University Study Claims Propane School Buses Outperform Diesel in Reducing NOx

An interesting article explores a university study that compared the emissions from propane- powered school buses and diesel school buses. According to the study propane- powered school buses had significantly less NOx emissions than diesel school buses.

A year-long study performed by the nonprofit Center for Alternative Fuels, Engines and Emissions (CAFEE) at West Virginia University, and commissioned by the propane industry, concluded that emissions from propane-powered school buses are significantly lower than emissions from diesel school buses.

CAFEE researchers used four school bus test vehicles last year to establish exhaust emissions and performance characteristics of propane-fueled vehicles. In all, the researchers gathered data from a total of 36 test routes.

Portable emissions measurement tests were run on all four engines with both hot and cold starts. The tests included a Horiba OBS-2200 gaseous Portable Emissions Measurement System (PEMS) for a 2015 propane and a 2014 diesel bus in January and February 2018, plus a Horiba OBS-ONE gaseous PEMS for the 2017 propane and diesel buses in July and August of that year.

The researchers concluded that NOx emissions were 15 to 19 times higher for the diesel school buses during routes on city and highway roads, while the propane buses reduced NOx by 95 percent.

Meanwhile, the researchers found that NOx emissions were 34 times higher for the diesel school buses on stop-and-go routes. The propane buses reduced NOx by 96 percent and CO₂ by 13 percent.

The researchers concluded that low ambient temperatures during the tests of the 2014 diesel bus and the 2015 propane bus “may have exacerbated the NOx emissions from the diesel school bus in addition to the low speed, low load operation contained in these routes and the inherent difficulties to maintain adequate temperatures in the SCR system.”

They also found that distance-specific carbon monoxide (CO) emissions measured from the 2015 propane bus were greater than those emissions from the 2014 diesel bus for all routes. However, the researchers pointed out that since 2010 there have been no nonattainment areas for CO in the U.S.

“This study is monumental from an emissions and health perspective for students, schools and communities across the country,” said Tucker Perkins, president and CEO of the Propane Education & Research Council (PERC), which commissioned the study. “Children arriving at school in propane buses aren’t exposed to harmful NOx emissions. They feel better and are more prepared to learn.”

PERC said over 900 school districts across the U.S. are currently operating propane school buses that transport nearly 1 million students to and from school.

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

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