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A new engine demonstrates the stringent off-road vehicle

The 55-kilowatt propane engine designed at SwRI features a lean-burn combustion system and electronic controls to deliver EPA Tier 3 emissions levels, rivaling the performance and fuel economy of a diesel engineer.

A lean-burn, propane engine developed by engineers at Southwest Research Institute (SwRI) demonstrates a low-emissions alternative to diesel power. The propane engine replaces a 60 kW diesel engine in a John Deere 5410 tractor and can be modified for other naturally aspirated off-road vehicles for the agricultural, construction and power generation industries.

"This prototype demonstrates that a clean, efficient alternative to diesel-powered tractors and other off-road equipment is feasible," said John T. Kubesh, a principal engineer in the SwRI Engine and Vehicle Research Division. "Such an engine would be especially practical in emissions non-attainment areas."

The propane engine features a lean-burn combustion system and electronic controls to deliver Tier 3 emissions levels, rivaling the performance and fuel economy of a diesel engine. The propane engine delivers 55 kW, nearly as much as the 60 kW diesel engine. Full-load thermal efficiency of 34.8 percent is nearly on par with the 35.4 percent efficiency of the diesel engine. Noise levels also are lower with the propane engine, which provides a 7-decibel reduction in noise over the diesel. The tractor also features the use of conformable fuel storage, used for the first time in an off-road vehicle. The new storage system enables higher fuel capacity and convenient, single-point refueling.

The propane engine produces significantly lower emissions than a diesel, meeting the Environmental Protection Agency (EPA) Tier 3 standards scheduled to go into effect in 2008. Tier 3 limits emissions to 4.7 grams per kilowatt-hour (g/kW-hr) of oxides of nitrogen (NOx) plus nonmethane hydrocarbon (NMHC). Current tractor diesels emit 9.5 g/kW-hr of NOx + NMHC, while the propane engine emits 3.95 g/kW-hr. Similarly, a diesel emits 0.23 g/kW-hr of particulate matter (PM), while the propane engine emits 0.05 g/kW-hr. At this time, Tier 3 calls for PM levels of 0.4 g/kW-hr, a carryover of the Tier 2 levels, however, future reductions in PM standards are expected. Because the propane engine is a lean-burn engine that also uses an oxidation catalyst, carbon monoxide (CO) emissions already are well below Tier 3 standards.

"We used existing CNG (compressed natural gas) and diesel engine hardware to the extent possible for this engine to help minimize costs," Kubesh said. "Should market demand ever lead to the propane engine being placed in production, the use of common diesel and automotive components will help keep costs low."

This engine development program was funded by the Propane Education and Research Council (PERC), Texas Alternative Fuels Council and the John Deere Product Engineering Center. The initial concept and support for this project was generated by the Alternative Fuels Research and Education Division of the Texas Railroad Commission.

In mid 2002, PERC will sponsor a follow-on project to gather feedback and real-world fuel-use data from operators in the Houston-Galveston area who will assess the tractor's performance and reliability.

Emissions reduction in off-road vehicles can be particularly challenging because the vehicles come in a broad range of engine sizes and are used in a vast array of applications and operating environments, including environments with excessive heat, dust and moisture. In addition, these engines are typically naturally aspirated designs, and solutions to the emissions problem used in the on-highway vehicle market aren't always practical.

Off-road engine manufacturers became subject to emissions regulations in the 1990s when off-road emissions were identified as a major source of air pollution. The EPA proposed the Tier 3 standards to help make significant, long-term improvements in air quality in many areas of the United States.

Published in the Spring 2002 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.

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