[Diy_efi] Air/Fuel meter now working! And L-jetronic

[Astrona]

With NA engine and L-jet we also know only the flow and not the real
density. There are pretty linear realtions between the flow and VE. Knowing
the temp and speed the fuel requirement is pretty mappable. Compared to
other 70's systems.

You're right, we need to know the pressure in cylinder not in some tubes.
But we can think so:
when 0.5L air @2bar abs pressure moves to cylinder, the same amount of air
needs to go through airflowmeter = 1L @ 1bar. It can be a bit delayed.
Although in free air airwaves are moving 33cm in 1 ms, and in 1m long intake
the delay would be 3ms, and in pressure they are moving even faster, BUT it
takes time for the pressure to stabilize since there are lots of
restrictions. That would be ideal if we know how big is the delay in every
condition.

At the same manifold pressure, temperature, throttle position and RPM - we
know the mass if we have volumetric efficiency table (flow speed). If added
air flow (speed) meter, we could forget these tables :D and put that system
onto whatever engine.

AFM is air-flow-meter
AFR is air-fuel-ratio
AFRM is air-fuel-ratio-meter
What WBO2-guys mean by AFM?

----- Original Message ----- 
From: "Adam Wade" <espresso_doppio at yahoo.com>
To: <diy_efi at diy-efi.org>
Sent: Friday, June 17, 2005 12:10 AM
Subject: Re: [Diy_efi] Air/Fuel meter now working! And L-jetronic


> --- Astrona <amdcpu at hot.ee> wrote:
>
> > What about 80's Saab, Volvo turbos?
>
> Ah, those were the LH-Jetronic, which used a hot wire
> MAF sensor.
>
> > AFM's act when pressure-differential is present.
>
> That's one way of looking at it, but it doesn't really
> capture the point of what it is doing.  It's measuring
> the speed with which air flows past the plate.
> However, the only way the ECU can know how much air
> mass is getting past is to know the density of said
> air.  If you were using a flapper-type VAF sensor
> (which you call an AFM, confusing since many people
> refer to a WBO2 as an "AFM"), you'd have to measure
> the temperature and pressure of the air that was
> passing the VAF; this would require taking these
> measurements inside the plenum.
>
> > So in constant 2bar they are shut.
>
> ITYM "open", but that is not the case unless the
> engine is flowing more volume (not more mass!) than
> the VAF is designed for.
>
> > Maybe they have AFM at the atmosphere-side and are
> > "reading" air volume at 1 atm.
>
> Since pressure varies greatly in the plenum, and not
> in direct relation to either throttle position or
> engine speed, you'd be getting an imprecise at best
> measure with which to compute ingested air mass.
> You'd have the same problem with a MAF located
> pre-turbo.  A MAF between plenum and throttle body
> would be better, although it seems to me that it would
> be less and less precise as the boost rose.
>
> | 82 Honda CX500 Turbo (Cassandra)  90 Kwak Zephyr 550 (Daphne) |
> | "It was like an emergency ward after a great catastrophe; it  |
> |   didn't matter what race or class the victims belonged to.   |
> |  They were all given the same miracle drug, which was coffee. |
> |   The catastrophe in this case, of course, was that the sun   |
> |     had come up again."                    -Kurt Vonnegut     |
> | M/C Fuel Inj. Hndbk. @ Amazon.com -  http://tinyurl.com/6o3ze |
>
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