Turbochargers: an interview with Garrett’s Martin Verschoor
by Terry Parkhurst. Copyright © 2006 Terry Parkhurst; all rights reserved; used by permission.
Martin Verschoor is the technical director of Garrett Engine Boosting Systems. He is originally from Holland; and known to most people within Garrett as simply “Mart.” Mart is the go-to guy in terms of questions on the future of turbo development. Here he shares his thoughts on American versus European performance parameters, and how the turbocharger can be applied to emerging technologies such as hybrid (gas IC and electric) cars and fuel cells - for both Garrett turbochargers and other brands.
Why are turbochargers more readily accepted in Europe and what do you think that need to be done to make turbos more popular in the United States?
There are a few elements in place and what it comes down to is economy and driving style, the European driving style. By applying turbocharging technology to engines, both to diesels and gas engines, a turbocharged car consumes less fuel than a non-turbocharged car. Comparing horsepower-to-horsepower, a turbocharged engine consumes less fuel in day-to-day use, than a non-turbocharged car does.
In Europe, where overtaking [is the key benchmark], rather than the 0-to-60 (mph) sprinting that is the benchmark in the U.S., and you have lighter, more dynamic vehicles that do better in overtaking than a heavy vehicle that might do better in a straight line, the engines are smaller. In Europe, if you go over two liters, that’s a large engine. In the U.S., three to four liters is where a big engine starts. And in Europe, fuel is so expensive, that even with the relatively small price advantage of diesel, diesel can be made more attractive with a turbo. Turbo-diesels in Europe are wonderful, responsive, and very powerful; plenty of low-end torque and you can still achieve 45 miles-to-the gallon in a midsize sedan.
What needs to done to make turbochargers more popular in the States?
I think turbos need to be tuned to “drivability” more than sheer horsepower. If you look at the turbo applications in the United States, fifteen years ago, they were basically highly souped-up, highly boosted, standard engines. If you take a different approach and used turbo-charging to increase the low-end of the engine, you’ll actually see better drivability from a two-liter engine than a three liter (non-turboed) engine: more torque, more low-end response, higher top end and better fuel consumption. American OEMs need to realize you don’t use turbos for horsepower alone, but to enhance the total driving experience.
You can make the engine 30 to 35 percent smaller, which takes all the weight away and you might use fewer cylinders and overall you have a lighter drive train.
Given that U.S. passenger cars and light trucks are mostly powered by gasoline rather than diesel, what technologies does Garrett have in place for gasoline engines vehicles?
Relatively conventional known, turbo technology that has been around for fifteen years, has not been applied to large scale to American vehicles. We have low-inertia, fast response turbos in our product line, which will do an excellent job in the average motor vehicle. But if you want to take it to the next level, you must be mindful of future emissions standards.
To meet those standards, you must run at higher exhaust gas temperatures than modern engines. To comply with (projected) fuel economy and emissions standards, you must make your turbocharger very heat resistant. You need to run over 1,000 degrees Centigrade to be able to meet emissions standards at full load conditions. Modern turbochargers are very capable of doing that. There’s the possibility that turbochargers will be the first requirement of modern gasoline.
Water-cooled bearings availability will help. Another thing you need is controls. How do you make it as transparent as possible? We have REA – rotary electronic actuators –, which allow us to match the turbo to the engine. You can also have a linear device; both are available. They can be used for waste gating, as well as controlling the compressor.
One of the most critical things to meet emissions regulations is fast catalyst light off. When you make a turbocharger lighter, smaller, you take a lot of heat inertia away. Modern turbos are 50 percent lighter than (they were) just five to ten years ago. With more accurate control, we can guarantee a faster light off and meet emissions compliance.
What do you do to make a turbocharger viable in the U.S.? It’s twofold. You want to make it drivable but also give it lasting emissions compliance. Compliance breaks down to cold start emissions – catalyst light off – and full load, heavy-duty compliance, for which you need high temperature capability.
What innovative technologies has Garrett developed to help meet these challenges in the U.S. market?
We also have a very low friction bearing system available, where even at very low exhaust gas flows, you can get significant boost pressure out of it.
VNT technology – variable nozzle technology – will be as beneficial to gasoline as diesel. The hot side of the turbocharger, the turbine, is where we try to obstruct energy out of the hot exhaust flow. At low engine speeds, where there is relatively little flow, little temperature, we locally accelerate the flow and there is better kinetic transfer of kinetic energy from the gas to the wheel. I like to compare it to a garden hose: if you have the hose further away, you squeeze the hose. VNT does miracles; it brings available torque down to almost idle speed. In the old days, you had to rev up your engine – gas or diesel – up to 2,000 rpm. Today you see full boost at about 1,500 rpm.
What is the challenge to adopt VNT to a gasoline engine? It is twofold. VNT is more sophisticated. There are more components involved. Because a gasoline’s turbo runs higher than a diesel, you have to demonstrate that a VNT is more high temperature capable. I don’t think that there are gearboxes and clutches out there that could handle the torque and power at low speeds that VNT could produce at low speeds. It would require significant upgrades in the power train of the vehicle. There’s such an improvement over naturally aspirated engines, that the step to bring VNT is further out. The OEMs have to work hand-in-hand with the suppliers (of turbochargers.)
What is E-boosting and what are its prospects? E-boosting stands for electrical-assisted boosting; by incorporating a very high speed electrical motor in rotating assembly of a turbocharger, you can drive it up to very high speeds, before you have exhaust gases to do so. It is very powerful, specifically when there is no exhaust gas available, such as at idle, or in stop and go.
It is entirely integrated inside the turbocharger, with virtually “real-estate” penalty to speak of. The size of the electric motor is about an inch long. It makes the turbocharger an inch longer, with no impact on the timing and virtually no impact on the weight. The trick is to make electrical motors are capable of motoring more than 120,000 rpm and withstand mechanical loads in excess of 200,000 rpm – because turbos spin that fast.
The other challenge is to get enough electrical energy into their designs. The majority of cars use 12 volt or a 14-volt alternator.42 volt would be a significant help. But we believe that electric boost is feasible with 12-volt systems. The prospect is very real for electric boost. You will see it in premium diesels such as the Renault Aspach (sic) or the Peugeot A06 (in Europe). They have limited space and need lots of power density and bottom end. I also clearly see it in high-end gasoline engines, built for high performance.
I could imagine it in a (Chevrolet) Corvette or (Ford) Mustang Cobra like vehicle, having an electrical-assist turbo. If you go to 42 volt or a hybrid, e boosting would also allow very aggressive downsizing of the (IC) engine. This would allow very aggressive downsizing of the engine. Instead of applying a three-liter V6, you could apply a one-liter internal combustion engine, equipped with an electrical boost turbo plus an electric motor. You can only do extreme downsizing – 50 percent or more – with electrical assist turbocharging.
Ceramics used to be a mainstay of turbos. What sort of metallurgy and materials does the future hold for Garrett turbos?
It goes back to temperatures. The new alloys must be more temperature resistant, both in gas and diesels. They must survive at more than 1,000 degree Centigrade. At the same time, we are looking for lighter alloys. For example, we are actively looking at ways to reduce the weight of the turbine wheel. The turbine wheel defines about three-quarters of the total inertia of the turbocharger. If you address the weight of that, and take away half of the weight of that, you’d take away half of the inertia.
Ceramics are an active way to reduce the inertia but they’ve proven to be relatively fragile and they don’t allow as much optimization for aerodynamics as alloys do – such as titanium.
There’s been an incredible reduction in inertia. The new materials will allow a 30 percent reduction in inertia in the near future.
What other vehicle systems does Garrett take into account when designing turbos for the future?
Everybody in the world talks about two future alternatives: hybrid and, further out, fuel cells. Hybrids would not need turbochargers, but the internal combustion part of the hybrid power train becomes better by boosting. You are able to extract more energy and improve fuel efficiency on a hybrid’s IC engine. On top of that, you have the availability of high-voltage electrical power, in excess of current designs; you have the potential to do electrical assisted, almost electrical driven boosting. That’s clearly where we see a lot of potential.
With fuel cells, although there are no moving parts, they burn fuel; some burn fossil fuels – butane or methanol. When you heat the fuel cell and create a chemical reaction, you get heat. There is warmer exhaust from a fuel cell; when you take the pressure or energy belts from inlet to outlets, of a fuel cell, you can drive a turbocharger.
To get reasonable power density, you need to compress the air. It absolutely requires supercharging. Part of the electricity is stolen away from the wheels; that electricity is taken to drive the fuel cell. You can take that energy requirement away by using a turbocharger. Only five to seven kilowatts is required to move the vehicle. You increase the overall efficiency of the system by several kilowatts (with a turbocharger). The fuel cell then produces 10 to 12 kilowatts. You see a substantial increase in increased power consumption reduction. You can see another 20 percent fuel economy enhancement.
There are also various types of hybrid applications. You save an incredible amount of fuel in the city – low speed stop-and-go. That’s where the fuel savings of the hybrid concept are. Hybrids only save fuel on the freeway, at constant speeds, because it has a small internal combustion engine; the electric motor does nothing. On the freeway, a downsized, turbo-boosted internal combustion engine in a hybrid will have a significant impact. You really help the long commuter.
How is Asia different from Europe and the U.S., and what does the future look like for technology in China, Japan and Korea?
It’s interesting to see how automotive interests, fuelled there by the automotive infrastructure – both fueling and roads – and the driving are playing on the same type of sensitivities: modern design, light but muscular, good handling and reasonable fuel economy. I would say that the Japanese, Korean and Chinese and European engine philosophies are virtually the same. Diesels are a bit bigger in Europe, because of the cost of fuel.
When you look at the Chinese mainland, very few people have private cars. So when you talk about turbocharging private cars, you have to talk about the availability of private cars. Fuels and car will be very expensive for a while. The average Chinese citizen will be very sensitive to cost. So diesels and downsized, turboed engines will be interesting, from an operating perspective.
I am not optimistic about a booming market for the next five years; but it will come, it will come. The main thing we see, as a company, will all be commercially driven. We see a high growth rate due to the commercial market.
It has been clearly demonstrated that to be successful in China, you have to bring the latest and the greatest, from day one. Other specific OEMs have made the mistake of bringing sending their obsolete manufacturing lines to China, and the Chinese choose the more modern over those. We, as a company, have a strong conviction, which you have to have the most modern technology, from day one.
The Chinese diesels OEMs have the same access to modern technology as anywhere else. VNT technology will be there soon. The emissions levels are at the Euro 2 level and will be at the Euro 3 level by 2008. They are really catching up fast from an emissions perspective. Of course, there are very few vehicles on the road, so in terms of tolerance, there are very few problems with emissions, unless you are in downtown Beijing or Shanghai.
In the period from 1990 to 2001, the total percentage of turbocharged and supercharged engines in the U.S., remained the same total – 1.7 percent – but superchargers, in that period of time, exceeded turbo users?
Yes there is a change. Turbos are clearly going to overtake, if not dominate the boosted market. But don’t forget that 20 percent of the imported cars (to the United States) are turbocharged. Consider the VW 1.8 turbo that sits in the Golf, the Audi and the VW Passat. There is no Saab imported to the U.S. that isn’t turbocharged – or look at the Volvo S40, S60 or S80.
There is always going to be a market for mechanical superchargers. But they don’t find as many fuel economy or power density benefits as a turbocharged engine. The reason they were relatively easily to install on engines, especially in “V” engines and that’s why you saw them on the American engines. They’re relatively straightforward from a manufacturing standpoint, but you don’t see the fuel economy or other benefits.
A turbocharger is a more elegant solution – but then I am biased. With a supercharger, it does nothing but making a bigger displacement of your engine, artificially increasing the displacement of your engine. With a turbocharger, you actually do some energy recovery and that’s where the difference is.
How do you define energy density?
If you want to talk in units, you think about kilowatts, versus liters of engine displacement. It’s a common perception that it is harder to get more than 100 horsepower out of a liter, in a normally aspirated engine. With a turbocharger you change that. In Formula 1, you saw as much as 600 horsepower out of a liter.
Turbocharging allows a hundred horsepower out of a liter, with still a lot of bottom-end drivability and torque. A relatively basic turbo charging system can substitute for a variable valve timing and variable induction – which are very costly. And you then have a better engine (overall).
A turbocharger can become a more sophisticated engine and save money?
On a two-liter engine, you have a better engine and less cost to the customer. You can save $1,000 to $2,000 on an engine.
Is turbo-lag a myth?
A properly engineered, turbocharged car, will have no turbo lag. You need to trick the car into turbo-lag. A turbocharged car tuned properly will have no turbo lag; but if it is tuned to the high-end, it may have some turbo lag.
Diesels have a natural, low speed torque behavior. Gasoline engines want to speed higher.
What does Garrett have for Japan and Korea?
Almost all Japanese and Korean OEMs are launching world-class turbo diesels. 45 percent of the engines sold in Europe are diesel and nobody wants to miss out on that. Japan and Korea are very much world players.