Advances in Diesel Engine Technology

Driven in large part by upcoming U.S. Environmental Protection Agency (EPA) regulations, fleet managers, maintenance technicians, truck drivers and engine manufacturers have developed a variety of emission-reduction technologies to minimize diesel emissions before the standards begin to take effect within the next few years.

The new EPA regulations target reductions of both particulate matter (PM) and nitrogen oxide (NOx) by 98 percent from 1988 levels – virtual elimination of these emissions from on-road engines. Similar requirements were proposed in April 2003 for off-road diesel vehicles, such as those used in construction, agricultural, and industrial applications. (See the insert on “Off-Road Heavy-Duty Diesel Vehicles” or “Diesel Emission Standards for Heavy-Duty On- and Off-Road Engines” for more information.)

In both cases, the regulations entail the use of new technologies to lessen the production of pollutants from combustion – such as engine design and fuel – and to minimize the amount of post-combustion pollutants released into the air. (See the insert on “Emission Control Technologies” for more information.) This insert summarizes the assortment of emission-reduction technologies available today and discusses recent advances in diesel fuel and engines.

Exhaust Gas Recirculation (EGR)

Nitrogen oxide (NOx) is formed as a by-product of high combustion temperatures. One common approach for lowering NOx emissions from diesel engine combustion is to utilize exhaust gas recirculation (EGR) technology. EGR involves recirculating a portion of the engine’s exhaust back to the engine at a lower temperature. The cooled gases have a higher heat capacity than air and contain less oxygen than air such that when it is reused, it lowers the temperature of combustion and subsequently reduces the formation of NOx.

Common-Rail Fuel Injection

Common-rail fuel injection is an advanced fuel pump technology that allows the use of higher injection pressures than systems incorporating conventional pumps. The use of a common rail from which the injectors are directly fed allows the pressure and injection timing to be precisely controlled by electronic means. By directly feeding the injectors from a single fuel pump, the electronic system optimizes the amount of fuel pressurized prior to injection.

This extremely high pressure allows finer vaporization of the fuel droplets, which means a far more homogenous mixture with the air in the cylinder. Therefore, combustion is more complete and exhaust emissions are reduced.

Combustion Chamber Design

In addition to improving the efficiency, effectiveness, and performance of the combustion process, engineers have also made advances in the configuration of the combustion chamber. By designing the chamber to have the correct configuration for the most effective combustion of the air and fuel mixture, the engine maximizes its power output at each stroke, maximizes fuel efficiency, and reduces combustion emissions.

Turbocharging

Unlike EGR, where a portion of the exhaust gases are used again in the combustion, turbocharging utilizes energy from the engine exhaust to boost performance by using it to drive a turbine wheel that turns a second turbine wheel, which forces more air into the cylinder. Forcing more oxygen into the chamber increases the efficiency of the combustion process, reduces emissions, and increases performance. Turbocharging technology is particularly beneficial in Colorado as heavy-duty trucks traverse mountain passes with lowered oxygen levels.

Electronic Engine Controls

Innovative computer technology and software used to monitor factors affecting diesel engine performance such as oxygen, combustion chamber, and exhaust temperatures, levels of NOx and other pollutants, play a key role in the success of some of the technologies discussed here and in other diesel technology inserts. For example, computers monitor the performance of EGR and the fuel injection process to maximize combustion efficiency.

Diesel Fuel

The sulfur content of diesel fuel in Colorado and much of the rest of the country is at approximately 300 parts per million (ppm) for on-road vehicles. EPA regulations, however, will necessitate that owners and operators begin using reduced sulfur content diesel. California already requires the use of highly-refined, ultra-low sulfur diesel fuel (ULSD) in many applications. ULSD has a sulfur content of up to 15 ppm, a 99 percent reduction. The ULSD fuel is currently available in California, Pennsylvania, and the Northeast, but refiners expect the fuel to be available nationwide by 2006 as the new EPA requirements begin. (See the insert on “Diesel Emission Standards for Heavy-Duty On- and Off-Road Engines” for more information.)

Because of the low sulfur content, fewer PM emissions are generated during the combustion process. At the same time, the fuel improves the effectiveness of post-combustion emission control technologies when they are used. (See the insert on “Emission Control Technologies” for more information.)

Case Studies/Success Stories

A 1999 test program initiated by the Manufacturers of Emission Control Technologies (MECA) used both standard diesel fuel (sulfur content of 368 ppm) and ULSD in a typical on-road, heavy-duty diesel engine to evaluate the performance of diesel particulate filters (DPFs), diesel oxidation catalysts (DOCs), selective catalytic reduction (SCR), and fuel-borne catalysts. The organization’s findings (supported by additional industry and government research) demonstrated that commercially available emission control technologies can significantly reduce PM and other pollutants and that the performance of the technologies are substantially improved with the use of ULSD.

Industry leaders in promoting clean diesel technologies include Bosch, BP, Caterpillar, Cummins, Detroit Diesel, Eaton, Exxon Mobil, Garrett, General Motors, International, Isuzu, Johnson Matthey, and Komatsu.

Sources

Diesel Technology Forum – www.dieselforum.com
Manufacturers of Emission Control Technologies – www.engine-manufacturers.org
U.S. Environmental Protection Agency – www.epa.gov/otaq