Injector sizing

[John]

weigh your car, go to the drag strip and estimate your HP from your times...

since i'm awd, that's pretty much my only alternative..



At 4:32 PM -0500 2/26/01, Pat Ford wrote:
>  great info so far but is there any way to get the bsfc without a dyno?
>
>Previously, you (Stewart Prince) wrote:
>{ Although the injector pulse width is larger at peak torque, the injector is
>{ usually sized on peak power because this is where fuel flow is maximum.
>{
>{  fuel flow (lbm per hour)=bsfc(lbm per hp-hr) x power (hp)
>{
>{ the fuel flow rate equation for an injector is
>{
>{ fuel flow (lbm per hour)=injector max flow(lbm per hour) x pulse 
>width (sec) /
>{ injection period (sec)/ #injectors
>{
>{ this equation should be corrected for pulse width offset, which is 
>usually about
>{ 1 millisecond.  injection period could be the engine period, or 
>the cam period,
>{ depending on how many times you inject per cycle.
>{ For instance, if the engine (assume 4 cyl) is to produce 100 hp 
>and the bsfc is
>{ .5 lbm per hp-hr, the fuel flow would be 50 lbm per hour.  Since 
>most injectors
>{ should open at a duty cycle of 85% at max power, we get about 15 
>lbm per hour
>{ static flow, per injector.  A more precise calculation would 
>include the injector
>{ offset, which does affect the sizing equation.  It is true that 
>the pulse width
>{ would be longer at peak torque, but since peak torque always 
>occurs at an rpm
>{ lower than peak power, the injector duty cycle is actually LOWER 
>here, thus one
>{ should size the injector at peak power, not peak torque.
>
>cool
>
>{
>{ Tlsalt at aol.com wrote:
>{
>{ > Greg Hermann wrote:
>{ >
>{ > the .55 bsfc does it. Try looking at the HP AT the torque peak to figure
>{ > out the pw (and duty cycle) you will need at the torque peak. HP is work
>{ > per unit time, and injector flow rate is a part of the determination of
>{ > fuel flow per unit time. They are consistent units. Torque has no time
>{ > factor in it.
>{ >
>{ > Hello Greg:
>{ >
>{ >     I am still puzzled how a 20% increase in BSFC can account for a 50%
>{ > increase in torque.  If torque is proportional to the mass of air consumed
>{ > doesn't the amount of fuel increase proportionally for a given air fuel
>{ > ratio.  Is there a thermal efficiency difference between NA and 
>supercharged
>{ > to explain it ?  The pulsewidth at peak torque is higher than at peak
>{ > horsepower, so I don't see how horsepower at peak torque is used 
>to calculate
>{ > peak torque pulsewidth.  Do you have a formula ?  I used the VE 
>based formula
>{ > to calculate the mass of air at peak torque and then a 13:1 AFR 
>to calculate
>{ > the injector puslewidth as a base setting for the Haltech fuel 
>curve. Since
>{ > the puslewidth is relate to a single event and the amount of air 
>inhaled per
>{ > event is greatest at peak torque, pulsewidth at peak torque should be the
>{ > longest in the fuel curve ? Do you agree ?  I understand the 
>time bit and the
>{ > maximum flow rate, duty cycle etc. for the ultimate fuel 
>delivery in lbs/hr
>{ > and the highest duty cycle I've seen in a data log was 84% at 
>WOT at redline
>{ > rpm.  I am having a hard time with this partially because the 
>original torque
>{ > curve of this engine was a peak at 1500 rpm and a flat line to 
>4500 rpm.  The
>{ > problem my be entirely in my head.
>{ >
>{ > Paul
>{ >
>{ > 
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>{ --
>{ STEWART PRINCE
>{
>{ PROFESSOR, MECHANICAL ENGINEERING
>{
>{ CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
>{
>{
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>--
>Pat Ford                           email: pford at qnx.com
>QNX Software Systems, Ltd.           WWW: http://www.qnx.com
>(613) 591-0931      (voice)         mail: 175 Terence Matthews         
>(613) 591-3579      (fax)                 Kanata, Ontario, Canada K2M 1W8
>
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