|
Thanks, Blake. I missed that
point.
I did find one minor error in your transcription of
your example to e mail - a digit was dropped. I also used 10700 rpm
as Lynn reported vice the 10000 rpm in you example.
With that using your approach (which is certainly simpler
and more accurate than the one I used) I came up with 110.19% VE which
would appear to give a PP a VE in the vicinity of 110% Ve.
But, again, it would be nice to know if there were
any restrictors or if that was clean and clear intake.
Lynn?
Ed
----- Original Message -----
Sent: Friday, June 01, 2007 4:35 PM
Subject: [FlyRotary] Re: PP Ve??? was Re: Intake CFM air
flow
> 12A Pports can do 310 HP at 10,700 RPM at
.667
>
> If the .667 is BSFC then start with that.
> density
of air at sea level 15C = .0765 lbs/cf
> air/fuel = 12
>
>
.667 bsfc x 310hp is 206.77 lbs/hr fuel
>
> 206.77lbs x 12 =
2481.24 lbs/hr air
>
> 2481.24 lbs/hr / 60min/hr =
41.354 lbs/min
>
> (41.354 lbs/min) / (.0765 lbs/cf) * (1728
ci/cf) = 93411 ci /min = 934113. Dropped a digit in transcription to e
mail.
>
> (93411ci/min) / (10000 rev/min) = 93.41
ci/rev
(934113
ci/min)/(10700 rev/min) = 87.300
ci/rev, I used the 10700 rpm Lynn cited in his
example
>
> 1300cc /
(2.54cm * 2.54cm * 2.54cm)/ci = 79.33 ci volume
>
> 93.41ci /
79.33ci = 1.1774 = 117.74 % VE
using the Ci/rev I got with 10700
rpm and 310 HP I arrived at
87.33 ci/79.22 ci = 110.19 %
VE
Good calculation approach,
I'll save it for later use
> > Blake > > > On 6/1/07, Ed Anderson
< eanderson@carolina.rr.com>
wrote:
>>
>>
>>
>>
>> 12A
Pports can do 310 HP at 10,700 RPM at .667 .
>>
>> Lynn E.
Hanover
>>
>>
>> Thanks for that Data point,
Lynn. I see if I can use it to get a gestimate
>> on PP
Ve.
>>
>> So if a 12A is 73 cubic inches then at 10700
rpm and 100%Ve it would flow
>>
>> 73*10700/(1728)
= 452 CFM air flow.
>>
>> So if at this 100%
Ve we get less power than 310HP then we can assume the
>> Ve of the 12A
must be greater than 100%Ve to give us more power.
>>
>> At
sea level standard day 1 cubic foot of air = 0.076 lbms. So for
that
>> flow we would have 0.076 * 452 = 34.35
lbs/min. Now I don't have any idea
>> what Air Fuel ratio a
rotary racer uses but I best power is reportedly to
>> close to
12:1
>>
>> Assuming a race air fuel ratio of around 12:1
then the fuel needed for that
>> ratio at that airflow.
Then the fuel needed would be 34.35 /12 := 2.8624
>> lb of
gasoline per minute.
>>
>> A lb of gasoline has
19000 BTU depending on octane. Higher octane has
>> less so
assuming 19000 BTU/Lbm gasoline, we can next calculate the power
>>
being produced in the engine.
>>
>> Converting 2.8624lb/min of
gasoline into lb/sec we have 2.8624/60 = 0.047708
>>
lb/sec.
>>
>> To find the BTU we have .048*19000 = 912
BTU/sec. IF ALL this energy were
>> converted to torque it would
give 912 *778 = 709536 ft-lbs of torque. or
>> divide by
550 = 1290 HP!!!
>>
>> Unfortunately, we know approx 50% goes
out the tail pipe as heat and another
>> 25% (more or less) is Waste
heat rejected by our coolers leaving us
>> somewhere around 25-30%
depending on whose estimate you use for efficiency
>> of a rotary
engine of 1290 *.25 = 322 HP or using 30% 1290 *.30 = 387
HP
>>
>>
>> Hummm, since the 12A PP is producing 310,
but the calculations shows it
>> should be getting closer to 322 HP
that would suggest a PP port 12A flows
>> less than 100% Ve. If
fact, it would suggest that the Ve of the 12A at
>> 10700 rpm is closer
to 310/322 *100 = 96.27%Ve.
>>
>> But, this is instantaneous
BHP, I have not subtracted for mechanical or
>> other
inefficiencies so taking a guess that amounts to around 5% of the
>>
total. Then to get a dyno of 310 HP the engine would need to
produce
>> 310*1.05 = 325 HP. So here we would get 325/322
= 101% Ve for the 12A at
>> 10700 rpm.
>>
>>
Given we know that some racers are restricted by the size of the
intakes
>> permitted (is this true for the PP, Lynn?) perhaps that is
why the VE seems
>> a bit on the low side. But, that's just a
guess. Well, that was my best
>> crack at trying to determine the
efficiency of a PP.
>>
>> So anybody else having an idea or
source of information or opinion - jump
>> in.
>>
>>
Ed
>
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