Controversial topics?

Tech questions that don't fit above forums

Moderator: Team

quicksilver
Member
Member
Posts: 167
Joined: Tue Apr 27, 2010 9:02 pm

Controversial topics?

Post by quicksilver » Wed Feb 15, 2012 11:27 pm

Hey fellas!

Well- I have a question. What are some things out there in the engine world that are debated upon? Im in college and I must write a research paper- however- I get to pick the topic. Thank god- It can be any topic that has controversy (an argument on both sides) and since this is what I love, it would be better (and beneficial) to write a research paper about something I actually give a shit about.

Im not looking for the research- thats what IM doing- Im looking for things that need research done.
If you would like (if I use your idea) Ill even come back and post a thread regarding my finds during the research or after it has been concluded.

Here's a couple I was thinking of:
Compression and its effect on airflow (does it increase airflow? does it just increase efficiency? does it do both?)
How a combustion chamber ignites (there are 3 different theory's out there as to exactly how a spark plug ignites a mixture in the combustion chamber)

Got anything guys?

rabbit
Member
Member
Posts: 88
Joined: Sun Apr 18, 2010 5:50 am

Re: Controversial topics?

Post by rabbit » Thu Feb 16, 2012 12:32 am

intake to exhaust flow ratio, as measured on the flow bench and spouted as gospel by many, and derided by many others.

that will keep you busy for about 20 years.

tonyg64
Member
Member
Posts: 176
Joined: Fri Sep 04, 2009 4:19 pm
Location: uk

Re: Controversial topics?

Post by tonyg64 » Thu Feb 16, 2012 1:56 am

Detonation and pre ignition should keep you busy too :D

Tony

Kevin Johnson
Guru
Guru
Posts: 7035
Joined: Tue Nov 22, 2005 5:41 am

Re: Controversial topics?

Post by Kevin Johnson » Thu Feb 16, 2012 6:18 am

quicksilver wrote:Hey fellas!

Well- I have a question. What are some things out there in the engine world that are debated upon? Im in college and I must write a research paper- however- I get to pick the topic. Thank god- It can be any topic that has controversy (an argument on both sides) and since this is what I love, it would be better (and beneficial) to write a research paper about something I actually give a shit about.

Im not looking for the research- thats what IM doing- Im looking for things that need research done.
If you would like (if I use your idea) Ill even come back and post a thread regarding my finds during the research or after it has been concluded.

Here's a couple I was thinking of:
Compression and its effect on airflow (does it increase airflow? does it just increase efficiency? does it do both?)
How a combustion chamber ignites (there are 3 different theory's out there as to exactly how a spark plug ignites a mixture in the combustion chamber)

Got anything guys?
Compare ignition to lightning. A good deal of knowledge of the complex and varied nature of lightning is evolving with high speed video. Compare/contrast with spark ignition.

Kevin Johnson
Guru
Guru
Posts: 7035
Joined: Tue Nov 22, 2005 5:41 am

Re: Controversial topics?

Post by Kevin Johnson » Thu Feb 16, 2012 6:19 am

Oh, yes, forgot. A definitive explanation of turbulence.

Daniel Jones
Member
Member
Posts: 175
Joined: Wed Dec 21, 2011 4:09 pm

Re: Controversial topics?

Post by Daniel Jones » Thu Feb 16, 2012 11:28 am

> Oh, yes, forgot. A definitive explanation of turbulence.

When I see hot rodders tossing around the term turbulence, I find they often
confuse it with pressure separation which a completely separate effect. Flow
separation and turbulence are NOT the same thing. They also seem to think
that turbulence is worse than laminar flow but that's not necessarily the case.
When laminar flow can be maintained, it does have less drag than the turbulent
flow. However, laminar flow can only (passively) be maintained by to slender
bodies, like airfoil sections, and then only sometimes. For low drag on a
shape that will not sustain laminar flow, you want to eliminate flow separation.
Inducing turbulence is a great way to do this.

The profile drag of an object can be split into two components:

Cd = Cdf + Cdp

where

Cd = profile drag coefficient
Cdp = pressure drag coefficient due to flow separation
Cdf = skin friction drag coefficient due to surface roughness
in the presence of laminar/turbulent flow

The drag which comprises the Cdf component is caused by the shear stress
induced when air molecules collide with the surface of a body. A smooth
surface will have a low Cdf. Also, the Cdf is lower for laminar flow and
higher for turbulent flow. Cdp, on the other hand, is caused by the
fore-and-aft pressure differential created by flow separation. Often
(usually?) Cdp is lower for turbulent flow and higher for laminar flow.
In many cases, inducing turbulence will dramatically decrease the pressure
drag component, decreasing the overall drag. Airplanes use this trick all
the time.

Back in the 19th century, when scientists were just beginning to study the
field of aerodynamics, an interesting observation was made with respect to
the drag of a cylinder. Since a cylinder is symmetric front-to-back (and
top-to-bottom), their early theories predicted it should have no drag (or
lift). If you plot the (theoretical) pressure distribution along the
surface of the cylinder (remembering that pressure acts perpendicular to a
surface) and decompose it into horizontal (drag) and vertical (lift)
components, you'll find that the pressure on the front face of the cylinder
(from -90 to +90 degrees) and the pressure on the rear face ( from +90 to
+270 degrees) are equal in magnitude but opposite in direction, exactly
canceling each other out. Therefore, there should be no drag (or lift).

However, if you actually measure the pressure distribution, you'll find
there are considerably lower pressures on the rear face, resulting in
considerable drag. This difference between predicted and observed drag
over a cylinder was particularly bothersome to early aerodynamicists who
termed the phenomenon d'Alembert's paradox. The problem was due to the
fact that the original analysis did not include the effects of skin
friction at the surface of the cylinder. When air flow comes in contact
with a surface, the flow adheres to the surface, altering its dynamics.
Conceptually, aerodynamicists split airflow up into two separate regions,
a region close to the surface where skin friction is important (termed the
boundary layer), and the area outside the boundary layer which is treated
as frictionless. The boundary layer can be further characterized as
either laminar or turbulent. Under laminar conditions, the flow moves
smoothly and follows the general contours of the body. Under turbulent
conditions, the flow becomes chaotic and random.

It turns out that a cylinder is a very high drag shape. At the speeds
a high performance street car travels, a cylinder has a drag Cd of
approximately 0.4. By comparison, an infinite flat plate sets the upper
limit with a Cd of 1.0. An efficient shape like an airfoil (that is aligned
with the airflow, i.e. is at 0 degrees angle of attack) may have a Cd of
0.005 to 0.01. Think about what this means. An airfoil that is 40 to 80
inches tall may have approximately the same drag as a 1 inch diameter cylinder.

Luckily, there are easy ways of reducing a cylinder's drag. Another thing
the early aerodynamicists noticed was that as you increased the speed of
the air flowing over a cylinder, eventually there was a drastic decrease in
drag. The reason lies in different effects laminar and turbulent boundary
layers have on flow separation. For reasons I won't get into here, laminar
boundary layers separate (detach from the body) much more easily than
turbulent ones. In the case of the cylinder, when the flow is laminar, the
boundary layer separates earlier, resulting in flow that is totally
separated from the rear face and a large wake. As the air flow speed is
increased, the transition from laminar to turbulent takes place on the front
face. The turbulent boundary layer stays attached longer so the separation
point moves rearward, resulting in a smaller wake and lower drag. In the
case of the cylinder, Cd can drop from 0.4 to less than 0.1.

You don't have to rely on high speeds to cause the boundary layer to "trip"
from laminar to turbulent. Small disturbances in the flow path can do the
same thing. A golf ball is a classic example. The dimples on a golf ball
are designed to promote turbulence and thus reduce drag on the ball in
flight. If a golf ball were smooth like a ping pong ball, it would have
much more drag. So instead of waxing your car, maybe you should let it get
hail damaged :)

If you look closely, you'll notice that some Indy and F1 helmets have a
boundary layer trip strip to reduce buffeting. It seems odd but promoting
turbulence can reduce buffeting by producing a smaller wake.

Another consequence of skin friction on a cylinder is that you can generate
substantial lift with a spinning cylinder. By spinning a cylinder you can
speed up the flow over the top and slow down flow under the bottom, resulting
in a lift producing pressure differential. I think this phenomenon is known
as the Magnus effect. BTW, the spinning tires on F1 and Indy cars are *huge*
sources of drag.

Technically speaking, separated flow is not turbulent, even though it is
random and chaotic (and very draggy). The laminar and turbulent concepts
apply only to the boundary layer, which is only a few inches thick. Beyond
the boundary layer, flow is treated as frictionless (inviscid). The boundary
layer is very important since it determines skin friction drag and the
tendency towards pressure separation (turbulent boundary layers are *less*
likely to detach). There is a drag increase associated with the transition
from laminar to turbulent flow but it is usually small compared to the drag
increase associated with separated flow.

This brings up another important aerodynamic term, the Reynolds number, which
is defined as:

Re_x = (Rho * V * X)/Mu

where:

Re_x = Reynolds number at location x (a dimensionless quantity)
Rho = freestream air density
V = freestream flow velocity
x = distance from the leading edge
Mu = freestream viscosity, a physical property of the gas (or liquid)
involved, varies with temperature, at standard conditions mu is
approximately 3.7373x10E-07 slug/(ft*sec) for air.

The location along the body at which the flow transitions from laminar to
turbulent determines the critical Reynolds number. Below this number, the
flow is laminar, above it is turbulent. Since the Reynolds number varies
linearly with the location along the body and with velocity, the faster you
go, the farther forward the transition point moves. At cruising speed on a
typical jet airliner, only a small region near the leading edge may be
laminar. Slow speed gliders with very slender (but still with rounded, blunt,
leading edges) may maintain laminar flow over most of the wing surface but
this is not the case for most practical aircraft. Note that glider wings
are typically designed with very short chord lengths (x distances) to help
promote laminar flow. Laminar flow is desirable when there is no pressure
separation.

Dan Jones

quicksilver
Member
Member
Posts: 167
Joined: Tue Apr 27, 2010 9:02 pm

Re: Controversial topics?

Post by quicksilver » Thu Feb 16, 2012 3:39 pm

Holy crap Dan.

I think thats 8x longer than what I would ever need. Great topic but- what are the major opposing arguments? Turbulent flow does XYZ vs pressure separation does XYZ?

Daniel Jones
Member
Member
Posts: 175
Joined: Wed Dec 21, 2011 4:09 pm

Re: Controversial topics?

Post by Daniel Jones » Thu Feb 16, 2012 3:54 pm

> Great topic but- what are the major opposing arguments? Turbulent flow does XYZ vs pressure separation does XYZ?

I don't think it really applies for your paper. It's not controversial within
academic circles. The term just gets abused and mis-applied by some people who
don't realize the difference. Sort of like the it torque versus power arguments.
There's no actual controversy in the sense that both concepts are well understood
within physics or engineering. It's just when someone misapplies the concepts
that controversy occurs. As I understand it, you're looking for an area of
current research where the answers aren't yet clear.

Dan Jones

User avatar
SWR
Guru
Guru
Posts: 2791
Joined: Sun Jan 29, 2006 5:39 pm
Location: Norway
Contact:

Re: Controversial topics?

Post by SWR » Thu Feb 16, 2012 8:06 pm

I would think that write-up is more poised at aircraft aero... "Boundary layer a few INCHES thick" would really be something in a port. :lol: And it made me think... I worked on a NA dragbike many years ago. Never got below 10 sec, it was 10.1, 10.4, 10.2, 10.05!, and such for a season. Decided to add nitrous to it to break the barrier. Placed the injector between carb and head, ran 9.78 first time out with NO GAS BOTTLES on the bike.

The port is 5-valve, BIG and rather lazy in the fps department. I know it's said to be fact that all ports are permanently turbulent, but here it seems that the extra turbulence added by the injector poking into the airstream in that slow port removed a flow separation problem.

Could it then be that the venturi shaping of the ports - moving MinCSA up the port - we now often do to 4- and 5-valve heads cure a flow separation problem in the running engine that the flowbench just doesn't have the power to reveal, by forcing the air to slight transsonic speeds locally and inducing turbulence due to the high Mach value?
-Bjørn

"Impossible? Nah...just needs more development time"

Kevin Johnson
Guru
Guru
Posts: 7035
Joined: Tue Nov 22, 2005 5:41 am

Re: Controversial topics?

Post by Kevin Johnson » Fri Feb 17, 2012 5:11 am

Daniel Jones wrote:> Great topic but- what are the major opposing arguments? Turbulent flow does XYZ vs pressure separation does XYZ?

I don't think it really applies for your paper. It's not controversial within
academic circles. The term just gets abused and mis-applied by some people who
don't realize the difference. Sort of like the it torque versus power arguments.
There's no actual controversy in the sense that both concepts are well understood
within physics or engineering. It's just when someone misapplies the concepts
that controversy occurs. As I understand it, you're looking for an area of
current research where the answers aren't yet clear.

Dan Jones
A caveat to Bridgman's position on dimensional analysis: he appeals to pure numbers as a leveling abstraction across mechanics allowing the manipulation/studying of relationships. Much current research on the nature of turbulence seeks revelation in number theory and flavors of group theory.
When I meet God, I am going to ask him two questions: Why relativity? And why turbulence? I really believe he will have an answer for the first.

User avatar
John Wallace
Guru
Guru
Posts: 1276
Joined: Tue Jan 04, 2005 10:20 am
Location: was Central Illinois - Now in Sunny Florida!
Contact:

Re: Controversial topics?

Post by John Wallace » Fri Feb 17, 2012 1:01 pm

You could always do the 'shift at maximum torque or at maximum HP ' topic.

:D

It's lasted a long time here and no further settled than when it started.
(or swayed any one side to the other)

:)
John Wallace
Pontiac Power RULES !
www.wallaceracing.com

quicksilver
Member
Member
Posts: 167
Joined: Tue Apr 27, 2010 9:02 pm

Re: Controversial topics?

Post by quicksilver » Sun Feb 19, 2012 3:34 pm

Yeah unfortunately I will probably ultimately end up doing a research paper on some bullshit topic that is completely non-related to my "give a shit" index. Had to turn in a preliminary list of topics to her friday, and only one was automotively themed. I got almost an immediate revolt via email on that topic, because she had absolutely no idea what it was. (shocker!)

So it will probably end up being gay marrage or stem cell research or some other "popular" cultural event. Well- I tried! :D

Ill squeeze as much automotive as I can into my classes. Its the only thing that can keep me motivated to have any interest in the work!

User avatar
John Wallace
Guru
Guru
Posts: 1276
Joined: Tue Jan 04, 2005 10:20 am
Location: was Central Illinois - Now in Sunny Florida!
Contact:

Re: Controversial topics?

Post by John Wallace » Wed Feb 22, 2012 10:07 am

You should have asked her, what to write about?
How would you know what she knows or doesn't know?

How about a paper on the controversy of writing what the teacher wants?

:D
John Wallace
Pontiac Power RULES !
www.wallaceracing.com

brad_m
Pro
Pro
Posts: 246
Joined: Fri Jul 29, 2011 11:54 pm
Location: Australia

Re: Controversial topics?

Post by brad_m » Sat Mar 17, 2012 5:35 am

Ford vs chev.

Dodge Freak
Guru
Guru
Posts: 1712
Joined: Sun Oct 21, 2007 6:56 pm

Re: Controversial topics?

Post by Dodge Freak » Sun Mar 25, 2012 11:59 pm

What makes more HP, a carburetor or F.I. :lol:

Post Reply