Rob Matheson | MIT
News Office http://newsoffice.mit.edu/
December 5, 2014 -- Noise, excessive vibration, and relative
inefficiency are drawbacks of the piston-based internal combustion engines
(ICE) that power today’s lawn and garden equipment, such as leaf blowers and
lawn trimmers.
But now
MIT startup LiquidPiston has developed a rotary ICE that it says is
significantly smaller, lighter, and quieter, as well as 20 percent more
fuel-efficient than the ICEs used in many such small-engine devices.
“If you
think of handheld tools — for example, a chain saw or hedge trimmer
— after about a half hour you don’t want to use it anymore because your
hand feels like it’s going to fall off,” says Alexander Shkolnik PhD ’10,
president of LiquidPiston and co-inventor of the engine. “Our engine has no
vibration at all and it’s a lot quieter. It should be a much nicer user
experience all around.”
LiquidPiston’s
70-cubic-centimeter engine, the X Mini, produces about 3.5 horsepower at 10,000
RPM; at 4 pounds, it’s also about 30 percent smaller than the four-stroke,
50-cubic-centimeter piston ICEs it aims to replace. When fully complete,
Shkolnik says, the X Mini could churn out about 5 horsepower at 15,000
revolutions per minute, and weigh 3 pounds.
The
engine runs the novel high-efficiency hybrid cycle (HEHC) — developed by
Shkolnik and his physicist father, Nikolay — that achieves combustion at
constant volume and overexpansion for greater energy extraction. With only two
moving parts, a rotor and shaft, and no poppet valves — commonly used in other
four-stroke ICEs to control fuel intake — the engine also has reduced noise,
vibration, and harshness characteristics, Shkolnik says.
Initial
applications will be handheld lawn and garden equipment, Shkolnik says. But the
engine can be scaled and modified for other applications, including mopeds,
drones, marine power equipment, robotics, range extenders, and auxiliary power
units for boats, planes, and other vehicles. The company has also demonstrated
proof-of-concept for high-efficiency diesel versions of the engine, including
the 70-horsepower X1 and the 40-horsepower X2, for generator and other
applications. The company hopes to eventually develop small diesel versions of
the X Mini engine for military applications.
“If you
look at a 3-kilowatt military generator, it’s a 270-pound gorilla that takes
five people to move around,” Shkolnik says. “You can imagine if we can make
that into a 15-pound device, it’s pretty revolutionary for them.”
Shkolnik
presented a paper on both the X2 and X Mini on Nov. 19 at the Society of
Automotive Engineers’ 2014 Small Engine Technology Conference and Exhibition in
Italy.
An
inverse Wankel
The X
Mini is essentially an upgrade in design and efficiency of the compact Wankel
rotary engine, invented in the 1950s and used today in sports cars, boats, and
some aircraft.
In the
Wankel, a rounded triangle rotor spins in an eccentric orbit within an oval
chamber, with each rotation producing three power strokes — where the
engine generates force. In the X Mini, an oval rotor spins within a modified,
rounded triangular housing.
“We’ve
inverted everything about the traditional rotary engine, and now we can execute
this new thermodynamic cycle [HEHC] and solve all the problems that were
plaguing the traditional Wankel engine” for small-engine applications, Shkolnik
says.
A
Wankel engine, for instance, uses a long combustion chamber (like a thin
crescent moon), which contributes to poor fuel economy — as the flame
can’t reach trailing edges of the chamber and gets quenched by the chamber’s
large surface area. The X Mini’s combustion chamber is rounder and fatter, so
the flame burns over less surface area.
Air and
fuel intake and gas exhaust in the X Mini occur through two ports in the rotor,
opened or closed as the rotor revolves, removing the need for valves.
Asymmetrical location of these ports slightly delays the exhaust process during
expansion. This allows for HEHC’s overexpansion process — from the
Atkinson thermodynamic cycle, used in some hybrid cars — where gas is expanded
in the chamber until there’s no pressure, allowing the engine more time to
extract energy from fuel. This design also accommodates HEHC’s “constant volume
combustion” — from the Otto thermodynamic cycle, used in spark-ignition piston
engines — where compressed gas is held in the chamber for an extended
period, letting the air and fuel mix and ignite completely before expanding,
resulting in increased expansion pressures and higher efficiency.
“It
takes a long time to burn fuel in an engine,” Shkolnik says. “In most engines,
by the time you’re burning fuel, you’re expanding gases, and you’re losing
efficiency from the combustion process. We keep combusting while the rotor is
at the top of the chamber and force combustion under those conditions. It’s
much more efficient that way.”
Additionally,
the X Mini has relocated the apex seals, leading to decreased oil consumption.
In Wankels, apex seals join the edges of the triangular rotor, where they slide
and move. Lubricating them requires supplying the air-fuel mixture with large
amounts of oil that burns and leaks, increasing emissions and oil consumption.
In the X Mini, however, these seals are located in the triangular-shaped
housing that stays put. “Now we can supply tiny amounts of oil through the
stationary housing, exactly how much oil the seal needs, and you’re not burning
any oil and you’re not losing any oil to the environment,” Shkolnik says.
LiquidPiston’s
“roadmap”
An
interest in robotics and artificial intelligence led Shkolnik to MIT as a PhD
student in electrical engineering and computer science in 2003. That year,
Nikolay Shkolnik filed his first HEHC patent, and his son learned about the MIT
$50K Entrepreneurship Competition (now $100K) in a class that focused on tech
entrepreneurship. They teamed up with students at the MIT Sloan School of
Management to create a business plan and pitch an HEHC engine in the 2004 competition,
where they took home the $10,000 runner-up prize to launch LiquidPiston.
The
competition itself proved helpful to the father-and-son entrepreneurs — who, at
that point, had no startup experience. In building a detailed business plan and
learning how to explain their technology to investors, “It really showed us a
roadmap for what to do and we were forced to think through a lot about issues
we were going to face,” Shkolnik says.
Over
the next six years, Shkolnik helped his father develop the LiquidPiston engine
out of the family garage, using skills he honed in MIT’s Robot Locomotion
Group, led by Russell Tedrake, an associate professor of electrical engineering
and computer science. “It was a lot of optimization, and control, and
simulations, and modeling,” he says. “All those same techniques are applicable
to designing an engine.”
Shkolnik
attributes much of LiquidPiston’s development to the extended MIT community.
During the $50K, venture capitalist Bill Frezza ’76, SM ’78 mentored the team;
his firm then became an early investor. MIT Sloan team members Brian
Roughan MBA ’05, Jennifer Andrews Burke MBA ’05, and Vikram Sahney MBA ’05
conducted market research, wrote the business plan, worked on business
development, and pitched the company to investors.
Mentors
from MIT’s Venture Mentoring Service (VMS) — including the late Dave Staelin,
who founded the VMS — also guided LiquidPiston’s growth, offering advice
on product development, hiring, and seeking venture capital. (So far, the
company has earned more than $15 million in funding.)
In
2006, after analyzing dozens of engine iterations, LiquidPiston earned a
$70,000 military grant to produce an initial diesel-engine prototype. (Today,
LiquidPiston has analyzed and patented about 60 different engine designs to
embody HEHC.)
Due to
overwhelming feedback from power equipment manufacturers — calling for lighter,
quieter, vibration-free engines — LiquidPiston recently pivoted to the X
Mini, which it developed and released in the last six months. The company has
now received interest from potential customers, and is speaking to engine
manufacturers interested in licensing the X Mini technology.
“In
addition to improving existing engine applications,” Shkolnik explains, “the X
Mini may enable entirely new applications not currently possible with current
engine or battery technology.”
Early
next year, the company plans to host a competition to solicit ideas from the
public surrounding these new uses for the X Mini. “We want to get the creative
juices flowing and open up to the wider community to see if there’s something
interesting,” Shkolnik says.
Rob Matheson | MIT News Office http://newsoffice.mit.edu/
No comments:
Post a Comment