Cummins has announced that its heavy duty on- and on/off-highway truck engines will not need urea injection to meet federal emissions limits in 2010, but that its medium-duty diesels will. Avoiding the urea method of cutting oxides of nitrogen, which some competitors have already committed to, means Cummins-powered heavy trucks won't need an extra aftertreatment device in its exhaust or a urea tank hung somewhere on its frame.
Multi-axle dump trucks and other construction-oriented vehicles with limited frame space are among those which will benefit from the development, and buyers of heavy trucks in general might prefer the seemingly simple approach. Cummins officials were restrained in noting that advantage during their announcement in mid-October because their smaller diesels must use the bulky urea-injection equipment.
In its larger engines, Cummins will cut oxides of nitrogen (NOx) — the principal target of regulations that will take effect in January 2010 — with greater amounts of cooled exhaust-gas recirculation. EGR is now successfully used in current North American engines; that and higher fuel-injection pressures and lower air-fuel ratios, all aided by more precise turbocharging and managed by more powerful microprocessors, will be enough to limit formation of NOx, Cummins engineers said. This strategy works in large displacement diesels, but not in smaller engines that work harder and see wider variances in operations, engineers explained. That's why Cummins' midrange models will need selective catalytic reduction (SCR), the more formal name for urea injection. Both heavy and medium-duty engines will continue to use diesel particulate filters in their exhausts.
High-pressure fuel injection is part of so-called common-rail fuel systems now employed by many diesel makers to improve combustion and meet increasingly stricter emissions limits here and abroad. Cummins' "XPI" system for 2010, developed with Scania of Sweden, will use pressures of 32,000 psi or more, and will combine with multi-phase injection to tightly structure the burning of the fuel-air mixture and help limit the formation of NOx and other pollutants.
The ratio of air to fuel, which has dropped from as high as 28:1 not long ago to 24:1 now, will drop further, to perhaps 19:1, engineers said. Reduction in the amount of air in the cylinders cuts oxygen, which reduces combustion temperatures and cuts formation of NOx. This is also the purpose of EGR, which sends exhaust gas into the cylinders to crowd out some oxygen-bearing air. Cummins' variable-geometry turbocharger assists in this by carefully modulating the amount of inlet air and the extent to which it's compressed.
Cummins and other builders now employ SCR in Europe and Japan, where different emissions regulations and more expensive fuel favor urea injection. American builders owned by European firms, like Volvo Powertrain and Detroit Diesel/Mercedes-Benz, have previously said they'll use SCR in North America in 2010, and have formed a consortium to develop an infrastructure to distribute and sell urea solution to truck operators.
The non-SCR approach for its larger diesels requires Cummins to expand its heavy-duty lineup from the current two models to three 2010 models. Today's 15-liter ISX will continue, though of course with '10 modifications, and it'll be augmented by 16- and 11.9-liter derivatives. The ISX-16 will cover ratings of 500 horsepower and higher; lesser ratings will be handled by the ISX-15 and the ISX-11.9. The 11.9 will replace the current 11-liter ISM truck engine, which will remain in production for industrial and export sales.
Cummins' midrange models will continue their current displacements/names: 6.7-liter ISB, 8.3-liter ISC and the 8.8-liter ISL, all with SCR, engineers said. Cummins already makes a 2010-legal engine, the ISB-based Turbo Diesel used by Dodge in its 3/4- and 1-ton pickups, and that will continue in '10 and beyond. This engine uses an NOx adsorber instead of SCR, which is simpler than the other methods, but does not work on engines with heavier duty cycles (CE Sept. '07, p. 70).
Cummins engineers are already working with truck builders to help them package the SCR urea tank into their chassis and plan for distribution of the liquid urea solution. Because urea dosage will be a small percentage of fuel use, tanks will be comparatively small. The tanks will have to be filled about as often as medium-duty chassis are lubed, engineers said. A Cummins-branded product called StableGuard will be sold in bulk and in several container sizes.
Caterpillar and International have not yet announced how they'll meet the 2010 limits. Neither has Paccar, which is developing its own heavy-duty diesels for use in its Kenworth and Peterbilt trucks. Those announcements are expected soon.