Diesel engines are widely used throughout the Department of Defense (DoD) for powering tactical and nontactical vehicles and vessels, off-road vehicles and equipment, engine-generator sets, aircraft ground-support equipment, and a variety of other applications. Although diesel engines are known to emit several types of pollutants into the atmosphere, human health concerns regarding small particulate matter (PM) have greatly increased interest in diesel PM emissions. PM emissions are regulated as a criteria pollutant by the National Ambient Air Quality Standards established by the Clean Air Act (CAA).

Although most regulations are directed at the certification of new diesel engines, increasingly, emphasis is being placed on in-service engines. To address these compliance requirements, many exhaust gas treatment devices are coming onto the market, but the selection of the optimal treatment technology (which also must meet the approval of applicable regulatory bodies) depends on several factors that must be evaluated for each application.

The primary objective of this project was to demonstrate two technologies as being capable of reducing diesel engine PM emissions by at least 50% and sufficiently robust to provide years of trouble-free service. Other objectives included achieving significant reductions in carbon monoxide (CO), hydrocarbon (HC), and hazardous air pollutant (HAP) emissions; maintaining vehicle fuel economy and drivability; and demonstrating the ease of installing the technologies.

This project demonstrated two diesel engine exhaust gas treatment devices believed to have the potential to assist DoD in meeting applicable PM regulatory requirements. In both cases, the technology consisted of a high-temperature filter designed to remove the PM from the exhaust stream. The difference between the two filter designs involves the filter pore size and thus ability to capture the PM emissions (50% vs. 85% PM reduction), as well as their method for regeneration. Both filters include the ability for in-use regeneration, the difference is that one is regenerated passively, using only the heat of the engine, while the other is actively regenerated using direct fuel injection into the filter. These two technologies were tested on eight DoD operated diesel engines at three DoD sites—Aberdeen Test Center, Camp Pendleton, and Cheyenne Mountain Air Force Station. The test periods varied from a few months to over one year.

The results of testing of the Environmental Solutions Worldwide, Inc. (ESW) passively regenerated filter showed that it reduced PM emissions by 50%, while reducing CO, HC, and HAP emissions. Backpressure, fuel usage, drivability, reliability, and installation requirements were also met sufficiently well so that this unit can be recommended for use with suitable DoD engine applications.

The Cummins, Inc. robust particulate filter (RPF) technology, however, performed irregularly in demonstration testing leading to frequent filter clogging and the subsequent removal of several test units prior to completion of the project. The filter manufacturer believes that this technology could be effectively applied as a retrofit application as long as strict guidelines are in place for evaluating the duty cycle of the target vehicle. However, significantly more testing would be needed to verify the technology. Based on this poor performance, Cummins Emissions Solutions (CES) has decided not to offer the RPF technology in the retrofit market.

The purchase of diesel filters represents a significant and many times unplanned cost to government diesel-powered equipment and vehicle fleet managers. These managers are faced with a multitude of choices in meeting current and proposed new regulations for reducing diesel PM emissions. Unfortunately, many of the commercial products available to address this problem are not suitable for common DoD engine duty cycles. Other products, although effective, may not meet government needs for maintainability and durability. This project provided information to assist government decision makers with the selection of appropriate diesel engine emissions control technologies.