Heavy-duty trucks, such as the 18-wheelers that transport many of the world's goods from farm or factory to market, are virtually all powered by diesel engines. They account for a significant portion of worldwide greenhouse gas emissions, but little has been done so far to curb their climate-change-inducing exhaust.
Researchers at MIT have devised a new way of powering these trucks that could drastically curb pollution, increase efficiency, and reduce or even eliminate their net greenhouse gas emissions.
The concept involves using a plug-in hybrid engine system, in which the truck would be primarily powered by batteries, but with a spark ignition engine (instead of a diesel engine). That engine, which would allow the trucks to conveniently travel the same distances as today's conventional diesel trucks, would be a flex-fuel model that could run on pure gasoline, pure alcohol, or blends of these fuels.
While the ultimate goal would be to power trucks entirely with batteries, the researchers say, this flex-fuel hybrid option could provide a way for such trucks to gain early entry into the marketplace by overcoming concerns about limited range, cost, or the need for excessive battery weight to achieve longer range.
The new concept was developed by MIT Energy Initiative and Plasma Fusion and Science Center research scientist Daniel Cohn and principal research engineer Leslie Bromberg. "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 [as opposed to the compression ignition used in diesels], because it's intrinsically much cleaner," Cohn says. Compared to a diesel engine vehicle, a gasoline-powered vehicle produces only a 10th as much nitrogen oxide (NOx) pollution, a major component of air pollution.
In addition, by using a flex-fuel configuration that allows it to run on gasoline, ethanol, methanol, or blends of these, such engines have the potential to emit far less greenhouse gas than pure gasoline engines do, and the incremental cost for the fuel flexibility is very small, Cohn and Bromberg say. If run on pure methanol or ethanol derived from renewable sources such as agricultural waste or municipal trash, the net greenhouse gas emissions could even be zero. "It's a way of making use of a low-greenhouse-gas fuel" when it's available, "but always having the option of running it with gasoline" to ensure maximum flexibility, Cohn says.