Paul,
During my combustion testing on rotary engines I kept finding an anomaly
of autoignition. Usually about 6 to 8 cycles on a normal 8000 RPM
sweep. It seemed to be caused by exhaust reversion continuing to the
next intake cycle and causing the auto ignition. Very scary to have an
uncontrolled ignition source.... but the good news was that the burn
rate on those cycles improved!
After a little study I discovered a Honda experiment that concluded with
a race bike for the Dakar rally that had a two-stroke engine running
without ignition and getting 20% better fuel economy. But the details
were very sketchy.
Fast forward to Formula 1 today. They are using what is known as
Turbulent Jet Ignition. This process is not new, it was discovered by
Ricardo and published in his papers from 1911. The latest version of
this process by Mahle uses a direct injector and spark plug in a very
small pocket that injects active radicals into the main combustion
chamber. The engine can then be operated almost like a diesel and the
burning process is spread throughout the combustion chamber by quenched
active radicals causing a very fast burn rate. Lean burns have been
demonstrated to lambda 2 or 30:1 AFR gasoline and throttling losses
greatly reduced.
This is why Formula One is now producing the same horsepower but is
using 40% less fuel.
Mahle is reportedly working with Ferrari but Mercedes seems to be way
ahead of them.
This ignition process seems to be a perfect fit for the rotary engine...
especially on aircraft where BSFC is so important.
Barry Bordes
How are you doing the combustion testing on rotary engines?
References for the Honda experiment?
http://papers.sae.org/2010-01-1457/
The reason Formula One engines are burning less fuel is because they are
turbo compound
hybrids. A formula 1 engine is either on full throttle or on the brakes.
The power recovery
from braking is a large part of that.
http://www.rotaryeng.net/Oxford-TC-talk.mp4
We have known for years that leaning the rotary up to 18:1 improves the
BSFC at the expense
of power.
If you have a leaking apex seal hot exhaust gases from the leading
chamber can
pre ignite the following chamber.
Paul Lamar
I am using an Optrand sensor in the leading spark plug. In conjunction
with a TFX logger.
See attachments for the type data it provides.
The first is a peak pressure single cycle with exhaust opening pressure
and temp.
The second shows burn rate
The third shows a complete 7000 rpm run.... tuning a new EFR turbo...
the lower cells around 4000 rpm are retarded.
I don't have the Honda paper number but check SAE 2010-01-2263 for past
and present research.
Barry Bordes
Looks like it is sparking After Top Dead Center.
We use 22 degrees BTC
Paul Lamar
That timing was initiated at approximately 22 deg BTDC. It takes the
kernel that long to grow into a readable pressure at 9 deg ATDC. The
rate then snowballs from the heat and pressure.
I adjust the timing to place the peak pressure at about 45 deg ATDC.
(less at lower RPM)
What we are seeing is how slow the burn is with standard ignition practices.
Barry Bordes
That is amazing. What does that device cost?
Paul Lamar
They have many systems from one to 28 high speed loggers. Sensors are extra.
Here is a link with lots of info.
Great knowledgeable support.
My contact is Clint Grey.
TFX Engine Technology - Engine Pressure Analyzers
<http://www.tfxengine.com/hardware3.html>
image
<http://www.tfxengine.com/hardware3.html>
Thanks.
I don't need a logger. A Maximite is a great logger. Super low cost.
This is some interesting research by Honda. Maybe they can use this to help
their lagging F1 turbo compound hybrid engine development.
"When the fuel is brought to the right pressure and temperature, the
molecules break down into what are known as active radical molecules.
These are highly unstable chemical compounds which are an intermediate
step in the actual combustion reaction. When hot exhaust gas remains in
the [chamber], it contains a small percentage of active radical
molecules; when these are combined with the incoming fuel charge, the
resulting mixture begins to auto-ignite at lower temperature that a pure
gasoline/air mixture. What we currently associate with auto-ignition is
engine knock, a phenomenon that occurs when the fuel ignites before the
spark plug fires."
Dan Gorsline clued me in on this.
Paul Lamar
Hi!: the concept in the Honda paper in the link you provided, of
Turbulent Jet Ignition Pre-Chamber Combustion System, is very
interesting, and the improvements in fuel economy, of top quality.
Regarding the fears expressed by Paul, of a leaking apex seal allowing
flame passing to the preceding chamber, this may have happened under
special circumstances, perhaps an engine raced under no load, but
usually, the mix in the trail part of combustion chamber in a Wankel RCE
may even not ignite.
An engineer from Chile, Marcos Langeani, published a SAE paper, 921444:
*On the Wankel Engine with High Pressure Recirculation of Unburned Gases
*
<http://papers.sae.org/921444/>
1992-11-01
Technical Paper
921444
Marcos Langeani
"Despite a real progress since their introduction in early sixties by
NSU, Wankel engines are still lagging behind their equivalent
reciprocating counterparts as far as fuel economy and emissions are
concerned. Fuel stratification during combustion promises further
progresses, but a similar move is expected for reciprocating units. A
type of stratified combustion system, which was called hybrid fuel
energy conversion system, is outlined in the text. One special
characteristic of such a system is the dilution of the already burned
gases by the air which does not participate in combustion, when engine
is operating at partial loads. The hybrid system features a deep recess
in the rotor housing which has the function of a prechamber. The
resultant geometry produces a significant recirculation of unburned
gases, late in the expansion process of the leading chamber to the
trailing chamber performing compression, with a major impact on engine
thermodynamic cycle."
Thus, the phenomenon of gas passing to the preceding chamber may not
necessarily be bad. Of course, a leaking apex seal would add to lower
bmep, but the subject may deserve discussion and study.
Comments?
Thanks, have a good season, best regards, + Salud
Jose Gros-Aymerich
Madrid, Spain
I disagree on the emissions! My RX8 pases the draconian emissions laws
in California with flying colors despite being over ten years old. In
aircraft
use it is only 5% behind a typical aircraft engine as far as fuel burn is
concerned. In turbo compound form it would be better than any piston
engine with a poppet exhaust valve.
Paul Lamar
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