In a paper being presented at WCX SAE World Congress Experience in Detroit this week, a team from MIT is proposing the use of a flex-fuel gasoline-alcohol engine approach for a series-hybrid powertrain for long-haul Class 8 trucks.
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.
In this approach the engine would provide comparable (or possibly greater) efficiency than a diesel engine while also providing around 90% lower NOx emissions than present cleanest diesel engine vehicles. Ethanol or methanol would be employed to increase knock resistance. Engines that could be deployed in the relatively near term could also use high rpm operation and /or water injection, to allow operation with a very small amount of alcohol in addition to a low concentration mixture such as E10 (or possibly with no additional alcohol). Further NOx reduction (by use of higher levels of EGR) and increased efficiency (by use of alcohol enhance heat recovery) could potentially be obtained over a longer term.
Compared to a diesel engine vehicle, a gasoline-powered vehicle produces only a tenth 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.
An all-electric heavy-duty truck will be very challenging, Cohn says, because of the cost and weight of the batteries needed to provide sufficient range. To meet the expected driving range of conventional diesel trucks, Cohn and Bromberg estimate, would require somewhere between 10 and 15 tons of batteries—a significant fraction of the payload such a truck could otherwise carry.