Study shows NOx benefits with propane-powered school buses

West Virginia University (WVU) researchers concluded emissions from propane school buses are significantly lower than those from diesel buses.

The conclusion comes from a year of testing in a study commissioned by the Propane Education & Research Council (PERC) where WVU’s Center for Alternative Fuel Engines and Emissions (CAFEE) completed two types of tests at different times in 2018 on four Blue Bird buses.

Test routes included both city and highway roads, and a stop-and-go route similar to standard school bus operation. Researchers installed a portable emissions measurement system to measure exhaust emissions on each vehicle and performed test runs on each bus with both cold and hot starts for a total of 36 test routes.

“This study is monumental from an emissions and health perspective for students, schools and communities across the country,” says Tucker Perkins, president and CEO of PERC. “Children arriving to school in propane buses aren’t exposed to harmful NOx emissions; they feel better and are more prepared to learn.”

Almost 1 million students in more than 900 school districts across the nation ride to school in propane school buses each day, PERC says.

The study’s results demonstrated that distance-specific NOx emissions measured from the diesel bus were significantly higher than those measured from the propane bus for tests conducted in early 2018.

For the city route, which included city and highway roads, NOx emissions were 15 to 19 times higher for the diesel school bus.

For the stop-and-go route, NOx emissions were 34 times higher for the diesel school bus. NOx was reduced by 96 percent and carbon dioxide by 13 percent with a propane bus.

Subsequent testing performed in late 2018 with newer model year and lower mileage propane and diesel buses validated the previous testing results, PERC adds.

“In real-world applications, particularly those with significant low speed or low load operation, propane vehicles can provide dramatically lower NOx emissions, compared to similar diesel vehicles,” says Ross Ryskamp, associate director for testing and development at CAFEE. “These findings are significant due to the fact that NOx and ozone are major non-attainment concerns for many areas across the nation.”

Ryskamp adds the findings from the in-use tests of high NOx emissions for medium- and heavy-duty diesel vehicles are supported by other studies in literature.

“We’re seeing the unmatched benefits of propane and how advanced this domestically produced fuel option is,” Perkins says. “On top of decreasing emissions, these reliable vehicles offer superior performance in cold weather and low total ownership costs.”

The full study, entitled “In-Use Emissions and Performance Testing of Propane-Fueled Engines,” can be found here.

*Photo courtesy of Propane Education & Research Council