From: "Sboese sboese@uwyo.edu" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: Renesis secondary injectors
Date: Fri, 7 May 2021 12:25:40 -0600
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Finn,

Rather than coming up with a way to electronically reduce or eliminate the =
pressure pulse measurements, you might consider reducing or eliminating the=
 pressure pulses in the first place.  It is my understanding that the (leak=
 prone) stock pulsation damper results in quieter injector operation.  This=
 makes sense if the injector, when it starts to close, is being slammed shu=
t with pressure pulse of at least 25 psi over the normal fuel rail pressure=
 when the damper isn=E2=80=99t present. It=E2=80=99s hard to imagine this a=
s a good thing, but maybe that=E2=80=99s just me.  Similar pulses may be oc=
curring at the dead ended primary injectors but you aren=E2=80=99t set up t=
o see them.

I chose to plumb the primary and secondary fuel rails in series and install=
ed about 2 ft of fire-sleeved hp rubber fuel injection line at the end of t=
he series.  The hope was that this rubber line would act as a more reliable=
 pulsation damper than the stock unit.  I say =E2=80=9Chope=E2=80=9D becaus=
e my fuel pressure regulator, pressure sensor, fuel pumps, filters, and sel=
ector valve are all located in a module in the cockpit and vented to outsid=
e of the fuselage.  As a result, I have not tried to measure the pulse ampl=
itude at the end of a rigid fuel rail and don=E2=80=99t really know how eff=
ective my setup is.  I do know it has been reliable so far (over 700 hr) an=
d that I got steady fuel pressure readings initially with a homemade logger=
 and later with a Dynon EMS D10.

I also provided a MAP reference to the fuel pressure sensor so the fuel pre=
ssure reading shows the pressure across only the injector and does not refl=
ect changes in MAP or altitude.

FWIW

Steve Boese=20


> On May 6, 2021, at 5:47 PM, Finn Lassen finn.lassen@verizon.net <flyrotar=
y@lancaironline.net> wrote:
>=20
> 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  puls=
es.
> 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 loggi=
ng.
>=20
> 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) . App=
arently 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 re=
liable fuel pressure readings.
>=20
> With today's 15 deg F lower OAT the engine transitions smoothly at the st=
aging 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 ex=
haust manifold is intense. That is a huge chunk of metal that'll radiate he=
at 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?
>=20
> Another suspect for odd behavior is the engine controller's temperature s=
ensor. I located it in the left radiator air scoop. Probably a bad idea whe=
n running on the ground.=20
>=20
> Finn