[Diy_efi] Intro, and q's about fuel economy

[Bernd Felsche]

On Sun, Dec 15, 2002 at 09:08:38PM -0600, Greg Hermann wrote:
> At 5:39 PM 12/15/02, James wrote:
> >On Sun, 15 Dec 2002, Greg Hermann wrote:

> >> You are going to have a _difficult_ time finding a small enough
> >> injector to run digital !!

> >We have one, I am told.

> >It's a 3.5 hp briggs and stratton lawnmower engine.  RPM will vary with
> >clutch engagment point and final gearing, but it's probably in the
> >neighborhood of 3-4k, maybe 5k but probably not.

Typ. 9.02 cu. in. capacity - Bore 2.56 in.  Stroke 1.75 in.
(148cc)

> OK--A 3.5 HP engine. Say _MAYBE_ you hop it up/improve its
> efficiency to where it's good for 6 HP. This will require about a

Might be able to get 10 hp or more; depends a lot on how
mechanically- and thermally- stressed the engine is in stock
config...

> 3 lb/hr. of fuel. Or, at, say, a 60% duty cycle at full power, a 5
> lb/hr. injector. Smallest injector _I_ know of is a 13.5 lb/hr
> one, made by Bosch. Check the archives here, there have been a
> number of times folks have been looking for little injectors.

There's 0-280-150-207 delivering 10.3 lb/hr (108.3 cc/min)
according to http://users.erols.com/srweiss/tableifc.htm

Getting a bit closer - up to about 35% maximum duty cycle at rated
pressure. Information on motorcycle (moped!) injectors isn't easy to
find...

Delivery is at rated pressure. One could reduce fuel pressure and
decrease fuel density by heating - measure the fuel temperature and
pressure at delivery to get an idea of the real fuel flow rate.
Use a small fuel reservoir in which you regulate temperature by
regulating the flow of waste heat from the engine or cooling air to
the reservoir.

HOT FUEL IS DANGEROUS. Be very careful. Do NOT try to exceed 70
degrees C at preheat unless the system is pressure tight.

Increase the load at "idle" by turning an alternator to charge a
battery. Kill the engine when the battery is nearly full and use the
battery power to boost acceleration from start. 

Budget permitting; get some EE folks to make you a starter-generator
flywheel. Use super-caps to smooth out the idle; absorbing power on
the power peak and throwing more in during compression.

42V electrics should earn bonus points with SAE. :-)

-- 
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