Diesel engine manufacturers are in the midst of one of their most innovative periods. Pushed both by market forces and government edict, engine manufactures are searching for answers for improved emissions, fuel efficiency and performance.

Various low-emission technologies have emerged as engine manufacturers look down the barrel of a 1998 consent decree that required compliance with 2004 EPA emissions standards by October 2002. The consent decree stemmed from the settlement of a government suit in which the EPA alleged manufacturers produced engines that used a different fuel software than what was tested, causing higher Nitrogen Oxides emissions.

Engine manufacturers also are gearing up for even more stringent emission standards set to begin in 2007. Diesel's most common pollutants -- NOx, Particulate Matter (PM) and Hydrocarbons (HC) -- must be reduced to 0.20, 0.01 and .14 grams/brake-horsepower-hour, respectively.

The following details the progress of engine manufacturers in meeting the 2002 standards. While there are many other companies that manufacture diesel engines, each company listed here markets to the school bus industry (Detroit Diesel partnered with Thomas Built Buses recently in a move to re-enter the field.) Information was obtained from companies' Web sites.

Caterpillar

Advanced Combustion Emissions Reduction Technology (ACERT (PDF)) is the next generation in Caterpillar's low-emission engines. According to Caterpillar, ACERT will significantly outperform Exhaust Gas Recirculation (EGR) engines, a common low-emission engine in the heavy-duty industry. However, ACERT engines will not be produced until next year, with selected models released in January 2003 and full production planned for October 2003. Failing to make the EPA's October 2002 deadline will cost the company as much as $9,000 per engine in fines, according to Bloomberg News.

Caterpillar also offers Dual-Fuel and Cat Clean Power low-emission engines. Dual Fuel is an electronically controlled engine configuration that uses diesel fuel and natural gas. Diesel is used as the ignition source before switching to natural gas once the engine has reached operating temperature. More than 85 percent of fuel use is natural gas. Duel Fuel meets the EPA's Low Emission Vehicle levels.

Cat Clean Power utilizing fuel injection, combustion, electronics and air systems technologies to reduce emissions. EPA-certified Cat Clean Power engines run on fuel blends and low-sulfur fuel, and are up to 12 percent cleaner in NOx emissions than EPA requirements.

Return to top

Cummins' 2002 ISX is a cooled EGR engine that meets 2002 EPA standards. In EGR engines (PDF), a small amount of hot exhaust gas is routed through the cooler and mixed with fresh air going into the engine. The process reduces temperature during combustion in the cylinder where oxides of nitrogen are formed. Cooler cylinder temperatures reduce production of NOx. Cummins introduced EGR in California in 1995. By 1997, a full line of on-highway EGR engines were introduced.

Return to top

International

International's low-emission engines feature Green Diesel Technology, which when used with ultra-low sulfur fuel creates a smokeless, odorless, low-polluting exhaust. Green Diesel engines use a catalyzed diesel particulate filter in place of a muffler to reduce hydrocarbons, carbon monoxide and particulate emissions. Green Diesel engines have been EPA certified and when used with ultra-low sulfur fuel meet 2007 EPA emissions standards.

International released a new medium duty diesel engine - the VT 365 -- in April 2002 for Type A-2 school buses. The V-8 engine uses various technologies to reduce emissions, meeting Clean Fuel Fleet Vehicle (CFFV) requirements. The CFFV rule requires fleet owners in certain areas of the country designated for improved air quality to purchase new vehicles that meet low-emission vehicle (LEV) standards.

The VT 365 meets LEV standards by using cooled EGR, Electro-Hydraulic Generation Two (G2) fuel injection technology and Electronic Variable Response Turbocharger (EVRT) technology. Additionally, these technologies are the building blocks International will use to meet the 2004 and 2007 emissions standards, the company said.

While cooled EGR is used throughout the industry, G2 is an exclusive International technology. G2 uses high-pressure injectors to manage fuel. The injectors are smaller than usual, allowing room for four valves per cylinder. Higher injection pressure combined with four valves per cylinder more completely mixes fuel and air for better combustion, thereby reducing emissions and increasing fuel efficiency. G2 works in tandem with EVRT technology. EVRT enhances the turbocharger with electronic controls to allow an infinitely adjustable supply of air. Adjustable airflow allows the engine to respond to all conditions - instant response at low speeds, more airflow at higher speeds. The process optimizes performance, lowering emissions and improving fuel economy.

Return to top

Mercedes

Mercedes' MBE 900 Series engine is not subject to the consent decree because it was not offered for sale in the U.S. in 1998. The MBE 900 Series engine is certified for the 1998 regulation of 4.0 g/bhp-hr NOx until 2004.