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Southwest Research Institute testing has demonstrated the feasibility of using closed-loop technology in off-road applications.

Engine B under development (above) and installed in an SwRI forklift.

To meet ambient air standards in California by the year 2010, emissions reductions will be required from off-road equipment using large, spark-ignited engines. Though regulation of agricultural and construction equipment is preempted by the federal government, California can adopt emissions standards for industrial equipment.

In November 1994, California's Air Resources Board (ARB) adopted a State Implementation Plan (SIP) for Ozone for submission to the EPA. The mobile source control portion of the SIP contained 16 control measures, designated Ml to M16. Control measures M11 and M12 concern industrial equipment powered by 19 to 131 kW (25 to 175 hp) gasoline and liquified petroleum gas (LPG) engines. Control measure M11 encompasses 60% of industrial equipment not preempted by the EPA.

In October 1998, the ARB adopted emissions standards and test procedures for large, spark-ignited off-road engines producing 19 kW (25 hp) or more that will require the application of advanced emissions-control technology. In January, the EPA indicated that it will likely propose emissions regulations for these engines similar to the California proposal.

With these actions framing the need for reduced emissions, a project was conducted by the Southwest Research Institute on behalf of ARB and the South Coast Air Quality Management District that was concerned primarily with nonpreempted equipment covered by control measure M11. This includes airport ground support equipment, forklifts not powered by diesel engines (i.e., not rough terrain), generator sets, surface mining equipment not otherwise primarily used in the construction industry, specialty vehicles, and turf-care equipment.

Since most engines in this group are automotive derivatives, they can take advantage of automotive emissions-control technologies. However, there are a number of application issues that must be addressed in the adaptation of these technologies to generators and forklifts (i.e., compact design, exhaust temperatures).

Five engines were selected by ARB for analysis (Table 1). Testing involved taking baseline measurements, and then emissions-reduction technologies were applied to engines B and E for durability evaluation. Test cycles were selected based on typical equipment-use patterns and other information provided by the engine and equipment manufacturers. The ISO 8178-C2 cycle was used for variable-speed applications such as forklifts, baggage-handling and tow/push equipment, scrubbers/sweepers, turf care equipment, and specialty vehicles. The ISO 8178-D2 cycle was employed for constant-speed applications such as generator sets, aircraft ground power, and refrigeration units. The gasoline used for the investigation met California Phase II fuel standards; the LPG met commercial HDS specifications.

All five engines are used in variable-speed applications and were tested with the ISO 8178-C2 cycle, while engines D and E were also evaluated using the ISO 8178-D2 cycle. All engines except engine A were baseline tested with both gasoline and LPG (Table 2).

Engine B, the primary focus of this article, generated approximately 10% lower brake-specific hydrocarbons (HC), 30% lower oxides of nitrogen (NOx), and 20% lower carbon monoxide (CO) than Engine A when fueled with gasoline. Two additional tests were conducted on Engine B using an LPG conversion kit, which resulted in an air/fuel ratio of 15.7:1 at full power. Compared to the gasoline results, NOx emissions increased 40%, while HC and CO emissions decreased 37% and 55%, respectively, due to the leaner calibration with the LPG system. Significantly lower fuel consumption was observed when the engine was equipped with the LPG conversion kit. This was due to leaner operation and higher energy density associated with LPG, which contains 9% more energy on a mass basis than California Phase II gasoline.

In addition to determination of criteria pollutants on the five baseline engines, selected unregulated emissions were measured on Engines B and E for application of emissions-reduction technology. Separate baseline tests were performed on these engines to accommodate special sampling equipment required for unregulated emissions measurement (Table 3).

The range of emissions-reduction technologies considered for all of the engines included optimization of air/fuel ratio calibration and spark timing, and the use of exhaust gas recirculation, air injection, improved open-loop carburetion, oxidation or a three-way catalyst, and a closed-loop fuel system. While several of the simpler approaches have been shown to have moderate effectiveness, meeting ARB's SIP goals required more advanced technologies.