Toyota, BMW agree: More is better!
(Fall 2003)
Newport, R.I. -- Both Toyota and BMW see possibilities for introduction of diesel cars into the North American market but only if ultra-low sulfur diesel (ULSD) also improves with consistently higher cetane and lower aromatics.
Toyota's novel "DPNR" system simultaneously slashes nitrogen oxides (NOx) and particulate matter (PM) with a novel "low-temperature combustion" scheme employing "massive" exhaust gas recirculation (EGR) and a combined PM/NOx trap.
But Toyota bluntly told the Diesel Engine Emissions Reduction (DEER) conference here (sponsored by U.S. Department of Energy) that U.S. diesel fuel is generally poor and highly variable on cetane/aromatics, making it harder to design an engine/emissions control scheme for North America.
Rather than the very low 40-cetane minimums/35% aromatics maximums allowed under U.S. EPA 2006 diesel rules, Toyota instead urges an over-50-cetane number minimum and aromatics levels more like those of California Air Resources Board (CARB) diesel (averaging around 21%, although the default limit is 10%).
"It is essential that diesel fuel cetane and aromatics must improve," Toyota powertrain general manager Tetsu Watanabe said here. "Fuel quality is a big problem--low average cetane number (44) and aromatics are high--35% average and 54% maximum in the U.S."
Ironically, Toyota showed that its "DPNR" test car fleet in Europe is meeting European emissions and performance goals even in countries with 300-ppm sulfur fuels.
However, Europe lacks the ultra-strict NOx/PM limits of U.S. EPA for Tier 2/Bin 5 or the equivalent California LEV-2 limits--and high-frequency desulfation threatens catalyst durability.
For emissions limits testing at U.S. EPA's laboratory in Ann Arbor, Mich., Toyota's DPNR car (with an European engine control calibration) used a 6-ppm sulfur fuel of 50.4 cetane and 26% aromatics, he said. While this car did very well on most EPA test modes, it fell short on "US06" mode and still hasn't proven EPA's 120,000/150,000 miles durability (see Diesel Fuel News 6/24/02, p6).
In contrast, Europe and Japan will have much better cetane/aromatics limits as well as ultra-low sulfur diesel (ULSD) by 2005, enabling "DPNR" cars in Europe and "DPNR" light trucks in Japan.
For the DPNR light truck, Toyota will employ an under-floor-mounted catalyst. In tests of over 200,000 kilometers, Toyota has found that this vehicle's NOx storage capacity works better with a 7ppm sulfur ULSD rather than a 40-ppm sulfur fuel.
BMW's Conquering Diesels
Meantime, BMW's sensational diesel sports cars (including test-drive cars supplied to DEER conference here) are tearing up the European market, as diesels now account for 68% of BMW-Europe sales compared to 35% world-wide, BMW official Fritz Steinparzer showed here.
"Particularly in the U.S. and some parts of Asia, the combination of a car in this [high-performance] segment with a diesel engine was up until now almost unthinkable--I feel sure that many people in the USA are not even aware that BMW produces diesel-powered cars," Steinparzer explained.
Now, thanks to huge strides in engine performance, BMW-Europe buyers actually prefer diesels over petrol engines, but its diesels aren't available in the U.S.
Upgrades in maximum cylinder pressure, common rail pressure, multi-injection (four events), boost pressure, turbine and compressor efficiency, fuel efficiency and ultra-low PM emissions (thanks to a new diesel particulate filter) mean BMW can achieve outstanding performance, low C[O.sub.2], and ultra-low criteria emissions--except for NOx.
Although BMW's latest engine/DPF technology can meet Euro standards, "the future NOx limits [in the U.S.] are very challenging and the development of new technologies is necessary," he said.
Aiding emissions compliance would be "better fuel quality similar to" European ULSD standards (much higher in cetane than U.S. average) and "slight legislation adaptations to take account of the specific diesel advantages" for long-term emission stability and C[O.sub.2]. However, U.S. EPA isn't inclined to relax NOx/PM limits in exchange for lower C[O.sub.2] (see Diesel Fuel News 3/18/02, p10).
