[DeTomaso] NPC- Definition of acceleration
Thomas Tornblom
Thomas.Tornblom at hax.se
Wed Oct 14 02:23:59 EDT 2009
wkooiman at earthlink.net skrev:
> What is the a/f ratio for nitro dragsters?
>
> Isn't 70cc of air vs. 2cc of fuel 35:1?
No, AFR is measured by weight, not volume.
>
> If this were gasoline, wouldn't it be closer to 70cc of air with ~5.5cc of fuel? (about 12:1)
No. Recalculating those 2cc:s of nitro, with an AFR of 1.7:1 into the
AFR for gasoline, 14.7:1, you would inject about .25cc of gas for each
cycle if you were running at stoichiometry, but about .28cc if you are
running a rich (12:1) AFR. Notice that this is at 3 bars (43 psi) of boost.
>
> Since this is nitro, wouldn't it be closer to maybe 70cc of air with 20cc of fuel? - or even more fuel?
No.
This is perhaps how this hydro lock myth started, if it is a myth.
Thomas
>
> -----Original Message-----
>> From: Thomas Tornblom <Thomas.Tornblom at hax.se>
>> Sent: Oct 13, 2009 1:19 PM
>> To: dave at damardirect.com
>> Cc: 'List Pantera' <detomaso at realbig.com>
>> Subject: Re: [DeTomaso] NPC- Definition of acceleration
>>
>> Dave McManus skrev:
>>> Ok, I sent the thread to my engineer super son-in-law for his 2 cents. He
>>> says he likes ACME rockets!
>>>
>>> IndyDave
>>>
>>> Here are his thoughts:
>>>
>>> His thought process is wrong as far as how he is looking at the volume of
>>> the engine. 500 cubic inches is not the volume of the cylinder, it is the
>>> displacement. You would have to figure out how many cc the heads are. You
>>> would then add that to the gap caused by the head gaskets times the diameter
>>> of the piston. He may know this but he did not include it in his
>>> calculation.
>> I know that I omitted the combustion chambers in my example. In my
>> hypothetical example I chose 500 cui as that is very close to 8 liters,
>> or one liter per cylinder, makes it simple to calculate :-)
>>
>> Normal Cleveland CC:s are on the order of 60-75cc, which is orders of
>> magnitude more than the amount of fuel needed in my calculation, and big
>> blocks normally have larger CC:s. There is thus no chance of hydro lock
>> for one missed spark, and most of the unburned fuel will be dumped
>> through the exhaust so I don't see how several missed sparks would
>> accumulate and cause hydro lock either.
>>
>>>
>>> Hydraulic lock also references that the mixture is incompressible. So
>>> basically you are taking 3 Liter of nitro / air (1L/cylinder compressed at 3
>>> bars) and jam it a 1L cylinder. The cylinder goes through its combustion
>>> cycle and further compresses the mixture. At TDC the volume of the cylinder
>>> is only the volume calculated above. At some pressure point its easier for
>>> the rod to set sail than continue on the compression path. The compression
>>> ratio is 6.5:1. The pressure inside the cylinder is much higher than the 3
>>> bars. I believe you can use pV=nRT from Thermodynamics here. Thus,
>>> p1V1=p2V2. That would mean the cylinder is at 19.5 bars or 280psi. I am
>>> sure they are minimizing the cc's of the head to maximize power and the
>>> hydraulic lock would be the limiting factor.
>> Yes, the pressure at ignition will be much higher, but that doesn't
>> matter. What matters is the amount of air you have shoved into the
>> cylinder, which happens to be 3 liters if you are running at 3 bars of
>> boost. No matter how much or little you compress this, the mass stays
>> the same, and thus the amount of fuel needed for stoichiometry. And I
>> calculated that to around 2cc. So you have 2cc of liquid, and 3 liters
>> if air crammed into a 70cc or so combustion chamber. Those 2cc:s are not
>> going to cause hydro lock.
>>
>> I'm willing to be proved wrong, but it would need some explanation.
>>
>> Rich fuel blends are frequently used to keep the internals cool, but it
>> appears to be orders of magnitude off, unless I've done some serious
>> thought error.
>>
>> There is no water injection on top-fuel dragsters, or? That would add
>> some liquid.
>>
>>>
>>> http://www.motortrend.com/features/112_0502_top_fuel_numbers/index.html
>>> Brandin Ray
>>> Forming & Shoring Design Engineer
>>> -----Original Message-----
>>> From: Göran Malmberg [mailto:hemipanter at hemipanter.se]
>>> Sent: Tuesday, October 13, 2009 3:35 AM
>>> To: michael at michaelshortt.com; 'Thomas Tornblom'
>>> Cc: 'List Pantera'
>>> Subject: Re: [DeTomaso] NPC- Definition of acceleration
>>>
>>> I believe we could say that the air is very much only a media for the
>>> supercharger to transport fuel in to the combustion chamber and not
>>> really for burning. At idle it is very rich and does literally shower
>>> out the exhaust. Another thing is that by using smaller diameter and
>>> longer stroke we can make the engine act as a bigger than 8 litre. By
>>> using larger combustion chamber we can stuff more fuel in to it as well
>>> as if the diameter was larger.
>>> Goran
>>>
>>> -----Ursprungligt meddelande-----
>>> Från: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com]
>>> För michael at michaelshortt.com
>>> Skickat: den 12 oktober 2009 23:07
>>> Till: Thomas Tornblom
>>> Kopia: List Pantera
>>> Ämne: Re: [DeTomaso] NPC- Definition of acceleration
>>>
>>> I don't know anything about all that math stuff, but I do know that a
>>> great
>>> deal of the air used in the "explosion" is contained in the fuel mixture
>>> itself ( like rocket fuel )
>>>
>>> And from having seen lots of them "blow up", they certainly do come
>>> apart
>>> with great explosive force, often removing the blower and scoop, heads
>>> and
>>> headers ( although nowadays they are held down by straps ) or they lose
>>> fire
>>> and dump loads of raw fuel out of the header pipe of the offending
>>> cylinder
>>> ( which you see on TV all of the time ). and sometimes the bottom end
>>> also
>>> comes apart ( and that's when all the action stops and the track has to
>>> be
>>> cleaned up ).
>>>
>>>
>>> Nothing else smells like Burnout tire smoke and Nitro methane, it smells
>>> like.............Victory!
>>>
>>>
>>> Michael Shortt
>>>
>>>
>>>
>>>
>>>
>>> On Mon, Oct 12, 2009 at 4:52 PM, Thomas Tornblom
>>> <Thomas.Tornblom at hax.se>wrote:
>>>
>>>> Göran Malmberg skrev:
>>>>> Problem arises if there is missfiering, the hydrolock is a result.
>>>> Is this really true btw?
>>>>
>>>> I just did a quick calculation and I don't see how there could be
>>> hydro
>>>> lock, even if it doesn't ignite.
>>>>
>>>> Assume a 500 cui engine, or 8 liter.
>>>> Air mass is ~9500l/kg at atmospheric pressure.
>>>> Density of nitro is 1.13 kg/l.
>>>> Lambda 1 AFR for nitro is 1.7:1 (by weight)
>>>> Assume 3 bar boost
>>>>
>>>> So each cylinder gets 1 liter of air at 3 bar boost per cycle, or
>>> 3/9500kg.
>>>> The amount of fuel (by weight) is 1/1.7 of the amount of air,
>>> 3/(9500x1.7).
>>>> The amount of fuel by volume is 1.13 x the amount by weight.
>>>>
>>>> So the volume of fuel per cycle is:
>>>>
>>>> 3/(9500x1.7x1.13), which if I have calculated everything correctly
>>>> amounts to 0.16cc.
>>>>
>>>> I don't see how this would result in a hydro lock, unless the
>>> combustion
>>>> chambers would have zero size.
>>>>
>>>> It appears that many of the items on this list are myths.
>>>>
>>>> Another list can be found here:
>>>>
>>> http://www.motortrend.com/features/112_0502_top_fuel_numbers/index.html
>>>> What I find interesting is that the crank only turns 569 turns over
>>> the
>>>> quarter mile, and the intake valves open just 284 times :-)
>>>>
>>>> Thomas
>>>>
>>>>
>>>>> Dual sparkpluggs is a good idea then.
>>>>> Goran
>>>>>
>>>>> -----Ursprungligt meddelande-----
>>>>> Från: detomaso-bounces at realbig.com
>>> [mailto:detomaso-bounces at realbig.com]
>>>>> För Sean Korb
>>>>> Skickat: den 12 oktober 2009 20:57
>>>>> Till: List Pantera
>>>>> Ämne: Re: [DeTomaso] NPC- Definition of acceleration
>>>>>
>>>>> 58-65 degrees spark advance. By the time the piston is at TDC, much
>>>>> of the charge has already burned.
>>>>>
>>>>> sean
>>>>>
>>>>> On Mon, Oct 12, 2009 at 2:28 PM, <adin at frontier.net> wrote:
>>>>>> An old, old email.
>>>>>>
>>>>>> But, if one thinks a moment . . . .(whew) running a 1.7 to 1 fuel
>>> mix
>>>>>> means that over 1/3 of the charge is "liquid" ?????? At that
>>>>>> compresion ratio, isn't that true hydro-lock????
>>>>>>
>>>>>> How does that work?
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Quoting "michael at michaelshortt.com" <michaelsavga at gmail.com>:
>>>>>>
>>>>>>> A friend sent this to me, fun read.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> For all of you old drag racers
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> THE DEFINITION OF ACCELERATION!!
>>>>>>>
>>>>>>> One top fuel dragster 500 cubic inch Hemi engine makes more
>>>>> horsepower
>>>>>>> than the first 4 rows of stock cars at the Daytona 500.
>>>>>>>
>>>>>>> It takes just 15/100ths of a second for all 6,000+ horsepower of
>>> an
>>>>> NHRA
>>>>>>> Top Fuel dragster engine to reach the rear wheels.
>>>>>>>
>>>>>>> Under full throttle, a dragster engine consumes 1-1/2 gallons of
>>>>> nitro
>>>>>>> methane per second. A fully loaded 747 consumes jet fuel at the
>>> same
>>>>> rate
>>>>>>> but with 25% less energy being produced.
>>>>>>>
>>>>>>> A stock Dodge Hemi V8 engine cannot produce enough power to drive
>>>>> the
>>>>>>> dragster's supercharger.
>>>>>>>
>>>>>>> With 3,000 CFM of air being rammed in by the supercharger on
>>>>> overdrive,
>>>>>>> the fuel mixture is compressed into a near-solid form before
>>>>> ignition.
>>>>>>> Cylinders run on the verge of hydraulic lock at full throttle.
>>>>>>>
>>>>>>> At the stoichiometric (stoichiometry: methodology and technology
>>> by
>>>>>>> which quantities of reactants and products in chemical reactions
>>> are
>>>>>>> determined) 1.7:1 air/fuel mixture of nitro methane, the flame
>>> front
>>>>>>> temperature measures 7,050 deg F.
>>>>>>>
>>>>>>> Nitro methane burns yellow. The spectacular white flame seen
>>> above
>>>>> the
>>>>>>> stacks at night is raw burning hydrogen, dissociated from
>>> atmospheric
>>>>> water
>>>>>>> vapor by the searing heat of the exhaust gases.
>>>>>>>
>>>>>>> Dual magnetos supply 44 amps to each spark plug. This is the
>>> output
>>>>> of
>>>>>>> an arc welder in each cylinder.
>>>>>>>
>>>>>>> Spark plug electrodes are totally consumed during a pass. After
>>>>>>> halfway, the engine is dieseling from compression, plus the glow
>>> of
>>>>> exhaust
>>>>>>> valves at 1,400 deg F. The engine can only be shut down by cutting
>>>>> the fuel
>>>>>>> flow.
>>>>>>>
>>>>>>> If spark momentarily fails early in the run, unburned nitro
>>>>> immediately
>>>>>>> builds up in
>>>>>>> the affected cylinder and then explodes with sufficient force to
>>> blow
>>>>>>> cylinder heads off the block in pieces or split the block in half.
>>>>>>>
>>>>>>> In order to exceed 300 mph in 4.. 5 seconds, dragsters must
>>>>> accelerate an
>>>>>>> average of over 4G's. In order to reach 200 mph (well before
>>>>> half-track),
>>>>>>> the launch acceleration approaches 8G's.
>>>>>>>
>>>>>>> Dragsters reach over 300 miles per hour before you have completed
>>>>>>> reading this one sentence.
>>>>>>>
>>>>>>> Top fuel engines turn approximately 540 revolutions from light to
>>>>> light!
>>>>>>> Including the burnout, the engine must only survive 900
>>> revolutions
>>>>> under
>>>>>>> load.
>>>>>>>
>>>>>>> The red line is actually quite high at 9,500 rpm.
>>>>>>>
>>>>>>> Assuming all the equipment is paid off, the crew worked for free,
>>>>> and
>>>>>>> for once NOTHING BLOWS UP, each run costs an estimate $1,000.00
>>> per
>>>>> second.
>>>>>>> The current top fuel dragster elapsed time record is 4.428
>>> seconds
>>>>> for
>>>>>>> the quarter mile (11/12/06, Tony Schumacher, at Pomona , CA ). The
>>>>> top speed
>>>>>>> record is 336.15 mph as measured over the last 66' of the run
>>>>> (05/25/05 Tony
>>>>>>> Schumacher, at Hebron , OH ).
>>>>>>>
>>>>>>> Putting all of this into perspective:
>>>>>>>
>>>>>>> You are driving the average $140,000 Lingenfelter 'twin-turbo'
>>>>> powered
>>>>>>> Corvette Z06. Over a mile up the road, a top fuel dragster is
>>> staged
>>>>> and
>>>>>>> ready to launch down a quarter mile strip as you pass. You have
>>> the
>>>>>>> advantage of a flying start. You run the 'Vette hard up through
>>> the
>>>>> gears
>>>>>>> and blast across the starting line and pass the dragster at an
>>> honest
>>>>> 200
>>>>>>> mph. The 'tree' goes green for both of you at that moment..
>>>>>>>
>>>>>>> The dragster launches and starts after you. You keep your foot
>>> down
>>>>>>> hard, but you hear an incredibly brutal whine that sears your
>>>>> eardrums and
>>>>>>> within 3 seconds, the dragster catches and passes you. He beats
>>> you
>>>>> to the
>>>>>>> finish line, a quarter mile away from where you just passed him.
>>>>>>>
>>>>>>> Think about it, from a standing start, the dragster had spotted
>>> you
>>>>> 200
>>>>>>> mph and not only caught, but nearly blasted you off the road when
>>> he
>>>>> passed
>>>>>>> you within a mere 1,320 foot long race course.
>>>>>>>
>>>>>>> ... and that my friend, is ACCELERATION!
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Michael L. Shortt
>>>>>>> Savannah, Georgia
>>>>>>> www.michaelshortt.com
>>>>>>> michael at michaelshortt.com
>>>>>>> 912-232-9390
>>>>>>>
>>>>>>>
>>>>>>> This email is protected by the Electronic Communications Privacy
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>>>>>
>>>> --
>>>> Real life: Thomas Törnblom Email:
>>> Thomas.Tornblom at Hax.SE
>>>> Snail mail: Banvallsvägen 14 Phone: +46 18 444 33 21
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