This interview series about the future of the car is produced in collaboration with Auto FutureTech – Summit 2008, a gathering of leading auto industry executives to discuss critical environmental and energy issues. Auto FutureTech will take place in Vancouver, B.C., Canada from March 12 – 14, 2008.

For the past 32 years, the fuel economy requirements for cars and trucks in the United States were stagnant. That all changed in December, when President Bush put his signature on a new law that slowly raises gas mileage standards for cars and trucks by 40 percent to an average 35 miles per gallon by 2020. As a result, carmakers will begin rolling out a parade of new advanced technologies to boost mpg. One of the most effective and feasible solutions may seem surprising to many American drivers. But diesel engine vehicles—that’s right, diesels—are on the rise, and could overtake hybrids as the darlings of the green car world. We spoke with Dr. Johannes-Joerg Rueger, vice president of engineering for diesel systems for Robert Bosch LLC, a leading manufacturer of diesel vehicle technologies.

Can you provide a high-level summary of Bosch’s work on advance vehicle technologies?

Bosch is working on all kinds of technology that reduces CO2 emissions and improves fuel economy, which makes us a company that can put things in perspective. We have second generation gasoline direct injection in combination with turbo-charging, and we have been working for many years on hybrid components. From Bosch’s perspective, diesel is the largest leverage that we have in certain markets like in the United States. Today, diesel is well below one percent of the passenger car market. And for all light-duty vehicles, we are at about five to six percent—compared to 50 percent in Europe.

Considering all the technologies that Bosch is working on, where does diesel fit in?

Diesel, compared to a standard gasoline engine, shows a fuel economy improvement of about 35 percent if you look at the European market. It’s very hard to draw that picture here in the U.S, because you have very few applications. But even if you look at the Grand Cherokee Jeep where you have a 3-liter diesel engine, and you compare that from a power and consumption perspective with a gasoline engine, which in that case would be a 5.7-liter engine, you have about 35 percent less fuel consumption. And we see further potential of at least 10 percent. So from our perspective, the gap even between an advanced gasoline engine and a diesel engine will be in the ballpark of 30 percent.

In Europe, we saw hesitation 10 to 15 years ago to equip luxury cars with diesel engines. This has completely changed. Nowadays, you have about 70 to 80 percent diesel share in the luxury segment. That means diesel is not just a rough engine just for people who drive light-duty vehicles, but it’s definitely an alternative for larger luxury vehicles as well.

How rapidly do you expect diesel cars to rise in the U.S.?

Our estimation for some time has been roughly 15 percent diesel share in light-duty plus passenger cars in 2015. That matches the expectation of most of the recent studies.

Do you think that U.S. customers can overcome their negative perceptions of diesel?

The key to overcoming those bad perceptions is to offer a variety of diesel cars in the marketplace that consumers can try out. We are convinced that the picture will change. Again, we’re talking about 15 percent diesel share by 2015. That means not over night. We’re not talking about the 50 percent we have in Europe. I don’t see that in the U.S., even in the long run.

To get there, you’ll need all the markets in the United States, including California. Yet, it’s so difficult to get a definitive answer on when diesels will be clean enough for California’s stricter emissions standards. When will see 50-state diesels?

The emissions standards in the U.S., and especially in California, are extremely tight. That’s clear. But many carmakers will enter the market. Mercedes, VW, Audi, BMW and most Asian carmakers will introduce diesels in all states.

But probably not in 2008.

The public announcements are that the German carmakers will enter those markets in late 2008. In the next year, we expect Asian OEMs as well, and you’ve probably seen some announcements, even from Toyota, that they will come to the market in 2010 with a diesel vehicle. We will definitely see a variety of different OEMs and different applications, down to passenger cars like a Jetta.

I’m pretty sure we’ll see those cars being introduced in the second half of 2008. I am definitely curious to see them at the dealerships.

Diesels can reduce greenhouse gas emissions, but do you see them ever becoming as clean as hybrids on smog-related emissions and particulates?

If you are talking about standard diesels, you have two challenges. Challenge number on is particulates, but with a particulate filter, you reduce them by 99 percent, nearly to zero. We are in an area where there shouldn’t be any further concerns about that. In Germany, we have about 70 percent of new vehicles equipped with a particulate filter. This is a proven valid technology.

So the problem is oxides of nitrogen (NOx) which contributes to smog?

Exactly. That’s a big challenge. That’s the reason why you don’t have cars equipped with diesel engines today meeting California’s low levels, known as Tier 2, Bin 5. In order to come to that level, you will need an after-treatment device, either a Selective Catalytic Reduction (SCR) filter or a lean NOx trap. Where you need the highest efficiency of NOx reduction, you will use an SCR filter, which is a urea-based system. They have been in the overseas market for about two years for commercial vehicles. So, there is experience with that technology already, and maturity of the technology is proven. These devices will not be just introduced in California, but will be the general technology used in diesels everywhere in the US.

If we consider that diesel is a petroleum-based fuel, and we look out to 25 or 30 years, does diesel have a long-term future?

Combustion engines, in general, have a long-term future. We won’t be able to replace all petroleum that we use today by renewable fuels. We have biofuels, and we will see synthetic biofuels in the market as well, which are called “second generation” biofuels. And of course, we’ll see electric driving as well.

The consensus these days is that we’re moving to an electric fuel infrastructure. Do you agree with that?

We will certainly see electric vehicles in the market. But if you look at the next 20 or 30 years, I don’t see that as the major contributor. Nevertheless, we have to work on that to make it come true by a certain time. But I don’t want to draw a picture that this is the ultimate solution that we should go for right now, because for the next 20 or 30 years, I definitely see combustion engines being the majority in the market.

By majority, you mean 51 percent?

Way more.

There’s a great deal of excitement about plug-in hybrids. And people talk about it as if it’s going to be widely available very soon.

It’s a good thing that we are working on it. It’s definitely necessary. Maybe if you look at the automotive business 10 years back, we didn’t put enough effort on improving fuel economy. But now, everybody wants to make a leap. I appreciate that people are working on electric and plug-in hybrids, but this won’t be available to the market tomorrow, and will not be 50 percent by 2010. Consumers are excited, but when they go to a dealer and look at cost, maybe the prices will be simply too high for those technologies. It’s mid- and long-term technology. In parallel, we have to do the first, second and third step, instead of just trying to do the fourth.