On paper, clean advanced technology diesel passenger cars and light-duty trucks should be charging into the US market. The changeover to Ultra Low Sulfur Diesel that takes affect this year—a profound change akin to the removal of lead from gasoline, according to the EPA—opens the door to advanced emissions aftertreatment controls that can meet tough US emissions regulations.
The torque and power of diesels should appeal to US drivers, and the increased fuel economy of diesels compared to current gasoline counterparts should appeal to drivers as well.
But while acknowledging all of the above and stating that they are planning diesel introductions into the US market, a panel at DEER 2006 comprising GM, DaimlerChrysler, BMW, Honda, Volkswagen the EPA and the Martec Group also noted some major hurdles to a rapid proliferation of diesel models in the US.
A common worry shared by the automakers is that the costs associated with overcoming some of the issues will further increase the price of diesels, reducing the economic incentive for buyers. Should the price of oil collapse, they worry about the potential for a repeat of the diesel boom and bust of the 1980s.
The technical hurdles can be grouped into two basic categories which are inter-related:
- Emissions compliance, specifically the NOx limits; and
- Fuel quality.
Emissions. The US Tier 2 regulations—which are converging with California LEV regulations—are the toughest in the world. A future Euro-5 diesel passenger car won’t qualify for Tier 2 Bin 5. Automakers are developing advanced combustion regimes with associated reductions in engine-out NOx and aftertreatment systems to hit the target.
On the NOx front, Lean NOx traps (LNT) and urea SCR systems are the leading approaches automakers are exploring. LNT has limitations in efficiency that make it less suited for larger vehicles and in durability, and urea SCR faces the fundamental issue of getting the EPA on board with its use, given potential issues with compliance. (How, in other words, do you ensure that drivers replenish the urea to ensure that the emissions aftertreatment system continues to work?)
Fuel quality. The variable range and threshold of some properties of US diesel fuel raises a number of issues for the automakers. For example, US diesel cetane numbers range from 38-58; European numbers range from 50-60. US aromatics can range from 13% to 50%.
The wide range and lower threshold of centane numbers drives a need for a variety of engine modifications, including more EGR, and more cold starting aids on the engine, according to Ford’s Brien Fulton in a separate presentation at DEER. High aromatics also increase engine deposits, EGR deposits and exhaust system deposits. These, and other factors, limit the synergies with European diesel powertrain technologies for the US.
The automakers. Of the automakers participating in the panel, GM was the least committal toward a product direction.
Diesel powertrains satisfy unique vehicle requirements in utility and large vehicles, but the economic payback diminishes as you go down in vehicle class...the proportion of the financial improvement diminishes, and it becomes more of a challenge to bear the cost of powertrain additions that go along with the diesel technology.
Not seeing a clear solution to meeting Tier 2 Bin 5 requirements, GM has been reluctant to introduce a vehicle.
In principle, if diesel is ever going to be widely accepted as a fuel solution in North America, it needs to be seen as comparable to its gasoline counterparts [in terms of emissions]. That ultimately is where we need to be. As long as there is a perception that diesel is an exception, it will never be widely accepted by the regulatory community or consumers.—Michael Potter, Chief Engineer, Diesel Technology, GM Powertrain-Europe
DaimlerChrysler, which is outspoken about its BLUETEC technology framework as being the “Tier 2 Bin 5” enabler (earlier post), is nonetheless primarily relying on Bin 8-compliant introductions over the next year. A big consumer factor for DaimlerChrysler is the image of diesel.
For an expanded diesel market, the image has to be right. If we are going to go into the mainstream, we’re looking at regular sedans and SUVs...it’s very important to get the image right.—Simon Godwin, DaimlerChrysler Manager for Regulatory Affairs
BMW is planning on diesels in both its sedans and SUVs for North America, and has sketched out a Tier 2 Bin 5 approach that relies on modified combustion, an advanced EGR system, an adapted fuel injection system, new control devices, additional sensors, OBD functions, a DPF and urea SCR system.
Wolfgang Mattes, BMW’s director of functional development, was particularly concerned about the problem of On-Board Diagnostics that meet US requirements.
We need some compromises to get diesel in [to the US market], such as the phase-in period for OBD.—Wolfgang Mattes
Honda, given its recently announced strategic direction to use diesel powertrains for fuel-efficiency in its larger vehicles, was very bullish about its technical approach (earlier post) as well as on the potential benefits of diesel.
We want to contribute for clean diesel technology as we have for the gasoline engine.—Yasuyuki Sando, Honda Senior Manager Advanced Powertrain
Volkswagen has been selling diesels in the US for more than 25 years. Diesels currently constitute about 15% of its US sales.
[Diesel] will succeed by delivering increased efficiency, reduced CO2 emissions, high levels of performance, and being the best platform for renewable fuels including biodiesel, sunfuel and sundiesel.—Klaus-Peter Schindler, Volkswagen
Schindler noted that diesels will compete against and have to coexist with other technologies, including advances in gasoline engine technology, the success of hydrogen, and the potential public focus on long-term solutions, such as hydrogen.