GMnext: Answering Your Diesel Questions

SEE ALSO: Editorial - Where are the Electric-Diesel Hybrids?

Editors Note: There have been a lot of comments and questions on the GMnext site regarding diesel fuel and its part in GM's alternative energy strategy. To continue the conversation, Charlie Freese, Executive Director of GM's Diesel Engineering and the members of GM's Powertrain Diesel Engineering team have some answers to your most commonly-asked questions:

1. Plain and simple, what are the advantages to using diesel fuel over regular gasoline?

Diesel engines provide vehicle fuel efficiency benefits of 25% fuel efficiency improvement over comparably powered gasoline powertrains and the advantages extend to 40-70% for heavy load hauling situations.

The advantages of diesel engines are clear. The problem is that diesel powertrains add considerable cost, compared with the equivalent gasoline powertrain. These costs are driven by the fact that the diesel engine is a more complex powertrain and by changes to global emissions legislation – particularly in the US.

Modern diesel engines require more complex high pressure fuel systems, variable geometry or staged turbochargers, cooled Exhaust Gas Recirculation (EGR) systems, more robust structures, and extensive after-treatment systems.

In the US, tailpipe standards for diesel vehicles are being updated so that diesel and gasoline vehicles will have to meet the same set of emissions standards. For diesels, this will mean an after-treatment system to control the NOx will be required, in addition to a diesel particulate filter to control the soot, which adds cost to the price of the diesel engine. Finally, fuel supply limitations in North America are also challenging in terms of available, high quality fuel when compared to what you might see in Europe today.

From a North American perspective, this means that it will take longer for North American customers to regain their initial purchase investment in a diesel (payback in terms of fuel economy) due to lower fuel prices and a less favorable tax scenario. Diesels offer the best value for larger vehicles and utility and working applications.

The costs associated with emissions compliance, taxation based on engine displacement, fuel consumption, and the price of fuel largely dictates the markets where diesels are popular today.

2. Some people think GM is overlooking diesel. What’s next for diesels in GM’s overall alternative energy strategy for its next century?

Diesel engines are a very important part of GM's global product portfolio. In fact, for 2008 GM offers 16 engine variants available in 41 vehicle lines around the world and sells over one million diesel engines annually. I can't reveal any future product plans, but you can be assured that the diesel will figure in our plans as we work to attain the stringent new CAFE standards in the U.S. and meet our customers' demand for improved fuel economy.

We recently announced plans to introduce a new premium Duramax 4.5L V-8 turbo Duramax diesel in the 2010 model year in the U.S. for light-duty trucks. The new 4.5L V-8 will be capable of meeting 2010 emissions standards, will be compliant in all 50 states, and will improve fuel efficiency by 25%.

We also announced (March 2007) a premium 2.9-liter V-6 turbo diesel that features state-of-the-art injection and combustion technology for low emissions and high performance for the Cadillac CTS in 2009. Opel, Saab and Vauxhall applications will follow. This new engine will be sold mainly in Europe.

3. Why is there a greater availability of diesel vehicles in Europe over North America? Why not make more diesels in North America?

Diesel engines are extremely popular in European passenger cars (over 50% penetration), which is largely driven by policies that favor diesel fuel use and limit displacement. The North American situation is very different. Although fuel prices have increased dramatically in recent years, the tax policy keeps U.S. pump prices significantly less than in Europe. Recently, U.S. diesel fuel prices have been trending higher than gasoline prices.

In the US, tailpipe standards for diesel vehicles are being updated so that diesel and gasoline vehicles will have to meet the same set of emissions standards. For diesels, this means that an after-treatment system to control the NOx will be required, in addition to a diesel particulate filter to control the soot, which adds cost to the price of the diesel engine.

This means it will take longer for North American customers to regain their initial purchase investment in a diesel (payback in terms of fuel economy) due to lower fuel prices and a less favorable tax scenario. Those benefits are achieved more rapidly when you drive a larger vehicles or use diesels for utility and working applications.

Finally, fuel limitations in North America are also very challenging in terms of available, high quality fuel that might compare more of what you might see in Europe today.

4. The diesel engines from many years ago get a bad rap. What developments have made them better today?

Diesel technology has evolved dramatically over the last 15 years - so much so that the diesel engine, particularly in Europe, is thought of as the fun-to-drive, high-performance engine. Turbocharging, common-rail direct injection technology, electronics and particulate filters are among the technologies that you will find in the clean diesels of today, which are helping diesels deliver high torque performance and noise levels comparable to gasoline powertrains. To control emissions and meet new standards, an after-treatment system (for NOx) will be required, in addition to a diesel particulate filter to control soot.

5. How do you think diesel fuel helps shape the future of personal transportation?

Although diesel engines provide vehicle fuel efficiency benefits, the diesel powertrains add considerable cost, when compared with gasoline powertrains delivering similar performance. GM believes a powertrain portfolio approach is necessary to meet our customers’ driving needs. Advanced gasoline engines will continue to offer the best value, for most applications. Hybrids make sense in highly transient operations and diesels offer the best balance for utility and working applications and offer advantages under high speed highway driving conditions like those found on the Autobahn.