Heavy-duty transport trucks like the 18-wheelers lumbering on the nation’s highways almost always run on diesel and contribute significantly to greenhouse gas emissions. A team of MIT engineers aims to change that.
The team has proposed a new way to power those trucks: a plug-in hybrid engine system. The truck would be mostly powered by batteries, but would use a spark ignition engine to get the motor running. That engine would allow the trucks to match the range of existing diesel-powered vehicles—but it would run on pure gasoline, pure alcohol or a blend of those fuels.
“We've been working for a number of years on ways to make engines for cars and trucks cleaner and more efficient, and we've been particularly interested in what you can do with spark ignition,” said research scientist Daniel Cohn. Spark ignition is much cleaner than the compression ignition used in diesel engines.
Cohn and principal research engineer Leslie Bromberg performed a detailed study of the engineering and economics that would need to be involved in developing the hybrid engine. They used detailed computer modeling of a wide range of engine characteristics and screened the results using artificial intelligence. They found that using an alcohol-gasoline mix, or even pure alcohol, matched the efficiency of diesel engine—and that swapping the hybrid for the diesel was practically and economically doable. The engineers have been working on two engine models to further develop this alternative.
The ultimate goal would be to have the trucks powered entirely by batteries—but the current technology makes it unfeasible today. Tesla will be producing a fully electric transport truck, but Cohn believes it will need 10 to 15 tons of batteries. This will place significant limits on its payload capacities—making it less appealing as an alternative to diesel.
In the meantime, these hybrid models would address marketplace concerns over limited range, high cost, or payload restrictions due to battery weight. “We think that the way to enable the use of electricity in these vehicles is with a plug-in hybrid,” said Cohn. Such an engine would weigh far less than its electric counterpart, be more fuel-efficient and produce only about a tenth as much greenhouse gases as today’s diesel engines.
“[Flex fuel] engines are cheaper, exhaust treatment systems are cheaper, and it's a way to ensure that they can meet the expected regulations,” Cohn says. “And combining that with electric propulsion in a hybrid system, given an ever-cleaner electric grid, can further reduce emissions and pollution from the trucking sector.”
Read more about the electrification of transport trucks at Demand for Electric Buses and Trucks Is Expected to Soar.