted by heat. Anything we can do that's cost-effective to maintain the heat that is already there, and in some cases, extract from it and turn it back into electrical or mechanical energy, those are ideas that we want to contemplate.

How are you better utilizing heat to achieve NOx goals?

Two thermal management strategies: one passive and one active. Fabricated manifolds that are modular, with air-gapped pipe—a pipe within a pipe—are passive. What that does is it allows air to be used as an insulation material. It reduces skin temperature and takes the heat coming right out of the engine, and prevents its loss. This is a lightweight strategy—it's a lot lighter than a cast manifold—so you get the benefits of weight reduction as well.

That heat can now be used downstream, and there’s the Cold Start Thermal Unit, which we originally designed several years ago as active regeneration for a diesel particulate filter. We thought instead of people having to do park regen on the side of the road, we can just burn fuel and burn off all the soot on a filter. Turns out, that's not where the market went so we put it on the bookshelf. Then we realized, it could have a second life in terms of heat generation for active management of catalysis light-off. So we shrunk it down and integrated it into the exhaust pipe. Now we can introduce incremental heat into the system when it's needed—either in a cold part of the duty cycle, or something that’s going to be enabling Real-Driving Emissions [test regulation], as that comes from Europe to North America. So that's a really important concept to think about, how do I introduce heat when it's needed on-demand in the most efficient way?

With passive and active [strategies], you can manage the temperature of the exhaust so that you optimize the catalysis that's happening either on the diesel oxidation catalyst or on the SCR brick.

Either of those in production today?

Fabricated manifolds are out in production in the light-vehicle space; they’ve been used in Europe. In the commercial-truck space, this is ready to go but it’s not in the market. Same thing with the cold-start unit, this is at a stage of development that we’d be ready for production if we got an RFQ tomorrow.

What about the possibility of delaying the use of the heat that's generated, to save it until needed?

On the real front-end of innovation at Tenneco, we've got a research group and we’re looking at, for instance, phase-change materials which do exactly that. How can you store energy? People think about a battery as an energy-storage mechanism, but there are phase-change materials where I can take energy in and go from one phase of the material to another and trap that energy, and then release it later on when I need it. The cold-start emphasis of the test cycles and the Real-Driving Emissions push that is coming our way is moving us into a new paradigm. We're going to need to have fidelity from the lab to the road, which we’ve never had before and now the Europeans are doing. That’s going to start to require very creative solutions.

You mentioned fuel efficiency and the potential of waste heat recovery. Where does this stand?

A common question is, where is waste heat recovery going from a cost-benefit standpoint? You can see that today at 50% brake thermal efficiency, probably not a business case, especially at $2.50/gallon for diesel. But when we get to 55% BTE, which I believe is probably in the 2022 to 2025 timeframe, and we get to a point where all the low-hanging fruit has already been absorbed—all the aero stuff is already on the vehicles today—harvesting back 3-4% of that energy that you were going to throw away anyhow—I call it ‘free heat’—that becomes the question. 

A traditional Rankine system has a distributed architecture—it's complicated. It's a tear-up for a powertrain guy. What we’ve done is taken all of those distributed components and we've packaged them into a very small ‘power pack,’ which can now be mounted on the frame rail. So if you've got complexity that you don't want to manage under the hood, you can now take all of those components and mount them right next to that Beyond Euro VI aftertreatment box, which has the evaporator in it, which is the first step of a Rankine system because you need the heat to boil the working fluid..Nobody has a crystal ball, but the reason it's important for suppliers like Tenneco to be investing in these types of development activities today, is when the customer is ready, this takes years to develop, years to validate, you need to start early.

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