Yes, for some reason the Rigol default
is 0V mid screen.
The EM3 software does average some channels like airspeed and
altitude that Tracy found fluctuated.
I don't think fuel pressure is one of them.
I've got 33 analog channels. I think the goal is to display and
log at least once each second. That gives up to 30mS to select,
let stabilize and A/D-convert each channel.
Found this note in the EM3 Data Acquisition Module program:
"99% of the time it will be in a delay waiting for the MAX6675 to
complete a conversion which takes about 170 ms.� Since there are
16 TC inputs, this loop will take approximately 2.72 seconds to
complete."
The MAX6675 outputs a digital (serial) result. It has four
8-channel muxes in front of it. (Yes, ideally there would be 8
MAX6675's for EGT inputs and 8 equivalent chips for CHT inputs but
I guess Tracy found that cost and/or space prohibitive.)
Uses three analog inputs in the PIC18F4620:
One for 8 channel 0-5V inputs
One for 8 channel 0-5V (was 0-2V) inputs
One for battery/system voltage input.
Note that one can specify how many CHT, EGT and other analog
inputs are used in order to speed it up.
I could try to modify the program to sample/average all 17 0-5V
channels while waiting for the MAX6675 to complete conversion of
one of the 16 CHT/EGT channels.
I'll have to look up the PIC18F4620 A/D conversion time specs.
But a lot easier to just add a capacitor to the fuel pressure
sensor, at least for now.
Note that I originally wanted to roll my own engine monitor. I
went with the EM3 in order to utilize its programming that reads
and displays data from the EC3 and also allows some programming of
the EC3.
Finn
On 5/7/2021 4:22 AM, Stephen Izett
stephen.izett@gmail.com wrote:
Hi Finn
Looking at your CRO screen shot, can you confirm
what I'm looking at?
Is it set for DC, 1V/Div, 5mSec/Div ?
If so where is 0v - Mid Screen?
I would have thought any processor based engine
monitoring system would read and average many samples and so
filter out any instantaneous �fluctuations in the pressure.
Cheers
Steve
OK, so I hooked up a scope to the fuel pressure
sensor.
Sensor has 50mV/psi sensitivity.
Below 20"Hg (secondaries not opening) just very slight
pulses.
But above 20"Hg -- about 4100 RPM -- I see 1.24V or
25psi peak-peak� pulses.
So that explains the wildly fluctuating fuel pressure
readings. Depending on when the pressure sensor voltage
is sampled by the engine monitor there can be 25 psi or
more difference in engine monitor readings and data
logging.
If you look at the picture I attached on May 4th, you'll
see the pressure sensor is located at the end of the
secondary fuel rail (solid tube) . Apparently the rubber
lines from the T-fitting to primary and secondary rails
are enough to somewhat dampen the primary injector fuel
pressure pulses. I probably should add an R-C filter
between sensor and monitor to get more reliable fuel
pressure readings.
With today's 15 deg F lower OAT the engine transitions
smoothly at the staging point. I'm again seeing cracks
in the JB-weld around primary runners, so possible that
they may be collapsing somewhat under high ambient temps
-- maybe not. Remember I'm using the stock exhaust
manifold. Even with the stock heat shield and an
additional 0.016 alum shield, the heat from the exhaust
manifold is intense. That is a huge chunk of metal
that'll radiate heat with low or no airflow over it
after shutdown. A definite drawback from using the stock
exhaust manifold. Maybe I don't have a leak in my welds
on the exhaust manifold and it was just higher OATs?
Another suspect for odd behavior is the engine
controller's temperature sensor. I located it in the
left radiator air scoop. Probably a bad idea when
running on the ground.
�
Finn
On 5/4/2021 2:08 PM, Charlie England
�ceengland7@gmail.com�wrote:
Does the pressure increase
have a solid 'step' at the exact staging point, or is
it just rising in that area? How much increase on the
gauge? Where is the reference for fuel pressure
measurement?
�
The pressure *regulator* should be referenced to MAP
(manifold pressure), and will raise absolute fuel
pressure as manifold pressure rises. If the gauge is
referenced to atmosphere (or absolute), it would
indicate a rise in pressure as the throttle is opened.
Charlie
On 5/4/2021 12:44 PM, William Schertz
�wschertz343@gmail.com�wrote:
Finn
No rx-8 injector experience, but if at
the staging point, if the EC-2-3 shuts off the
primary injectors, and the secondaries haven't
opened, fuel out of the manifold decreases, so the
pumps would raise the pressure. Are you confident
that the controller is reducing the primaries and
starting the secondaries at the same time?
Bill
Is the
fuel pressure really increasing or is it
the EM2/3 reading?� Steve B. has posted
good advice for tuning around the staging
point with different size injectors.�
�
Bobby
�
From:�Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net]�
Sent:�Tuesday,
May 04, 2021 11:46 AM
To:�Rotary
motors in aircraft
Subject:�[FlyRotary]
Renesis secondary injectors
�
I noticed that my indicated fuel
consumption appeared to be about 50% higher
than actual.
So I decided to start calibrating
engine monitor fuel flow.
The first step is to check/adjust
fuel flow around the staging point (20"Hg)
where the secondary injectors open
(secondary injectors are larger than primary
injectors on the 4-port Renesis).
I thought I had previously tuned
the engine for a smooth transition around
the staging point, at least to the point
when I didn't notice anything when dvancing
throttle through the staging point.
However, now doing stationary run
ups around the staging point (especially
when engine is getting hot) I get the weird
phenomenon of it going very lean when
secondary injectors (supposedly) open.
Another odd thing is that fuel pressure�increases
markedly.
On the�HomebuiltAirplanes.com�forum
a guy that raced RV-8s for a couple of
seasons mentioned troubles with the stock
Renesis injectors.
Now I'm wondering if I have
(intermittently) bad secondary injectors --
not opening when they should.
However, I'm confused by the rise
in fuel pressure. Is there a injector
failure mode where pressure in intake
runners could push back through the injector
into the fuel line?
Note that these are factory-new,
maybe 10 to 20 hours of total engine run (or
attempted run) time.
Another possibility is heated
secondary fuel rail. But if there were
boiling fuel there the fuel pressure should
still drop when secondary injectors open...
I tried to look but didn't find a
chart of 87 octane 10% ethanol boiling point
vs temperature.
Anybody here had any trouble with
stock Renesis injectors? Symptoms? Other
ideas?
Finn
RX-8 4-port:
Primary: Denso 195500-4430��� 33.3 lb/hr @
43.5 psi (350cc/min)��� 13.8 ohm�
Secondary: Denso 195500-4460��� 51.4 lb/hr @
43.5 psi (540cc/min)��� 13.8 ohm
�
Disclaimer
The
information contained in this communication
from the sender is confidential. It is
intended solely for use by the recipient and
others authorized to receive it. If you are
not the recipient, you are hereby notified
that any disclosure, copying, distribution or
taking action in relation of the contents of
this information is strictly prohibited and
may be unlawful.
This email has been scanned for viruses and
malware, and may have been automatically
archived by�Mimecast Ltd, an innovator in
Software as a Service (SaaS) for business.
Providing a�safer�and�more useful�place
for your human generated data. Specializing
in; Security, archiving and compliance. To
find out more�Click Here.
<NewFile2.jpg>--
Homepage:
�http://www.flyrotary.com/
Archive
and UnSub: ��http://mail.lancaironline.net:81/lists/flyrotary/List.html