Six days into its transcontinental journey, the Big Green Bus pulled into Canaan Friday at the home of Vali Valenti, where she happily played host for the night for her son, Jules, and his 12 traveling companions. The young people, all Dartmouth students or 2011 graduates, are making a 12,000 mile-journey across the continental United States in a bus powered by waste vegetable oil. ...

“We try to demonstrate good practices,” said Jules Valenti of Canaan, who graduated Phi Beta Kappa from Dartmouth this spring with a bachelor’s degree in mechanical engineering. Mr. Valenti, who earned his first undergraduate degree in physics from Bowdoin, is one of four engineers on board. They designed the vegetable-oil fuel system that propels the bus through most of its journey.

“Everyone on the crew has his own role,” said Mr. Valenti. “We organize everything and coordinate the different jobs, from public relations to engineering the bus.

He lifted panels on the side of the bus to reveal the 290-gallon tanks that contain the waste vegetable oil used to power the bus. There are two tanks, one for “dirty” oil, that contains bits of food and water from the cooking process at fast-food restaurants, and the other for “clean” oil that has had those contaminants removed. Mr. Valenti explained that dirty oil is allowed to settle, and then the contaminants are drained off from the bottom of the tank. The oil is then transferred to the clean tank to power the bus.

The engineering students also designed a heating system that raises the oil’s temperature to from 160 to 190 degrees Fahrenheit, the temperature needed to ensure that the oil does not foul the engine.