Ha ha, you're right off-course about these, but then again, a honda type R and BMW's isn't exactly what most people here in Europe (this could be the key
) call normal cars. Reading the next posts I thought it is very funny you all start throwing in your 200 HP+ engines...Especially BMW is very performance oriented, together with AUDI.
But I have a hard time to believe that an average mans car like a standard spec. Ford Focus/Fiat Bravo/VW Bora/VW Passat/Citroen Picasso do have tuned intake and exhaust...
But back to the topic itself:
I'm by no means an expert, I only know the basics about these things, but if you want to know the exact wave behaviour in complex systems why not consult a fluid/acoustics engineer, he could probably make and simulate a FEM model of the whole thing.
I have some sheets somewhere were a more complex model is drawn, including something like this:
e-pipe-\__chamber-\
e-pipe-/ ..................chamber-->exhaust
e-pipe-\__chanber-/
e-pipe-/
(amazing what you can do with slashes ain't it
Maybe I could dig these up in the afternoon, it is a very rainy day anyway...
JinMTVT said:
The best path as I see it for what it seems like you're asking for is to study acoustical transmission lines, then how to determine the electrical transmission line analogy. Then you can apply the highly developed theory for electrical transmission lines to the problem.
The pipes have a characteristic impedance, and if they're mismatched there will be standing waves and resonances in the line. The resonances are easily heard when an engine is reved with an open or free flow muffler. Think about impedance matching especially at discontinuities where the line impedance changes.
Want to tell us more about the planned intake and exhaust system?
Pete B.
PB2 said:
i very like the way of your post ...
I cannot tell you about 1 planned intake/exhaust system, as what i would like is to learn how all this works..not for 1 system, but for all of them
i tried to reverse-engineered a few intake/exahust systems by measuring, using specs and trying to figure out what the engineers tried to achieve....without much success
G.Kleinschmidt: nice link // thanks
turbo is not allowed in the class we want to use this car for ... turbo is all alowed on streets though
but turbo or not, it doesn't change the laws and i still need to learn it all ...
it all applies to turbo also, and even if exhaust scavenging is not a big issue on FI engines, getting negative pressure waves at the intake while the valve is openned because of badly timmed waves is just as nefast on a FI engine as on an NA one ..
I think that what one needs to learn in terms of engine design/tunning, is to control the timing of the different waves on both intake and exhaust systems,
and either remove its bad effect or use it to advantage ..
we've all seen the short straight exhausts at the rear of the 50's F1 cars, wich were merely long enough to remove all unwanted possibilities, so the need to tune anything with the exhaust was not required, and since it was not completly understood back then, it was a safer bet to move it all out of the way
Then what we need here,
is the knowledge required to be able to control the wave's timing //
now what exactly are we talking about here?
that is the part where i'll need help from you guy
i can compute speed of sound VS distance of ports and all pretty easily, but once u start putting plenums and open pipes and all in the picture, i get mixed up pretty fast!
🙂
Speedsmile: well i ain't goint to cite some "cheap" cars as an example of a "tunned" engine nah ?
keep in mind that even economical cars like smart, fit and hybrid cars are just as much or even more tunned than big sports cars
you'd be amazed to see how muhc thinking and tunning most manufacturers put into their engine breathing systems ..even for cheap cars
as i said, you only have to design once,
then it's all done by manufacturing..so the costs aren't that great .. even so when experience is backing u up
You appeared to hint at diesel earlier.
It is becoming increasingly popular to run gas with diesel in Australia. You burn LPG (propane/butane) and diesel at the same time, up to 40% more torque from an unmodified engine than diesel alone. These usually run with a gasifier and a computer controlled metering valve for the gas.
However there are injectors available now that can handle Liquid LPG. so you get more accurate fuel control and the refrigeration effect which increases your air density.
A finely tuned electronically controlled direct diesel injection with liquid gas port injection engine would be quite a torque monster.
If power is your only aim have you considered explosion assisted exhaust extraction? Injecting fuel into certain parts of the exhaust and igniting it may be of benefit to create reverbrations or even to create gas flow past a ventiri to suck the exhaust out.
I suspect such a system would be frowned upon by scrutineers but the spectators would love it.
It is becoming increasingly popular to run gas with diesel in Australia. You burn LPG (propane/butane) and diesel at the same time, up to 40% more torque from an unmodified engine than diesel alone. These usually run with a gasifier and a computer controlled metering valve for the gas.
However there are injectors available now that can handle Liquid LPG. so you get more accurate fuel control and the refrigeration effect which increases your air density.
A finely tuned electronically controlled direct diesel injection with liquid gas port injection engine would be quite a torque monster.
If power is your only aim have you considered explosion assisted exhaust extraction? Injecting fuel into certain parts of the exhaust and igniting it may be of benefit to create reverbrations or even to create gas flow past a ventiri to suck the exhaust out.
I suspect such a system would be frowned upon by scrutineers but the spectators would love it.
The engine we will be workin on for the years to come will be developped and tested on alcool, with hydrogen as the main goal.
( i'll let the hydrogen distribution process and storage problems to big companies .. )
it's eays to shell in some nitro or other liquid gaz and get some increase in torque ....
but the limit will still be there for maximum timing VS pressure the engine can tolerate ...
we aim at going almost tenfolds what power engine have today ... my goal is already set for
1cc >= 1HP
we will be working with 50 to 100cc engine for starts,
shoudl be pretty easy to get up to 0.5hp/cc right at the beginning..getting up the the 1/1 ratio will be the harder
and maitaining the ratio with bigger engines will also be very hard ...we'll see where we get!
Soichiro Honda still own the record for all NA engines
( alot better than what F1 engine do presently )
at 50cc = 15hp @ 22Krpm back in the 60's 😛
FI F1 carsin the 80's did 1:1 ( 1500cc 1500hp on qualifying trims ) with 60+boost and crazy fuels
( note that is for my engine project..not for our racing cars engines ... )
( i'll let the hydrogen distribution process and storage problems to big companies .. )
it's eays to shell in some nitro or other liquid gaz and get some increase in torque ....
but the limit will still be there for maximum timing VS pressure the engine can tolerate ...
we aim at going almost tenfolds what power engine have today ... my goal is already set for
1cc >= 1HP
we will be working with 50 to 100cc engine for starts,
shoudl be pretty easy to get up to 0.5hp/cc right at the beginning..getting up the the 1/1 ratio will be the harder
and maitaining the ratio with bigger engines will also be very hard ...we'll see where we get!
Soichiro Honda still own the record for all NA engines
( alot better than what F1 engine do presently )
at 50cc = 15hp @ 22Krpm back in the 60's 😛
FI F1 carsin the 80's did 1:1 ( 1500cc 1500hp on qualifying trims ) with 60+boost and crazy fuels
( note that is for my engine project..not for our racing cars engines ... )
JinMTVT said:
I was going to suggest some things that you might try if we had a specific example to talk about. Then you can extrapolate to the general case.
I'm familiar the the DOHC Alfa Romeo design so I'll use that. This is a hemi head design with 2 DCOE Weber carbs in the Veloce models and of course there are newer injected models.
I've had spare parts laying around here for years so it would not be too hard to set up a head, intake manifold, and the Webers on a bench, and then put a small ~3 inch speaker where the cylinder would be. Calculate the frequency of the pulsed valve air flow, and drive the speaker at that frequency. Open the intake valve and use a small microphone to probe down the carb and into the manifold to measure the acoustical standing waves in the line (VSWR in electrical systems). You can then see how this changes vs. frequency (engine RPM) with different length velocity stacks, different tapers, and filters. It might actually work better (reduced standing waves) with the acoustical resistance provided by an intake filter.
Similar things could be done on the exhaust side, and with multiple cylinders where it might be interesting to explore crossover pipes.
It is interesting that there's probably resonance from the intake to exhaust side during the cam overlap period.
I've not read about anyone ever doing this, and I'd enjoy consulting on such a project if anyone is interested.
Pete B.
PB2 said:
Well i'd enjoy workin on such project to learn and see what can be done with that ..
you already pointed somehting that i never thought of ..
air filter = accoustic resistance ..
it's simple things like that, each in its place, that makes one understand how the system works
What do you think could be analysed using soundwaves in an engine system ?
what do you think and air filter and it's position VS cylinder head ( distance relation ) does in the intake system ? what exactly does an accoustical resistance do in phisical terms ?
i have 200+ cylinder heads lying around in my entrepot,
and some matching intake manifold to go along
could also setup on my side to get some comparative results ( though i have no alfa romeo at all 😛 )
The intake system that I've described is much like transmission line woofer loading. The valve and piston are the driving function and the pipe heading back to the air filter is the resonator. When a wave travels down the line there is a certain chracteristic impedance associated with the line, and when it opens to the air there is a sharp discontinuity due to the change in impedance, it is essentially unterminated, and the energy reflects back down the line, until it hits another mismatch, the (closed) valve and or opening into the combustion chamber. Standing waves can occur in the line, due to reflections such as these. Some resistance at the opening, such as an air filter might better match the line impedance and reduce or eliminate these reflections. Also, a velocity stack is like horn loading a speaker and it too can provide a resistive load to the line. However, I have a feeling that most velocity stacks are not highly optimized from an acoustical standpoint.
Let me ask you, are dyno curves smoothed? Do you actually find peaks and dips in the power perhaps due to these resonances?
Let me also ask, can you identify a problem that you think is associated with the acoustics of the intake or exhaust system?
It looks like most of the major auto makers have experimented with VLIM so it seems that there is something to it:
http://en.wikipedia.org/wiki/Variable_Length_Intake_Manifold
Pete B.
Let me ask you, are dyno curves smoothed? Do you actually find peaks and dips in the power perhaps due to these resonances?
Let me also ask, can you identify a problem that you think is associated with the acoustics of the intake or exhaust system?
It looks like most of the major auto makers have experimented with VLIM so it seems that there is something to it:
http://en.wikipedia.org/wiki/Variable_Length_Intake_Manifold
Pete B.
JinMTVT said:
PB2 said:
Correct ...
just what exactly is a standing wave VS regular wave ?
if we think of the volume of each "chamber" in the intake path ..do they all introduce their own reverberation?
they talk about helmoltz reosnnator,
does it only apply to the plenum section or other "single" sections ?
First let me mention that there are two types of systems, really ways of modelling systems, distributed and lumped. A Helmholtz resonator is a lumped system at the frequencies of interest, the cavity is an air spring, and the pipe is an acoustical mass, the two resonate just as any mass spring system does.
Not the best description but it should do:
http://en.wikipedia.org/wiki/Helmholtz_resonance
Transmission lines must be treated as distributed systems, with inductance and capacitance per unit length, or acoustical mass and compliance:
http://en.wikipedia.org/wiki/Transmission_line
http://en.wikipedia.org/wiki/Standing_wave
Transmission lines have a characteristic impedance, 300, and often 75 or 50 for twinlead and coax, and there are no reflections or standing waves when they're match terminated.
Pete B.
Not the best description but it should do:
http://en.wikipedia.org/wiki/Helmholtz_resonance
Transmission lines must be treated as distributed systems, with inductance and capacitance per unit length, or acoustical mass and compliance:
http://en.wikipedia.org/wiki/Transmission_line
http://en.wikipedia.org/wiki/Standing_wave
Transmission lines have a characteristic impedance, 300, and often 75 or 50 for twinlead and coax, and there are no reflections or standing waves when they're match terminated.
Pete B.
Have you ever seen a velocity stack that looks like this?
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=264-315
Pete B.
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=264-315
Pete B.
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