Pulsed injectors on/off times

[Ameer Antar]

Well, I did some of the math, and on a 1.8L engine at 500rpm idle and at .2 
bar absolute pressure, I get 5 CFM of air. Does this sound right? Any way 
w/ that figure, comes to 4.439 lbs air/hr. At a 14:1 afr ratio that means 
.317 lbs fuel/hr. If an injector has a minimum pulse of 5%, then the max 
flow of the injector should be 6lbs/hr...and I don't think they even make 
those. So are the injectors actually turned off at idle in some cars? This 
doesn't make sense to me. How does the engine run at idle, if not all the 
cylinders get fuel. I thought every cylinder must get the exact amount of 
air and fuel at every rpm including idle.

Maybe my question should really be how much is too much? How big of an 
injector can I use [and still have idle] on a car w/ a given engine size, 
rpm, and volumetric efficiency? Any ideas? thanks.

-ameer


At 10:17 PM 2/11/2001 , you wrote:
>At 9:19 PM -0500 2/11/01, Ameer Antar wrote:
>
>
>>  If it's too big, the injector might be so large that it can't turn on 
>> for a short enough time to run the engine at idle, by flooding it w/ too 
>> much fuel.
>
>This usually isn't a problem if the car is equipped with a varying fuel 
>pressure regulator; for example, the 200q20v regulator "matches" rail 
>pressure with manifold pressure(not directly; fuel pressure is always at 
>least 1bar above manifold.)  For example, at idle, the fuel rail pressure 
>will be much lower than full throttle with 1.8bar in the manifold.  Best 
>of both worlds.
>
>
>>  So what's the standard figure for minimum injector output...5-10%? Or 
>> can injectors be shut off completely by the ECU
>
>Yes, they frequently are, during deceleration(driver's foot completely off 
>the accelerator and hence idle switch closed.)  This is also true on CIS cars.
>
>Brett
>--
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>Brett Dikeman                           Systems Engineer
>ProAct Technologies Corporation         914-872-8043
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