Exmark Manufacturing has begun production of propane-powered lawnmowers with electronic fuel injection. "It's got an oxygen sensor that senses the exhaust gases and it knows whether the fuel mixture is too rich or too lean for that condition. It sends back a signal to the [engine control unit], telling if it needs to make an adjustment. It's constantly measuring," said Exmark's chief development engineer, Garry Busboom. "There have been a number of our customers over the past years that have been looking for products that have a lower carbon footprint and are more green, and propane fits that bill," Busboom said.