As we enter 2004, all manufacturers are now in compliance with the latest emissions regulations from the Environmental Protection Agency (EPA). The next round of emissions controls takes effect January 2007, followed three years later by even tighter controls.

The EPA heavy-duty emissions standards for the latest engines call for no more than 0.1 grams per horsepower-hour for particulate matter and 2.5 g/hp-hr of oxides of nitrogen (NOx). The particulates have been linked to a variety of respiratory diseases, while NOx helps form smog. The problem is that higher combustion temperature, which reduces particulates, increases NOx formation. Reducing temperature to reduce NOx increases particulates.

Most engine manufacturers mix a portion of the exhaust back into the intake air. This reduces oxygen content, lowering burn temperature for NOx control, while using higher injection pressures and more precise injection timing to reduce particulates. This exhaust gas recirculation, or EGR, can be external, in which case it must be cooled, or internal, as Mack does with its vocational engines. Caterpillar is the only manufacturer not using EGR.

Here's a rundown of each engine makers' technologies:

Caterpillar

Caterpillar developed Advanced Combustion Emission Reduction Technology, or ACERT, to control emissions without EGR. Cat engines use a combination of a flexible fuel system with: variable electronic pulse controlled fuel injection; a flexible air system with two-stage wastegated turbochargers; integrated electronics to more closely control engine functions and after-treatment to remove remaining pollutants from the exhaust stream.

Cat did not have its engines fully developed by the October 2002 deadline, so they used interim technology in their "bridge engines." They had to pay a fine for each bridge engine sold. Like other engine manufacturers, Cat has increased engine displacement to maintain power ratings. The popular C-12 has been enlarged to 13 liters (redesignated C-13) and offered from 335 hp to 430 hp. The larger C-15 provides 435hp to 550 hp.

Cummins

Cummins' ISX was the first engine to be certified to the new standards. It uses cooled EGR. Because of the reliability experienced to date, Cummins extended their "Uptime Guarantee," a program to assure customers they will be able to maintain uptime or Cummins will provide an alternative tractor. Details are available from Cummins.

Cummins uses variable geometry turbochargers to maintain intake pressures and provide improved response. Eleven-liter ISM engines go to 450 hp, while the 15-liter ISX delivers ratings to 565 hp.

Detroit Diesel

Detroit Diesel Series 60 engines also use cooled EGR and a variable geometry turbocharger to help meet the new standards. They claim their engines are the lightest and most fuel efficient big bore engines, at 2,640 pounds, including engine brakes.

The company dropped its 11.1-liter engines and expanded the 14.0 liter range. Detroits now come in 12.7 liters, from 390 hp to 455 hp, and in 14.0 liters, from 455 hp up to 515 hp.

International

The International Truck and Engine Corporation recently introduced a replacement for their 53-cubic-inch engine. The larger HT570 is designed for regional and local use. This 9-liter engine produces from 295 hp to 340 hp. It uses a turbocharger with adjustable vanes, cooled EGR and an electro-hydraulic fuel injection system to meet 2004 emissions requirements.

The HT570 is available in International 7000 series and 8500 trucks designed for heavy-duty jobs and higher-mileage applications.

Mack

Mack's Application Specific Engine Technology (ASET) matches the company's best technology to each application. The standard engine in Mack Vision and CH Series on-highway trucks is the Mack Econodyne with cooled EGR (C-EGR). Vocational engines in Mack's Granite Series use Internal EGR (I-EGR) to help meet standards. For on-highway steady state operations, C-EGR similar to other makers' is most effective. Vocational trucks often vary loads and speeds, so Mack developed I-EGR which they feel is better under those conditions. With I-EGR, some exhaust gas stays in the cylinder from one combustion cycle to the next, diluting the incoming charge just as on-highway C-EGR would, with less complexity and less weight.

Mack's C-EGR 12-liter engines are available from 310 hp to 460 hp. Vocational I-EGR ratings are 300 hp to 460 hp.

Mercedes-Benz

Although the Mercedes-Benz MBE 4000 was available in the U.S before October 2002, sales grew after that date because its purchasers did not have to worry about unproven new technologies. Mercedes was not part of the 1998 agreement, so it did not have to meet the more stringent standards until this past January.

The 12.8-liter MBE 4000 now uses cooled EGR with sophisticated electronic fuel management for emissions controls. It is available from 350 hp to 450 hp. It weighs 2,117 pounds, complete with its standard engine brake. This compares favorably with other 12- and 13-liter engines. Maximum braking horsepower is increased to 538 with the addition of the Turbobrake, a device that redirects airflow against the turbine blades, accelerating the impeller to increase mass airflow. MBE 4000 engines are available in Freightliner, Sterling and Western Star trucks.

Volvo

The new VE-D12 family of 12.1-liter engines is available in Volvo's on-highway and vocational trucks. They use cooled EGR, managed with Volvo's V-Pulse Technology, which uses pressure pulses created by the exhaust valves. The pulses push as much as 30 percent of exhaust through the EGR cooler.

Volvo also uses modulating unit injectors to shape the fuel charge to lower peak cylinder temperature while reducing unburned fuel. The VE-D12 engines reduce emissions during idling with the Exhaust Pressure Governor. It provides back pressure in the exhaust when coolant temperature falls below 149 degrees F and stays on until the engine warms to 158 degrees F. Volvo VE-D12 ratings run from 365 hp to 465 hp.

What will the future bring?

In 2007, new regulations call for a reduction in NOx from 2.5 g/hp-hour to 1.2 g/hp-hour, with a further reduction by 2010 to only 0.2 g/hp-hour. Particulates, now at 0.1 g/hp-hour will be cut a further 90 percent to 0.01 g/hp-hour. As low as today's emissions are, by 2010 the maximum allowable total emissions will be less than 1 percent of those. In order to meet these standards, we will need ultra-low sulfur diesel (ULSD) with only 15 parts per million (ppm) sulfur. Today's LSD has 500 ppm. ULSD will be available by mid 2006.

Last June at the TMC Emissions Summit in Phoenix, Ariz., engineers speculated that complex after-treatments will be needed to meet the ultra-strict standards. Some engine makers are developing Selective Catalytic Reduction (SCR) systems similar to those being introduced in Europe. They require urea to be injected into the exhaust. An entire new infrastructure would be needed to deliver urea to truckstops and fueling facilities, along with separate urea tanks on all trucks using SCR.

As little as six months ago, the alternative was thought to be extremely costly and fragile particulate traps. But progress has been made refining existing technologies, and several makers are experimenting with minimal or no after-treatment. Diesel Particulate Filter (DPF), an alternative to SCR that does not require urea, could become the preferred technology in 2007.

Whatever the technologies may be, engine manufacturers are assuring their customers that there will be engines to test far enough in advance of the 2007 deadline. That will give buyers confidence in the next generation's reliability and durability, so we may be able to avoid the panicked pre-buying that preceded the October 2002 engine introductions.