According to the research, 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).
Washington: In new research, engineers have devised a new way of
powering heavy-duty truck that could drastically curb pollution,
increase efficiency, and reduce or even eliminate their net greenhouse
gas emissions.
The study was presented at the annual SAE International conference meeting.
Heavy-duty trucks used for transportation across the world are virtually all powered by diesel engines accounting for a major portion of worldwide greenhouse gas emissions, but little has been done so far to curb their climate-change-inducing exhaust.
According to the research, 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 said, 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 diesel), because it’s intrinsically much cleaner,” Cohn said.
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 said.
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 said.
The engine they propose for such a hybrid is a version of one the two researchers have been working on for years, developing a highly efficient, flexible-fuel gasoline engine that would weigh far less, be more fuel-efficient, and produce a tenth as much air pollution as the best of today’s diesel-powered vehicles.
In order to match the efficiency of diesel, a mix of alcohol with the
gasoline, or even pure alcohol, can be used, and this can be processed
using renewable energy sources, they found.
Detailed computer
modelling of a whole range of desired engine characteristics, combined
with a screening of the results using an artificial intelligence system,
yielded clear indications of the most promising pathways and showed
that such substitutions are indeed practically and financially feasible.
In
both the present diesel and the proposed flex-fuel vehicles, the
emissions are measured at the tailpipe, after a variety of
emissions-control systems have done their work in both cases, so the
comparison is a realistic measure of real-world emissions.
The
combination of a hybrid drive and a flex-fuel engine is “a way to enable
the introduction of an electric drive into the heavy truck sector, by
making it possible to meet range and cost requirements, and doing it in a
way that’s clean,” Cohn said.
Bromberg said that gasoline engines have become much more efficient and clean over the years, and the relative cost of diesel fuel has gone up so that the cost advantages that led to the near-universal adoption of diesel for heavy trucking no longer prevail.
“Over time, gas engines have become more and more efficient, and they
have an inherent advantage in producing less air pollution,” he said.
And by using the engine in a hybrid system, it can always operate at its
optimum speed, maximizing its efficiency.
Methane is an
extremely potent greenhouse gas, so if it can be diverted to produce a
useful fuel by converting it to methanol through a simple chemical
process, “that’s one of the most attractive ways to make a clean fuel. I
think the alcohol fuels overall have a lot of promise,” Bromberg said.
“The
engines are cheaper, exhaust treatment systems are cheaper, and it’s a
way to ensure that they can meet the expected regulations. 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,” said Cohn.
Pure electric propulsion for trucks
is the ultimate goal, but today’s batteries don’t make that a realistic
option yet, Cohn said: “Batteries are great, but let’s be realistic
about what they can provide.”
And the combination they propose can address two major challenges at once, they said, “We don’t know which is going to be stronger, the desire to reduce greenhouse gases, or the desire to reduce air pollution,” Cohn said.
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